,,climate ,,and ,,time ,illustration3 ,,frontispiece ,n4 ,,winter ,,solstice ,,in ,,aphelion4 ,n4 ,,winter ,,solstice ,,in ,,perihelion4 ,w4 ,a4 ,k4 ,johnston1 ,edinbr4 and ,london4 ,,climate ,,and ,,time ,,in ,,their ,,geological ,,relations ,a ,,theory ,,of ,,secular ,,changes ,,of ,,the ,,earth',s ,,climate ,,by ,,james ,,croll ,,of ,h4,m4 ,,geological ,,survey ,,of ,,scotland ,,london ,,daldy1 ,,isbister1 ,,co4 #ef1 ,,ludgate ,,hill #ahge ,,london3 ,,printed ,,by ,,virtue ,,and ,,co41 ,,city ,,road4 ,,preface4 ,in the following pages ,i have endeavoured to give a full and concise statement of the facts and arguments adduced in support of the theory of ,secular ,changes of the ,earth's ,climate4 ,considerable portions of the volume have already appeared in substance as separate papers in the ,philosophical ,magazine and other journals during the past ten or twelve years4 ,the theory1 especially in as far as it relates to the cause of the glacial epoch1 appears to be gradually gaining acceptance with geologists4 ,this1 doubtless1 is owing to the greatly increased and constantly increasing knowledge of the drift-phenomena1 which has induced the almost general conviction that a climate such as that of the glacial epoch could only have resulted from cosmical causes4 ,considerable attention has been devoted to objections1 and to the removal of slight misapprehensions1 which have naturally arisen in regard to a subject comparatively new and1 in many respects1 complex1 and beset with formidable difficulties4 ,i have studiously avoided introducing anything of a hypothetical character4 ,all the conclusions are based either on known facts or admitted physical principles4 ,in short1 the aim of the work1 as will be shown in the introductory chapter1 is to prove that secular changes of climate follow1 as a necessary effect1 from admitted physical agencies1 and that these changes1 in as far as the past climatic condition of the globe is concerned1 fully meet the demand of the geologist4 ,the volume1 though not intended as a popular treatise1 will be found1 ,i trust1 to be perfectly plain and intelligible even to readers not familiar with physical science4 ,i avail myself of this opportunity of expressing my obligations to my colleagues1 ,mr4 ,james ,geikie1 ,mr4 ,robert ,l4 ,jack1 ,mr4 ,robert ,etheridge1 jun41 and also to ,mr4 ,james ,paton1 of the ,edinburgh ,museum of ,science and ,art1 for their valuable assistance rendered while these pages were passing through the press4 ,to the kindness of ,mr4 ,james ,bennie ,i am indebted for the copious index at the end of the volume1 as well as for many of the facts relating to the glacial deposits of the ,west of ,scotland4 ,,james ,,croll4 ,,edinburgh1 ,march1 #ahge4 ,,contents4 ,,chapter ,i4 ,,introduction4 ,,page ,the ,fundamental ,problem of ,geology4--,geology a ,dynamical ,science4--,the ,nature of a ,geological ,principle4--,theories of ,geological ,climate4--,geological ,climate dependent on ,astronomical ,causes4--,an ,important ,consideration overlooked4--,abstract of the ,line of ,argument pursued in the ,volume #a ,,chapter ,,ii4 ,,ocean-,,currents ,,in ,,relation ,,to ,,the ,,distribution ,,of ,,heat ,,over ,,the ,,globe4 ,the absolute ,heating-power of ,ocean-currents4--,volume of the ,gulf-stream4--,absolute ,amount of ,heat conveyed by it4--,greater ,portion of ,moisture in ,inter-tropical ,regions falls as ,rain in those ,regions4--,land along the ,equator tends to lower the ,temperature of the ,globe4--,influence of ,gulf-stream on ,climate of ,europe4--,temperature of ,space4--,radiation of a ,particle4--,professor ,dove on ,normal ,temperature4--,temperature of ,equator and ,poles in the ,absence of ,ocean-currents4--,temperature of ,london1 how much due to ,ocean-currents #bc ,,chapter ,,iii4 ,,ocean-,,currents ,,in ,,relation ,,to ,,the ,,distribution ,,of ,,heat ,,over ,,the ,,globe4--7,continued47 ,influence of the ,gulf-stream on the ,climate of the ,arctic ,regions4--,absolute ,amount of ,heat received by the ,arctic ,regions from the ,sun4--,influence of ,ocean-currents shown by another ,method4--,temperature of a ,globe all ,water or all ,land according to ,professor ,j4 ,d4 ,forbes4--,an important ,consideration overlooked4--,without ,ocean-currents the ,globe would not be habitable4--,conclusions not affected by ,imperfection of ,data #de ,,chapter ,,iv4 ,,outline ,,oe ,,the ,,physical ,,agencies ,,which ,,lead ,,to ,,secular ,,changes ,,of ,,climate4 ,eccentricity of the ,earth's ,orbit2 its ,effect on ,climate4--,glacial ,epoch not the direct ,result of an ,increase of ,eccentricity4--,an important ,consideration overlooked4--,change of ,eccentricity affects ,climate only indirectly4--,agencies which are brought into ,operation by an ,increase of ,eccentricity4--,how an ,accumulation of ,snow is produced4--,the ,effect of ,snow on the ,summer ,temperature4--,reason of the ,low ,summer ,temperature of ,polar ,regions4--,deflection of ,ocean-currents the chief ,cause of ,secular ,changes of ,climate4--,how the foregoing ,causes deflect ,ocean-currents4--,nearness of the ,sun in ,perigee a ,cause of the ,accumulation of ,ice4--,a remarkable ,circumstance regarding the ,causes which lead to ,secular ,changes of ,climate4--,the primary ,cause an ,increase of ,eccentricity4--,mean ,temperature of whole ,earth should be greater in ,aphelion than in ,perihelion4--,professor ,tyndall on the ,glacial ,epoch4--,a general ,reduction of ,temperature will not produce a ,glacial ,epoch4--,objection from the present ,condition of the ,planet ,mars #ed ,,chapter ,v4 ,,reason ,,why ,,the ,,southern ,,hemisphere ,,is ,,colder ,,than ,,the ,,northern4 ,adhmar's ,explanation4--,adhmar's ,theory founded upon a physical ,mistake in regard to ,radiation4--,professor ,j4 ,d4 ,forbes on ,underground ,temperature4--,generally accepted ,explanation4--,low ,temperature of ,southern ,hemisphere attributed to ,preponderance of ,sea4--,heat transferred from ,southern to ,northern ,hemisphere by ,ocean-current the true ,explanation4--,a large ,portion of the ,heat of the ,gulf-stream derived from the ,southern ,hemisphere #ha ,,chapter ,,vi4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,lieut4 ,,maury',s ,,theory4 ,introduction4--,ocean-currents1 according to ,maury1 due to ,difference of ,specific ,gravity4--,difference of ,specific ,gravity resulting from ,difference of ,temperature4--,difference of ,specific ,gravity resulting from ,difference of ,saltness4--,maury's two ,causes neutralize each other4--,how1 according to him1 ,difference in ,saltness acts as a ,cause #ie ,,chapter ,,vii4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,lieut4 ,,maury',s ,,theory4--7,continued47 ,methods of determining the ,question4--,the ,force resulting from ,difference of ,specific ,gravity4--,sir ,john ,herschel's ,estimate of the ,force4--,maximum ,density of ,sea-,water4--,rate of ,decrease of ,temperature of ,ocean at ,equator4--,the actual ,amount of ,force resulting from ,difference of ,specific ,gravity4--,m4 ,dubuat's ,experiments #aae ,,chapter ,,viii4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,dr4 ,,carpenter',s ,,theory4 ,gulf-stream according to ,dr4 ,carpenter not due to ,difference of ,specific ,gravity4--,facts to be ,explained4--,the ,explanation of the ,facts4--,the ,explanation hypothetical4--,the ,cause assigned for the hypothetical ,mode of ,circulation4--,under ,currents account for all the ,facts better than the ,gravitation ,hypothesis4--,known ,condition of the ,ocean inconsistent with that ,hypothesis #abb ,,chapter ,,ix4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,the ,,mechanics ,,of ,,dr4 ,,carpenter',s ,,theory4 ,experimental ,illustration of the ,theory4--,the ,force exerted by ,gravity4--,work performed by ,gravity4--,circulation not by ,convection4--,circulation depends on ,difference in ,density of the ,equatorial and ,polar ,columns4--,absolute ,amount of ,work which can be performed by ,gravity4--,how ,underflow is produced4--,how ,vertical ,descent at the ,poles and ,ascent at the ,equator is produced4--,the ,gibraltar ,current4--,mistake in ,mechanics concerning it4--,the ,baltic ,current #ade ,,chapter ,x4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,dr4 ,,carpenter',s ,,theory4--,,objections ,,considered4 ,modus ,operandi of the ,matter4--,polar ,cold considered by ,dr4 ,carpenter the ,primum ,mobile4--,supposed ,influence of ,heat derived from the ,earth's ,crust4--,circulation without ,difference of ,level4--,a ,confusion of ,ideas in ,reference to the supposed ,agency of ,polar ,cold4--,m4 ,dubuat's ,experiments4--,a ,begging of the ,question at ,issue4--,pressure as a ,cause of ,circulation #agb ,,chapter ,,xi4 ,,the ,,inadequacy ,,of ,,the ,,gravitation ,,theory ,,proved ,,by ,,another ,,method4 ,quantity of ,heat which can be conveyed by the ,general ,oceanic ,circulation trifling4--,tendency in the ,advocates of the ,gravitation ,theory to under-estimate the ,volume of the ,gulf-stream4--,volume of the ,stream as determined by the ,challenger4--,immense ,volume of ,warm ,water discovered by ,captain ,nares4--,condition of ,north ,atlantic inconsistent with the ,gravitation ,theory4--,dr4 ,carpenter's ,estimate of the ,thermal ,work of the ,gulf-stream #aia ,,chapter ,,xii4 ,,mr4 ,a4 ,g4 ,,findlay',s ,,objections ,,considered4 ,mr4 ,findlay's ,estimate of the ,volume of the ,gulf-stream4--,mean ,temperature of a ,cross ,section less than ,mean ,temperature of ,stream4--,reason of such ,diversity of ,opinion regarding ,ocean-currents4--,more rigid ,method of ,investigation necessary #bjc ,,chapter ,,xiii4 ,,the ,,wind ,,theory ,,of ,,oceanic ,,circulation4 ,ocean-,currents not due alone to the ,trade-winds4--,an ,objection by ,maury4--,trade-winds do not explain the ,great ,antarctic ,current4--,ocean-currents due to the ,system of ,winds4--,the ,system of ,currents agrees with the ,system of the ,winds4--,chart showing the ,agreement between the ,system of ,currents and ,system of ,winds4--,cause of the ,gibraltar ,current4--,north ,atlantic an immense ,whirlpool4--,theory of ,under ,currents4--,difficulty regarding ,under ,currents obviated4--,work performed by the ,wind in impelling the ,water forward4--,the ,challenger's crucial ,test of the ,wind and ,gravitation ,theories4--,north ,atlantic above the ,level of ,equator4--,thermal ,condition of the ,southern ,ocean irreconcilable with the ,gravitation ,theory #baj ,,chapter ,,xiv4 ,,the ,,wind ,,theory ,,of ,,oceanic ,,circulation ,,in ,,relation ,,to ,,change ,,of ,,climate4 ,direction of ,currents depends on ,direction of the ,winds4--,causes which affect the ,direction of ,currents will affect ,climate4--,how ,change of ,eccentricity affects the ,mode of ,distribution of the ,winds4--,mutual ,reaction of ,cause and ,effect4--,displacement of the ,great ,equatorial ,current4--,displacement of the ,median ,line between the ,trades1 and its ,effect on ,currents4--,ocean-currents in ,relation to the ,distribution of ,plants and ,animals4--,alternate ,cold and ,warm ,periods in ,north and ,south4--,mr4 ,darwin's ,views quoted4--,how ,glaciers at the ,equator may be accounted for4--,migration across the ,equator #bbf ,,chapter ,,xv4 ,,warm ,,inter-,,glacial ,,periods4 ,alternate ,cold and ,warm ,periods4--,warm ,inter-glacial ,periods a ,test of ,theories4--,reason why their ,occurrence has not been hitherto recognised4--,instances of ,warm ,inter-glacial ,periods4--,dranse1 ,drnten1 ,hoxne1 ,chapelhall1 ,craiglockhart1 ,leith ,walk1 ,redhall ,quarry1 ,beith1 ,crofthead1 ,kilmaurs1 ,sweden1 ,ohio1 ,cromer1 ,mundesley1 c41 c4--,cave and ,river ,deposits4--,occurrence of ,arctic and ,warm ,animals in some ,beds accounted for4--,mr4 ,boyd ,dawkins's ,objections4--,occurrence of ,southern ,shells in ,glacial ,deposits4--,evidence of ,warm ,inter-glacial ,periods from ,mineral ,borings4--,striated ,pavements4--,reason why ,inter-glacial ,land-surfaces are so rare #bcf ,,chapter ,,xvi4 ,,warm ,,inter-,,glacial ,,periods ,,in ,,arctic ,,regions4 ,cold ,periods best marked in ,temperate1 and ,warm ,periods in ,arctic1 ,regions4--,state of ,arctic ,regions during ,glacial ,period4--,effects of ,removal of ,ice from ,arctic ,regions4--,ocean-currents2 ,influence on ,arctic ,climate4--,reason why ,remains of ,inter-glacial ,period are rare in ,arctic ,regions4--,remains of ,ancient ,forests in ,banks's ,land1 ,prince ,patrick's ,island1 c4--,opinions of ,sir ,r4 ,murchison1 ,captain ,osborn1 and ,professor ,haughton4--,tree dug up by ,sir ,e4 ,belcher in lat4 #ge ,n4 #beh ,,chapter ,,xvii4 ,,former ,,glacial ,,epochs4--,,reason ,,of ,,the ,,imperfection ,,of ,,geological ,,records ,,in ,,reference ,,to ,,them4 ,two ,reasons why so little is known of ,glacial ,epochs4--,evidence of ,glaciation to be found on ,land-surfaces4--,where are all our ancient ,land-surfaces8--,the stratified ,rocks consist of a ,series of old ,sea-bottoms4--,transformation of a ,land-surface into a ,sea-bottom obliterates all ,traces of ,glaciation4--,why so little remains of the ,boulder ,clays of former ,glacial ,epochs4--,records of the ,glacial ,epoch are fast disappearing4--,icebergs do not striate the ,sea-bottom4--,mr4 ,campbell's ,observations on the ,coast of ,labrador4--,amount of ,material transported by ,icebergs much exaggerated4--,mr4 ,packard on the ,glacial ,phenomena of ,labrador4--,boulder ,clay the ,product of ,land-ice4--,palontological ,evidence4--,paucity of ,life characteristic of a ,glacial ,period4--,warm ,periods better represented by ,organic ,remains than cold4--,why the ,climate of the ,tertiary ,period was supposed to be warmer than the present4--,mr4 ,james ,geikie on the ,defects of ,palontological ,evidence4--,conclusion #bff ,,chapter ,,xviii4 ,,former ,,glacial ,,epochs2 ,,geological ,,evidence ,,of4 ,cambrian ,conglomerate of ,islay and ,north-west of ,scotland4--,ice-action in ,ayrshire and ,wigtownshire during ,silurian ,period4--,silurian ,limestones in ,arctic ,legions4--,professor ,ramsay on ,ice-action during ,old ,red ,sandstone ,period4--,warm ,climate in ,arctic ,regions during ,old ,red ,sandstone ,period4--,professor ,geikie and ,mr4 ,james ,geikie on a ,glacial ,conglomerate of ,lower ,carboniferous ,age4--,professor ,haughton and ,professor ,dawson on ,evidence of ,ice-action during ,coal ,period4--,mr4 ,w4 ,t4 ,blanford on ,glaciation in ,india during ,carboniferous ,period4--,carboniferous ,formations of ,arctic ,regions4--,professor ,ramsay on ,permian ,glaciers4--,permian ,conglomerate in ,arran4--,professor ,hull on ,boulder ,clay of ,permian ,age4--,permian ,boulder ,clay of ,natal4--,oolitic ,boulder ,conglomerate in ,sutherlandshire4---,warm ,climate in ,north ,greenland during ,oolitic ,period4--,mr4 ,godwin-,austen on ,ice-action during ,cretaceous ,period4--,glacial ,conglomerates of ,eocene ,age in the ,alps4--,m4 ,gastaldi on the ,ice-transported ,limestone ,blocks of the ,superga4--,professor ,heer on the ,climate of ,north ,greenland during ,miocene ,period #bib ,,chapter ,,xix4 ,,geological ,,time4--,,probable ,,date ,,of ,,the ,,glacial ,,epoch4 ,geological ,time measurable from ,astronomical ,data4--,m4 ,leverrier's ,formul4--,tables of ,eccentricity for #c1jjj1jjj ,years in the ,past and #a1jjj1jjj ,years in the ,future4--,how the ,tables have been computed4--,why the ,glacial ,epoch is more recent than had been supposed4--,figures convey a very inadequate ,conception of immense ,duration4--,mode of representing a ,million of ,years4--,probable ,date of the ,glacial ,epoch #caa ,,chapter ,,xx4 ,,geological ,,time4--,,method ,,of ,,measuring ,,the ,,rate ,,of ,,suba,,rial ,,denudation4 ,rate of ,subarial ,denudation a ,measure of ,time4--,rate determined from ,sediment of the ,mississippi4--,amount of ,sediment carried down by the ,mississippi2 by the ,ganges4--,professor ,geikie on ,modern ,denudation4--,professor ,geikie on the ,amount of ,sediment conveyed by ,european ,rivers4--,rate at which the ,surface of the ,globe is being denuded4--,alfred ,tylor on the ,sediment of the ,mississippi4--,the ,law which determines the ,rate of ,denudation4--,the ,globe becoming less oblate4--,carrying ,power of our ,river ,systems the true ,measure of ,denudation4--,marine ,denudation1 trifling in comparison to ,subarial4--,previous ,methods of measuring ,geological ,time4--,circumstances which show the recent ,date of the ,glacial ,epoch4--,professor ,ramsay on ,geological ,time #cbi ,,chapter ,,xxi4 ,,the ,,probable ,,age ,,and ,,origin ,,of ,,the ,,sun4 ,gravitation ,theory4--,amount of ,heat emitted by the ,sun4--,meteoric ,theory4--,helmholtz's ,condensation ,theory4--,confusion of ,ideas4--,gravitation not the chief ,source of the ,sun's ,heat4--,original ,heat4--,source of ,original ,heat4--,original ,heat derived from ,motion in ,space4--,conclusion as to ,date of ,glacial ,epoch4--,false ,analogy4--,probable ,date of ,eocene and ,miocene ,periods #cdf ,,chapter ,,xxii4 ,a ,,method ,,of ,,determining ,,the ,,mean ,,thickness ,,of ,,the ,,sedimentary ,,rocks ,,of ,,the ,,globe4 ,prevailing ,methods defective4--,maximum ,thickness of ,british ,rocks4--,three ,elements in the ,question4--,professor ,huxley on the ,rate of ,deposition4--,thickness of ,sedimentary ,rocks enormously over-estimated4--,observed ,thickness no ,measure of mean ,thickness4--,deposition of ,sediment principally along ,sea-margin4--,mistaken ,inference regarding the ,absence of a ,formation4--,immense ,antiquity of existing ,oceans #cfj ,,chapter ,,xxiii4 ,,the ,,physical ,,cause ,,of ,,the ,,submergence ,,and ,,emergence ,,of ,,the ,,land ,,during ,,the ,,glacial ,,epoch4 ,displacement of the ,earth's ,centre of ,gravity by ,polar ,ice-cap4--,simple ,method of estimating ,amount of ,displacement4--,note by ,sir ,w4 ,thomson on foregoing ,method4--,difference between ,continental ,ice and a ,glacier4--,probable ,thickness of the ,antarctic ,ice-cap4--,probable ,thickness of ,greenland ,ice-sheet4--,the ,icebergs of the ,southern ,ocean4--,inadequate ,conceptions regarding the ,magnitude of ,continental ,ice #cfh ,,chapter ,,xxiv4 ,,the ,,physical ,,cause ,,of ,,the ,,submergence ,,and ,,emergence ,,of ,,the ,,land ,,during ,,the ,,glacial ,,epoch4--7,continued47 ,extent of ,submergence from ,displacement of ,earth's ,centre of ,gravity4--,circumstances which show that the ,glacial ,submergence resulted from ,displacement of the ,earth's ,centre of ,gravity4--,agreement between ,theory and ,observed ,facts4--,sir ,charles ,lyell on submerged ,areas during ,tertiary ,period4--,oscillations of ,sea-,level in ,relation to ,distribution4--,extent of ,submergence on the ,hypothesis that the ,earth is fluid in the ,interior #chg ,,chapter ,,xxv4 ,,the ,,influence ,,of ,,the ,,obliquity ,,of ,,the ,,ecliptic ,,on ,,climate ,,and ,,on ,,the ,,level ,,of ,,the ,,sea4 ,the direct ,effect of ,change of ,obliquity on ,climate4--,mr4 ,stockwell on the maximum ,change of ,obliquity4--,how ,obliquity affects the ,distribution of ,heat over the ,globe4--,increase of ,obliquity diminishes the ,heat at the ,equator and increases that at the ,poles4--,influence of ,change of ,obliquity on the ,level of the ,sea4--,when the ,obliquity was last at its superior ,limit4--,probable ,date of the #be-;foot raised ,beach4--,probable ,extent of ,rise of ,sea-level resulting from ,increase of ,obliquity4--,lieutenant-,colonel ,drayson's and ,mr4 ,belt's ,theories4--,sir ,charles ,lyell on ,influence of ,obliquity #cih ,,chapter ,,xxvi4 ,,coal ,,an ,,inter-,,glacial ,,formation4 ,climate of ,coal ,period ,inter-glacial in ,character4--,coal ,plants indicate an ,equable1 not a ,tropical ,climate4--,conditions necessary for ,preservation of ,coal ,plants4--,oscillations of ,sea-level necessarily implied4--,why our ,coal-fields contain more than ,one ,coal-seam4--,time required to form a ,bed of ,coal4--,why ,coal ,strata contain so little evidence of ,ice-action4--,land ,flat during ,coal ,period4--,leading ,idea of the ,theory4--,carboniferous ,limestones #dbj ,,chapter ,,xxvii4 ,,path ,,of ,,the ,,ice-,,sheet ,,in ,,north-,,western ,,europe ,,and ,,its ,,relations ,,to ,,the ,,boulder ,,clay ,,of ,,caithness4 ,character of ,caithness ,boulder ,clay4--,theories of the ,origin of the ,caithness ,clay4--,mr4 ,jamieson's ,theory4--,mr4 ,c4 ,w4 ,peach's ,theory4--,the proposed ,theory4--,thickness of ,scottish ,ice-sheet4--,pentlands striated on their ,summits4--,scandinavian ,ice-sheet4--,north ,sea filled with ,land-ice4--,great ,baltic ,glacier4--,jutland and ,denmark crossed by ,ice4--,sir ,r4 ,murchison's ,observations4--,orkney1 ,shetland1 and ,faroe ,islands striated across4--,loess accounted for4--,professor ,geikie's ,suggestion4--,professor ,geikie and ,b4 ,n4 ,peach's ,observations on ,east ,coast of ,caithness4--,evidence from ,chalk ,flints and ,oolitic ,fossils in ,boulder ,clay #dce ,,chapter ,,xxviii4 ,,north ,,of ,,england ,,ice-,,sheet1 ,,and ,,transport ,,of ,,wastdale ,,crag ,,blocks4 ,transport of ,blocks2 ,theories of4--,evidence of ,continental ,ice4--,pennine ,range probably striated on ,summit4--,glacial ,drift in ,centre of ,england4--,mr4 ,lacy on ,drift of ,cotteswold ,hills4--,england probably crossed by ,land-ice4--,mr4 ,jack's ,suggestion4--,shedding of ,ice ,north and ,south4--,south of ,england ,ice-sheet4--,glaciation of ,west ,somerset4--,why ,ice-markings are so rare in ,south of ,england4--,form of ,contortion produced by ,land-ice #def ,,chapter ,,xxix4 ,,evidence ,,from ,,buried ,,river ,,channels ,,of ,a ,,continental ,,period ,,in ,,britain4 ,remarks on the ,drift ,deposits4--,examination of ,drift by ,borings4--,buried ,river ,channel from ,kilsyth to ,grangemouth4--,channels not excavated by ,sea nor by ,ice4--,section of buried ,channel at ,grangemouth4--,mr4 ,milne ,home's ,theory4--,german ,ocean dry ,land4--,buried ,river ,channel from ,kilsyth to the ,clyde4--,journal of ,borings4--,marine ,origin of the ,drift ,deposits4--,evidence of ,inter-glacial ,periods4--,oscillations of ,sea-,level4--,other buried ,river ,channels #dff ,,chapter ,,xxx4 ,,the ,,physical ,,cause ,,of ,,the ,,motion ,,of ,,glaciers4--,,theories ,,of ,,glacier-,,motion4 ,why the ,question of ,glacier-motion has been found to be so difficult4--,the ,regelation ,theory4--,it accounts for the ,continuity of a ,glacier1 but not for its ,motion4--,gravitation proved by ,canon ,moseley insufficient to shear the ,ice of a ,glacier4--,mr4 ,matthew's ,experiment4--,no ,parallel between the bending of an ,ice ,plank and the shearing of a ,glacier4--,mr4 ,ball's ,objection to ,canon ,moseley's ,experiment4--,canon ,moseley's ,method of determining the ,unit of ,shear4--,defect of ,method4--,motion of a ,glacier in some ,way dependent on ,heat4--,canon ,moseley's ,theory4--,objections to his ,theory4--,professor ,james ,thomson's ,theory4--,this ,theory fails to explain ,glacier-motion4--,de ,saussure and ,hopkins's 8,sliding0 ,theories4--,m4 ,charpentier's 8,dilatation0 ,theory4--,important ,element in the ,theory #die ,,chapter ,,xxxi4 ,,the ,,physical ,,cause ,,of ,,the ,,motion ,,of ,,glaciers4--,,the ,,molecular ,,theory4 ,present ,state of the ,question4--,heat necessary to the ,motion of a ,glacier4--,ice does not shear in the ,solid ,state4--,motion of a ,glacier molecular4--,how ,heat is transmitted through ,ice4--,momentary ,loss of ,shearing ,force4--,the ,rationale of ,regelation4--,the ,origin of 8,crevasses40--,effects of ,tension4--,modification of ,theory4--,fluid ,molecules crystallize in ,interstices4--,expansive ,force of crystallizing ,molecules a ,cause of ,motion4--,internal molecular ,pressure the chief ,moving ,power4--,how ,ice can excavate a ,rock ,basin4--,how ,ice can ascend a ,slope4--,how deep ,river ,valleys are striated across4--,a remarkable ,example in the ,valley of the ,tay4--,how ,boulders can he carried from a lower to a higher ,level #ead ,,appendix4 ,i4 ,opinions expressed previous to #ahfd regarding the ,influence of the ,eccentricity of the ,earth's ,orbit on ,climate #ebh ,,ii4 ,on the ,nature of ,heat-,vibrations #edd ,,iii4 ,on the ,reason why the ,difference of ,reading between a ,thermometer exposed to direct ,sunshine and ,one ,shaded diminishes as we ascend in the ,atmosphere #edg ,,iv4 ,remarks on ,mr4 ,j4 ,y4 ,buchanan's ,theory of the ,vertical ,distribution of ,temperature of the ,ocean #eej ,v4 ,on the ,cause of the ,cooling ,effect produced on ,solids by ,tension #eeb ,,vi4 ,the ,cause of ,regelation #eed ,,vii4 ,list of ,papers which have appeared in ,dr4 ,a4 ,petermann's ,geographische ,mittheilungen relating to the ,gulf-stream and ,thermal ,condition of the ,arctic ,regions #eef ,,viii4 ,list of ,papers by the ,author to which ,reference is made in this ,volume #efj ,,index #efc ,,list ,,of ,,plates4 ,,earth',s ,,orbit ,,when ,,eccentricity ,,is ,,at ,,its ,,superior ,,limit ,frontispiece4 ,,plate ,i4 ,,showing ,,agreement ,,between ,,the ,,system ,,of ,,ocean-,,currents ,,and ,,winds ,to face page #bab ,,ii4 ,,showing ,,how ,,opposing ,,currents ,,intersect ,,each ,,other #bai ,,iii4 ,,section ,,of ,,mid-,,atlantic #bbb ,,iv4 ,,diagram ,,representing ,,the ,,variations ,,of ,,eccentricity ,,of ,,the ,,earth',s ,,orbit #cac ,v4 ,,showing ,,probable ,,path ,,of ,,the ,,ice ,,in ,,north-,,western ,,europe #ddi ,,vi4 ,,showing ,,path ,,of ,,ice ,,across ,,caithness #dec ,,vii4 ,,map ,,of ,,the ,,midland ,,valley 7,,scotland71 ,,showing ,,buried ,,river ,,channels #dga ,,chapter ,i4 ,,introduction4 ,the ,fundamental ,problem of ,geology4--,geology a ,dynamical ,science4--,the ,nature of a ,geological ,principle4--,theories of ,geological ,climate4--,geological ,climate dependent on ,astronomical ,causes4--,an ,important ,consideration overlooked4--,abstract of the ,line of ,argument pursued in the ,volume4 ,the ,fundamental ,problem of ,geology4--,the investigation of the successive changes and modifications which the earth's crust has undergone during past ages is the province of geology4 ,it will be at once admitted that an acquaintance with the agencies by means of which those successive changes and modifications were effected1 is of paramount importance to the geologist4 ,what1 then1 are those agencies8 ,although volcanic and other subterranean eruptions1 earthquakes1 upheavals1 and subsidences of the land have taken place in all ages1 yet no truth is now better established than that it is not by these convulsions and cataclysms of nature that those great changes were effected4 ,it was rather by the ordinary agencies that we see every day at work around us1 such as rain1 rivers1 heat and cold1 frost and snow4 ,the valleys were not produced by violent dislocations1 nor the hills by sudden upheavals1 but were actually carved out of the solid rock1 silently and gently1 by the agencies to which we have referred4 8,the tools10 to quote the words of ,professor ,geikie1 8by which this great work has been done are of the simplest and most every-day order--the air1 rain1 frosts1 springs1 brooks1 rivers1 glaciers1 icebergs1 and the sea4 ,these tools have been at work from the earliest times of which any geological record has been preserved4 ,indeed1 it is out of the accumulated chips and dust which they have made1 afterwards hardened into solid rock and upheaved1 that the very framework of our continents has been formed40#a ,it will be observed--and this is the point requiring particular attention--that the agencies referred to are the ordinary meteorological or climatic agencies4 ,in fact1 it is these agencies which constitute climate4 ,the various peculiarities or modifications of climate result from a preponderance of one or more of these agencies over the rest4 ,when heat1 for example1 predominates1 we have a hot or tropical climate4 ,when cold and frost predominate1 we have a rigorous or arctic climate4 ,with moisture in excess1 we have a damp and rainy climate2 and so on4 ,but this is not all4 ,these climatic agencies are not only the factors which carved out the rocky face of the globe into hill and dale1 and spread over the whole a mantle of soil2 but by them are determined the character of the flora and fauna which exist on that soil4 ,the flora and fauna of a district are determined mainly by the character of the climate1 and not by the nature of the soil1 or the conformation of the ground4 ,it is from difference of climate that tropical life differs so much from arctic1 and both these from the life of temperate regions4 ,it is climate1 and climate alone1 that causes the orange and the vine to blossom1 and the olive to flourish1 in the south1 but denies them to the north1 of ,europe4 ,it is climate1 and climate alone1 that enables the forest tree to grow on the plain1 but not on the mountain top2 that causes wheat and barley to flourish on the mainland of ,scotland1 but not on the steppes of ,siberia4 ,again1 if we compare flat countries with mountainous1 highlands with lowlands1 or islands with continents1 we shall find that difference of climatic conditions is the chief reason why life in the one differs so much from life in the other4 ,and if we turn to the sea we find that organic life is there as much under the domain of climate as on the land1 only the conditions are much less complex4 ,for in the case of the sea1 difference in the temperature of the water may be said to constitute almost the only difference of climatic conditions4 ,if there is one fact more clearly brought out than another by the recent deep-sea explorations1 it is this1 that nothing exercises so much influence on organic life in the ocean as the temperature of the water4 ,in fact1 so much is this the case1 that warm zones were found to be almost equivalent to zones of life4 ,it was found that even the enormous pressure at the bottom of the ocean does not exercise so much influence on life as the temperature of the water4 ,there are few1 ,i presume1 who reflect on the subject that will not readily admit that1 whether as regards the great physical changes which are taking place on the surface of our globe1 or as regards the growth and distribution of plant and animal life1 the ordinary climatic agents are the real agents at work1 and that1 compared with them1 all other agencies sink into insignificance4 ,it will also be admitted that what holds true of the present holds equally true of the past4 ,climatic agents are not only now the most important and influential2 they have been so during all past geological ages4 ,they were so during the ,cainozoic as much as during the present2 and there is no reason for supposing they were otherwise during the remoter ,mesozoic and ,palozoic epochs4 ,they have been the principal factors concerned in that long succession of events and changes which have taken place since the time of the solidification of the earth's crust4 ,the stratified rocks of the globe contain all the records which now remain of their action1 and it is the special duty of the geologist to investigate and read those records4 ,it will be at once admitted that in order to a proper understanding of the events embodied in these records1 an acquaintance with the agencies by which they were produced is of the utmost importance4 ,in fact1 it is only by this means that we can hope to arrive at their rational explanation4 ,a knowledge of the agents1 and of the laws of their operations1 is1 in all the physical sciences1 the means by which we arrive at a rational comprehension of the effects produced4 ,if we have before us some complex and intricate effects which have been produced by heat1 or by light1 or by electricity1 c41 in order to understand them we must make ourselves acquainted with the agents by which they were produced and the laws of their action4 ,if the effects to be considered be1 for example1 those of heat1 then we must make ourselves acquainted with this agent and its laws4 ,if they be of electricity1 then a knowledge of electricity and its laws becomes requisite4 ,this is no mere arbitrary mode of procedure which may be adopted in one science and rejected in another4 ,it is in reality a necessity of thought arising out of the very constitution of our intellect2 for the objective law of the agent is the conception by means of which the effects are subjectively united in a rational unity4 ,we may describe1 arrange1 and classify the effects as we may1 but without a knowledge of the laws of the agent we can have no rational unity4 ,we have not got the higher conception by which they can be comprehended4 ,it is this relationship between the effects and the laws of the agent1 a knowledge of which really constitutes a science4 ,we might examine1 arrange1 and describe for a thousand years the effects produced by heat1 and still we should have no science of heat unless we had a knowledge of the laws of that agent4 ,the effects would never be seen to be necessarily connected with anything known to us2 we could not connect them with any rational principle from which they could be deduced priori4 ,the same remarks hold1 of course1 equally true of all sciences1 in which the things to be considered stand in the relationship of cause and effect4 ,geology is no exception4 ,it is not like systematic botany1 a mere science of classification4 ,it has to explain and account for effects produced2 and these effects can no more be explained without a knowledge of the laws of the agents which produced them1 than can the effects of heat without a knowledge of the laws of heat4 ,the only distinction between geology and heat1 light1 electricity1 c41 is1 that in geology the effects to be explained have almost all occurred already1 whereas in these other sciences effects actually taking place have to be explained4 ,but this distinction is of no importance to our present purpose1 for effects which have already occurred can no more be explained without a knowledge of the laws of the agent which produced them than can effects which are in the act of occurring4 ,it is1 moreover1 not strictly true that all the effects to be explained by the geologist are already past4 ,it falls within the scope of his science to account for the changes which are at present taking place on the earth's crust4 ,no amount of description1 arrangement1 and classification1 however perfect or accurate1 of the facts which come under the eye of the geologist can ever constitute a science of geology any more than a description and classification of the effects of heat could constitute a science of heat4 ,this will1 no doubt1 be admitted by every one who reflects upon the subject1 and it will be maintained that geology1 like every other science1 must possess principles applicable to the facts4 ,but here confusion and misconception will arise unless there be distinct and definite ideas as to what ought to constitute a geological principle4 ,it is not every statement or rule that may apply to a great many facts1 which will constitute a geological principle4 ,a geological principle must bear the same characteristics as the principles of those sciences to which we have referred4 ,what1 then1 is the nature of the principles of light1 heat1 electricity1 c48 ,the principles of heat are the laws of heat4 ,the principles of electricity are the laws of electricity4 ,and these laws are nothing more nor less than the ways according to which these agents produce their effects4 ,the principles of geology are therefore the laws of geology4 ,but the laws of geology must be simply the laws of the geological agents1 or1 in other words1 the methods by which they produce their effects4 ,any other so-called principle can be nothing more than an empirical rule1 adopted for convenience4 ,possessing no rationality in itself1 it cannot be justly regarded as a principle4 ,in order to rationality the principle must be either resolvable into1 or logically deducible from1 the laws of the agents4 ,unless it possess this quality we cannot give the explanation priori4 ,the reason of all this is perfectly obvious4 ,the things to be explained are effects2 and the relationship between cause and effect affords the subjective connection between the principle and the explanation4 ,the explanation follows from the principle simply as the effect results from the laws of the agent or cause4 ,theories of ,geological ,climate4--,we have already seen that the geological agents are chiefly the ordinary climatic agents4 ,consequently1 the main principles of geology must be the laws of the climatic agents1 or some logical deductions from them4 ,it therefore follows that1 in order to a purely scientific geology1 the grand problem must be one of geological climate4 ,it is through geological climate that we can hope to arrive ultimately at principles which will afford a rational explanation of the multifarious facts which have been accumulating during the past century4 ,the facts of geology are as essential to the establishment of the principles1 as the facts of heat1 light1 and electricity are essential to the establishment of the principles of these sciences4 ,a theory of geological climate devised without reference to the facts would be about as worthless as a theory of heat or of electricity devised without reference to the facts of these sciences4 ,it has all along been an admitted opinion among geologists that the climatic condition of our globe has not1 during past ages1 been uniformly the same as at present4 ,for a long time it was supposed that during the ,cambrian1 ,silurian1 and other early geological periods1 the climate of our globe was much hotter than now1 and that ever since it has been gradually becoming cooler4 ,and this high temperature of ,palozoic ages was generally referred to the influence of the earth's internal heat4 ,it has1 however1 been proved by ,sir ,william ,thomson#b that the general climate of our globe could not have been sensibly affected by internal heat at any time more than ten thousand years after the commencement of the solidification of the surface4 ,this physicist has proved that the present influence of internal heat on the temperature amounts to about only #a_/geth of a degree4 ,not only is the theory of internal heat now generally abandoned1 but it is admitted that we have no good geological evidence that climate was much hotter during ,palozoic ages than now2 and much less1 that it has been becoming uniformly colder4 ,the great discovery of the glacial epoch1 and more lately that of a mild and temperate condition of climate extending during the ,miocene and other periods to ,north ,greenland1 have introduced a complete revolution of ideas in reference to geological climate4 ,those discoveries showed that our globe has not only undergone changes of climate1 but changes of the most extraordinary character4 ,they showed that at one time not only an arctic condition of climate prevailed in our island1 but that the greater part of the temperate region down to comparatively low latitudes was buried under ice1 while at other periods ,greenland and the ,arctic regions1 probably up to the ,north ,pole1 were not only free from ice1 but were covered with a rich and luxuriant vegetation4 ,to account for these extraordinary changes of climate has generally been regarded as the most difficult and perplexing problem which has fallen to the lot of the geologist4 ,some have attempted to explain them by assuming a displacement of the earth's axis of rotation in consequence of the uprising of large mountain masses on some part of the earth's surface4 ,but it has been shown by ,professor ,airy1#c ,sir ,william ,thomson1#d and others1 that the earth's equatorial protuberance is such that no geological change on its surface could ever possibly alter the position of the axis of rotation to an extent which could at all sensibly affect climate4 ,others1 again1 have tried to explain the change of climate by supposing1 with ,poisson1 that the earth during its past geological history may have passed through hotter and colder parts of space4 ,this is not a very satisfactory hypothesis4 ,there is no doubt a difference in the quantity of force in the form of heat passing through different parts of space2 but space itself is not a substance which can possibly be either cold or hot4 ,if1 therefore1 we were to adopt this hypothesis1 we must assume that the earth during the hot periods must have been in the vicinity of some other great source of heat and light besides the sun4 ,but the proximity of a mass of such magnitude as would be sufficient to affect to any great extent the earth's climate would1 by its gravity1 seriously disarrange the mechanism of our solar system4 ,consequently1 if our solar system had ever1 during any former period of its history1 really come into the vicinity of such a mass1 the orbits of the planets ought at the present day to afford some evidence of it4 ,but again1 in order to account for a cold period1 such as the glacial epoch1 we have to assume that the earth must have come into the vicinity of a cold body4#e ,but recent discoveries in regard to inter-glacial periods are wholly irreconcilable with this theory4 ,a change in the obliquity of the ecliptic has frequently been1 and still is1 appealed to as an explanation of geological climate4 ,this theory appears1 however1 to be beset by a twofold objection3 7#a71 it can be shown from celestial mechanics1 that the variations in the obliquity of the ecliptic must always have been so small that they could not materially affect the climatic condition of the globe2 and 7#b71 even admitting that the obliquity could change to an indefinite extent1 it can be shown#f that no increase or decrease1 however great1 could possibly account for either the glacial epoch or a warm temperate condition of climate in polar regions4 ,the theory that the sun is a variable star1 and that the glacial epochs of the geologists may correspond to periods of decrease in the sun's heat1 has lately been advanced4 ,this theory is also open to two objections3 7#a71 a general diminution of heat#g never could produce a glacial epoch2 and 7#b71 even if it could1 it would not explain inter-glacial periods4 ,the only other theory on the subject worthy of notice is that of ,sir ,charles ,lyell4 ,those extraordinary changes of climate are1 according to his theory1 attributed to differences in the distribution of land and water4 ,sir ,charles concludes that1 were the land all collected round the poles1 while the equatorial zones were occupied by the ocean1 the general temperature would be lowered to an extent that would account for the glacial epoch4 ,and1 on the other hand1 were the land all collected along the equator1 while the polar regions were covered with sea1 this would raise the temperature of the globe to an enormous extent4 ,it will be shown in subsequent chapters that this theory does not duly take into account the prodigious influence exerted on climate by means of the heat conveyed from equatorial to temperate and polar regions by means of ocean-currents4 ,in ,chapters ,,ii4 and ,,iii4 ,i have endeavoured to prove 7#a71 that were it not for the heat conveyed from equatorial to temperate and polar regions by this means1 the thermal condition of the globe would be totally different from what it is at present2 and 7#b71 that the effect of placing all the land along the equator would be diametrically the opposite of that which ,sir ,charles supposes4 ,but supposing that difference in the distribution of land and water would produce the effects attributed to it1 nevertheless it would not account for those extraordinary changes of climate which have occurred during geological epochs4 ,take1 for example1 the glacial epoch4 ,geologists almost all agree that little or no change has taken place in the relative distribution of sea and land since that epoch4 ,all our main continents and islands not only existed then as they do now1 but every year is adding to the amount of evidence which goes to show that so recent1 geologically considered1 is the glacial epoch that the very contour of the surface was pretty much the same then as it is at the present day4 ,but this is not all2 for even should we assume 7#a71 that a difference in the distribution of sea and land would produce the effects referred to1 and 7#b71 that we had good geological evidence to show that at a very recent period a form of distribution existed which would produce the necessary glacial conditions1 still the glacial epoch would not be explained1 for the phenomena of warm inter-glacial periods would completely upset the theory4 ,geological ,climate depending on ,astronomical ,causes4--,for a good many years past1 an impression has been gradually gaining ground amongst geologists that the glacial epoch1 as well as the extraordinary condition of climate which prevailed in arctic regions during the ,miocene and other periods1 must some way or other have resulted from a cosmical cause2 but all seemed at a loss to conjecture what that cause could possibly be4 ,it was apparent that the cosmical cause must be sought for in the relations of our earth to the sun2 but a change in the obliquity of the ecliptic and the eccentricity of the earth's orbit are the only changes from which any sensible effect on climate could possibly be expected to result4 ,it was shown1 however1 by ,laplace that the change of obliquity was confined within so narrow limits that it has scarcely ever been appealed to as a cause seriously affecting climate4 ,the only remaining cause to which appeal could be made was the change in the eccentricity of the earth's orbit--precession of the equinoxes without eccentricity producing1 of course1 no effect whatever on climate4 ,upwards of forty years ago ,sir ,john ,herschel and a few other astronomers directed their attention to the consideration of this cause1 but the result arrived at was adverse to the supposition that change of eccentricity could greatly affect the climate of our globe4 ,as some misapprehension seems to prevail with reference to this1 ,i would take the liberty of briefly adverting to the history of the matter1--referring the reader to the ,appendix for fuller details4 ,about the beginning of the century some writers attributed the lower temperature of the southern hemisphere to the fact that the sun remains about seven days less on that hemisphere than on the northern2 their view being that the southern hemisphere on this account receives seven days less heat than the northern4 ,sir ,charles ,lyell1 in the first edition of his 8,principles10 published in #ahcj1 refers to this as a cause which might produce some slight effect on climate4 ,sir ,charles's remarks seem to have directed ,sir ,john ,herschel's attention to the subject1 for in the latter part of the same year he read a paper before the ,geological ,society on the astronomical causes which may influence geological phenomena1 in which1 after pointing out the mistake into which ,sir ,charles had been led in concluding that the southern hemisphere receives less heat than the northern1 he considers the question as to whether geological climate could be influenced by changes in the eccentricity of the earth's orbit4 ,he did not appear at the time to have been aware of the conclusions arrived at by ,lagrange regarding the superior limit of the eccentricity of the earth's orbit2 but he came to the conclusion that possibly the climate of our globe may have been affected by variations in the eccentricity of its orbit4 8,an amount of variation10 he says1 8which we need not hesitate to admit 7at least provisionally7 as a possible one1 may be productive of considerable diversity of climate1 and may operate during great periods of time either to mitigate or to exaggerate the difference of winter and summer temperatures1 so as to produce alternately in the same latitude of either hemisphere a perpetual spring1 or the extreme vicissitudes of a burning summer and a rigorous winter40 ,this opinion1 however1 was unfortunately to a great extent nullified by the statement which shortly afterwards appeared in his 8,treatise on ,astronomy10 and also in the 8,outlines of ,astronomy10 to the effect that the elliptic form of the earth's orbit has but a very trifling influence in producing variation of temperature corresponding to the sun's distance2 the reason being that whatever may be the ellipticity of the orbit1 it follows that equal amounts of heat are received from the sun in passing over equal angles round it1 in whatever part of the ellipse those angles may be situated4 ,those angles will of course be described in unequal times1 but the greater proximity of the sun exactly compensates for the more rapid description1 and thus an equilibrium of heat is maintained4 ,the sun1 for example1 is much nearer the earth when he is over the southern hemisphere than he is when over the northern2 but the southern hemisphere does not on this account receive more heat than the northern2 for1 owing to the greater velocity of the earth when nearest the sun1 the sun does not remain so long on the southern hemisphere as he does on the northern4 ,these two effects so exactly counterbalance each other that1 whatever be the extent of the eccentricity1 the total amount of heat reaching both hemispheres is the same4 ,and he considered that this beautiful compensating principle would protect the climate of our globe from being seriously affected by an increase in the eccentricity of its orbit1 unless the extent of that increase was very great4 8,were it not10 he says1 8for this1 the eccentricity of the orbit would materially influence the transition of seasons4 ,the fluctuation of distance amounts to nearly #a_/cjth of its mean quantity1 and consequently the fluctuation in the sun's direct heating power to double this1 or #a_/aeth of the whole4 ,now the perihelion of the orbit is situated nearly at the place of the northern winter solstice2 so that1 were it not for the compensation we have just described1 the effect would be to exaggerate the difference of summer and winter in the southern hemisphere1 and to moderate it in the northern2 thus producing a more violent alternation of climate in the one hemisphere1 and an approach to perpetual spring in the other4 ,as it is1 however1 no such inequality subsists1 but an equal and impartial distribution of heat and light is accorded to both40#h ,herschel's opinion was shortly afterwards adopted and advocated by ,arago#i and by ,humboldt4#aj ,arago1 for example1 states that so little is the climate of our globe affected by the eccentricity of its orbit1 that even were the orbit to become as eccentric as that of the planet ,pallas 7that is1 as great as #jbd71 8still this would not alter in any appreciable manner the mean thermometrical state of the globe40 ,this idea1 supported by these great authorities1 got possession of the public mind2 and ever since it has been almost universally regarded as settled that the great changes of climate indicated by geological phenomena could not have resulted from any change in the relation of the earth to the sun4 ,there is1 however1 one effect that was not regarded as compensated4 ,the total amount of heat received by the earth is inversely proportional to the minor axis of its orbit2 and it follows1 therefore1 that the greater the eccentricity1 the greater is the total amount of heat received by the earth4 ,on this account it was concluded that an increase of eccentricity would tend to a certain extent to produce a warmer climate4 ,all those conclusions to which ,i refer1 arrived at by astronomers1 are perfectly legitimate so far as the direct effects of eccentricity are concerned2 and it was quite natural1 and1 in fact1 proper to conclude that there was nothing in the mere increase of eccentricity that could produce a glacial epoch4 ,how unnatural would it have been to have concluded that an increase in the quantity of heat received from the sun should lower the temperature1 and cover the country with snow and ice6 ,neither would excessively cold winters1 followed by excessively hot summers1 produce a glacial epoch4 ,to assert1 therefore1 that the purely astronomical causes could produce such an effect would be simply absurd4 ,important ,consideration overlooked4--,the important fact1 however1 was overlooked that1 although the glacial epoch could not result directly from an increase of eccentricity1 it might nevertheless do so indirectly4 ,although an increase of eccentricity could have no direct tendency to lower the temperature and cover our country with ice1 yet it might bring into operation physical agents which would produce this effect4 ,if1 instead of endeavouring to trace a direct connection between a high condition of eccentricity and a glacial condition of climate1 we turn our attention to the consideration of what are the physical effects which result from an increase of eccentricity1 we shall find that a host of physical agencies are brought into operation1 the combined effect of which is to lower to a very great extent the temperature of the hemisphere whose winters occur in aphelion1 and to raise to nearly as great an extent the temperature of the opposite hemisphere1 whose winters of course occur in perihelion4 ,until attention was directed to those physical circumstances to which ,i refer1 it was impossible that the true cause of the glacial epoch could have been discovered2 and1 moreover1 many of the indirect and physical effects1 which in reality were those that brought about the glacial epoch1 could not1 in the nature of things1 have been known previously to recent discoveries in the science of heat4 ,the consideration and discussion of those various physical agencies are the chief aim of the following pages4 ,abstract of the ,line of ,argument pursued in this ,volume4--,i shall now proceed to give a brief abstract of the line of argument pursued in this volume4 ,but as a considerable portion of it is devoted to the consideration of objections and difficulties bearing either directly or indirectly on the theory1 it will be necessary to point out what those difficulties are1 how they arose1 and the methods which have been adopted to overcome them4 ,chapter ,,iv4 contains an outline of the physical agencies affecting climate which are brought into operation by an increase of eccentricity4 ,by far the most important of all those agencies1 and the one which mainly brought about the glacial epoch1 is the ,deflection of ,ocean-,currents4 ,the consideration of the indirect physical connection between a high state of eccentricity and the deflection of ocean-currents1 and also the enormous influence on climate which results from this deflection constitute not only the most important part of the subject1 but the one beset with the greatest amount of difficulties4 ,the difficulties besetting this part of the theory arise mainly from the imperfect state of our knowledge1 7#ast7 with reference to the absolute amount of heat transferred from equatorial to temperate and polar regions by means of ocean-currents and the influence which the heat thus transferred has on the distribution of temperature on the earth's surface2 and 7#bnd7 in connection with the physical cause of ocean circulation4 ,in ,chapters ,,ii4 and ,,iii4 ,i have entered at considerable length into the consideration of the effects of ocean currents on the distribution of heat over the globe4 ,the only current of which anything like an accurate estimate of volume and temperature has been made is the ,gulf-stream4 ,in reference to this stream we have a means of determining in absolute measure the quantity of heat conveyed by it4 ,on the necessary computation being made1 it is found that the amount transferred by the ,gulf-stream from equatorial regions into the ,north ,atlantic is enormously greater than was ever anticipated1 amounting to no less than one-fifth part of the entire heat possessed by the ,north ,atlantic4 ,this striking fact casts a new light on the question of the distribution of heat over the globe4 ,it will be seen that to such an extent is the temperature of the equatorial regions lowered1 and that of high temperate1 and polar regions raised1 by means of ocean currents1 that were they to cease1 and each latitude to depend solely on the heat received directly from the sun1 only a very small portion of the globe would be habitable by the present order of beings4 ,this being the case1 it becomes obvious to what an extent the deflection of ocean currents must affect temperature4 ,for example1 were the ,gulf-stream stopped1 and the heat conveyed by it deflected into the ,southern ,ocean1 how enormously would this tend to lower the temperature of the northern hemisphere1 and raise the temperature south of the equator4 ,chapters ,,vi41 ,,vii41 ,,viii41 ,,ix41 ,x41 and ,,xiii41 are devoted to the consideration of the physical cause of oceanic circulation4 ,this has been found to be the most difficult and perplexing part of the whole inquiry4 ,the difficulties mainly arise from the great diversity of opinion and confusion of ideas prevailing in regard to the mechanics of the subject4 ,there are two theories propounded to account for oceanic circulation2 the one which may be called the ,wind theory1 and the other the ,gravitation theory2 and this diversity of opinion and confusion of ideas prevail in connection with both theories4 ,as the question of the cause of oceanic circulation has not only a direct and important bearing on the subject of the present volume1 but is further one of much general interest1 ,i have entered somewhat fully into the matter4 ,the ,gravitation theories may be divided into two classes4 ,the first of these attributes the ,gulf-stream and other sensible currents of the ocean to difference of specific gravity1 resulting from difference of temperature between the sea in equatorial and polar regions4 ,the leading advocate of this theory was the late ,lieutenant ,maury1 who brought it so much into prominence in his interesting book on the 8,physical ,geography of the ,sea40 ,the other class does not admit that the sensible currents of the ocean can be produced by difference of specific gravity2 but they maintain that difference of temperature between the sea in equatorial and polar regions produces a general movement of the upper portion of the sea from the equator to the poles1 and a counter-movement of the under portion from the poles to the equator4 ,this form of the gravitation theory has been ably and zealously advocated by ,dr4 ,carpenter1 who may be regarded as its representative4 ,the ,wind theories also divide into two classes4 ,according to the one ocean currents are caused and maintained by the impulse of the trade-winds1 while according to the other they are due not to the impulse of the trade-winds alone1 but to that of the prevailing winds of the globe1 regarded as a general system4 ,the former of these is the one generally accepted2 the latter is that advocated in the present volume4 ,the relations which these theories bear to the question of secular change of climate1 will be found stated at length in ,chapter ,,vi4 ,it will1 however1 be better to state here in a few words what those relations are4 ,when the eccentricity of the earth's orbit attains a high value1 the hemisphere1 whose winter solstice occurs in aphelion1 has1 for reasons which are explained in ,chapter ,,iv41 its temperature lowered1 while that of the opposite hemisphere is raised4 ,let us suppose the northern hemisphere to be the cold one1 and the southern the warm one4 ,the difference of temperature between the equator and the ,north ,pole will then be greater than between the equator and the ,south ,pole2 according1 therefore1 to theory1 the trades of the northern hemisphere will be stronger than those of the southern1 and will consequently blow across the equator to some distance on the southern hemisphere4 ,this state of things will tend to deflect equatorial currents southwards1 impelling the warm water of the equatorial regions more into the southern or warm hemisphere than into the northern or cold hemisphere4 ,the tendency of all this will be to exaggerate the difference of temperature already existing between the two hemispheres4 ,if1 on the other hand1 the great ocean currents which convey the warm equatorial waters to temperate and polar regions be not produced by the impulse of the winds1 but by difference of temperature1 as ,maury maintains1 then in the case above supposed the equatorial waters would be deflected more into the northern or cold hemisphere than into the southern or warm hemisphere1 because the difference of temperature between the equator and the poles would be greater on the cold than on the warm hemisphere4 ,this1 of course1 would tend to neutralize or counteract that difference of temperature between the two hemispheres which had been previously produced by eccentricity4 ,in short1 this theory of circulation would effectually prevent eccentricity from seriously affecting climate4 ,chapters ,,vi4 and ,,vii4 have been devoted to an examination of this form of the gravitation theory4 ,the above remarks apply equally to ,dr4 ,carpenter's form of the theory2 for according to a doctrine of ,general ,oceanic ,circulation resulting from difference of specific gravity between the water at the equator and at the poles1 the equatorial water will be carried more to the cold than to the warm hemisphere4 ,it is perfectly true that a belief in a general oceanic circulation may be held quite consistently with the theory of secular changes of climate1 provided it be admitted that not this general circulation but ocean currents are the great agency employed in distributing heat over the globe4 ,the advocates of the theory1 however1 admit no such thing1 but regard ocean currents as of secondary importance4 ,it may be stated that the existence of this general ocean circulation has never been detected by actual observation4 ,it is simply assumed in order to account for certain facts1 and it is asserted that such a circulation must take place as a physical necessity4 ,i freely admit that were it not that the warm water of equatorial regions is being constantly carried off by means of ocean currents such as the ,gulf-stream1 it would accumulate till1 in order to restoration of equilibrium1 such a general movement as is supposed would be generated4 ,but it will be shown that the warm water in equatorial regions is being drained off so rapidly by ocean currents that the actual density of an equatorial column differs so little from that of a polar column that the force of gravity resulting from that difference is so infinitesimal that it is doubtful whether it is sufficient to produce sensible motion4 ,i have also shown in ,chapter ,,viii4 that all the facts which this theory is designed to explain are not only explained by the wind theory1 but are deducible from it as necessary consequences4 ,in ,chapter ,,xi4 it is proved1 by contrasting the quantity of heat conveyed by ocean currents from inter-tropical to temperate and polar regions with such an amount as could possibly be conveyed by means of a general oceanic circulation1 that the latter sinks into insignificance before the former4 ,in ,chapters ,x4 and ,,xii4 the various objections which have been advanced by ,dr4 ,carpenter and ,mr4 ,findlay are discussed at considerable length1 and in ,chapter ,,ix4 ,i have entered somewhat minutely into an examination of the mechanics of the gravitation theory4 ,a statement of the wind theory is given in ,chapter ,,xiii42 and in ,chapter ,,xiv4 is shown the relation of this theory to the theory of ,secular changes of climate4 ,this terminates the part of the inquiry relating to oceanic circulation4 ,we now come to the crucial test of the theories respecting the cause of the glacial epoch1 viz41 ,warm ,inter-glacial ,periods4 ,in ,chapters ,,xv4 and ,,xvi4 ,i have given a statement of the geological facts which go to prove that that long epoch known as the ,glacial was not one of continuous cold1 but consisted of a succession of cold and warm periods4 ,this condition of things is utterly inexplicable on every theory of the cause of the glacial epoch which has hitherto been advanced2 but1 according to the physical theory of secular changes of climate under consideration1 it follows as a necessary consequence4 ,in fact1 the amount of geological evidence which has already been accumulated in reference to inter-glacial periods may now be regarded as perfectly sufficient to establish the truth of that theory4 ,if the glacial epoch resulted from some accidental distribution of sea and land1 then there may or may not have been more than one glacial epoch1 but if it resulted from the cause which we have assigned1 then there must have been during the geological history of the globe a succession of glacial epochs corresponding to the secular variations in the eccentricity of the earth's orbit4 ,a belief in the existence of recurring glacial epochs has been steadily gaining ground for many years past4 ,i have1 in ,chapter ,,xviii41 given at some length the facts on which this belief rests4 ,it is true that the geological evidence of glacial epochs in prior ages is meagre in comparison with that of the glacial epoch of ,post-tertiary times2 but there is a reason for this in the nature of geological evidence itself4 ,chapter ,,xvii4 deals with the geological records of former glacial epochs1 showing that they are not only imperfect1 but that there is good reason why they should be so1 and that the imperfection of the records in reference to them cannot be advanced as an argument against their existence4 ,if the glacial epoch resulted from a high condition of eccentricity1 we have not only a means of determining the positive date of that epoch1 but we have also a means of determining geological time in absolute measure4 ,for if the glacial epochs of prior ages correspond to periods of high eccentricity1 then the intervals between those periods of high eccentricity become the measure of the intervals between the glacial epochs4 ,the researches of ,lagrange and ,leverrier into the secular variations of the elements of the orbits of the planets enable us to determine with tolerable accuracy the values of the eccentricity of the earth's orbit for1 at least1 four millions of years past and future4 ,with the view of determining those values1 ,i several years ago computed from ,leverrier's formula the eccentricity of the earth's orbit and longitude of the perihelion1 at intervals of ten thousand and fifty thousand years during a period of three millions of years in the past1 and one million of years in the future4 ,the tables containing these values will be found in ,chapter ,,xix4 ,these tables not only give us the date of the glacial epoch1 but they afford1 as will be seen from ,chapter ,,xxi41 evidence as to the probable date of the ,eocene and ,miocene periods4 ,ten years ago1 when the theory was first advanced1 it was beset by a very formidable difficulty1 arising from the opinions which then prevailed in reference to geological time4 ,one or two glacial epochs in the course of a million of years was a conclusion which at that time scarcely any geologist would admit1 and most would have felt inclined to have placed the last glacial epoch at least one million of years back4 ,but then if we assume that the glacial epoch was due to a high state of eccentricity1 we should be compelled to admit of at least two glacial epochs during that lapse of time4 ,it was the modern doctrine that the great changes undergone by the earth's crust were produced1 not by convulsions of nature1 but by the slow and almost imperceptible action1 of rain1 rivers1 snow1 frost1 ice1 c41 which impressed so strongly on the mind of the geologist the vast duration of geological periods4 ,when it was considered that the rocky face of our globe had been carved into hills and dales1 and ultimately worn down to the sea-level by means of those apparently trifling agents1 not only once or twice1 but many times1 during past ages1 it was not surprising that the views entertained by geologists regarding the immense antiquity of our globe should not have harmonised with the deductions of physical science on the subject4 ,it had been shown by ,sir ,william ,thomson and others1 from physical considerations relating to the age of the sun's heat and the secular cooling of our globe1 that the geological history of our earth's crust must be limited to a period of something like one hundred millions of years4 ,but these speculations had but little weight when pitted against the stern and undeniable facts of subarial denudation4 ,how1 then1 were the two to be reconciled8 ,was it the physicist who had under-estimated geological time1 or the geologist who had over-estimated it8 ,few familiar with modern physics1 and who have given special attention to the subject1 would admit that the sun could have been dissipating his heat at the present enormous rate for a period much beyond one hundred millions of years4 ,the probability was that the amount of work performed on the earth's crust by the denuding agents in a period so immense as a million of years was1 for reasons stated in ,chapter ,,xx41 very much under-estimated4 ,but the difficulty was how to prove this4 ,how was it possible to measure the rate of operation of agents so numerous and diversified acting with such extreme slowness and irregularity over so immense areas8 ,in other words1 how was it possible to measure the rate of subarial denudation8 ,pondering over this problem about ten years ago1 an extremely simple and obvious method of solving it suggested itself to my mind4 ,this method--the details of which will be found in ,chapter ,,xx4--showed that the rate of subarial denudation is enormously greater than had been supposed4 ,the method is now pretty generally accepted1 and the result has already been to bring about a complete reconciliation between physics and geology in reference to time4 ,chapter ,,xxi4 contains an account of the gravitation theories of the origin of the sun's heat4 ,the energy possessed by the sun is generally supposed to have been derived from gravitation1 combustion being totally inadequate as a source4 ,but something more than gravitation is required before we can account for even one hundred millions of years' heat4 ,gravitation could not supply even one-half that amount4 ,there must be some other and greater source than that of gravitation4 ,there is1 however1 as is indicated1 an obvious source from which far more energy may have been derived than could have been obtained from gravitation4 ,the method of determining the rate of subarial denudation enables us also to arrive at a rough estimate of the actual mean thickness of the stratified rocks of the globe4 ,it will be seen from ,chapter ,,xxii4 that the mean thickness is far less than is generally supposed4 ,the physical cause of the submergence of the land during the glacial epoch1 and the influence of change in the obliquity of the ecliptic on climate1 are next considered4 ,in ,chapter ,,xxvi4 ,i have given the reasons which induce me to believe that coal is an inter-glacial formation4 ,the next two chapters--the one on the path of the ice in north-western ,europe1 the other on the north of ,england ice-sheet--are reprints of papers which appeared a few years ago in the ,geological ,magazine4 ,recent observations have confirmed the truth of the views advanced in these two chapters1 and they are rapidly gaining acceptance among geologists4 ,i have given1 at the conclusion1 a statement of the molecular theory of glacier motion--a theory which ,i have been led to modify considerably on one particular point4 ,there is one point to which ,i wish particularly to direct attention--viz41 that ,i have studiously avoided introducing into the theories propounded anything of a hypothetical nature4 ,there is not1 so far as ,i am aware1 from beginning to end of this volume1 a single hypothetical element3 nowhere have ,i attempted to give a hypothetical explanation4 ,the conclusions are in every case derived either from facts or from what ,i believe to be admitted principles4 ,in short1 ,i have aimed to prove that the theory of secular changes of climate follows1 as a necessary consequence1 from the admitted principles of physical science4 ,,chapter ,,ii4 ,,oceans-,,currents ,,in ,,relation ,,to ,,the ,,distribution ,,of ,,heat ,,over ,,the ,,globe4 ,the absolute ,heating-power of ,ocean-currents4--,volume of the ,gulf-stream4--,absolute ,amount of ,heat conveyed by it4--,greater ,portion of ,moisture in inter-tropical ,regions falls as ,rain in those ,regions4--,land along the ,equator tends to lower the ,temperature of the ,globe4--,influence of ,gulf-stream on ,climate of ,europe4--,temperature of ,space4--,radiation of a ,particle4--,professor ,dove on ,normal ,temperature4--,temperature of ,equator and ,poles in the ,absence of ,ocean-currents4--,temperature of ,london1 how much due to ,ocean-currents4 ,the absolute ,heating-power of ,ocean-currents4--,there is perhaps no physical agent concerned in the distribution of heat over the surface of the globe the influence of which has been so much underrated as that of ocean-currents4 ,this is1 no doubt1 owing to the fact that although their surface-temperature1 direction1 and general influence have obtained considerable attention1 yet little or nothing has been done towards determining the absolute amount of heat or of cold conveyed by them or the resulting absolute increase or decrease of temperature4 ,the modern method of determining the amount of heat-effects in absolute measure is1 doubtless1 destined to cast new light on all questions connected with climate1 as it has done1 and is still doing1 in every department of physics where energy1 under the form of heat1 is being studied4 ,but this method has hardly as yet been attempted in questions of meteorology2 and owing to the complicated nature of the phenomena with which the meteorologist has generally to deal1 its application will very often prove practically impossible4 ,nevertheless1 it is particularly suitable to all questions relating to the direct thermal effects of currents1 whatever the nature of these currents may happen to be4 ,in the application of the method to an ocean-current1 the two most important elements required as data are the volume of the stream and its mean temperature4 ,but although we know something of the temperature of most of the great ocean-currents1 yet1 with the exception of the ,gulf-stream1 little has been ascertained regarding their volume4 ,the breadth1 depth1 and temperature of the ,gulf-stream have formed the subject of extensive and accurate observations by the ,united ,states ,coast ,survey4 ,in the memoirs and charts of that survey cross-sections of the stream at various places are given1 showing its breadth and depth1 and also the temperature of the water from the surface to the bottom4 ,we are thus enabled to determine with some precision the mean temperature of the stream4 ,and knowing its mean velocity at any given section1 we have likewise a means of determining the number of cubic feet of water passing through that section in a given time4 ,but although we can obtain with tolerable accuracy the mean temperature1 yet observations regarding the velocity of the water at all depths have unfortunately not been made at any particular section4 ,consequently we have no means of estimating as accurately as we could wish the volume of the current4 ,nevertheless1 since we know the surface-velocity of the water at places where some of the sections were taken1 we are enabled to make at least a rough estimate of the volume4 ,from an examination of the published sections1 ,i came to the conclusion some years ago#aa that the total quantity of water conveyed by the stream is probably equal to that of a stream fifty miles broad and #a1jjj feet deep1#ab flowing at the rate of four miles an hour1 and that the mean temperature of the entire mass of moving water is not under #fe at the moment of leaving the ,gulf4 ,but to prevent the possibility of any objections being raised on the grounds that ,i may have over-estimated the volume of the stream1 ,i shall take the velocity to be two miles instead of four miles an hour4 ,we are warranted1 ,i think1 in concluding that the stream before it returns from its northern journey is on an average cooled down to at least #dj1ac consequently it loses #be of heat4 ,each cubic foot of water1 therefore1 in this case carries from the tropics for distribution upwards of #a1aeh1jjj foot-pounds of heat4 ,according to the above estimate of the size and velocity of the stream1 which in ,chapter ,,xi4 will be shown to be an under-estimate1 #b1ghg1hdj1jjj1jjj cubic feet of water are conveyed from the ,gulf per hour1 or #ff1ijh1afj1jjj1jjj cubic feet daily4 ,consequently the total quantity of heat thus transferred per day amounts to #gg1dgi1fej1jjj1jjj1jjj1jjj foot-pounds4 ,this estimate of the volume of the stream is considerably less by one-half than that given both by ,captain ,maury and by ,sir ,john ,herschel4 ,captain ,maury considers the ,gulf-stream equal to a stream thirty-two miles broad and #a1bjj feet deep1 flowing at the rate of five knots an hour4#ad ,this gives #f1afe1gjj1jjj1jjj cubic feet per hour as the quantity of water conveyed by this stream4 ,sir ,john ,herschel's estimate is still greater4 ,he considers it equal to a stream thirty miles broad and #b1bjj feet deep1 flowing at the rate of four miles an hour4#ae ,this makes the quantity #g1cei1ijj1jjj1jjj cubic feet per hour4 ,dr4 ,colding1 in his elaborate memoir on the ,gulf-stream1 estimates the volume at #e1gfj1jjj1jjj1jjj cubic feet per hour1 while ,mr4 ,laughton's estimate is nearly double that of mine4 ,from observations made by ,sir ,john ,herschel and by ,m4 ,pouillet on the direct heat of the sun1 it is found that1 were no heat absorbed by the atmosphere1 about eighty-three foot-pounds per second would fall upon a square foot of surface placed at right angles to the sun's rays4#af ,mr4 ,meech estimates that the quantity of heat cut off by the atmosphere is equal to about twenty-two per cent4 of the total amount received from the sun4 ,m4 ,pouillet estimates the loss at twenty-four per cent4 ,taking the former estimate1 #fdgd foot-pounds per second will therefore be the quantity of heat falling on a square foot of the earth's surface when the sun is in the zenith4 ,and were the sun to remain stationary in the zenith for twelve hours1 #b1gif1gfh foot-pounds would fall upon the surface4 ,it can be shown that the total amount of heat received upon a unit surface on the equator1 during the twelve hours from sunrise till sunset at the time of the equinoxes1 is to the total amount which would be received upon that surface1 were the sun to remain in the zenith during those twelve hours1 as the diameter of a circle to half its circumference1 or as #a to #aegjh4 ,it follows1 therefore1 that a square foot of surface on the equator receives from the sun at the time of the equinoxes #a1ghj1dgd foot-pounds daily1 and a square mile #di1fcf1gej1jjj1jjj foot-pounds daily4 ,but this amounts to only #a_/aefjiceth part of the quantity of heat daily conveyed from the tropics by the ,gulf-stream4 ,in other words1 the ,gulf-stream conveys as much heat as is received from the sun by #a1efj1ice square miles at the equator4 ,the amount thus conveyed is equal to all the heat which falls upon the globe within thirty-two miles on each side of the equator4 ,according to calculations made by ,mr4 ,meech1#ag the annual quantity of heat received by a unit surface on the frigid zone1 taking the mean of the whole zone1 is #ede_/abth of that received at the equator2 consequently the quantity of heat conveyed by the ,gulf-stream in one year is equal to the heat which falls on an average on #c1dcf1ijj square miles of the arctic regions4 ,the frigid zone or arctic regions contain #h1acj1jjj square miles4 ,there is actually1 therefore1 nearly one-half as much heat transferred from tropical regions by the ,gulf-stream as is received from the sun by the entire arctic regions1 the quantity conveyed from the tropics by the stream to that received from the sun by the arctic regions being nearly as two to five4 ,but we have been assuming in our calculations that the percentage of heat absorbed by the atmosphere is no greater in polar regions than it is at the equator1 which is not the case4 ,if we make due allowance for the extra amount absorbed in polar regions in consequence of the obliqueness of the sun's rays1 the total quantity of heat conveyed by the ,gulf-stream will probably be nearly equal to one-half the amount received from the sun by the entire arctic regions4 ,if we compare the quantity of heat conveyed by the ,gulf-stream with that conveyed by means of arial currents1 the result is equally startling4 ,the density of air to that of water is as #a to #ggj1 and its specific heat to that of water is as #a to #db2 consequently the same amount of heat that would raise #a cubic foot of water #a would raise #ggj cubic feet of air #db1 or #c1bcd cubic feet #a4 ,the quantity of heat conveyed by the ,gulf-stream is therefore equal to that which would be conveyed by a current of air #c1bcd times the volume of the ,gulf-stream1 at the same temperature and moving with the same velocity4 ,taking1 as before1 the width of the stream at fifty miles1 and its depth at #a1jjj feet1 and its velocity at two miles an hour1 it follows that1 in order to convey an equal amount of heat from the tropics by means of an arial current1 it would be necessary to have a current about #a mile deep1 and at the temperature of #fe1 blowing at the rate of two miles an hour from every part of the equator over the northern hemisphere towards the pole4 ,if its velocity were equal to that of a good sailing-breeze1 which ,sir ,john ,herschel states to be about twenty-one miles an hour1 the current would require to be above #fjj feet deep4 ,a greater quantity of heat is probably conveyed by the ,gulf-stream alone from the tropical to the temperate and arctic regions than by all the arial currents which flow from the equator4 ,we are apt1 on the other hand1 to over-estimate the amount of the heat conveyed from tropical regions to us by means of arial currents4 ,the only currents which flow from the equatorial regions are the upper currents1 or anti-trades as they are called4 ,but it is not possible that much heat can be conveyed directly by them4 ,the upper currents of the trade-winds1 even at the equator1 are nowhere below the snow-line2 they must therefore lie in a region of which the temperature is actually below the freezing-point4 ,in fact1 if those currents were warm1 they would elevate the snow-line above themselves4 ,the heated air rising off the hot burning ground at the equator1 after ascending a few miles1 becomes exposed to the intense cold of the upper regions of the atmosphere2 it then very soon loses all its heat1 and returns from the equator much colder than it went thither4 ,it is impossible that we can receive any heat directly from the equatorial regions by means of arial currents4 ,it is perfectly true that the south-west wind1 to which we owe so much of our warmth in this country1 is a continuation of the anti-trade2 but the heat which this wind brings to us is not derived from the equatorial regions4 ,this will appear evident1 if we but reflect that1 before the upper current descends to the snow-line after leaving the equator1 it must traverse a space of at least #b1jjj miles2 and to perform this long journey several days will be required4 ,during all this time the air is in a region below the freezing-point2 and it is perfectly obvious that by the time it begins to descend it must have acquired the temperature of the region in which it has been travelling4 ,if such be the case1 it is evident that a wind whose temperature is below #cb could never warm a country such as ours1 where the temperature does not fall below #ch or #ci4 ,the heat of our south-west winds is derived1 not directly from the equator1 but from the warm water of the ,atlantic--in fact1 from the ,gulf-stream4 ,the upper current acquires its heat after it descends to the earth4 ,there is one way1 however1 whereby heat is indirectly conveyed from the equator by the anti-trades2 that is1 in the form of aqueous vapour4 ,in the formation of one pound of water from aqueous vapour1 as ,professor ,tyndall strikingly remarks1 a quantity of heat is given out sufficient to melt five pounds of cast iron4#ah ,it must1 however1 be borne in mind that the greater part of the moisture of the south-west and west winds is derived from the ocean in temperate regions4 ,the upper current receives the greater part of its moisture after it descends to the earth1 whilst the moisture received at the equator is in great part condensed1 and falls as rain in those regions4 ,this latter assertion has been so frequently called in question that ,i shall give my reasons for making it4 ,according to ,dr4 ,keith ,johnston 78,physical ,atlas07 the mean rainfall of the torrid regions is ninety-six inches per annum1 while that of the temperate regions amounts to only thirty-seven inches4 ,if the greater part of the moisture of the torrid regions does not fall as rain in those regions1 it must fall as such beyond them4 ,now the area of the torrid to that of the two temperate regions is about as #cic to #ea4 ,consequently ninety-six inches of rain spread over the temperate regions would give seventy-four inches2 but this is double the actual rainfall of the temperate regions4 ,if1 again1 it were spread over both temperate and polar regions this would yield sixty-four inches1 which1 however1 is nearly double the mean rainfall of the temperate and polar regions4 ,if we add to this the amount of moisture derived from the ocean within temperate and polar regions1 we should have a far greater rainfall for these latitudes than for the torrid region1 and we know1 of course1 that it is actually far less4 ,this proves the truth of the assertion that by far the greater part of the moisture of the torrid regions falls in those regions as rain4 ,it will hardly do to object that the above may probably be an over-estimate of the amount of rainfall in the torrid zone1 for it is not at all likely that any error will ever be found which will affect the general conclusion at which we have arrived4 ,dr4 ,carpenter1 in proof of the small rainfall of the torrid zone1 adduces the case of the ,red ,sea1 where1 although evaporation is excessive1 almost no rain falls4 ,but the reason why the vapour raised from the ,red ,sea does not fall in that region as rain1 is no doubt owing to the fact that this sea is only a narrow strip of water in a dry and parched land1 the air above which is too greedy of moisture to admit of the vapour being deposited as rain4 ,over a wide expanse of ocean1 however1 where the air above is kept to a great extent in a constant state of saturation1 the case is totally different4 ,land at the ,equator tends to ,lower the ,temperature of the ,globe4--,the foregoing considerations1 as well as many others which might be stated1 lead to the conclusion that1 in order to raise the mean temperature of the whole earth1 water should be placed along the equator1 and not land1 as is supposed by ,sir ,charles ,lyell and others4 ,for if land is placed at the equator1 the possibility of conveying the sun's heat from the equatorial regions by means of ocean-currents is prevented4 ,the transference of heat could then be effected only by means of the upper currents of the trades2 for the heat conveyed by conduction along the solid crust1 if any1 can have no sensible effect on climate4 ,but these currents1 as we have just seen1 are ill-adapted for conveying heat4 ,the surface of the ground at the equator becomes intensely heated by the sun's rays4 ,this causes it to radiate its heat more rapidly into space than a surface of water heated under the same conditions4 ,again1 the air in contact with the hot ground becomes also more rapidly heated than in contact with water1 and consequently the ascending current of air carries off a greater amount of heat4 ,but were the heat thus carried away transferred by means of the upper currents to high latitudes and there employed to warm the earth1 then it might to a considerable extent compensate for the absence of ocean-currents1 and in this case land at the equator might be nearly as well adapted as water for raising the temperature of the whole earth4 ,but such is not the case2 for the heat carried up by the ascending current at the equator is not employed in warming the earth1 but is thrown off into the cold stellar space above4 ,this ascending current1 instead of being employed in warming the globe1 is in reality one of the most effectual means that the earth has of getting quit of the heat received from the sun1 and of thus maintaining a much lower temperature than it would otherwise possess4 ,it is in the equatorial regions that the earth loses as well as gains the greater part of its heat2 so that1 of all places1 here ought to be placed the substance best adapted for preventing the dissipation of the earth's heat into space1 in order to raise the general temperature of the earth4 ,water1 of all substances in nature1 seems to possess this quality to the greatest extent2 and1 besides1 it is a fluid1 and therefore adapted by means of currents to carry the heat which it receives from the sun to every region of the globe4 ,these results show 7although they have reference to only one stream7 that the general influence of ocean-currents on the distribution of heat over the surface of the globe must be very great4 ,if the quantity of heat transferred from equatorial regions by the ,gulf-stream alone is nearly equal to all the heat received from the sun by the arctic regions1 then how enormous must be the quantity conveyed from equatorial regions by all the ocean-currents together6 ,influence of the ,gulf-stream on the ,climate of ,europe4--,in a paper read before the ,british ,association at ,exeter1 ,mr4 ,a4 ,g4 ,findlay objects to the conclusions at which ,i have arrived in former papers on the subject1 that ,i have not taken into account the great length of time that the water requires in order to circulate1 and the interference it has to encounter in its passage4 ,the objection is1 that a stream so comparatively small as the ,gulf-stream1 after spreading out over such a large area of the ,atlantic1 and moving so slowly across to the shores of ,europe1 losing heat all the way1 would not be able to produce any very sensible influence on the climate of ,europe4 ,i am unable to perceive the force of this objection4 ,why1 the very efficiency of the stream as a heating agent necessarily depends upon the slowness of its motion4 ,did the ,gulf-stream move as rapidly along its whole course as it does in the ,straits of ,florida1 it could produce no sensible effect on the climate of ,europe4 ,it does not require much consideration to perceive this4 7#a7 ,if the stream during its course continued narrow1 deep1 and rapid1 it would have little opportunity of losing its heat1 and the water would carry back to the tropics the heat which it ought to have given off in the temperate and polar regions4 7#b7 ,the ,gulf-stream does not heat the shores of ,europe by direct radiation4 ,our island1 for example1 is not heated by radiation from a stream of warm water flowing along its shores4 ,the ,gulf-stream heats our island indirectly by heating the winds which blow over it to our shores4 ,the anti-trades1 or upper return-currents1 as we have seen1 bring no heat from the tropical regions4 ,after traversing some #b1jjj miles in a region of extreme cold they descend on the ,atlantic as a cold current1 and there absorb the heat and moisture which they carry to north-eastern ,europe4 ,those arial currents derive their heat from the ,gulf-stream1 or if it is preferred1 from the warm water poured into the ,atlantic by the ,gulf-stream4 ,how1 then1 are these winds heated by the warm water8 ,the air is heated in two ways1 viz41 by direct radiation from the water1 and by contact with the water4 ,now1 if the ,gulf-stream continued a narrow and deep current during its entire course similar to what it is at the ,straits of ,florida1 it could have little or no opportunity of communicating its heat to the air either by radiation or by contact4 ,if the stream were only about forty or fifty miles in breadth1 the arial particles in their passage across it would not be in contact with the warm water more than an hour or two4 ,moreover1 the number of particles in contact with the water1 owing to the narrowness of the stream1 would be small1 and there would therefore be little opportunity for the air becoming heated by contact4 ,the same also holds true in regard to radiation4 ,the more we widen the stream and increase its area1 the more we increase its radiating surface2 and the greater the radiating surface1 the greater is the quantity of heat thrown off4 ,but this is not all2 the number of arial particles heated by radiation increases in proportion to the area of the radiating surface2 consequently1 the wider the area over which the waters of the ,gulf-stream are spread1 the more effectual will the stream be as a heating agent4 ,and1 again1 in order that a very wide area of the ,atlantic may be covered with the warm waters of the stream1 slowness of motion is essential4 ,mr4 ,findlay supposes that fully one-half of the ,gulf-stream passes into the south-eastern branch1 and that it is only the north-eastern branch of the current that can be effectual in raising the temperature of ,europe4 ,but it appears to me that it is to this south-eastern portion of the current1 and not to the north-eastern1 that we1 in this country1 are chiefly indebted for our heat4 ,the south-west winds1 to which we owe our heat1 derive their temperature from this south-eastern portion which flows away in the direction of the ,azores4 ,the south-west winds which blow over the northern portion of the current which flows past our island up into the arctic seas cannot possibly cross this country1 but will go to heat ,norway and northern ,europe4 ,the north-eastern portion of the stream1 no doubt1 protects us from the ice of ,greenland by warming the north-west winds which come to us from that cold region4 ,mr4 ,buchan1 ,secretary of the ,scottish ,meteorological ,society1 has shown#ai that in a large tract of the ,atlantic between latitudes #bj and #dj ,n41 the mean pressure of the atmosphere is greater than in any other place on the globe4 ,to the west of ,madeira1 between longitude #aj and #dj ,w41 the mean annual pressure amounts to #cjb inches1 while between ,iceland and ,spitzbergen it is only #bif1 a lower mean pressure than is found in any other place on the northern hemisphere4 ,there must consequently1 he concludes1 be a general tendency in the air to flow from the former to the latter place along the earth's surface4 ,now1 the air in moving from the lower to the higher latitudes tends to take a north-easterly direction1 and in this case will pass over our island in its course4 ,this region of high pressure1 however1 is situated in the very path of the south-eastern branch of the ,gulf-stream1 and consequently the winds blowing therefrom will carry directly to ,britain the heat of the ,gulf-stream4 ,as we shall presently see1 it is as essential to the heating of our island as to that of the southern portion of ,europe1 that a very large proportion of the waters of the ,gulf-stream should spread over the surface of the ,atlantic and never pass up into the arctic regions4 ,even according to ,mr4 ,findlay's own theory1 it is to the south-west wind1 heated by the warm waters of the ,atlantic1 that we are indebted for the high temperature of our climate4 ,but he seems to be under the impression that the ,atlantic would be able to supply the necessary heat independently of the ,gulf-stream4 ,this1 it seems to me1 is the fundamental error of all those who doubt the efficiency of the stream4 ,it is a mistake1 however1 into which one is very apt to fall who does not adopt the more rigid method of determining heat-results in absolute measure4 ,when we apply this method1 we find that the ,atlantic1 without the aid of such a current as the ,gulf-stream1 would be wholly unable to supply the necessary amount of heat to the south-west winds4 ,the quantity of heat conveyed by the ,gulf-stream1 as we have seen1 is equal to all the heat received from the sun by #a1efj1ice square miles at the equator4 ,the mean annual quantity of heat received from the sun by the temperate regions per unit surface is to that received by the equator as #ijh to #ab4bj ,consequently1 the quantity of heat conveyed by the stream is equal to all the heat received from the sun by #b1jfb1ifj square miles of the temperate regions4 ,the total area of the ,atlantic from the latitude of the ,straits of ,florida1 #bjj miles north of the tropic of ,cancer1 up to the ,arctic ,circle1 including also the ,german ,ocean1 is about #h1ejj1jjj square miles4 ,in this case the quantity of heat carried by the ,gulf-stream into the ,atlantic through the ,straits of ,florida1 is to that received by this entire area from the sun as #a to #dab1 or in round numbers as #a to #d4 ,it therefore follows that one-fifth of all the heat possessed by the waters of the ,atlantic over that area1 even supposing that they absorb every ray that falls upon them1 is derived from the ,gulf-stream4 ,would those who call in question the efficiency of the ,gulf-stream be willing to admit that a decrease of one-fourth in the total amount of heat received from the sun1 over the entire area of the ,atlantic from within #bjj miles of the tropical zone up to the arctic regions1 would not sensibly affect the climate of northern ,europe8 ,if they would not willingly admit this1 why1 then1 contend that the ,gulf-stream does not affect climate8 for the stoppage of the ,gulf-stream would deprive the ,atlantic of #gg1dgi1fej1jjj1jjj1jjj1jjj foot-pounds of energy in the form of heat per day1 a quantity equal to one-fourth of all the heat received from the sun by that area4 ,how much1 then1 of the temperature of the south-west winds derived from the water of the ,atlantic is due to the ,gulf-stream8 ,were the sun extinguished1 the temperature over the whole earth would sink to nearly that of stellar space1 which1 according to the investigations of ,sir ,john ,herschel#ba and of ,m4 ,pouillet1#bb is not above #bci ,f4 ,were the earth possessed of no atmosphere1 the temperature of its surface would sink to exactly that of space1 or to that indicated by a thermometer exposed to no other heat-influence than that of radiation from the stars4 ,but the presence of the atmospheric envelope would slightly modify the conditions of things2 for the heat from the stars 7which of course constitutes what is called the temperature of space7 would1 like the sun's heat1 pass more freely through the atmosphere than the heat radiated back from the earth1 and there would in consequence of this be an accumulation of heat on the earth's surface4 ,the temperature would therefore stand a little higher than that of space2 or1 in other words1 it would stand a little higher than it would otherwise do were the earth exposed in space to the direct radiation of the stars without the atmospheric envelope4 ,but1 for reasons which will presently be stated1 we may in the meantime1 till further light is cast upon this matter1 take -#bci ,f4 as probably not far from what would be the temperature of the earth's surface were the sun extinguished4 ,suppose now that we take the mean annual temperature of the ,atlantic at1 say1 #ef4bc ,then #bci #ef #bie represents the number of degrees of rise due to the heat which it receives4 ,in other words1 it takes all the heat that the ,atlantic receives to maintain its temperature #bie above the temperature of space4 ,stop the ,gulf-stream1 and the ,atlantic would be deprived of one-fifth of the heat which it possesses4 ,then1 if it takes five parts of heat to maintain a temperature of #bie above that of space1 the four parts which would remain after the stream was stopped would only be able to maintain a temperature of four-fifths of #bie1 or #bcf above that of space3 the stoppage of the ,gulf-stream would therefore deprive the ,atlantic of an amount of heat which would be sufficient to maintain its temperature #ei above what it would otherwise be1 did it depend alone upon the heat received directly from the sun4 ,it does not1 of course1 follow that the ,gulf-stream actually maintains the temperature #ei above what it would otherwise be were there no ocean-currents1 because the actual heating-effect of the stream is neutralized to a very considerable extent by cold currents from the arctic regions4 ,but #ei of rise represents its actual power2 consequently #ei1 minus the lowering effect of the cold currents1 represents the actual rise4 ,what the rise may amount to at any particular place must be determined by other means4 ,this method of calculating how much the temperature of the earth's surface would rise or fall from an increase or a decrease in the absolute amount of heat received is that adopted by ,sir ,john ,herschel in his 8,outlines of ,astronomy10 #cfi;a4 ,about three years ago1 in an article in the ,reader1 ,i endeavoured to show that this method is not rigidly correct4 ,it has been shown from the experiments of ,dulong and ,petit1 ,dr4 ,balfour ,stewart1 ,professor ,draper1 and others1 that the rate at which a body radiates its heat off into space is not directly proportionate to its absolute temperature4 ,the rate at which a body loses its heat as its temperature rises increases more rapidly than the temperature4 ,as a body rises in temperature the rate at which it radiates off its heat increases2 the rate of this increase1 however1 is not uniform1 but increases with the temperature4 ,consequently the temperature is not lowered in proportion to the decrease of the sun's heat4 ,but at the comparatively low temperature with which we have at present to deal1 the error resulting from assuming the decrease of temperature to be proportionate to the decrease of heat would not be great4 ,it may be remarked1 however1 that the experiments referred to were made on solids2 but1 from certain results arrived at by ,dr4 ,balfour ,stewart1 it would seem that the radiation of a material particle may be proportionate to its absolute temperature4#bd ,this physicist found that the radiation of a thick plate of glass increases more rapidly than that of a thin plate as the temperature rises1 and that1 if we go on continually diminishing the thickness of the plate whose radiation at different temperatures we are ascertaining1 we find that as it grows thinner and thinner the rate at which it radiates off its heat as its temperature rises becomes less and less4 ,in other words1 as the plate grows thinner and thinner its rate of radiation becomes more and more proportionate to its absolute temperature4 ,and we can hardly resist the conviction that if we could possibly go on diminishing the thickness of the plate till we reached a film so thin as to embrace but only one particle in its thickness1 its rate of radiation would be proportionate to its temperature4 ,dr4 ,balfour ,stewart has very ingeniously suggested the probable reason why the rate of radiation of thick plates increases with rise of temperature more rapidly than that of thin4 ,it is this3 all substances are more diathermanous for heat of high temperatures than for heat of low temperatures4 ,when a body is at a low temperature1 we may suppose that only the exterior rows of particles supply the radiation1 the heat from the interior particles being all stopped by the exterior ones1 the substance being very opaque for heat of low temperature2 while at a high temperature we may imagine that part of the heat from the interior particles is allowed to pass1 thereby swelling the total radiation4 ,but as the plate becomes thinner and thinner1 the obstructions to interior radiation become less and less1 and as these obstructions are greater for radiation at low temperatures than for radiation at high temperatures1 it necessarily follows that1 by reducing the thickness of the plate1 we assist radiation at low temperatures more than we do at high4 ,in a gas1 where each particle may be assumed to radiate by itself1 and where the particles stand at a considerable distance from one another1 the obstruction to interior radiation must be far less than in a solid4 ,in this case the rate at which a gas radiates off its heat as its temperature rises must increase more slowly than that of a solid substance4 ,in other words1 its rate of radiation must correspond more nearly to its absolute temperature than that of a solid4 ,if this be the case1 a reduction in the amount of heat received from the sun1 owing to an increase of his distance1 should tend to produce a greater lowering effect on the temperature of the air than it does on the temperature of the solid ground4 ,but as the temperature of our climate is determined by the temperature of the air1 it must follow that the error of assuming that the decrease of temperature would be proportionate to the decrease in the intensity of the sun's heat may not be great4 ,it may be observed here1 although it does not bear directly on this point1 that although the air in a room1 for example1 or at the earth's surface is principally cooled by convection rather than by radiation1 yet it is by radiation alone that the earth's atmosphere parts with its heat to stellar space2 and this is the chief matter with which we are at present concerned4 ,air1 like all other gases1 is a bad radiator2 and this tends to protect it from being cooled to such an extent as it would otherwise be1 were it a good radiator like solids4 ,true1 it is also a bad absorber2 but as it is cooled by radiation into space1 and heated1 not altogether by absorption1 but to a very large extent by convection1 it on the whole gains its heat more easily than it loses it1 and consequently must stand at a higher temperature than it would do were it heated by absorption alone4 ,but1 to return2 the error of regarding the decrease of temperature as proportionate to the decrease in the amount of heat received1 is probably neutralized by one of an opposite nature1 viz41 that of taking space at too high a temperature2 for by so doing we make the result too small4 ,we know that absolute zero is at least #dic below the melting-point of ice4 ,this is #bbb below that of space4 ,consequently1 if the heat derived from the stars is able to maintain a temperature of #bci1 or #bbb of absolute temperature1 then nearly as much heat is derived from the stars as from the sun4 ,but if so1 why do the stars give so much heat and so very little light8 ,if the radiation from the stars could maintain a thermometer #bbb above absolute zero1 then space must be far more transparent to heat-rays than to light-rays1 or else the stars give out a great amount of heat1 but very little light1 neither of which suppositions is probably true4 ,the probability is1 ,i venture to presume1 that the temperature of space is not very much above absolute zero4 ,at the time when these investigations into the probable temperature of space were made1 at least as regards the labours of ,pouillet1 the modern science of heat had no existence1 and little or nothing was then known with certainty regarding absolute zero4 ,in this case the whole matter would require to be reconsidered4 ,the result of such an investigation in all probability would be to assign a lower temperature to stellar space than #bci4 ,taking all these various considerations into account1 it is probable that if we adopt #bci as the temperature of space1 we shall not be far from the truth in assuming that the absolute temperature of a place above that of space is proportionate to the amount of heat received from the sun4 ,we may1 therefore1 in this case conclude that #ei of rise is probably not very far from the truth1 as representing the influence of the ,gulf-stream4 ,the ,gulf-stream1 instead of producing little or no effect1 produces an effect far greater than is generally supposed4 ,our island has a mean annual temperature of about #ab above the normal due to its latitude4 ,this excess of temperature has been justly attributed to the influence of the ,gulf-stream4 ,but it is singular how this excess should have been taken as the measure of the rise resulting from the influence of the stream4 ,these figures only represent the number of degrees that the mean normal temperature of our island stands above what is called the normal temperature of the latitude4 ,the mode in which ,professor ,dove constructed his ,tables of normal temperature was as follows3--,he took the temperature of thirty-six equidistant points on every ten degrees of latitude4 ,the mean temperature of these thirty-six points he calls in each case the normal temperature of the parallel4 ,the excess above the normal merely represents how much the stream raises our temperature above the mean of all places on the same latitude1 but it affords us no information regarding the absolute rise produced4 ,in the ,pacific1 as well as in the ,atlantic1 there are immense masses of water flowing from the tropical to the temperate regions4 ,now1 unless we know how much of the normal temperature of a latitude is due to ocean-currents1 and how much to the direct heat of the sun1 we could not possibly1 from ,professor ,dove's ,tables1 form the most distant conjecture as to how much of our temperature is derived from the ,gulf-stream4 ,the overlooking of this fact has led to a general misconception regarding the positive influence of the ,gulf-stream on temperature4 ,the #ab marked in ,tables of normal temperature do not represent the absolute effect of the stream1 but merely show how much the stream raises the temperature of our country above the mean of all places on the same latitude4 ,other places have their temperature raised by ocean-currents as well as this country2 only the ,gulf-stream produces a rise of several degrees over and above that produced by other streams in the same latitude4 ,at present there is a difference merely of #hj between the mean temperature of the equator and the poles2#be but were each part of the globe's surface to depend only upon the direct heat which it receives from the sun1 there ought1 according to theory1 to be a difference of more than #bjj4 ,the annual quantity of heat received at the equator is to that received at the poles 7supposing the proportionate quantity absorbed by the atmosphere to be the same in both cases7 as #ab to #dih1 or1 say1 as #ab to #e4 ,consequently1 if the temperatures of the equator and the poles be taken as proportionate to the absolute amount of heat received from the sun1 then the temperature of the equator above that of space must be to that of the poles above that of space as #ab to #e4 ,what ought1 therefore1 to be the temperatures of the equator and the poles1 did each place depend solely upon the heat which it receives directly from the sun8 ,were all ocean and arial currents stopped1 so that there could be no transference of heat from one part of the earth's surface to another1 what ought to be the temperatures of the equator and the poles8 ,we can at least arrive at a rough estimate on this point4 ,if we diminish the quantity of warm water conveyed from the equatorial regions to the temperate and arctic regions1 the temperature of the equator will begin to rise1 and that of the poles to sink4 ,it is probable1 however1 that this process would affect the temperature of the poles more than it would that of the equator2 for as the warm water flows from the equator to the poles1 the area over which it is spread becomes less and less4 ,but as the water from the tropics has to raise the temperature of the temperate regions as well as the polar1 the difference of effect at the equator and poles might not1 on that account1 be so very great4 ,let us take a rough estimate4 ,say that1 as the temperature of the equator rises one degree1 the temperature of the poles sinks one degree and a half4 ,the mean annual temperature of the globe is about #eh4 ,the mean temperature of the equator is #hj1 and that of the poles #j4 ,let ocean and arial currents now begin to cease1 the temperature of the equator commences to rise and the temperature of the poles to sink4 ,for every degree that the temperature of the equator rises1 that of the poles sinks #a2 and when the currents are all stopped and each place becomes dependent solely upon the direct rays of the sun1 the mean annual temperature of the equator above that of space will be to that of the poles1 above that of space1 as #ab to #e4 ,when this proportion is reached1 the equator will be #cgd above that of space1 and the poles #aef2 for #cgd is to #aef as #ab is to #e4 ,the temperature of space we have seen to be #bci1 consequently the temperature of the equator will in this case be #ace1 reckoned from the zero of the ,fahrenheit thermometer1 and the poles #hc below zero4 ,the equator would therefore be #ee warmer than at present1 and the poles #hc colder4 ,the difference between the temperature of the equator and the poles will in this case amount to #bah4 ,now1 if we take into account the quantity of positive energy in the form of heat carried by warm currents from the equator to the temperate and polar regions1 and also the quantity of negative energy 7cold7 carried by cold currents from the polar regions to the equator1 we shall find that they are sufficient to reduce the difference of temperature between the poles and the equator from #bah to #hj4 ,the quantity of heat received in the latitude of ,london1 for example1 is to that received at the equator nearly as #ab to #h4 ,this1 according to theory1 should produce a difference of about #abe4 ,the temperature of the equator above that of space1 as we have seen1 would be #cgd4 ,therefore #bdi above that of space would represent the temperature of the latitude of ,london4 ,this would give #aj as its temperature4 ,the stoppage of all ocean and arial currents would thus increase the difference between the equator and the latitude of ,london by about #he4 ,the stoppage of ocean-currents would not be nearly so much felt1 of course1 in the latitude of ,london as at the equator and the poles1 because1 as has been already noticed1 in all latitudes midway between the equator and the poles the two sets of currents to a considerable extent compensate each other--the warm currents from the equator raise the temperature1 while the cold ones from the poles lower it2 but as the warm currents chiefly keep on the surface and the cold return-currents are principally under-currents1 the heating effect very greatly exceeds the cooling effect4 ,now1 as we have seen1 the stoppage of all currents would raise the temperature of the equator #ee2 that is to say1 the rise at the equator alone would increase the difference of temperature between the equator and that of ,london by #ee4 ,but the actual difference1 as we have seen1 ought to be #he2 consequently the temperature of ,london would be lowered #cj by the stoppage of the currents4 ,for if we raise the temperature of the equator #ee and lower the temperature of ,london #cj1 we then increase the difference by #he4 ,the normal temperature of the latitude of ,london being #dj1 the stoppage of all ocean and arial currents would thus reduce it to #aj4 ,but the ,gulf-stream raises the actual mean temperature of ,london #aj above the normal4 ,consequently #cj #aj #dj represents the actual rise at ,london due to the influence of the ,gulf-stream over and above all the lowering effects resulting from arctic currents4 ,on some parts of the ,american shores on the latitude of ,london1 the temperature is #aj below the normal4 ,the stoppage of all ocean and arial currents would therefore lower the temperature there only #bj4 ,it is at the equator and the poles that the great system of ocean and arial currents produces its maximum effects4 ,the influence becomes less and less as we recede from those places1 and between them there is a point where the influence of warm currents from the equator and of cold currents from the poles exactly neutralize each other4 ,at this point the stoppage of ocean-currents would not sensibly affect temperature4 ,this point1 of course1 is not situated on the same latitude in all meridians1 but varies according to the position of the meridian in relation to land1 and ocean-currents1 whether cold or hot1 and other circumstances4 ,a line drawn round the globe through these various points would be very irregular4 ,at one place1 such as on the western side of the ,atlantic1 where the arctic current predominates1 the neutral line would be deflected towards the equator1 while on the eastern side1 where warm currents predominate1 the line would be deflected towards the north4 ,it is a difficult problem to determine the mean position of this line2 it probably lies somewhere not far north of the tropics4 ,,chapter ,,iii4 ,,ocean-,,currents ,,in ,,relation ,,to ,,the ,,distribution ,,of ,,heat ,,over ,,the ,,globe4--7,continued47 ,influence of the ,gulf-stream on the ,climate of the ,arctic ,regions4--,absolute ,amount of ,heat received by the ,arctic ,regions from the ,sun4--,influence of ,ocean-currents shown by another ,method4--,temperature of a ,globe all ,water or all ,land according to ,professor ,j4 ,d4 ,forbes4--,an important ,consideration overlooked4--,without ,ocean-currents the ,globe would not be habitable4--,conclusions not affected by ,imperfection of ,data4 ,influence of the ,gulf-stream on the ,climate of the ,arctic ,regions4--,does the ,gulf-stream pass into the arctic regions8 ,are the seas around ,spitzbergen and ,north ,greenland heated by the warm water of the stream8 ,those who deny this nevertheless admit the existence of an arctic current4 ,they admit that an immense mass of cold water is continually flowing south from the polar regions around ,greenland into the ,atlantic4 ,if it be admitted1 then1 that a mass of water flows across the arctic circle from north to south1 it must also be admitted that an equal mass flows across from south to north4 ,it is also evident that the water crossing from south to north must be warmer than the water crossing from north to south2 for the temperate regions are warmer than the arctic1 and the ocean in temperate regions warmer than the ocean in the arctic2 consequently the current which flows into the arctic seas1 to compensate for the cold arctic current1 must be a warmer current4 ,is the ,gulf-stream this warm current8 ,does this compensating warm current proceed from the ,atlantic or from the ,pacific8 ,if it proceeds from the ,atlantic1 it is simply the warm water of the ,gulf-stream4 ,we may call it the warm water of the ,atlantic if we choose2 but this cannot materially affect the question at issue1 for the heat which the waters of the ,atlantic possess is derived1 as we have seen1 to an enormous extent from the water brought from the tropics by the ,gulf-stream4 ,if we deny that the warm compensating current comes from the ,atlantic1 then we must assume that it comes from the ,pacific4 ,but if the cold current flows from the arctic regions into the ,atlantic1 and the warm compensating current from the ,pacific into the arctic regions1 the highest temperature should be found on the ,pacific side of the arctic regions and not on the ,atlantic side2 the reverse1 however1 is the case4 ,in the ,atlantic1 for example1 the #da isothermal line reaches to latitude #fecj1 while in the ,pacific it nowhere goes beyond latitude #eg4 ,the #bg isotherm reaches to latitude #ge in the ,atlantic1 but in the ,pacific it does not pass beyond #fd4 ,and the #ad isotherm reaches the north of ,spitzbergen in latitude #hj1 whereas on the ,pacific side of the arctic regions it does not reach to latitude #gb4 ,on no point of the earth's surface does the mean annual temperature rise so high above the normal as in the northern ,atlantic1 just at the arctic circle1 at a spot believed to be in the middle of the ,gulf-stream4 ,this place is no less than #bbe above the normal1 while in the northern ,pacific the temperature does not anywhere rise more than #i above the normal4 ,these facts prove that the warm current passes up the ,atlantic into the arctic regions and not up the ,pacific1 or at least that the larger amount of warm water must pass into the arctic regions through the ,atlantic4 ,in other words1 the ,gulf-stream is the warm compensating current4 ,not only must there be a warm stream1 but one of very considerable magnitude1 in order to compensate for the great amount of cold water that is constantly flowing from the arctic regions1 and also to maintain the temperature of those regions so much above the temperature of space as they actually are4 ,no doubt1 when the results of the late dredging expedition are published1 they will cast much additional light on the direction and character of the currents forming the north-eastern branch of the ,gulf-stream4 ,the average quantity of heat received by the arctic regions as a whole per unit surface to that received at the equator1 as we have already seen1 is as #ede to #ab1 assuming that the percentage of rays cut off by the atmosphere is the same at both places4 ,in this case the mean annual temperature of the arctic regions1 taken as a whole1 would be about #fi1 did those regions depend entirely for their temperature upon the heat received directly from the sun4 ,but the temperature would not even reach to this2 for the percentage of rays cut off by the atmosphere in arctic regions is generally believed to be greater than at the equator1 and consequently the actual mean quantity of heat received by the arctic regions will be less than #edeabths of what is received at the equator4 ,in the article on ,climate in the 8,encyclopdia ,britannica0 there is a ,table calculated upon the principle that the quantity of heat cut off is proportionate to the number of arial particles which the rays have to encounter before reaching the surface of the earth--that1 as a general rule1 if the tracts of the rays follow an arithmetical progression1 the diminished force with which the rays reach the ground will form a decreasing geometrical progression4 ,according to this ,table about #ge per cent4 of the sun's rays are cut off by the atmosphere in arctic regions4 ,if #ge per cent4 of the rays were cut off by the atmosphere in arctic regions1 then the direct rays of the sun could not maintain a mean temperature #ajj above that of space4 ,but this is no doubt much too high a percentage for the quantity of heat cut off2 for recent discoveries in regard to the absorption of radiant heat by gases and vapours prove that ,tables computed on this principle must be incorrect4 ,the researches of ,tyndall and ,melloni show that when rays pass through any substance1 the absorption is rapid at first3 but the rays are soon 8sifted10 as it is called1 and they then pass onwards with but little further obstruction4 ,still1 however1 owing to the dense fogs which prevail in arctic regions1 the quantity of heat cut off must be considerable4 ,if as much as #ej per cent4 of the sun's rays are cut off by the atmosphere in arctic regions1 the amount of heat received directly from the sun would not be sufficient to maintain a mean annual temperature of #ajj4 ,consequently the arctic regions must depend to an enormous extent upon ocean-currents for their temperature4 ,influence of ,ocean-currents shown by another ,method4--,that the temperature of the arctic regions would sink enormously1 and the temperature of the equator rise enormously1 were all ocean-currents stopped1 can be shown by another method--viz41 by taking the mean annual temperature from the equator to the pole along a meridian passing through the ocean1 say1 the ,atlantic1 and comparing it with the mean annual temperature taken along a meridian passing through a great continent1 say1 the ,asiatic4 ,professor ,j4 ,d4 ,forbes1 in an interesting memoir1#bf has endeavoured by this method to determine what would be the temperature of the equator and the poles were the globe all water or all land4 ,he has taken the temperature of the two meridians from the tables and charts of ,professor ,dove1 and ascertained the exact proportion of land and water on every #aj of latitude from the equator to the poles1 with the view of determining what proportion of the average temperature of the globe in each parallel is due to the land1 and what to the water which respectively belongs to it4 ,he next endeavours to obtain a formula for expressing the mean temperature of a given parallel1 and thence arrives at 8an approximate answer to the inquiry as to what would have been the equatorial or polar temperature of the globe1 or that of any latitude1 had its surface been entirely composed of land or of water40 ,the result at which he arrived is this3 that1 were the surface of the globe all water1 #gag would be the temperature of the equator1 and #abe the temperature of the poles2 and were the surface all land1 #ajih would be the temperature of the equator1 and #bef the temperature of the poles4 ,but in ,professor ,forbes's calculations no account whatever is taken of the influence of currents1 whether of water or of air1 and the difference of temperature is attributed wholly to difference of latitude and the physical properties of land and water in relation to their powers in absorbing and detaining the sun's rays1 and to the laws of conduction and of convection which regulate the internal motion of heat in the one and in the other4 ,he considers that the effects of currents are all compensatory4 8,if a current of hot water10 he says1 8moderates the cold of a ,lapland winter1 the counter-current1 which brings the cold of ,greenland to the shores of the ,united ,states1 in a great measure restores the balance of temperature1 so far as it is disturbed by this particular influence4 ,the prevalent winds1 in like manner1 including the trade-winds1 though they render some portions of continents1 on the average1 hotter or colder than others1 produce just the contrary effect elsewhere4 ,each continent1 if it has a cold eastern shore1 has likewise a warm western one2 and even local winds have for the most part established laws of compensation4 ,in a given parallel of latitude all these secondary causes of local climate may be imagined to be mutually compensatory1 and the outstanding gradation of mean or normal temperature will mainly depend1 #ast1 upon the effect of latitude simply2 #bnd1 on the distribution of land and water considered in their primary or statical effect40 ,it is singular that a physicist so acute as ,professor ,forbes should1 in a question such as this1 leave out of account the influence of currents1 under the impression that their effects were compensatory4 ,if there is a constant transference of hot water from the equatorial regions to the polar1 and of cold water from the polar regions to the equatorial 7a thing which ,professor ,forbes admitted71 then there can only be one place between the equator and the pole where the two sets of currents compensate each other4 ,at all places on the equatorial side of this point a cooling effect is the result4 ,starting from this neutral point1 the preponderance of the cooling effect over the heating increases as we approach towards the equator1 and the preponderance of the heating effect over the cooling increases as we recede from this point towards the pole--the cooling effect reaching a maximum at the equator1 and the heating effect a maximum at the pole4 ,had ,professor ,forbes observed this important fact1 he would have seen at once that the low temperature of the land in high latitudes1 in comparison with that of the sea1 was no index whatever as to how much the temperature of those regions would sink were the sea entirely removed and the surface to become land2 for the present high temperature of the sea is not due wholly to the mere physical properties of water1 but to a great extent is due to the heat brought by currents from the equator4 ,now1 unless it is known how much of the absolute temperature of the ocean in those latitudes is due to currents1 we cannot tell how much the removal of the sea would lower the absolute temperature of those places4 ,were the sea removed1 the continents in high latitudes would not simply lose the heating advantages which they presently derive from the mere fact of their proximity to so much sea1 but the removal would1 in addition to this1 deprive them of an enormous amount of heat which they at present receive from the tropics by means of ocean-currents4 ,and1 on the other hand1 at the equator1 were the sea removed1 the continents there would not simply lose the cooling influences which result from their proximity to so much water1 but1 in addition to this1 they would have to endure the scorching effects which would result from the heat which is at present carried away from the tropics by ocean-currents4 ,we have already seen that ,professor ,forbes concluded that the removal of the sea would raise the mean temperature of the equator #cj1 and lower the temperature of the poles #bh2 it is therefore perfectly certain that1 had he added to his result the effect due to ocean-currents1 and had he been aware that about one-fifth of all the heat possessed by the ,atlantic is actually derived from the equator by means of the ,gulf-stream1 he would have assigned a temperature to the equator and the poles1 of a globe all land1 differing not very far from what ,i have concluded would be the temperature of those places were all ocean and arial currents stopped1 and each place to depend solely upon the heat which it received directly from the sun4 ,without ,ocean-currents the ,globe would not be habitable4--,all these foregoing considerations show to what an extent the climatic condition of our globe is due to the thermal influences of ocean-currents4 ,as regards the northern hemisphere1 we have two immense oceans1 the ,pacific and the ,atlantic1 extending from the equator to near the north pole1 or perhaps to the pole altogether4 ,between these two oceans lie two great continents1 the eastern and the western4 ,owing to the earth's spherical form1 far too much heat is received at the equator and far too little at high latitudes to make the earth a suitable habitation for sentient beings4 ,the function of these two great oceans is to remove the heat from the equator and carry it to temperate and polar regions4 ,arial currents could not do this4 ,they might remove the heat from the equator1 but they could not1 as we have already seen1 carry it to the temperate and polar regions2 for the greater portion of the heat which arial currents remove from the equator is dissipated into stellar space3 the ocean alone can convey the heat to distant shores4 ,but arial currents have a most important function2 for of what avail would it be1 though ocean-currents should carry heat to high latitudes1 if there were no means of distributing the heat thus conveyed over the land8 ,the function of arial currents is to do this4 ,upon this twofold arrangement depends the thermal condition of the globe4 ,exclude the waters of the ,pacific and the ,atlantic from temperate and polar regions and place them at the equator1 and nothing now existing on the globe could live in high latitudes4 ,were these two great oceans placed beside each other on one side of the globe1 and the two great continents placed beside each other on the other side1 the northern hemisphere would not then be suitable for the present order of things3 the land on the central and on the eastern side of the united continent would be far too cold4 ,the foregoing ,conclusions not affected by the ,imperfection of the ,data4--,the general results at which we have arrived in reference to the influence of ocean-currents on the climatic condition of the globe are not affected by the imperfection of the data employed4 ,it is perfectly true that considerable uncertainty prevails regarding some of the data2 but1 after making the fullest allowance for every possible error1 the influence of currents is so enormous that the general conclusion cannot be materially affected4 ,i can hardly imagine that any one familiar with the physics of the subject will be likely to think that1 owing to possible errors in the data1 the effects have probably been doubled4 ,even admitting1 however1 that this were proved to be the case1 still that would not materially alter the general conclusion at which we have arrived4 ,the influence of ocean-currents in the distribution of heat over the surface of the globe would still be admittedly enormous1 whether we concluded that owing to them the present temperature of the equator is #ee or #bg colder than it would otherwise be1 or the poles #hc or #da hotter than they would be did no currents exist4 ,nay1 more1 suppose we should again halve the result2 even in that case we should have to admit that1 owing to ocean-currents1 the equator is about #ad colder and the poles about #ba hotter than they would otherwise be2 in other words1 we should have to admit that1 were it not for ocean-currents1 the mean temperature of the equator would be about #ajj and the mean temperature of the poles about #ba4 ,if the influence of ocean-currents in reducing the difference between the temperature of the equator and poles amounted to only a few degrees1 it would of course be needless to put much weight on any results arrived at by the method of calculation which ,i have adopted2 but when it is a matter of two hundred degrees1 it is not at all likely that the general results will be very much affected by any errors which may ever be found in the data4 ,objections of a palontological nature have frequently been urged against the opinion that our island is much indebted for its mild climate to the influence of the ,gulf-stream2 but1 from what has already been stated1 it must be apparent that all objections of that nature are of little avail4 ,the palontologist may detect1 from the character of the flora and fauna brought up from the sea-bottom by dredging and other means1 the presence of a warm or of a cold current2 but this can never enable him to prove that the temperate and polar regions are not affected to an enormous extent by warm water conveyed from the equatorial regions4 ,for anything that palontology can show to the contrary1 were ocean-currents to cease1 the mean annual temperature of our island might sink below the present midwinter temperature of ,siberia4 ,what would be the thermal condition of our globe were there no ocean-currents is a question for the physicist2 not for the naturalist4 ,,chapter ,,iv4 ,,outline ,,of ,,the ,,physical ,,agencies ,,which ,,lead ,,to ,,secular ,,changes ,,of ,,climate4 ,eccentricity of the ,earth's ,orbit2 its ,effect on ,climate4--,glacial ,epoch not the direct ,result of an ,increase of ,eccentricity4--,an important ,consideration overlooked4--,change of ,eccentricity affects ,climate only indirectly4--,agencies which are brought into ,operation by an ,increase of ,eccentricity4--,how an ,accumulation of ,snow is produced4--,the ,effect of ,snow on the ,summer ,temperature4--,reason of the low ,summer ,temperature of ,polar ,regions4--,deflection of ,ocean-currents the chief ,cause of secular ,changes of ,climate4--,how the foregoing ,causes deflect ,ocean-currents4--,nearness of the ,sun in ,perigee a ,cause of the ,accumulation of ,ice4--,a remarkable ,circumstance regarding the ,causes which lead to secular ,changes of ,climate4--,the primary ,cause an ,increase of ,eccentricity4--,mean ,temperature of whole ,earth should be greater in ,aphelion than in ,perihelion4--,professor ,tyndall on the ,glacial ,epoch4--,a general ,reduction of ,temperature will not produce a ,glacial ,epoch4--,objection from the present ,condition of the ,planet ,mars4 ,primary cause of ,change of ,eccentricity of the ,earth's ,orbit4--,there are two causes affecting the position of the earth in relation to the sun1 which must1 to a very large extent1 influence the earth's climate2 viz41 the precession of the equinoxes and the change in the eccentricity of the earth's orbit4 ,if we duly examine the combined influence of these two causes1 we shall find that the northern and southern portions of the globe are subject to an excessively slow secular change of climate1 consisting in a slow periodic change of alternate warmer and colder cycles4 ,according to the calculations of ,leverrier1 the superior limit of the earth's eccentricity is #jjggge4bg ,the eccentricity is at present diminishing1 and will continue to do so during #bc1ihj years1 from the year #ahjj ,a4,d41 when its value will be then #jjcad4 ,the change in the eccentricity of the earth's orbit may affect the climate in two different ways2 viz41 by either increasing or diminishing the mean annual amount of heat received from the sun1 or by increasing or diminishing the difference between summer and winter temperature4 ,let us consider the former case first4 ,the total quantity of heat received from the sun during one revolution is inversely proportional to the minor axis4 ,the difference of the minor axis of the orbit when at its maximum and its minimum state of eccentricity is as #iig to #ajjj4 ,this small amount of difference cannot therefore sensibly affect the climate4 ,hence we must seek for our cause in the second case under consideration4 ,there is of course as yet some little uncertainty in regard to the exact mean distance of the sun4 ,i shall1 however1 in the present volume assume it to be #ia1djj1jjj miles4 ,when the eccentricity is at its superior limit1 the distance of the sun from the earth1 when the latter is in the aphelion of its orbit1 is no less than #ih1ejf1cej miles2 and when in the perihelion it is only #hd1bic1fej miles4 ,the earth is therefore #ad1bab1gjj miles further from the sun in the former position than in the latter4 ,the direct heat of the sun being inversely as the square of the distance1 it follows that the amount of heat received by the earth when in these two positions will be as #ai to #bf4 ,taking the present eccentricity to be #jafh1 the earth's distance during winter1 when nearest to the sun1 is #hi1hfd1dhj miles4 ,suppose now that1 according to the precession of the equinoxes1 winter in our northern hemisphere should happen when the earth is in the aphelion of its orbit1 at the time when the orbit is at its greatest eccentricity2 the earth would then be #h1fda1hgj miles further from the sun in winter than at present4 ,the direct heat of the sun would therefore be one-fifth less during that season than at present2 and in summer one-fifth greater4 ,this enormous difference would affect the climate to a very great extent4 ,but if winter under these circumstances should happen when the earth is in the perihelion of its orbit1 the earth would then be #ad1bab1gjj miles nearer the sun in winter than in summer4 ,in this case the difference between winter and summer in the latitude of this country would be almost annihilated4 ,but as the winter in the one hemisphere corresponds with the summer in the other1 it follows that while the one hemisphere would be enduring the greatest extremes of summer heat and winter cold1 the other would be enjoying a perpetual summer4 ,it is quite true that whatever may be the eccentricity of the earth's orbit1 the two hemispheres must receive equal quantities of heat per annum2 for proximity to the sun is exactly compensated by the effect of swifter motion--the total amount of heat received from the sun between the two equinoxes is the same in both halves of the year1 whatever the eccentricity of the earth's orbit may be4 ,for example1 whatever extra heat the southern hemisphere may at present receive from the sun during its summer months owing to greater proximity to the sun1 is exactly compensated by a corresponding loss arising from the shortness of the season2 and1 on the other hand1 whatever deficiency of heat we in the northern hemisphere may at present have during our summer half year in consequence of the earth's distance from the sun1 is also exactly compensated by a corresponding length of season4 ,it has been shown in the introductory chapter that a simple change in the sun's distance would not alone produce a glacial epoch1 and that those physicists who confined their attention to purely astronomical effects were perfectly correct in affirming that no increase of eccentricity of the earth's orbit could account for that epoch4 ,but the important fact was overlooked that although the glacial epoch could not result directly from an increase of eccentricity1 it might nevertheless do so indirectly4 ,the glacial epoch1 as ,i hope to show1 was not due directly to an increase in the eccentricity of the earth's orbit1 but to a number of physical agents that were brought into operation as a result of an increase4 ,i shall now proceed to give an outline of what these physical agents were1 how they were brought into operation1 and the way in which they led to the glacial epoch4 ,when the eccentricity is about its superior limit1 the combined effect of all those causes to which ,i allude is to lower to a very great extent the temperature of the hemisphere whose winters occur in aphelion1 and to raise to nearly as great an extent the temperature of the opposite hemisphere1 where winter of course occurs in perihelion4 ,with the eccentricity at its superior limit and the winter occurring in the aphelion1 the earth would be #h1fda1hgj miles further from the sun during that season than at present4 ,the reduction in the amount of heat received from the sun owing to this increased distance would1 upon the principle we have stated in ,chapter ,,ii41 lower the midwinter temperature to an enormous extent4 ,in temperate regions the greater portion of the moisture of the air is at present precipitated in the form of rain1 and the very small portion which falls as snow disappears in the course of a few weeks at most4 ,but in the circumstances under consideration1 the mean winter temperature would be lowered so much below the freezing-point that what now falls as rain during that season would then fall as snow4 ,this is not all2 the winters would then not only be colder than now1 but they would also be much longer4 ,at present the winters are nearly eight days shorter than the summers2 but with the eccentricity at its superior limit and the winter solstice in aphelion1 the length of the winters would exceed that of the summers by no fewer than thirty-six days4 ,the lowering of the temperature and the lengthening of the winter would both tend to the same effect1 viz41 to increase the amount of snow accumulated during the winter2 for1 other things being equal1 the larger the snow-accumulating period the greater the accumulation4 ,i may remark1 however1 that the absolute quantity of heat received during winter is not affected by the decrease in the sun's heat1#bh for the additional length of the season compensates for this decrease4 ,as regards the absolute amount of heat received1 increase of the sun's distance and lengthening of the winter are compensatory1 but not so in regard to the amount of snow accumulated4 ,the consequence of this state of things would be that1 at the commencement of the short summer1 the ground would be covered with the winter's accumulation of snow4 ,again1 the presence of so much snow would lower the summer temperature1 and prevent to a great extent the melting of the snow4 ,there are three separate ways whereby accumulated masses of snow and ice tend to lower the summer temperature1 viz43-- ,first4 ,by means of direct radiation4 ,no matter what the intensity of the sun's rays may be1 the temperature of snow and ice can never rise above #cb4 ,hence the presence of snow and ice tends by direct radiation to lower the temperature of all surrounding bodies to #cb4 ,in ,greenland1 a country covered with snow and ice1 the pitch has been seen to melt on the side of a ship exposed to the direct rays of the sun1 while at the same time the surrounding air was far below the freezing-point2 a thermometer exposed to the direct radiation of the sun has been observed to stand above #ajj1 while the air surrounding the instrument was actually #ab below the freezing-point4#bi ,a similar experience has been recorded by travellers on the snow-fields of the ,alps4#cj ,these results1 surprising as they no doubt appear1 are what we ought to expect under the circumstances4 ,the diathermancy of air has been well established by the researches of ,professor ,tyndall on radiant heat4 ,perfectly dry air seems to be nearly incapable of absorbing radiant heat4 ,the entire radiation passes through it almost without any sensible absorption4 ,consequently the pitch on the side of the ship may be melted1 or the bulb of the thermometer raised to a high temperature by the direct rays of the sun1 while the surrounding air remains intensely cold4 8,a joint of meat10 says ,professor ,tyndall1 8might be roasted before a fire1 the air around the joint being cold as ice40#ca ,the air is cooled by contact with the snow-covered ground1 but is not heated by the radiation from the sun4 ,when the air is humid and charged with aqueous vapour1 a similar cooling effect also takes place1 but in a slightly different way4 ,air charged with aqueous vapour is a good absorber of radiant heat1 but it can only absorb those rays which agree with it in period4 ,it so happens that rays from snow and ice are1 of all others1 those which it absorbs best4 ,the humid air will absorb the total radiation from the snow and ice1 but it will allow the greater part of1 if not nearly all1 the sun's rays to pass unabsorbed4 ,but during the day1 when the sun is shining1 the radiation from the snow and ice to the air is negative2 that is1 the snow and ice cool the air by radiation4 ,the result is1 the air is cooled by radiation from the snow and ice 7or rather1 we should say1 to the snow and ice7 more rapidly than it is heated by the sun2 and1 as a consequence1 in a country like ,greenland1 covered with an icy mantle1 the temperature of the air1 even during summer1 seldom rises above the freezing-point4 ,snow is a good reflector1 but as simple reflection does not change the character of the rays they would not be absorbed by the air1 but would pass into stellar space4 ,were it not for the ice1 the summers of ,north ,greenland1 owing to the continuance of the sun above the horizon1 would be as warm as those of ,england2 but1 instead of this1 the ,greenland summers are colder than our winters4 ,cover ,india with an ice sheet1 and its summers would be colder than those of ,england4 ,second4 ,another cause of the cooling effect is that the rays which fall on snow and ice are to a great extent reflected back into space4#cb ,but those that are not reflected1 but absorbed1 do not raise the temperature1 for they disappear in the mechanical work of melting the ice4 ,the latent heat of ice is about #adb ,f42 consequently in the melting of every pound of ice a quantity of heat sufficient to raise one pound of water #adb disappears1 and is completely lost1 so far as temperature is concerned4 ,this quantity of heat is consumed1 not in raising the temperature of the ice1 but in the mechanical work of tearing the molecules separate against the forces of cohesion binding them together into the solid form4 ,no matter what the intensity of the sun's heat may be1 the surface of the ground will remain permanently at #cb so long as the snow and ice continue unmelted4 9999,p#a3missing page number ,third4 ,snow and ice lower the temperature by chilling the air and condensing the vapour into thick fogs4 ,the great strength of the sun's rays during summer1 due to his nearness at that season1 would1 in the first place1 tend to produce an increased amount of evaporation4 ,but the presence of snow-clad mountains and an icy sea would chill the atmosphere and condense the vapour into thick fogs4 ,the thick fogs and cloudy sky would effectually prevent the sun's rays from reaching the earth1 and the snow1 in consequence1 would remain unmelted during the entire summer4 ,in fact1 we have this very condition of things exemplified in some of the islands of the ,southern ,ocean at the present day4 ,sandwich ,land1 which is in the same parallel of latitude as the north of ,scotland1 is covered with ice and snow the entire summer2 and in the island of ,south ,georgia1 which is in the same parallel as the centre of ,england1 the perpetual snow descends to the very sea-beach4 ,the following is ,captain ,cook's description of this dismal place3--8,we thought it very extraordinary10 he says1 8that an island between the latitudes of #ed and #ee should1 in the very height of summer1 be almost wholly covered with frozen snow1 in some places many fathoms deep4444 ,the head of the bay was terminated by ice-cliffs of considerable height2 pieces of which were continually breaking off1 which made a noise like a cannon4 ,nor were the interior parts of the country less horrible4 ,the savage rocks raised their lofty summits till lost in the clouds1 and valleys were covered with seemingly perpetual snow4 ,not a tree nor a shrub of any size were to be seen4 ,the only signs of vegetation were a strong-bladed grass growing in tufts1 wild burnet1 and a plant-like moss seen on the rocks4444 ,we are inclined to think that the interior parts1 on account of their elevation1 never enjoy heat enough to melt the snow in such quantities as to produce a river1 nor did we find even a stream of fresh water on the whole coast40#cc ,captain ,sir ,james ,ross found the perpetual snow at the sea-level at ,admiralty ,inlet1 ,south ,shetland1 in lat4 #fd2 and while near this place the thermometer in the very middle of summer fell at night to #bc ,f42 and so rapidly was the young ice forming around the ship that he began1 he says1 8to have serious apprehensions of the ships being frozen in40#cd ,at the comparatively low latitude of #ei ,s41 in long4 #aga ,e4 7the corresponding latitude of our ,orkney ,islands71 snow was falling on the longest day1 and the surface of the sea at #cb4ce ,and during the month of ,february 7the month corresponding to ,august in our hemisphere7 there were only three days in which they were not assailed by snow-showers4#cf ,in the ,straits of ,magellan1 in #ec ,s4 lat41 where the direct heat of the sun ought to be as great as in the centre of ,england1 ,,mm4 ,churrca and ,galcano have seen snow fall in the middle of summer2 and though the day was eighteen hours long1 the thermometer seldom rose above #db or #dd1 and never above #ea4cg ,this rigorous condition of climate chiefly results from the rays of the sun being intercepted by the dense fogs which envelope those regions during the entire summer2 and the fogs again are due to the air being chilled by the presence of the snow-clad mountains and the immense masses of floating ice which come from the antarctic seas4 ,the reduction of the sun's heat and lengthening of the winter1 which would take place when the eccentricity is near to its superior limit and the winter in aphelion1 would in this country produce a state of things perhaps as bad as1 if not worse than1 that which at present exists in ,south ,georgia and ,south ,shetland4 ,if we turn our attention to the polar regions1 we shall find that the cooling effects of snow and ice are even still more marked4 ,the coldness of the summers in polar regions is owing almost solely to this cause4 ,captain ,scoresby states that1 in regard to the arctic regions1 the general obscurity of the atmosphere arising from fogs or clouds is such that the sun is frequently invisible during several successive days4 ,at such times1 when the sun is near the northern tropic1 there is scarcely any sensible quantity of light from noon till midnight4#ch 8,and snow10 he says1 8is so common in the arctic regions1 that it may be boldly stated that in nine days out of ten during the months of ,april1 ,may1 and ,june more or less falls40#ci ,on the north side of ,hudson's ,bay1 for example1 where the quantity of floating ice during summer is enormous1 and dense fogs prevail1 the mean temperature of ,june does not rise above the freezing-point1 being actually #ace below the normal temperature2 while in some parts of ,asia under the same latitude1 where there is comparatively little ice1 the mean temperature of ,june is as high as #fj4 ,the mean temperature of ,van ,rensselaer ,harbour1 in lat4 #gh #cg ,n41 long4 #gj #ec ,w41 was accurately determined from hourly observations made day and night over a period of two years by ,dr4 ,kane4 ,it was found to be as follows3-- ,winter #bhei ,spring #ajei ,summer #ccch ,autumn - #djc ,but although the quantity of heat received from the sun at that latitude ought to have been greater during the summer than in ,england1#dj yet nevertheless the temperature is only #ach above the freezing-point4 ,the temperature of ,port ,bowen1 lat4 #gc #ad ,n41 was found to be as follows3-- ,winter #beji ,spring - #egg ,summer #cddj ,autumn #ajeh ,here the summer is only #bd above the freezing-point4 ,the condition of things in the antarctic regions is even still worse than in the arctic4 ,captain ,sir ,james ,ross1 when between lat4 #ff ,s4 and #gg #e ,s41 during the months of ,january and ,february1 #ahda1 found the mean temperature to be only #bfe2 and there were only two days when it rose even to the freezing-point4 ,when near the ice-barrier on the #hth of ,february1 #ahda1 a season of the year equivalent to ,august in ,england1 he had the thermometer at #ab at noon2 and so rapidly was the young ice forming around the ships1 that it was with difficulty that he escaped being frozen in for the winter4 8,three days later10 he says1 8the thick falling snow prevented our seeing to any distance before us2 the waves as they broke over the ships froze as they fell on the decks and rigging1 and covered our clothes with a thick coating of ice40#da ,on visiting the barrier next year about the same season1 he again ran the risk of being frozen in4 ,he states that the surface of the sea presented one unbroken sheet of young ice as far as the eye could discover from the masthead4 ,lieutenant ,wilkes1 of the ,american ,exploring ,expedition1 says that the temperature they experienced in the antarctic regions surprised him1 for they seldom1 if ever1 had it above #cj1 even at midday4 ,captain ,nares1 when in latitude #fd,s41 between the #acth and #beth ,february last 7#ahgd71 found the mean temperature of the air to be #cae2 a lower temperature than is met with in the arctic regions1 in ,august1 ten degrees nearer the pole4#db ,these extraordinarily low temperatures during summer1 which we have just been detailing1 were due solely to the presence of snow and ice4 ,in ,south ,georgia1 ,sandwich ,land1 and some other places which we have noticed1 the summers ought to be about as warm as those of ,england2 yet to such an extent is the air cooled by means of floating ice coming from the antarctic regions1 and the rays of the sun enfeebled by the dense fogs which prevail1 that there is actually not heat sufficient even in the very middle of summer to melt the snow lying on the sea-beach4 ,we read with astonishment that a country in the latitude of ,england should in the very middle of summer be covered with snow down to the sea-shore--the thermometer seldom rising much above the freezing-point4 ,but we do not consider it so surprising that the summer temperature of the polar regions should be low1 for we are accustomed to regard a low temperature as the normal condition of things there4 ,we are1 however1 mistaken if we suppose that the influence of ice on climate is less marked at the poles than at such places as ,south ,georgia or ,sandwich ,land4 ,it is true that a low summer temperature is the normal state of matters in very high latitudes1 but it is so only in consequence of the perpetual presence of snow and ice4 ,when we speak of the normal temperature of a place we mean1 of course1 as we have already seen1 the normal temperature under the present condition of things4 ,but were the ice removed from those regions1 our present ,tables of normal summer temperature would be valueless4 ,these ,tables give us the normal ,june temperature while the ice remains1 but they do not afford us the least idea as to what that temperature would be were the ice removed4 ,the mere removal of the ice1 all things else remaining the same1 would raise the summer temperature enormously4 ,the actual ,june temperature of ,melville ,island1 for example1 is #cg1 and ,port ,franklin1 ,nova ,zembla1 #cfe2 but were the ice removed from the arctic regions1 we should then find that the summer temperature of those places would be about as high as that of ,england4 ,this will be evident from the following considerations3-- ,the temperature of a place1 other things being equal1 is proportionate to the quantity of heat received from the sun4 ,if ,greenland receives per given surface as much heat from the sun as ,england1 its temperature ought to be as high as that of ,england4 ,now1 from ,may #aj till ,august #c1 a period of eighty-five days1 the quantity of heat received from the sun in consequence of his remaining above the horizon is actually greater at the north pole than at the equator4 ,column ,,ii4 of the following ,table1 calculated by ,mr4 ,meech1#dc represents the quantity of heat received from the sun on the #aeth of ,june at every #aj of latitude4 ,to simplify the ,table1 ,i have taken #ajj as the unit quantity received at the equator on that day instead of the unit adopted by ,mr4 ,meech3-- ---------------------------------------- ---- ,i4 ,,ii4 ,,iii4 ,latitude4 ,quantity ,june of heat4 temperature4 ---------------------------------------- ---- ,equator #j #ajj #hjj #aj #aaa #haa #bj #aah #haa #cj #abc #ggc #dj #abe #fhj #ej #abe #ehh #fj #abc #ead #gj #abg #cib #hj #acc #cjb ,north ,pole #ij #acf #bgd ---------------------------------------- ---- ,the calculations are1 of course1 made upon the supposition that the quantity of rays cut off in passing through the atmosphere is the same at the poles as at the equator1 which1 as we know1 is not exactly the case4 ,but1 notwithstanding the extra loss of solar heat in high latitudes caused by the greater amount of rays that are cut off1 still1 if the temperature of the arctic summers were at all proportionate to the quantity of heat received from the sun1 it ought to be very much higher than it actually is4 ,column ,,iii4 represents the actual mean ,june temperature1 according to ,prof4 ,dove1 at the corresponding latitudes4 ,a comparison of these two columns will show the very great deficiency of temperature in high latitudes during summer4 ,at the equator1 for example1 the quantity of heat received is represented by #ajj and the temperature #hj2 while at the pole the temperature is only #bgd1 although the amount of heat received is #acf4 ,this low temperature during summer1 from what has been already shown1 is due chiefly to the presence of snow and ice4 ,if by some means or other we could remove the snow and ice from the arctic regions1 they would then enjoy a temperate1 if not a hot1 summer4 ,in ,greenland1 as we have already seen1 snow falls even in the very middle of summer1 more or less1 nine days out of ten2 but remove the snow from the northern hemisphere1 and a snow-shower in ,greenland during summer would be as great a rarity as it would be on the plains of ,india4 ,other things being equal1 the quantity of solar heat received in ,greenland during summer is considerably greater than in ,england4 ,consequently1 were it not for snow and ice1 it would enjoy as warm a climate during summer as that of ,england4 ,conversely1 let the polar snow and ice extend to the latitude of ,england1 and the summers of that country would be as cold as those of ,greenland4 ,our summers would then be as cold as our winters are at present1 and snow in the very middle of summer would perhaps be as common as rain4 ,mr4 ,murphy's ,theory4--,in a paper read before the ,geological ,society by ,mr4 ,murphy#dd he admits that the glacial climate was due to an increase of eccentricity1 but maintains in opposition to me that the glaciated hemisphere must be that in which the summer occurs in aphelion during the greatest eccentricity of the earth's orbit4 ,i fear that ,mr4 ,murphy must be resting his theory on the mistaken idea that a summer in aphelion ought to melt less snow and ice than one in perihelion4 ,it is quite true that the longer summer in aphelion--other things being equal--is colder than the shorter one in perihelion1 but the quantity of heat received from the sun is the same in both cases4 ,consequently the quantity of snow and ice melted ought also to be the same2 for the amount melted is in proportion to the quantity of energy in the form of heat received4 ,it is true that with us at present less snow and ice are melted during a cold summer than during a warm one4 ,but this is not a case in point1 for during a cold summer we have less heat than during a warm summer1 the length of both being the same4 ,the coldness of the summers in this case is owing chiefly to a portion of the heat which we ought to receive from the sun being cut off by some obstructing cause4 ,the reason why we have so little snow1 and consequently so little ice1 in temperate regions1 is not1 as ,mr4 ,murphy seems to suppose1 that the heat of summer melts it all1 but that there is so little to melt4 ,and the reason why we have so little to melt is that1 owing to the warmth of our winters1 we have generally rain instead of snow4 ,but if you increase the eccentricity very much1 and place the winter in perihelion1 we should probably have no snow whatever1 and1 as far as glaciation is concerned1 it would then matter very little what sort of summer we had4 ,but it is not correct to say that the perihelion summer of the glacial epoch must have been hot4 ,there are physical reasons1 as we have just seen1 which go to prove that1 notwithstanding the nearness of the sun at that season1 the temperature would seldom1 if ever1 rise much above the freezing-point4 ,besides1 ,mr4 ,murphy overlooks the fact that the nearness of the sun during summer was nearly as essential to the production of the ice1 as we shall shortly see1 as his great distance during winter4 ,we must now proceed to the consideration of an agency which is brought into operation by the foregoing condition of things1 an agency far more potent than any which has yet come under our notice1 viz41 the ,deflection of ,ocean-currents4 ,deflection of ,ocean-currents the chief ,cause of secular ,changes of ,climate4--,the enormous extent to which the thermal condition of the globe is affected by ocean-currents seems to cast new light on the mystery of geological climate4 ,what1 for example1 would be the condition of ,europe were the ,gulf-stream stopped1 and the ,atlantic thus deprived of one-fifth of the absolute amount of heat which it is now receiving above what it has in virtue of the temperature of space8 ,if the results just arrived at be at all justifiable1 it follows that the stoppage of the stream would lower the temperature of northern ,europe to an extent that would induce a condition of climate as severe as that of ,north ,greenland2 and were the warm currents of the ,north ,pacific also at the same time to be stopped1 the northern hemisphere would assuredly be subjected to a state of general glaciation4 ,suppose also that the warm currents1 having been withdrawn from the northern hemisphere1 should flow into the ,southern ,ocean3 what then would be the condition of the southern hemisphere8 ,such a transference of heat would raise the temperature of the latter hemisphere about as much as it would lower the temperature of the former4 ,it would consequently raise the mean temperature of the antarctic regions much above the freezing-point1 and the ice under which those regions are at present buried would1 to a great extent at least1 disappear4 ,the northern hemisphere1 thus deprived of the heat from the equator1 would be under a condition of things similar to that which prevailed during the glacial epoch2 while the other hemisphere1 receiving the heat from the equator1 would be under a condition of climate similar to what we know prevailed in the northern hemisphere during a part of the ,upper ,miocene period1 when ,north ,greenland enjoyed a climate as mild as that of ,england at the present day4 ,this is no mere picture of the imagination1 no mere hypothesis devised to meet a difficult case2 for if what has already been stated be not completely erroneous1 all this follows as a necessary consequence from physical principles4 ,if the warm currents of the equatorial regions be all deflected into one hemisphere1 such must be the condition of things4 ,how then do the agencies which we have been considering deflect ocean-currents8 ,how the foregoing ,causes deflect ,ocean-currents4--,a high condition of eccentricity tends1 we have seen1 to produce an accumulation of snow and ice on the hemisphere whose winters occur in aphelion4 ,this accumulation tends in turn to lower the summer temperature1 to cut off the sun's rays1 and so to retard the melting of the snow4 ,in short1 it tends to produce on that hemisphere a state of glaciation4 ,exactly opposite effects take place on the other hemisphere1 which has its winter in perihelion4 ,there the shortness of the winters and the highness of the temperature1 owing to the sun's nearness1 combine to prevent the accumulation of snow4 ,the general result is that the one hemisphere is cooled and the other heated4 ,this state of things now brings into play the agencies which lead to the deflection of the ,gulf-stream and other great ocean-currents4 ,owing to the great difference between the temperature of the equator and the poles1 there is a constant flow of air from the poles to the equator4 ,it is to this that the trade-winds owe their existence4 ,now as the strength of these winds1 as a general rule1 will depend upon the difference of temperature that may exist between the equator and higher latitudes1 it follows that the trades on the cold hemisphere will be stronger than those on the warm4 ,when the polar and temperate regions of the one hemisphere are covered to a large extent with snow and ice1 the air1 as we have just seen1 is kept almost at the freezing-point during both summer and winter4 ,the trades on that hemisphere will1 of necessity1 be exceedingly powerful2 while on the other hemisphere1 where there is comparatively little snow and ice1 and the air is warm1 the trades will1 as a consequence1 be weak4 ,suppose now the northern hemisphere to be the cold one4 ,the north-east trade-winds of this hemisphere will far exceed in strength the south-east trade-winds of the southern hemisphere4 ,the median-line between the trades will consequently lie to a very considerable distance to the south of the equator4 ,we have a good example of this at the present day4 ,the difference of temperature between the two hemispheres at present is but trifling to what it would be in the case under consideration2 yet we find that the south-east trades of the ,atlantic blow with greater force than the north-east trades1 and the result is that the south-east trades sometimes extend to #aj or #ae ,n4 lat41 whereas the north-east trades seldom blow south of the equator4 ,the effect of the northern trades blowing across the equator to a great distance will be to impel the warm water of the tropics over into the ,southern ,ocean4 ,but this is not all2 not only would the median-line of the trades be shifted southwards1 but the great equatorial currents of the globe would also be shifted southwards4 ,let us now consider how this would affect the ,gulf-stream4 ,the ,south ,american continent is shaped somewhat in the form of a triangle1 with one of its angular corners1 called ,cape ,st4 ,roque1 pointing eastwards4 ,the equatorial current of the ,atlantic impinges against this corner2 but as the greater portion of the current lies a little to the north of the corner1 it flows westward into the ,gulf of ,mexico and forms the ,gulf-stream4 ,a considerable portion of the water1 however1 strikes the land to the south of the ,cape and is deflected along the shores of ,brazil into the ,southern ,ocean1 forming what is known as the ,brazilian current4 ,now it is perfectly obvious that the shifting of the equatorial current of the ,atlantic only a few degrees to the south of its present position--a thing which would certainly take place under the conditions which we have been detailing--would turn the entire current into the ,brazilian branch1 and instead of flowing chiefly into the ,gulf of ,mexico as at present1 it would all flow into the ,southern ,ocean1 and the ,gulf-stream would consequently be stopped4 ,the stoppage of the ,gulf-stream1 combined with all those causes which we have just been considering1 would place ,europe under glacial conditions2 while1 at the same time1 the temperature of the ,southern ,ocean would1 in consequence of the enormous quantity of warm water received1 have its temperature 7already high from other causes7 raised enormously4 ,deflection of the ,gulf-stream during the ,glacial ,epoch indicated by the ,difference between the ,clyde and ,canadian ,shell-beds4--,that the glaciation of north-western ,europe resulted to a great extent from the stoppage of the ,gulf-stream may1 ,i think1 be inferred from a circumstance pointed out by the ,rev4 ,mr4 ,crosskey1 several years ago1 in a paper read before the ,glasgow ,geological ,society4#de ,he showed that the difference between the glacial shells of ,canada and those now existing in the ,gulf of ,st4 ,lawrence is much less marked than the difference between the glacial shells of the ,clyde beds and those now existing in the ,firth4 ,and from this he justly infers that the change of climate in ,canada since the glacial epoch has been far less complete than in ,scotland4 ,the return of the ,gulf-stream has raised the mean annual temperature of our island no less than #ae above the normal1 while ,canada1 deprived of its influence and exposed to a cold stream from polar regions1 has been kept nearly as much below the normal4 ,let us compare the present temperature of the two countries4 ,in making our comparison we must1 of course1 compare places on the same latitude4 ,it will not do1 for example1 to compare ,glasgow with ,montreal or ,quebec1 places on the latitude of the south of ,france and north of ,italy4 ,it will be found that the difference of temperature between the two countries is so enormous as to appear scarcely credible to those who have not examined the matter4 ,the temperatures have all been taken from ,professor ,dove's work on the 8,distribution of ,heat over the ,surface of the ,globe10 and his ,tables published in the ,report of the ,british ,association for #ahdg4 ,the mean temperature of ,scotland for ,january is about #ch ,f41 while in some parts of ,labrador1 on the same latitude1 and all along the central parts of ,north ,america lying to the north of ,upper ,canada1 it is actually #aj1 and in many places #ac below zero4 ,the ,january temperature at the ,cumberland ,house1 which is situated on the latitude of the centre of ,england1 is more than #ac below zero4 ,here is a difference of no less than #ea4 ,the normal temperature for the month of ,january in the latitude of ,glasgow1 according to ,professor ,dove1 is #aj4 ,consequently1 owing to the influence of the ,gulf-stream1 we are #bh warmer during that month than we would otherwise be1 while vast tracts of country in ,america are #bc colder than they should be4 ,the ,july temperature of ,glasgow is #fa1 while on the same latitude in ,labrador and places to the west it is only #di4 ,glasgow during that month is #c above the normal temperature1 while ,america1 owing to the influence of the cold polar stream1 is #i below it4 ,the mean annual temperature of ,glasgow is nearly #ej1 while in ,america1 on the same latitude1 it is only #cj1 and in many places as low as #bc4 ,the mean normal temperature for the whole year is #ce4 ,our mean annual temperature is therefore #ae above the normal1 and that of ,america from #e to #ab below it4 ,the ,american winters are excessively cold1 owing to the continental character of the climate1 and the absence of any benefit from the ,gulf-stream1 while the summers1 which would otherwise be warm1 are1 in the latitude of ,glasgow1 cooled down to a great extent by the cold ice from ,greenland2 and the consequence is1 that the mean annual temperature is about #bj or #bg below that of ours4 ,the mean annual temperature of the ,gulf of ,st4 ,lawrence is as low as that of ,lapland or ,iceland4 ,it is no wonder1 then1 that the shells which flourished in ,canada during the glacial epoch have not left the gulf and the neighbouring seas4 ,we have good reason to believe that the climate of ,america during the glacial epoch was even then somewhat more severe than that of ,western ,europe1 for the erratics of ,america extend as far south as latitude #dj1 while on the old continent they are not found much beyond latitude #ej4 ,this difference may have resulted from the fact that the western side of a continent is always warmer than the eastern4 ,in order to determine whether the cold was as great in ,america during the glacial epoch as in ,western ,europe1 we must not compare the fossils found in the glacial beds about ,montreal1 for example1 with those found in the ,clyde beds1 for ,montreal lies much further to the south than the ,clyde4 ,the ,clyde beds must be compared with those of ,labrador1 while the beds of ,montreal must be compared with those of the south of ,france and the north of ,italy1 if any are to be found there4 ,on the whole1 it may be concluded that had the ,gulf-stream not returned to our shores at the close of the glacial epoch1 and had its place been supplied by a cold stream from the polar regions1 similar to that which washes the shores of ,north ,america1 it is highly probable that nearly every species found in our glacial beds would have had their representatives flourishing in the ,british seas at the present day4 ,it is no doubt true that when we compare the places in which the ,canadian shell-beds referred to by ,mr4 ,crosskey are situated with places on the same latitude in ,europe1 the difference of climate resulting from the influence of the ,gulf-stream is not so great as between ,scotland and those places which we have been considering2 but still the difference is sufficiently great to account for why the change of climate in ,canada has been less complete than in ,scotland4 ,and what holds true in regard to the currents of the ,atlantic holds also true1 though perhaps not to the same extent1 of the currents of the ,pacific4 ,nearness of the ,sun in ,perigee a ,cause of the ,accumulation of ,ice4--,but there is still another cause which must be noticed3--,a strong under current of air from the north implies an equally strong upper current to the north4 ,now if the effect of the under current would be to impel the warm water at the equator to the south1 the effect of the upper current would be to carry the aqueous vapour formed at the equator to the north2 the upper current1 on reaching the snow and ice of temperate regions1 would deposit its moisture in the form of snow2 so that1 notwithstanding the great cold of the glacial epoch1 it is probable that the quantity of snow falling in the northern regions would be enormous4 ,this would be particularly the case during summer1 when the earth would be in the perihelion and the heat at the equator great4 ,the equator would be the furnace where evaporation would take place1 and the snow and ice of temperate regions would act as a condenser4 ,heat to produce evaporation is just as essential to the accumulation of snow and ice as cold to produce condensation4 ,now at ,midsummer1 on the supposition of the eccentricity being at its superior limit1 the sun would be #h1fda1hgj miles nearer than at present during that season4 ,the effect would be that the intensity of the sun's rays would be one-fifth greater than now4 ,that is to say1 for every five rays received by the ocean at present1 six rays would be received then1 consequently the evaporation during summer would be excessive4 ,but the ice-covered land would condense the vapour into snow4 ,it would1 no doubt1 be during summer that the greatest snowfall would take place4 ,in fact1 the nearness of the sun during that season was as essential to the production of the glacial epoch as was his distance during winter4 ,the direct effect of eccentricity is to produce on one of the hemispheres a long and cold winter4 ,this alone would not lead to a condition of things so severe as that which we know prevailed during the glacial epoch4 ,but the snow and ice thus produced would bring into operation1 as we have seen1 a host of physical agencies whose combined efforts would be quite sufficient to do this4 ,a remarkable ,circumstance regarding those ,causes which lead to ,secular ,changes of ,climate4--,there is one remarkable circumstance connected with those physical causes which deserves special notice4 ,they not only all lead to one result1 viz41 an accumulation of snow and ice1 but they react on one another4 ,it is quite a common thing in physics for the effect to react on the cause4 ,in electricity and magnetism1 for example1 cause and effect in almost every case mutually act and react upon each other4 ,but it is usually1 if not universally1 the case that the reaction of the effect tends to weaken the cause4 ,the weakening influences of this reaction tend to impose a limit on the efficiency of the cause4 ,but1 strange to say1 in regard to the physical causes concerned in the bringing about of the glacial condition of climate1 cause and effect mutually reacted so as to strengthen each other4 ,and this circumstance had a great deal to do with the extraordinary results produced4 ,we have seen that the accumulation of snow and ice on the ground resulting from the long and cold winters tended to cool the air and produce fogs which cut off the sun's rays4 ,the rays thus cut off diminished the melting power of the sun1 and so increased the accumulation4 ,as the snow and ice continued to accumulate1 more and more of the rays were cut off2 and on the other hand1 as the rays continued to be cut off1 the rate of accumulation increased1 because the quantity of snow and ice melted became thus annually less and less4 ,again1 during the long and dreary winters of the glacial epoch the earth would be radiating off its heat into space4 ,had the heat thus lost simply gone to lower the temperature1 the lowering of the temperature would have tended to diminish the rate of loss2 but the necessary result of this was the formation of snow and ice rather than the lowering of temperature4 ,and1 again1 the formation of snow and ice facilitated the rate at which the earth lost its heat2 and on the other hand1 the more rapidly the earth parted with its heat1 the more rapidly were the snow and ice formed4 ,further1 as the snow and ice accumulated on the one hemisphere1 they at the same time continued to diminish on the other4 ,this tended to increase the strength of the trade-winds on the cold hemisphere1 and to weaken those on the warm4 ,the effect of this on ocean currents would be to impel the warm water of the tropics more to the warm hemisphere than to the cold4 ,suppose the northern hemisphere to be the cold one1 then as the snow and ice began gradually to accumulate there1 the ocean currents of that hemisphere would begin to decrease in volume1 while those on the southern1 or warm1 hemisphere1 would pari passu increase4 ,this withdrawal of heat from the northern hemisphere would tend1 of course1 to lower the temperature of that hemisphere and thus favour the accumulation of snow and ice4 ,as the snow and ice accumulated the ocean currents would decrease1 and1 on the other hand1 as the ocean currents diminished the snow and ice would accumulate1--the two effects mutually strengthening each other4 ,the same must have held true in regard to arial currents4 ,the more the polar and temperate regions became covered with snow and ice1 the stronger would become the trades and anti-trades of the hemisphere2 and the stronger those winds became1 the greater would be the amount of moisture transferred from the tropical regions by the anti-trades to the temperate regions2 and on the other hand1 the more moisture those winds brought to temperate regions1 the greater would be the quantity of snow produced4 ,the same process of mutual action and reaction would take place among the agencies in operation on the warm hemisphere1 only the result produced would be diametrically opposite of that produced in the cold hemisphere4 ,on this warm hemisphere action and reaction would tend to raise the mean temperature and diminish the quantity of snow and ice existing in temperate and polar regions4 ,had it been possible for each of those various physical agents which we have been considering to produce its direct effects without influencing the other agents or being influenced by them1 its real efficiency in bringing about either the glacial condition of climate or the warm condition of climate would not have been so great4 ,the primary cause that set all those various physical agencies in operation which brought about the glacial epoch1 was a high state of eccentricity of the earth's orbit4 ,when the eccentricity is at a high value1 snow and ice begin to accumulate1 owing to the increasing length and coldness of the winter on that hemisphere whose winter solstice is approaching toward the aphelion4 ,the accumulating snow then begins to bring into operation all the various agencies which we have been describing2 and1 as we have just seen1 these1 when once in full operation1 mutually aid one another4 ,as the eccentricity increases century by century1 the temperate regions become more and more covered with snow and ice1 first by reason of the continued increase in the coldness and length of the winters1 and secondly1 and chiefly1 owing to the continued increase in the potency of those physical agents which have been called into operation4 ,this glacial state of things goes on at an increasing rate1 and reaches a maximum when the solstice-point arrives at the aphelion4 ,after the solstice passes the aphelion1 a contrary process commences4 ,the snow and ice gradually begin to diminish on the cold hemisphere and to make their appearance on the other hemisphere4 ,the glaciated hemisphere turns1 by degrees1 warmer and the warm hemisphere colder1 and this continues to go on for a period of ten or twelve thousand years1 until the winter solstice reaches the perihelion4 ,by this time the conditions of the two hemispheres have been reversed2 the formerly glaciated hemisphere has now become the warm one1 and the warm hemisphere the glaciated4 ,the transference of the ice from the one hemisphere to the other continues as long as the eccentricity remains at a high value4 ,this will1 perhaps1 be better understood from an inspection of the frontispiece4 ,the ,mean ,temperature of the whole ,earth should be greater in ,aphelion than in ,perihelion4--,when the eccentricity becomes reduced to about its present value1 its influence on climate is but little felt4 ,it is1 however1 probable that the present extension of ice on the southern hemisphere may1 to a considerable extent1 be the result of eccentricity4 ,the difference in the climatic conditions of the two hemispheres is just what should be according to theory3--7#a7 ,the mean temperature of that hemisphere is less than that of the northern4 7#b7 ,the winters of the southern hemisphere are colder than those of the northern4 7#c7 ,the summers1 though occurring in perihelion1 are also comparatively cold2 this1 as we have seen1 is what ought to be according to theory4 7#d7 ,the mean temperature of the whole earth is greater in ,june1 when the earth is in aphelion1 than in ,december1 when it is in perihelion4 ,this1 ,i venture to affirm1 is also what ought to follow according to theory1 although this very fact has been adduced as a proof that eccentricity has at present but little effect on the climatic condition of our globe4 ,that the mean temperature of the whole earth would1 during the glacial epoch1 be greater when the earth was in aphelion than when in perihelion will1 ,i think1 be apparent from the following considerations3--,when the earth was in the perihelion1 the sun would be over the hemisphere nearly covered with snow and ice4 ,the great strength of the sun's rays would in this case have little effect in raising the temperature2 it would be spent in melting the snow and ice4 ,but when the earth was in the aphelion1 the sun would be over the hemisphere comparatively free1 or perhaps wholly free1 from snow and ice4 ,consequently1 though the intensity of the sun's rays would be less than when the earth was in perihelion1 still it ought to have produced a higher temperature1 because it would be chiefly employed in heating the ground and not consumed in melting snow and ice4 ,professor ,tyndall on the ,glacial ,epoch4--8,so natural10 says ,professor ,tyndall1 8was the association of ice and cold1 that even celebrated men assumed that all that is needed to produce a great extension of our glaciers is a diminution of the sun's temperature4 ,had they gone through the foregoing reflections and calculations1 they would probably have demanded more heat instead of less for the production of a glacial epoch4 ,what they really needed were condensers sufficiently powerful to congeal the vapour generated by the heat of the sun40 7,the ,forms of ,water1 p4 #aed4 ,see also1 to the same effect1 ,heat ,considered as a ,mode of ,motion1 chap4 vi47 ,i do not know to whom ,professor ,tyndall here refers1 but certainly his remarks have no application to the theory under consideration1 for according to it1 as we have just seen1 the ice of the glacial epoch was about as much due to the nearness of the sun in perigee as to his great distance in apogee4 ,there is one theory1 however1 to which his remarks justly apply1 viz41 the theory that the great changes of climate during geological ages resulted from the passage of our globe through different temperatures of space4 ,what ,professor ,tyndall says shows plainly that the glacial epoch was not brought about by our earth passing through a cold part of space4 ,a general reduction of temperature over the whole globe certainly would not produce a glacial epoch4 ,suppose the sun were extinguished and our globe exposed to the temperature of stellar space 7#bci ,f471 this would certainly freeze the ocean solid from its surface to its bottom1 but it would not cover the land with ice4 ,professor ,tyndall's conclusions are1 of course1 equally conclusive against ,professor ,balfour ,stewart's theory1 that the glacial epoch may have resulted from a general diminution in the intensity of the sun's heat4 ,nevertheless it would be in direct opposition to the well-established facts of geology to assume that the ice periods of the glacial epoch were warm periods4 ,we are as certain from palontological evidence that the cold was then much greater than now1 as we are from physical evidence that the accumulation of ice was greater than now4 ,our glacial shell-beds and remains of the mammoth1 the reindeer1 and musk-ox1 tell of cold as truly as the markings on the rocks do of ice4 ,objection from the ,present ,condition of the ,planet ,mars4--,it has been urged as an objection by ,professor ,charles ,martins#df and others1 that if a high state of eccentricity could produce a glacial epoch1 the planet ,mars ought to be at present under a glacial condition4 ,the eccentricity of its orbit amounts to #jjicbb1 and one of its southern winter solstices is1 according to ,dr4 ,oudemans1 of ,batavia1#dg within #ag #da #h of aphelion4 ,consequently1 it is supposed that one of the hemispheres should be in a glacial state and the other free from snow and ice4 ,but it is believed that the snow accumulates around each pole during its winter and disappears to a great extent during its summer4 ,there would be force in this objection were it maintained that eccentricity alone can produce a glacial condition of climate1 but such is not the case1 and there is no good ground for concluding that those physical agencies which led to the glacial epoch of our globe exist in the planet ,mars4 ,it is perfectly certain that either water must be different in constitution in that planet from what it is in our earth1 or else its atmospheric envelope must be totally different from ours4 ,for it is evident from what has been stated in ,chapter ,,ii41 that were our globe to be removed to the distance of ,mars from the sun1 the lowering of the temperature resulting from the decrease in the sun's heat would not only destroy every living thing1 but would convert the ocean into solid ice4 ,but it must be observed that the eccentricity of ,mars' orbit is at present far from its superior limit of #jadbbd1 and it may so happen in the economy of nature that when it approaches to that limit a glacial condition of things may supervene4 ,the truth is1 however1 that very little seems to be known with certainty regarding the climatic condition of ,mars4 ,this is obvious from the fact that some astronomers believe that the planet possesses a dense atmosphere which protects it from cold2 while others maintain that its atmosphere is so exceedingly thin that its mean temperature is below the freezing-point4 ,some assert that the climatic condition of ,mars resembles very much that of our earth1 while others affirm that its seas are actually frozen solid to the bottom1 and the poles covered with ice thirty or forty miles in thickness4 ,for reasons which will be explained in the ,appendix1 ,mars1 notwithstanding its greater distance from the sun1 may enjoy a climate as warm as that of our earth4 ,,chapter ,v4 ,,reason ,,why ,,the ,,southern ,,hemisphere ,,is ,,colder ,,than ,,the ,,northern4 ,adhmar's ,explanation4--,adhmar's ,theory founded upon a physical ,mistake in regard to ,radiation4--,professor ,j4 ,d4 ,forbes on ,underground ,temperature4--,generally accepted ,explanation4--,low ,temperature of ,southern ,hemisphere attributed to ,preponderance of ,sea4--,heat transferred from ,southern to ,northern ,hemisphere by ,ocean-current the true ,explanation4--,a large ,portion of the ,heat of the ,gulf-stream derived from the ,southern ,hemisphere4 ,adhmar's ,explanation4--,it has long been known that on the southern hemisphere the temperature is lower and the accumulation of ice greater than on the northern4 ,this difference has usually been attributed to the great preponderance of sea on the southern hemisphere4 ,m4 ,adhmar1 on the other hand1 attempts to explain this difference by referring it to the difference in the amount of heat lost by the two hemispheres in consequence of the difference of seven days in the length of their respective winters4 ,as the northern winter is shorter than the summer1 he concludes that there is an accumulation of heat on that hemisphere1 while1 on the other hand1 the southern winter being longer than the summer1 there is therefore a loss of heat on the southern hemisphere4 8,the south pole10 he says1 8loses in one year more heat than it receives1 because the total duration of its night surpasses that of its day by #afh hours2 and the contrary takes place for the north pole4 ,if1 for example1 we take for unity the mean quantity of heat which the sun sends off in one hour1 the heat accumulated at the end of the year at the north pole will be expressed by #afh1 while the heat lost by the south pole will be equal to #afh times what the radiation lessens it by in one hour1 so that at the end of the year the difference in the heat of the two hemispheres will be represented by #ccf times what the earth receives from the sun or loses in an hour by radiation40#dh ,adhmar supposes that about #aj1jjj years hence1 when our northern winter will occur in aphelion and the southern in perihelion1 the climatic conditions of the two hemispheres will be reversed2 the ice will melt at the south pole1 and the northern hemisphere will become enveloped in one continuous mass of ice1 leagues in thickness1 extending down to temperate regions4 ,this theory seems to be based upon an erroneous interpretation of a principle1 first pointed out1 so far as ,i am aware1 by ,humboldt in his memoir 8,on ,isothermal ,lines and ,distribution of ,heat over the ,globe40#di ,this principle may be stated as follows3-- ,although the total quantity of heat received by the earth from the sun in one revolution is inversely proportional to the minor axis of the orbit1 yet this amount1 as was proved by ,d',alembert1 is equally distributed between the two hemispheres1 whatever the eccentricity may be4 ,whatever extra heat the southern hemisphere may at present receive from the sun daily during its summer months owing to greater proximity to the sun1 is exactly compensated by a corresponding loss arising from the shortness of the season2 and1 on the other hand1 whatever daily deficiency of heat we in the northern hemisphere may at present have during our summer half-year1 in consequence of the earth's distance from the sun1 is also exactly compensated by a corresponding length of season4 ,but the surface temperature of our globe depends as much upon the amount of heat radiated into space as upon the amount derived from the sun1 and it has been thought by some that this compensating principle holds true only in regard to the latter4 ,in the case of the heat lost by radiation the reverse is supposed to take place4 ,the southern hemisphere1 it is asserted1 has not only a colder winter than the northern in consequence of the sun's greater distance1 but it has also a longer winter2 and the extra loss of heat from radiation during winter is not compensated by its nearness to the sun during summer1 for it gains no additional heat from this proximity4 ,and in the same way it is argued that as our winter in the northern hemisphere1 owing to the less distance of the sun1 is not only warmer than that of the southern hemisphere1 but is also at the same time shorter1 so our hemisphere is not cooled to such an extent as the southern4 ,and thus the mean temperature of the winter half-year1 as well as the intensity of the sun's heat1 is affected by a change in the sun's distance4 ,although ,i always regarded this cause of ,humboldt's to be utterly inadequate to produce such effects as those attributed to it by ,adhmar1 still1 in my earlier papers#ej ,i stated it to be a vera causa which ought to produce some sensible effect on climate4 ,but shortly afterwards on a more careful consideration of the whole subject1 ,i was led to suspect that the circumstance in question can1 according to theory1 produce little or no effect on the climatic condition of our globe4 ,as there appears to be a considerable amount of misapprehension in reference to this point1 which forms the basis of ,adhmar's theory1 ,i may here give it a brief consideration4#ea ,the rate at which the earth radiates into space the heat received from the sun depends upon the temperature of its surface2 and the temperature of its surface 7other things being equal7 depends upon the rate at which the heat is received4 ,the greater the rate at which the earth receives heat from the sun1 the greater will therefore be the rate at which it will lose that heat by radiation4 ,now the total quantity of heat received during winter by the southern hemisphere is exactly equal to that received during winter by the northern4 ,but as the southern winter is longer than the northern1 the rate at which the heat is received1 and consequently the rate of radiation1 during that season must be less on the southern hemisphere than on the northern4 ,thus the southern hemisphere loses heat during a longer period than the northern1 and therefore the less rate of radiation 7were it not for a circumstance presently to be noticed7 would wholly compensate for the longer period1 and the total quantity of heat lost during winter would be the same on both hemispheres4 ,the southern summer is shorter than the northern1 but the heat is more intense1 and the surface of the ground kept at a higher temperature2 consequently the rate of radiation into space is greater4 ,when the rate at which a body receives heat is increased1 the temperature of the body rises till the rate of radiation equals the rate of absorption1 after which equilibrium is restored2 and when the rate of absorption is diminished1 the temperature falls till the rate of radiation equals that of absorption4 ,but notwithstanding all this1 owing to the slow conductivity of the ground for heat1 more heat will pass into it during the longer summer of aphelion than during the shorter one of perihelion2 for the amount of heat which passes into the ground depends on the length of time during which the earth is receiving heat1 as well as upon the amount received4 ,in like manner1 more heat will pass out of the ground during the longer winter in aphelion than during the shorter one in perihelion4 ,suppose the length of the days on the one hemisphere 7say the northern7 to be #bc hours1 and the length of the nights1 say one hour2 while on the other hemisphere the days are one hour and the nights #bc hours4 ,suppose also that the quantity of heat received from the sun by the southern hemisphere during the day of one hour to be equal to that received by the northern hemisphere during the day of #bc hours4 ,it is evident that although the surface of the ground on the southern hemisphere would receive as much heat from the sun during the short day of one hour as the surface of the northern hemisphere during the long day of #bc hours1 yet1 owing to the slow conductivity of the ground for heat1 the amount absorbed would not be nearly so much on the southern hemisphere as on the northern4 ,the temperature of the surface during the day1 it is true1 would be far higher on the southern hemisphere than on the northern1 and consequently the rate at which the heat would pass into the ground would be greater on that hemisphere than on the northern2 but1 notwithstanding the greater rate of absorption resulting from the high temperature of the surface1 it would not compensate for the shortness of the day4 ,on the other hand1 the surface of the ground on the southern hemisphere would be colder during the long night of #bc hours than it would be on the northern during the short night of only one hour2 and the low temperature of the ground would tend to lessen the rate of radiation into space4 ,but the decrease in the rate of radiation would not compensate fully for the great length of the night4 ,the general and combined result of all those causes would be that a slight accumulation of heat would take place on the northern hemisphere and a slight loss on the southern4 ,but this loss of heat on the one hemisphere and gain on the other would not go on accumulating at a uniform rate year by year1 as ,adhmar supposes4 ,of course we are at present simply considering the earth as an absorber and radiator of heat1 without taking into account the effects of distribution of sea and land and other modifying causes1 and are assuming that everything is the same in both hemispheres1 with the exception that the winter of the one hemisphere is longer than that of the other4 ,what1 then1 is the amount of heat stored up by the one hemisphere and lost by the other8 ,is it such an amount as to sensibly affect climate8 ,the experiments and observations which have been made on underground temperature afford us a means of making at least a rough estimate of the amount4 ,and from these it will be seen that the influence of an excess of seven or eight days in the length of the southern winter over the northern could hardly produce an effect that would be sensible4 ,observations were made at ,edinburgh by ,professor ,j4 ,d4 ,forbes on three different substances2 viz41 sandstone1 sand1 and trap-rock4 ,by calculation1 we find from the data afforded by those observations that the total quantity of heat accumulated in the ground during the summer above the mean temperature was as follows3--,in the sandstone-rock1 a quantity sufficient to raise the temperature of the rock #a ,c4 to a depth of #he feet #f inches2 in the sand a quantity sufficient to raise the temperature #a ,c4 to a depth of #gb feet #f inches2 and in the trap-rock a quantity only sufficient to raise the temperature #a ,c4 to a depth of #fa feet #f inches4 ,taking the specific heat of the sandstone per unit volume1 as determined by ,regnault1 at #dfbc1 and that of sand at #cjjf1 and trap at #ebhc1 and reducing all the results to one standard1 viz41 that of water1 we find that the quantity of heat stored up in the sandstone would1 if applied to water1 raise its temperature #a ,c4 to a depth of #ci feet #f inches2 that stored up in the sand would raise the temperature of the water #a ,c4 to a depth of #ba feet #h inches1 and that stored up in the trap would raise the water #a ,c4 to the depth of #cb feet #f inches4 ,we may take the mean of these three results as representing pretty accurately the quantity stored up in the general surface of the country4 ,this would be equal to #ca feet #c inches depth of water raised #a ,c4 ,the quantity of heat lost by radiation during winter below the mean was found to be about equal to that stored up during summer4 ,the total quantity of heat per square foot of surface received by the equator from sunrise till sunset at the time of the equinoxes1 allowing #bb per cent4 for the amount cut off in passing through the atmosphere1 is #a1ghj1dgd foot-pounds4 ,in the latitude of ,edinburgh about #ich1dfj foot-pounds per square foot of surface is received1 assuming that not more than #bb per cent4 is cut off by the atmosphere4 ,at this rate a quantity of heat would be received from the sun in two days ten hours 7say1 three days7 sufficient to raise the temperature of the water #a ,c4 to the required depth of #ca feet #c inches4 ,consequently the total quantity of heat stored up during summer in the latitude of ,edinburgh is only equal to what we receive from the sun during three days at the time of the equinoxes4 ,three days' sunshine during the middle of ,march or ,september1 if applied to raise the temperature of the ground1 would restore all the heat lost during the entire winter2 and another three days' sunshine would confer on the ground as much heat as is stored up during the entire summer4 ,but it must be observed that the total duration of sunshine in winter is to that of summer in the latitude of ,edinburgh only about as #d to #g4 ,here is a difference of two months4 ,but this is not all2 the quantity of heat received during winter is scarcely one-third of that received during summer2 yet1 notwithstanding this enormous difference between summer and winter1 the ground during winter loses only about six days' sun-heat below the maximum amount possessed by it in summer4 ,but if what has already been stated is correct1 this loss of heat sustained by the earth during winter is not chiefly owing to radiation during the longer absence of the sun1 but to the decrease in the quantity of heat received in consequence of his longer absence combined with the obliquity of his rays during that season4 ,now in the case of the two hemispheres1 although the southern winter is longer than the northern1 yet the quantity of heat received by each is the same4 ,but supposing it held true1 which it does not1 that the loss of heat sustained by the earth in winter is as much owing to radiation resulting from the excess in the length of the winter nights over those of the summer as to the deficiency of heat received in winter from that received in summer1 three days' heat would then in this case be the amount lost by radiation in consequence of this excess in the length of the winter nights4 ,the total length of the winter nights to those of the summer is1 as we have seen1 about as #g to #d4 ,this is a difference of nearly #abjj hours4 ,but the excess of the south polar winter over the north amounts to only about #ahd hours4 ,now if #abjj hours give a loss of three days' sun-heat1 #ahd hours will give a loss of scarcely #e hours4 ,it is no doubt true that the two cases are not exactly analogous2 but it is obvious that any error which can possibly arise from regarding them as such cannot materially alter the conclusion to which we have arrived4 ,supposing the effect were double1 or even quadruple1 what we have concluded it to be1 still it would not amount to a loss of two days' heat1 which could certainly have little or no influence on climate4 ,but even assuming all the preceding reasoning to be incorrect1 and that the southern hemisphere1 in consequence of its longer winter1 loses heat to the extravagant extent of #afh hours1 supposed by ,adhmar1 still this could not materially affect climate4 ,the climate is influenced by the mere temperature of the surface of the ground1 and not by the quantity of heat or cold that may be stored up under the surface4 ,the climate is determined1 so far as the ground is concerned1 by the temperature of the surface1 and is wholly independent of the temperature which may exist under the surface4 ,underground temperature can only affect climate through the surface4 ,if the surface could1 for example1 be kept covered with perpetual snow1 we should have a cold and sterile climate1 although the temperature of the ground under the snow was actually at the boiling-point4 ,let the ground to a depth of1 say #dj or #ej feet1 be deprived of an amount of heat equal to that received from the sun in #afh hours4 ,this could produce little or no sensible effect on climate2 for1 owing to the slow conductivity of the ground for heat1 this loss would not sensibly affect the temperature of the surface1 as it would take several months for the sun's heat to penetrate to that depth and restore the lost heat4 ,the cold1 if ,i may be allowed to use the expression1 would come so slowly out to the surface that its effect in lowering the temperature of the surface would scarcely be sensible4 ,and1 again1 if we suppose the #afh hours' heat to be lost by the mere surface of the ground1 the effect would certainly be sensible1 but it would only be so for a few days4 ,we might in this case have a week's frozen soil1 but that would be all4 ,before the air had time to become very sensibly affected by the low temperature of the surface the frozen soil would be thawed4 ,the storing up of heat or cold in the ground has in reality very little to do with climate4 ,some physicists explain1 for example1 why the month of ,july is warmer than ,june by referring it to the fact that by the month of ,july the ground has become possessed of a larger accumulation of heat than it possessed in ,june4 ,this explanation is evidently erroneous4 ,the ground in ,july certainly possesses a greater store of heat than it did in ,june2 but this is not the reason why the former month is hotter than the latter4 ,july is hotter than ,june because the air 7not the ground7 has become possessed of a larger store of heat than it had in ,june4 ,now the air is warmer in ,july than in ,june because1 receiving little increase of temperature from the direct rays of the sun1 it is heated chiefly by radiation from the earth and by contact with its warm surface4 ,consequently1 although the sun's heat is greater in ,june than it is in ,july1 it is near the middle of ,july before the air becomes possessed of its maximum store of heat4 ,we therefore say that ,july is hotter than ,june because the air is hotter1 and consequently the temperature in the shade is greater in the former month than in the latter4 ,it is therefore1 ,i presume1 quite apparent that ,adhmar's theory fails to explain why the southern hemisphere is colder than the northern4 ,the generally accepted ,explanation4--,the difference in the mean temperature of the two hemispheres is usually attributed to the proportion of sea to land in the southern hemisphere and of land to sea in the northern hemisphere4 ,this1 no doubt1 will account for the greater annual range of temperature on the northern hemisphere1 but it seems to me that it will not account for the excess of mean temperature possessed by that hemisphere over the southern4 ,the general influence of land on climate is to exaggerate the variation of temperature due to the seasons4 ,on continents the summers are hotter and the winters colder than on the ocean4 ,the days are also hotter and the nights colder on land than on sea4 ,this is a result which follows from the mere physical properties of land and water1 independently of currents1 whether of ocean or of air4 ,but it nevertheless follows1 according to theory 7and this is a point which has been overlooked71 that the mean annual temperature of the ocean ought to be greater than that of the land in equatorial regions as well as in temperate and polar regions4 ,this will appear obvious for the following reasons3--7#a7 ,the ground stores up heat only by the slow process of conduction1 whereas water1 by the mobility of its particles and its transparency for heat-rays1 especially those from the sun1 becomes heated to a considerable depth rapidly4 ,the quantity of heat stored up in the ground is thus comparatively small1 while the quantity stored up in the ocean is great4 7#b7 ,the air is probably heated more rapidly by contact with the ground than with the ocean2 but1 on the other hand1 it is heated far more rapidly by radiation from the ocean than from the land4 ,the aqueous vapour of the air is to a great extent diathermanous to radiation from the ground1 while it absorbs the rays from water and thus becomes heated4 7#c7 ,the air radiates back a considerable portion of its heat1 and the ocean absorbs this radiation from the air more readily than the ground does4 ,the ocean will not reflect the heat from the aqueous vapour of the air1 but absorbs it1 while the ground does the opposite4 ,radiation from the air1 therefore1 tends more readily to heat the ocean than it does the land4 7#d7 ,the aqueous vapour of the air acts as a screen to prevent the loss by radiation from water1 while it allows radiation from the ground to pass more freely into space2 the atmosphere over the ocean consequently throws back a greater amount of heat than is thrown back by the atmosphere over the land4 ,the sea in this case has a much greater difficulty than the land has in getting quit of the heat received from the sun2 in other words1 the land tends to lose its heat more rapidly than the sea4 ,the consequence of all these circumstances is that the ocean must stand at a higher mean temperature than the land4 ,a state of equilibrium is never gained until the rate at which a body is receiving heat is equal to the rate at which it is losing it2 but as equal surfaces of sea and land receive from the sun the same amount of heat1 it therefore follows that1 in order that the sea may get quit of its heat as rapidly as the land1 it must stand at a higher temperature than the land4 ,the temperature of the sea must continue to rise till the amount of heat thrown off into space equals that received from the sun2 when this point is reached1 equilibrium is established and the temperature remains stationary4 ,but1 owing to the greater difficulty that the sea has in getting rid of its heat1 the mean temperature of equilibrium of the ocean must be higher than that of the land2 consequently the mean temperature of the ocean1 and also of the air immediately over it1 in tropical regions should be higher than the mean temperature of the land and the air over it4 ,the greater portion of the southern hemisphere1 however1 is occupied by water1 and why then1 it may be asked1 is this water hemisphere colder than the land hemisphere8 ,ought it not also to follow that the sea in inter-tropical regions should be warmer than the land under the same parallels2 yet1 as we know1 the reverse is actually found to be the case4 ,how then is all this to be explained1 if the foregoing reasoning be correct8 ,we find when we examine ,professor ,dove's charts of mean annual temperature1 that the ocean in inter-tropical regions has a mean annual temperature below the normal1 and the land a mean annual temperature above the normal4 ,both in the ,pacific and in the ,atlantic the mean temperature sinks to #bc below the normal1 while on the land it rises #df above the normal4 ,the explanation in this case is obviously this3 the temperature of the ocean in inter-tropical regions1 as we have already seen1 is kept much lower than it would otherwise be by the enormous amount of heat that is being constantly carried away from those regions into temperate and polar regions1 and of cold that is being constantly carried from temperate and polar regions to the tropical regions by means of ocean-currents4 ,the same principle which explains why the sea in inter-tropical regions has a lower mean annual temperature than the land1 explains also why the southern hemisphere has a lower mean annual temperature than the northern4 ,the temperature of the southern hemisphere is lowered by the transference of heat by means of ocean-currents4 ,heat transferred from the ,southern to the ,northern ,hemisphere by ,ocean-currents the true ,explanation4--,the great ocean-currents of the globe take their rise in three immense streams from the ,southern ,ocean1 which1 on reaching the tropical regions1 become deflected in a westerly direction and flow along the southern side of the equator for thousands of miles4 ,perhaps more than one half of this mass of moving water returns into the ,southern ,ocean without ever crossing the equator1 but the quantity which crosses over to the northern hemisphere is enormous4 ,this constant flow of water from the southern hemisphere to the northern in the form of surface currents must be compensated by under currents of equal magnitude from the northern hemisphere to the southern4 ,the currents1 however1 which cross the equator are far higher in temperature than their compensating under currents2 consequently there is a constant transference of heat from the southern hemisphere to the northern4 ,any currents taking their rise in the northern hemisphere and flowing across into the southern are comparatively trifling1 and the amount of heat transferred by them is also trifling4 ,there are one or two currents of considerable size1 such as the ,brazilian branch of the great equatorial current of the ,atlantic1 and a part of the ,south ,equatorial ,drift-current of the ,pacific1 which cross the equator from north to south2 but these cannot be regarded as northern currents2 they are simply southern currents deflected back after crossing over to the northern hemisphere4 ,the heat which these currents possess is chiefly obtained on the southern hemisphere before crossing over to the northern2 and although the northern hemisphere may not gain much heat by means of them1 it1 on the other hand1 does not lose much1 for the heat which they give out in their progress along the southern hemisphere does not belong to the northern hemisphere4 ,but1 after making the fullest allowance for the amount of heat carried across the equator from the northern hemisphere to the southern1 we shall find1 if we compare the mean temperature of the currents from south to north with that of the great compensating under currents and the one or two small surface currents1 that the former is very much higher than the latter4 ,the mean temperature of the water crossing the equator from south to north is probably not under #fe1 that of the under currents is probably not over #ci4 ,but to the under currents we must add the surface currents from north to south2 and assuming that this will raise the mean temperature of the entire mass of water flowing south to1 say1 #de1 we have still a difference of #bj between the temperature of the masses flowing north and south4 ,each cubic foot of water which crosses the equator will in this case transfer about #ife1jjj foot-pounds of heat from the southern hemisphere to the northern4 ,if we had any means of ascertaining the volume of those great currents crossing the equator1 we should then be able to make a rough estimate of the total amount of heat transferred from the southern hemisphere to the northern2 but as yet no accurate estimate has been made on this point4 ,let us assume1 what is probably below the truth1 that the total amount of water crossing the equator is at least double that of the ,gulf-stream as it passes through the ,straits of ,florida1 which amount we have already found to be equal to #ff1ijh1afj1jjj1jjj cubic feet daily4 ,taking the quantity of heat conveyed by each cubic foot of water of the ,gulf-stream as #a1aeh1jjj foot-pounds1 it is found1 as we have seen1 that an amount of heat is conveyed by this current equal to all the heat that falls within #cb miles on each side of the equator4 ,then1 if each cubic foot of water crossing the equator transfers #ife1jjj foot-pounds1 and the quantity of water be double that of the ,gulf-stream1 it follows that the amount of heat transferred from the southern hemisphere to the northern is equal to all the heat falling within #eb miles on each side of the equator1 or equal to all the heat falling on the southern hemisphere within #ajd miles of the equator4 ,this quantity taken from the southern hemisphere and added to the northern will therefore make a difference in the amount of heat possessed by the two hemispheres equal to all the heat which falls on the southern hemisphere within somewhat more than #bjh miles of the equator4 ,a large ,portion of the ,heat of the ,gulf-stream derived from the ,southern ,hemisphere4--,it can be proved that a very large portion of the heat conveyed by the ,gulf-stream comes from the southern hemisphere4 ,the proof is as follows3-- ,if all the heat came from the northern hemisphere1 it could only come from that portion of the ,atlantic1 ,caribbean ,sea1 and ,gulf of ,mexico which lies to the north of the equator4 ,the entire area of these seas1 extending to the ,tropic of ,cancer1 is about #g1gjj1jjj square miles4 ,but this area is not sufficient to supply the current passing through the 8,narrows0 with the necessary heat4 ,were the heat which passes through the ,straits of ,florida derived exclusively from this area1 the following table would then represent the relative quantity per unit surface possessed by the ,atlantic in the three zones1 assuming that one half of the heat of the ,gulf-stream passes into the arctic regions and the other half remains to warm the temperate regions#eb3-- ,from the equator to the ,tropic of ,cancer #ggc ,from the ,tropic of ,cancer to the ,arctic ,circle #hdh ,from the ,arctic ,circle to the ,north ,pole #faj ,these figures show that the ,atlantic1 from the equator to the ,tropic of ,cancer1 would be as cold as from the ,tropic of ,cancer to the ,north ,pole1 were it not that a large proportion of the heat possessed by the ,gulf-stream is derived from the southern hemisphere4 ,,chapter ,,vi4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,lieut4 ,,maury',s ,,theory4 ,introduction4--,ocean-currents1 according to ,maury1 due to ,difference of ,specific ,gravity4--,difference of ,specific ,gravity resulting from ,difference of ,temperature4--,difference of ,specific ,gravity resulting from ,difference of ,saltness4--,maury's two ,causes neutralize each other4--,how1 according to him1 ,difference in ,saltness acts as a ,cause4 ,introduction4--,few subjects have excited more interest and attention than the cause of ocean circulation2 and yet few are in a more imperfect and unsatisfactory condition1 nor is there any question regarding which a greater diversity of opinion has prevailed4 ,our incomplete acquaintance with the facts relating to the currents of the ocean and the modes of circulation actually in operation1 is no doubt one reason for this state of things4 ,but doubtless the principal cause of such diversity of opinion lies in the fact that the question is one which properly belongs to the domain of physics and mechanics1 while as yet no physicist of note 7if we except ,dr4 ,colding1 of ,copenhagen7 has given1 as far as ,i know1 any special attention to the subject4 ,it is true that in works of meteorology and physical geography reference is continually made to such eminent physicists as ,herschel1 ,pouillet1 ,buff1 and others2 but when we turn to the writings of these authors we find merely a few remarks expressive of their opinions on the subject1 and no special discussion or investigation of the matter1 nor anything which could warrant us in concluding that such investigations have ever been made4 ,at present the question cannot be decided by a reference to authorities4 ,the various theories on the subject may be classed under two divisions2 the first of these attributes the motion of the water to the impulse of the wind1 and the second to the force of gravity resulting from difference of density4 ,but even amongst those who adopt the former theory1 it is generally held that the winds are not the sole cause1 but that1 to a certain extent at least1 difference of specific gravity contributes to produce motion of the waters4 ,this is a very natural conclusion2 and in the present state of physical geography on this subject one can hardly be expected to hold any other view4 ,the supporters of the latter theory may be subdivided into two classes4 ,the first of these 7of which ,maury may be regarded as the representative7 attributes the ,gulf-stream1 and other sensible currents of the ocean1 to difference of specific gravity4 ,the other class 7at present the more popular of the two1 and of which ,dr4 ,carpenter may be considered the representative7 denies altogether that such currents can be produced by difference of specific gravity1#ec and affirms that there is a general movement of the upper portion of the ocean from the equator to the poles1 and a counter-movement of the under portion from the poles to the equator4 ,this movement is attributed to difference of specific gravity between equatorial and polar water1 resulting from difference of temperature4 ,the widespread popularity of the gravitation theory is no doubt1 to a great extent1 owing to the very great prominence given to it by ,lieut4 ,maury in his interesting and popular work1 8,the ,physical ,geography of the ,sea40 ,another cause which must have favoured the reception of this theory is the ease with which it is perceived how1 according to it1 circulation of the waters of the ocean is supposed to follow4 ,one has no difficulty1 for example1 in perceiving that if the inter-tropical waters of the ocean are expanded by heat1 and the waters around the poles contracted by cold1 the surface of the ocean will stand at a higher level at the equator than at the poles4 ,equilibrium being thus disturbed1 the water at the equator will tend to flow towards the poles as a surface current1 and the water at the poles towards the equator as an under current4 ,this1 at first sight1 looks well1 especially to those who take but a superficial view of the matter4 ,we shall examine this theory at some length1 for two reasons3 #a1 because it lies at the root of a great deal of the confusion and misconception which have prevailed in regard to the whole subject of ocean-currents3 #b1 because1 if the theory is correct1 it militates strongly against the physical theory of secular changes of climate advanced in this volume4 ,we have already seen 7,chapter ,,iv47 that when the eccentricity of the earth's orbit reaches a high value1 a combination of physical circumstances tends to lower the temperature of the hemisphere which has its winter solstice in aphelion1 and to raise the temperature of the opposite hemisphere1 whose winter solstice will1 of course1 be in perihelion4 ,the direct result of this state of things1 as was shown1 is to strengthen the force of the trade-winds on the cold hemisphere1 and to weaken their strength on the warm hemisphere3 and this1 in turn1 we also saw1 tends to impel the warm water of the inter-tropical region on to the warm hemisphere1 and to prevent it1 in a very large degree1 from passing into the cold hemisphere4 ,this deflection of the ocean-currents tends to an enormous extent to increase the difference of temperature previously existing between the two hemispheres4 ,in other words1 the warm and equable condition of the one hemisphere1 and the cold and glacial condition of the other1 are1 to a great extent1 due to this deflection of ocean-currents4 ,but if the theory be correct which attributes the motion of ocean-currents to a difference in density between the sea in inter-tropical and polar regions1 then it follows that these currents 7other things being equal7 ought to be stronger on the cold hemisphere than on the warm1 because there is a greater difference of temperature and1 consequently1 a greater difference of density1 between the polar seas of the cold hemisphere and the equatorial seas1 than between the polar seas of the warm hemisphere and the equatorial seas4 ,and this being the case1 notwithstanding the influence of the trade-winds of the cold hemisphere blowing over upon the warm1 the currents will1 in all probability1 be stronger on the cold hemisphere than on the warm4 ,in other words1 the influence of the powerful trade-winds of the cold hemisphere to transfer the warm water of the equator to the warm hemisphere will probably be more than counterbalanced by the tendency of the warm and buoyant waters of the equator to flow towards the dense and cold waters around the pole of the cold hemisphere4 ,but if ocean-currents are due not to difference in specific gravity1 but to the influence of the winds1 then it is evident that the waters at the equator will be impelled1 not into the cold hemisphere1 but into the warm4 ,for this reason ,i have been the more anxious to prove that inter-tropical heat is conveyed to temperate and polar regions by ocean-currents1 and not by means of any general movement of the ocean resulting from difference of gravity4 ,i shall therefore on this account enter more fully into this part of the subject than ,i otherwise would have done4 ,irrespective of all this1 however1 the important nature of the whole question1 and the very general interest it excites1 warrant a full consideration of the subject4 ,i shall consider first that form of the gravitation theory advocated by ,maury in his work on the 8,physical ,geography of the ,sea10 which attributes the motion of the ,gulf-stream and other sensible currents of the ocean to differences of specific gravity4 ,one reason which has induced me to select ,maury's work is1 that it not only contains a much fuller discussion on the cause of the motion of ocean-currents than is to be found anywhere else1 but also that it has probably passed through a greater number of editions than any other book of a scientific character in the ,english language in the same length of time4 ,examination of ,lieut4 ,maury's ,gravitation ,theory4--,although ,lieut4 ,maury has expounded his views on the cause of ocean-currents at great length in the various editions of his work1 yet it is somewhat difficult to discover what they really are4 ,this arises chiefly from the generally confused and sometimes contradictory nature of his hydrodynamical conceptions4 ,after a repeated perusal of several editions of his book1 the following1 ,i trust1 will be found to be a pretty accurate representation of his theory3-- ,ocean-currents1 according to ,maury1 due to ,difference of ,specific ,gravity4--,although ,maury alludes to a number of causes which1 he thinks1 tend to produce currents1 yet he deems their influence so small that1 practically1 all currents may be referred to difference of specific gravity4 8,if we except10 he says1 8the tides1 and the partial currents of the sea1 such as those that may be created by the wind1 we may lay it down as a rule that all the currents of the ocean owe their origin to the differences of specific gravity between sea-water at one place and sea-water at another2 for wherever there is such a difference1 whether it be owing to difference of temperature or to difference of saltness1 c41 it is a difference that disturbs equilibrium1 and currents are the consequence0 7 #dfg7ed4 ,to the same effect see #hif1 #cg1 #eab1 #ebj1 and #ecg4 ,notwithstanding the fact that he is continually referring to difference of specific gravity as the great cause of currents1 it is difficult to understand in what way he conceives this difference to act as a cause4 ,difference of specific gravity between the waters of the ocean at one place and another can give rise to currents only through the influence of the earth's gravity4 ,all currents resulting from difference of specific gravity can be ultimately resolved into the general principle that the molecules that are specifically heavier descend and displace those that are specifically lighter4 ,if1 for example1 the ocean at the equator be expanded by heat or by any other cause1 it will be forced by the denser waters in temperate and polar regions to rise so that its surface shall stand at a higher level than the surface of the ocean in these regions4 ,the surface of the ocean will become an inclined plane1 sloping from the equator to the poles4 ,hydro-statically1 the ocean1 considered as a mass1 will then be in a state of equilibrium2 but the individual molecules will not be in equilibrium4 ,the molecules at the surface in this case may be regarded as lying on an inclined plane sloping from the equator down to the poles1 and as these molecules are at liberty to move they will not remain at rest1 but will descend the incline towards the poles4 ,when the waters at the equator are expanded1 or the waters at the poles contracted1 gravitation makes1 as it were1 a twofold effort to restore equilibrium4 ,it in the first place sinks the waters at the poles1 and raises the waters at the equator1 in order that the two masses may balance each other2 but this very effort of gravitation to restore equilibrium to the mass destroys the equilibrium of the molecules by disturbing the level of the ocean4 ,it then1 in the second place1 endeavours to restore equilibrium to the molecules by pulling the lighter surface water at the equator down the incline towards the poles4 ,this tends not only to restore the level of the ocean1 but to bring the lighter water to occupy the surface and the denser water the bottom of the ocean2 and when this is done1 complete equilibrium is restored1 both to the mass of the ocean and to its individual molecules1 and all further motion ceases4 ,but if heat be constantly applied to the waters of the equatorial regions1 and cold to those of the polar regions1 and a permanent disturbance of equilibrium maintained1 then the continual effort of gravitation to restore equilibrium will give rise to a constant current4 ,in this case1 the heat and the cold 7the agents which disturb the equilibrium of the ocean7 may be regarded as causes of the current1 inasmuch as without them the current would not exist2 but the real efficient cause1 that which impels the water forward1 is the force of gravity4 ,but the force of gravity1 as has already been noticed1 cannot produce motion 7perform work7 unless the thing acted upon descend4 ,descent is implied in the very conception of a current produced by difference of specific gravity4 ,but ,maury speaks as if difference of specific gravity could give rise to a current without any descent4 8,it is not necessary10 he says1 8to associate with oceanic currents the idea that they must of necessity1 as on land1 run from a higher to a lower level4 ,so far from this being the case1 some currents of the sea actually run up hill1 while others run on a level4 ,the ,gulf-stream is of the first class0 7 #djc74 8,the top of the ,gulf-stream runs on a level with the ocean2 therefore we know it is not a descending current0 7 #ah74 ,and in #i he says that between the ,straits of ,florida and ,cape ,hatteras the waters of the ,gulf-stream 8are actually forced up an inclined plane1 whose submarine ascent is not less than #aj inches to the mile40 ,to the same effect see #be1 #ei4 ,it is perfectly true that 8it is not necessary to associate with ocean-currents the idea that they must of necessity1 as on land1 run from a higher to a lower level40 ,but the reason of this is that ocean-currents do not1 like the currents on land1 owe their motion to the force of gravitation4 ,if ocean-currents result from difference of specific gravity between the waters in tropical and polar regions1 as ,maury maintains1 then it is necessary to assume that they are descending currents4 ,whatever be the cause which may give rise to a difference of specific gravity1 the motion which results from this difference is due wholly to the force of gravity2 but gravity can produce no motion unless the water descend4 ,this fact must be particularly borne in mind while we are considering ,maury's theory that currents are the result of difference of specific gravity4 ,ocean-currents1 then1 according to that writer1 owe their existence to the difference of specific gravity between the waters of inter-tropical and polar regions4 ,this difference of specific gravity he attributes to two causes--7#a7 to difference as to temperature1 7#b7 to difference as to saltness4 ,there are one or two causes of a minor nature affecting the specific gravity of the sea1 to which he alludes2 but these two determine the general result4 ,let us begin with the consideration of the first of these two causes1 viz43-- ,difference of ,specific ,gravity resulting from ,difference of ,temperature4--,maury explains his views on this point by means of an illustration4 8,let us now suppose10 he says1 8that all the water within the tropics1 to the depth of one hundred fathoms1 suddenly becomes oil4 ,the aqueous equilibrium of the planet would thereby be disturbed1 and a general system of currents and counter currents would be immediately commenced--the oil1 in an unbroken sheet on the surface1 running toward the poles1 and the water1 in an under current1 toward the equator4 ,the oil is supposed1 as it reaches the polar basin1 to be reconverted into water1 and the water to become oil as it crosses ,cancer and ,capricorn1 rising to the surface in inter-tropical regions1 and returning as before0 7 #bj74 8,now10 he says 7 #bb71 8do not the cold waters of the north1 and the warm waters of the ,gulf1 made specifically lighter by tropical heat1 and which we see actually preserving such a system of counter currents1 hold1 at least in some degree1 the relation of the supposed water and oil80 ,in #bd he calculates that at the ,narrows of ,bemini the difference in weight between the volume of the ,gulf-water that crosses a section of the stream in one second1 and an equal volume of water at the ocean temperature of the latitude1 supposing the two volumes to be equally salt1 is fifteen millions of pounds4 ,consequently the force per second operating to propel the waters of the ,gulf towards the pole would in this case1 he concludes1 be the 8equilibrating tendency due to fifteen millions of pounds of water in the latitude of ,bemini40 ,in #eaa and #eab he states that the effect of expanding the waters at the torrid zone by heat1 and of contracting the waters at the frigid zone by cold1 is to produce a set of surface-currents of warm and light water from the equator towards the poles1 and another set of under currents of cooler and heavy water from the poles towards the equator4 7,see also to the same effect #eac1 #ead1 #hif47 ,there can be no doubt that his conclusion is that the waters in inter-tropical regions are expanded by heat1 while those in polar regions are contracted by cold1 and that this tends to produce a surface current from the equator to the poles1 and an under current from the poles to the equator4 8,we shall now consider his second great cause of ocean currents1 viz43-- ,difference of ,specific ,gravity resulting from ,difference in ,degree of ,saltness4--,maury maintains1 and that correctly1 that saltness increases the density of water--that1 other things being equal1 the saltest water is the densest4 ,he suggests 8that one of the purposes which1 in the grand design1 it was probably intended to accomplish by having the sea salt and not fresh1 was to impart to its waters the forces and powers necessary to make their circulation complete0 7 #die74 ,now it is perfectly obvious that if difference in saltness is to co-operate with difference in temperature in the production of ocean-currents1 the saltest waters1 and consequently the densest1 must be in the polar regions1 and the waters least salt1 and consequently lightest1 must be in equatorial and inter-tropical regions4 ,were the saltest waters at the equator1 and the freshest at the poles1 it would tend to neutralize the effect due to heat1 and1 instead of producing a current1 would simply tend to prevent the existence of the currents which otherwise would result from difference of temperature4 ,a very considerable portion of his work1 however1 is devoted to proving that the waters of equatorial and inter-tropical regions are salter and heavier than those of the polar regions2 and yet1 notwithstanding this1 he endeavours to show that this difference in respect to saltness between the waters of the equatorial and the polar regions is one of the chief causes1 if not the chief cause1 of ocean-currents4 ,in fact1 it is for this special end that so much labour is bestowed in proving that the saltest water is in the equatorial and inter-tropical regions1 and the freshest in the polar4 8,in the present state of our knowledge10 he says1 8concerning this wonderful phenomenon 7for the ,gulf-stream is one of the most marvellous things in the ocean7 we can do little more than conjecture4 ,but we have two causes in operation which we may safely assume are among those concerned in producing the ,gulf-stream4 ,one of these is the increased saltness of its water after the trade-winds have been supplied with vapour from it1 be it much or little2 and the other is the diminished quantum of salt which the ,baltic and the ,northern ,seas contain0 7 #cg74 8,now here we have1 on one side1 the ,caribbean ,sea and ,gulf of ,mexico1 with their waters of brine2 on the other1 the great ,polar ,basin1 the ,baltic1 and the ,north ,sea1 the two latter with waters that are but little more than brackish4 ,in one set of these sea-basins the water is heavy1 in the other it is light4 ,between them the ocean intervenes2 but water is bound to seek and to maintain its level2 and here1 therefore1 we unmask one of the agents concerned in causing the ,gulf-stream0 7 #ch74 ,to the same effect see #eb1 #ebb1 #ebc1 #ebd1 #ebe1 #ebf1 #ebh1 #ecj1 #eed1 #eef4 ,lieut4 ,maury's two causes neutralize each other4 ,here we have two theories put forth regarding the cause of ocean-currents1 the one in direct opposition to the other4 ,according to the one theory1 ocean-currents exist because the waters of equatorial regions1 in consequence of their higher temperature1 are less dense than the waters of the polar regions2 but according to the other theory1 ocean-currents exist because the waters of equatorial regions1 in consequence of their greater saltness1 are more dense than the waters of the polar regions4 ,if the one cause be assigned as a reason why ocean-currents exist1 then the other can be equally assigned as a reason why they should not exist4 ,according to both theories it is the difference of density between the equatorial and polar waters that gives rise to currents2 but while the one theory maintains that the equatorial waters are lighter than the polar1 the other holds that they are heavier4 ,either the one theory or the other may be true1 or neither2 but it is logically impossible that both of them can4 ,let it be observed that it is not two currents1 the one contrary to the other1 with which we have at present to do2 it is not temperature producing currents in one direction1 and saltness producing currents in the contrary direction4 ,we have two theories regarding the origin of currents1 the one diametrically opposed to the other4 ,the tendency of the one cause assigned is to prevent the action of the other4 ,if temperature is allowed to act1 it will make the inter-tropical waters lighter than the polar1 and then1 according to theory1 a current will result4 ,but if we bring saltness into play 7the other cause7 it will do the reverse3 it will increase the density of the inter-tropical waters and diminish the density of the polar2 and so far as it acts it will diminish the currents produced by temperature1 because it will diminish the difference of specific gravity between the inter-tropical and polar regions which had been previously caused by temperature4 ,and when the effects of saltness are as powerful as those of temperature1 the difference of specific gravity produced by temperature will be completely effaced1 or1 in other words1 the waters of the equatorial and polar seas will be of the same density1 and consequently no current will exist4 ,and so long as the two causes continue in action1 no current can arise1 unless the energy of the one cause should happen to exceed that of the other2 and even then a current will only exist to the extent by which the strength of the one exceeds that of the other4 ,the contrary nature of the two theories will be better seen by considering the way in which it is supposed that difference in saltness is produced and acts as a cause4 ,if there is a constant current resulting from the difference in saltness between the equatorial and polar waters1 then there must be a cause which maintains this difference4 ,the current is simply the effort to restore the equilibrium lost by the difference2 and the current would very soon do this1 and then all motion would cease1 were there not a constantly operating cause maintaining the disturbance4 ,what1 then1 according to ,maury1 is the cause of this disturbance1 or1 in other words1 what is it that keeps the equatorial waters salter than the polar8 ,the agencies in operation are stated by him to be heat1 radiation1 evaporation1 precipitation1 and secretion of solid matter in the form of shells1 c4 ,the two most important1 however1 are evaporation and precipitation4 ,the trade-winds enter the equatorial regions as relatively dry winds thirsting for vapour2 consequently they absorb far more moisture than they give out2 and the result is that in inter-tropical regions1 evaporation is much in excess of precipitation2 and as fresh water only is taken up1 the salt being left behind1 the process1 of course1 tends to increase the saltness of the inter-tropical seas4 ,again1 in polar and extra-tropical regions the reverse is the case2 precipitation is in excess of evaporation4 ,this tends in turn to diminish the saltness of the waters of those regions4 7,see on these points #ca1 #cc1 #cd1 #cg1 #agi1 #eag1 #ebf1 and #eeb47 ,in the system of circulation produced by difference of temperature1 as we have already seen1 the surface-currents flow from the equator to the poles1 and the under or return currents from the poles to the equator2 but in the system produced by difference of saltness1 the surface currents flow from the poles to the equator1 and the return under currents from the equator to the poles4 ,that the surface currents produced by difference of saltness flow from the poles to the equator1 ,maury thinks is evident for the two following reasons3-- 7#a7 ,as evaporation is in excess of precipitation in inter-tropical regions1 more water is taken off the surface of the ocean in those regions than falls upon it in the form of rain4 ,this excess of water falls in the form of rain on temperate and polar regions1 where1 consequently1 precipitation is in excess of evaporation4 ,the lifting of the water off the equatorial regions and its deposit on the polar tend to lower the level of the ocean in equatorial regions and to raise the level in polar2 consequently1 in order to restore the level of the ocean1 the surface water at the polar regions flows towards the equatorial regions4 7#b7 ,as the water taken up at the equator is fresh1 and the salt is left behind1 the ocean1 in inter-tropical regions1 is thus made saltier and consequently denser4 ,this dense water1 therefore1 sinks and passes away as an under current4 ,this water1 evaporated from inter-tropical regions1 falls as fresh and lighter water in temperate and polar regions2 and therefore not only is the level of the ocean raised1 but the waters are made lighter4 ,hence1 in order to restore equilibrium1 the waters in temperate and polar regions will flow as a surface current towards the equator4 ,under currents will flow from the equator to the poles1 and surface or upper currents from the poles to the equator4 ,difference in temperature and difference in saltness1 therefore1 in every respect tend to produce opposite effects4 ,that the above is a fair representation of the way in which ,maury supposes difference in saltness to act as a cause in the production of ocean-currents will appear from the following quotations3-- 8,in those regions1 as in the trade-wind region1 where evaporation is in excess of precipitation1 the general level of this supposed sea would be altered1 and immediately as much water as is carried off by evaporation would commence to flow in from north and south toward the trade-wind or evaporation region1 to restore the level0 7 #eji74 8,on the other hand1 the winds have taken this vapour1 borne it off to the extra-tropical regions1 and precipitated it1 we will suppose1 where precipitation is in excess of evaporation4 ,here is another alteration of sea-level1 by elevation instead of by depression2 and hence we have the motive power for a surface current from each pole towards the equator1 the object of which is only to supply the demand for evaporation in the trade-wind regions0 7 #eaj74 ,the above result would follow1 supposing the ocean to be fresh4 ,he then proceeds to consider an additional result that follows in consequence of the saltness of the ocean4 8,let evaporation now commence in the trade-wind region1 as it was supposed to do in the case of the freshwater seas1 and as it actually goes on in nature--and what takes place8 ,why a lowering of the sea-level as before4 ,but as the vapour of salt water is fresh1 or nearly so1 fresh water only is taken up from the ocean2 that which remains behind is therefore more salt4 ,thus1 while the level is lowered in the salt sea1 the equilibrium is destroyed because of the saltness of the water2 for the water that remains after evaporation takes place is1 on account of the solid matter held in solution1 specifically heavier than it was before any portion of it was converted into vapour0 7 #eag74 8,the vapour is taken from the surface-water2 the surface-water thereby becomes more salt1 and1 under certain conditions1 heavier4 ,when it becomes heavier1 it sinks2 and hence we have1 due to the salts of the sea1 a vertical circulation1 namely1 a descent of heavier--because salter and cooler--water from the surface1 and an ascent of water that is lighter--because it is not so salt--from the depths below0 7 #eah74 ,in section #eai he goes on to show that this vapour removed from the inter-tropical region is precipitated in the polar regions1 where precipitation is in excess of evaporation4 8,in the precipitating regions1 therefore1 the level is destroyed1 as before explained1 by elevation1 and in the evaporating regions by depression2 which1 as already stated1 gives rise to a system of surface currents1 moved by gravity alone1 from the poles towards the equator0 7 #ebj74 8,this fresh water being emptied into the ,polar ,sea and agitated by the winds1 becomes mixed with the salt2 but as the agitation of the sea by the winds is supposed to extend to no great depth1 it is only the upper layer of salt water1 and that to a moderate depth1 which becomes mixed with the fresh4 ,the specific gravity of this upper layer1 therefore1 is diminished just as much as the specific gravity of the sea-water in the evaporating regions was increased4 ,and thus we have a surface current of saltish water from the poles towards the equator1 and an under current of water salter and heavier from the equator to the poles0 7 #ebb74 8,this property of saltness imparts to the waters of the ocean another peculiarity1 by which the sea is still better adapted for the regulation of climates1 and it is this3 by evaporating fresh water from the salt in the tropics1 the surface water becomes heavier than the average of sea-water4 ,this heavy water is also warm water2 it sinks1 and being a good retainer1 but a bad conductor1 of heat1 this water is employed in transporting through under currents heat for the mitigation of climates in far distant regions0 7 #ebf74 8,for instance1 let us suppose the waters in a certain part of the torrid zone to be #ij1 but by reason of the fresh water which has been taken from them in a state of vapour1 and consequently1 by reason of the proportionate increase of salts1 these waters are heavier than waters that may be cooler1 but not so salt4 ,this being the case1 the tendency would be for this warm but salt and heavy water to flow off as an under current towards the polar or some other regions of lighter water0 7 #eed74 ,that ,maury supposes the warm water at the equator to flow to the polar regions as an under current is further evident from the fact that he maintains that the climate of the arctic regions is mitigated by a warm under current1 which comes from the equatorial regions1 and passes up through ,davis ,straits 7see #ecdedd74 ,the question now suggests itself3 to which of these two antagonistic causes does ,maury really suppose ocean-currents must be referred8 ,whether does he suppose1 difference in temperature or difference in saltness1 to be the real cause8 ,i have been unable to find anything from which we can reasonably conclude that he prefers the one cause to the other4 ,it would seem that he regards both as real causes1 and that he has failed to perceive that the one is destructive of the other4 ,but it is difficult to conceive how he could believe that the sea in equatorial regions1 by virtue of its higher temperature1 is lighter than the sea in polar regions1 while at the same time it is not lighter but heavier1 in consequence of its greater saltness--how he could believe that the warm water at the equator flows to the poles as an upper current1 and the cold water at the poles to the equator as an under current1 while at the same time the warm water at the equator does not flow to the poles as a surface current1 nor the cold water at the poles to the equator as an under current1 but the reverse4 ,and yet1 unless these absolute impossibilities be possible1 how can an ocean-current be the result of both causes8 ,the only explanation of the matter appears to be that ,maury has failed to perceive the contradictory nature of his two theories4 ,this fact is particularly seen when he comes to apply his two theories to the case of the ,gulf-stream4 ,he maintains1 as has already been stated1 that the waters of the ,gulf-stream are salter than the waters of the sea through which they flow 7see #c1 #bh1 #bi1 #cj1 #cd1 and several other places74 ,and he states1 as we have already seen 7see p4 #ajd71 that the existence of the ,gulf-stream is due principally to the difference of density of the water of the ,caribbean ,sea and the ,gulf of ,mexico as compared with that of the great ,polar ,basin and the ,north ,sea4 ,there can be no doubt whatever that it is the density of the waters of the ,gulf-stream at its fountain-head1 the ,gulf of ,mexico1 resulting from its superior saltness1 and the deficiency of density of the waters in polar regions and the ,north ,sea1 c41 that is here considered to be unmasked as one of the agents4 ,if this be a cause of the motion of the ,gulf-stream1 how then can the difference of temperature between the waters of inter-tropical and polar regions assist as a cause8 ,this difference of temperature will simply tend to undo all that has been done by difference of saltness3 for it will tend to make the waters of the ,gulf of ,mexico lighter1 and the waters of the polar regions heavier4 ,but ,maury maintains1 as we have seen1 that this difference of temperature is also a cause1 which shows that he does not perceive the contradiction4 ,this is still further apparent4 ,he holds1 as stated1 that 8the waters of the ,gulf-stream are salter than the waters of the sea through which they flow10 and that this excess in saltness1 by making the water heavier1 is a cause of the motion of the stream4 ,but he maintains that1 notwithstanding the effect which greater saltness has in increasing the density of the waters of the ,gulf-stream1 yet1 owing to their higher temperature1 they are actually lighter than the water through which they flow2 and as a proof that this is the case1 he adduces the fact that the surface of the ,gulf-stream is roof-shaped 7 #cida71 which it could not be were its waters not actually lighter than the waters through which the stream flows4 ,so it turns out that1 in contradiction to what he had already stated1 it is the lesser density of the waters of the ,gulf-stream that is the real cause of their motion4 ,the greater saltness of the waters1 to which he attributes so much1 can in no way be regarded as a cause of motion4 ,its effect1 so far as it goes1 is to stop the motion of the stream rather than to assist it4 ,but1 again1 although he asserts that difference of saltness and difference of temperature are both causes of ocean-currents1 yet he appears actually to admit that temperature and saltness neutralize each other so as to prevent change in the specific gravity of the ocean1 as will be seen from the following quotation3-- 8,it is the trade-winds1 then1 which prevent the thermal and specific gravity curves from conforming with each other in inter-tropical seas4 ,the water they suck up is fresh water2 and the salt it contained1 being left behind1 is just sufficient to counterbalance1 by its weight1 the effect of thermal dilatation upon the specific gravity of sea-water between the parallels of #cd north and south4 ,as we go from #cd to the equator1 the water grows warmer and expands4 ,it would become lighter2 but the trade-winds1 by taking up vapour without salt1 make the water salter1 and therefore heavier4 ,the conclusion is1 the proportion of salt in sea-water1 its expansibility between #fb and #hb1 and the thirst of the trade-winds for vapour are1 where they blow1 so balanced as to produce perfect compensation2 and a more beautiful compensation cannot1 it appears to me1 be found in the mechanism of the universe than that which we have here stumbled upon4 ,it is a triple adjustment2 the power of the sun to expand1 the power of the winds to evaporate1 and the quantity of salts in the sea--these are so proportioned and adjusted that when both the wind and the sun have each played with its forces upon the inter-tropical waters of the ocean1 the residuum of heat and of salt should be just such as to balance each other in their effects2 and so the aqueous equilibrium of the torrid zone is preserved0 7 #dcf1 eleventh edition74 8,between #ce or #dj and the equator evaporation is in excess of precipitation2 and though1 as we approach the equator on either side from these parallels1 the solar ray warms and expands the surface-water of the sea1 the winds1 by the vapour they carry off1 and the salt they leave behind1 prevent it from making that water lighter0 7 #dcg1 eleventh edition74 8,philosophers have admired the relations between the size of the earth1 the force of gravity1 and the strength of fibre in the flower-stalks of plants2 but how much more exquisite is the system of counterpoises and adjustments here presented between the sea and its salts1 the winds and the heat of the sun60 7 #dch1 eleventh edition74 ,how can this be reconciled with all that precedes regarding ocean-currents being the result of difference of specific gravity caused by a difference of temperature and difference of saltness8 ,here is a distinct recognition of the fact that difference in saltness1 instead of producing currents1 tends rather to prevent the existence of currents1 by counteracting the effects of difference in temperature4 ,and so effectually does it do this1 that for #dj1 or nearly #c1jjj miles1 on each side of the equator there is absolutely no difference in the specific gravity of the ocean1 and consequently nothing1 either as regards difference of temperature or difference of saltness1 that can possibly give rise to a current4 ,but it is evident that1 if between the equator and latitude #dj the two effects completely neutralize each other1 it is not at all likely that between latitude #dj and the poles they will not to a large extent do the same thing4 ,and if so1 how can ocean-currents be due either to difference in temperature or to difference in saltness1 far less to both4 ,if there be any difference of specific gravity of the ocean between latitude #dj and the poles1 it must be only to the extent by which the one cause has failed to neutralize the other4 ,if1 for example1 the waters in latitude #dj1 by virtue of higher temperature1 are less dense than the waters in the polar regions1 they can be so only to the extent that difference in saltness has failed to neutralize the effect of difference in temperature4 ,and if currents result1 they can do so only to the extent that difference in saltness has thus fallen short of being able to produce complete compensation4 ,maury1 after stating his views on compensation1 seems to become aware of this2 but1 strangely1 he does not appear to perceive1 or1 at least1 he does not make any allusion to the fact1 that all this is fatal to his theories about ocean-currents being the combined result of differences of temperature and of saltness4 ,for1 in opposition to all that he had previously advanced regarding the difficulty of finding a cause sufficiently powerful to account for such currents as the ,gulf-stream1 and the great importance that difference in saltness had in their production1 he now begins to maintain that so great is the influence of difference in temperature that difference in saltness1 and a number of other compensating causes are actually necessary to prevent the ocean-currents from becoming too powerful4 8,if all the inter-tropical heat of the sun10 he says1 8were to pass into the seas upon which it falls1 simply raising the temperature of their waters1 it would create a thermo-dynamical force in the ocean capable of transporting water scalding hot from the torrid zone1 and spreading it while still in the tepid state around the poles4444 ,now1 suppose there were no trade-winds to evaporate and to counteract the dynamical force of the sun1 this hot and light water1 by becoming hotter and lighter1 would flow off in currents with almost mill-tail velocity towards the poles1 covering the intervening sea with a mantle of warmth as a garment4 ,the cool and heavy water of the polar basin1 coming out as under currents1 would flow equatorially with equal velocity40 8,thus two antagonistic forces are unmasked1 and1 being unmasked1 we discover in them a most exquisite adjustment--a compensation--by which the dynamical forces that reside in the sunbeam and the trade-wind are made to counterbalance each other1 by which the climates of inter-tropical seas are regulated1 and by which the set1 force1 and volume of oceanic currents are measured0 7 #dcg and #dch1 eleventh edition74 ,,chapter ,,vii4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,lieut4 ,,maury',s ,,theory 7continued74 ,methods of determining the ,question4--,the ,force resulting from ,difference of ,specific ,gravity4--,sir ,john ,herschel's ,estimate of the ,force4--,maximum ,density of ,sea-,water4--,rate of ,decrease of ,temperature of ,ocean at ,equator4---,the actual ,amount of ,force resulting from ,difference of ,specific ,gravity4--,m4 ,dubuat's ,experiments4 ,how the ,question may be ,determined4--,whether the circulation of the ocean is due to difference in specific gravity or not may be determined in three ways3 viz4 7#a7 by direct experiment2 7#b7 by ascertaining the absolute amount of force acting on the water to produce motion1 in virtue of difference of specific gravity1 and thereafter comparing it with the force which has been shown by experiment to be necessary to the production of sensible motion2 or 7#c7 by determining the greatest possible amount of work which gravity can perform on the waters in virtue of difference of specific gravity1 and then ascertaining if the work of gravity does or does not equal the work of the resistances in the required motion4 ,but ,maury has not adopted either of these methods4 ,the ,force resulting from ,difference of ,specific ,gravity4--,i shall consider first whether the force resulting from difference of specific gravity be sufficient to account for the motion of ocean-currents4 ,the inadequacy of this cause has been so clearly shown by ,sir ,john ,herschel1 that one might expect that little else would be required than simply to quote his words on the subject1 which are as follows3-- 8,first1 then1 if there were no atmosphere1 there would be no ,gulf-stream1 or any other considerable ocean-current 7as distinguished from a mere surface-drift7 whatever4 ,by the action of the sun's rays1 the surface of the ocean becomes most heated1 and the heated water will1 therefore1 neither directly tend to ascend 7which it could not do without leaving the sea7 nor to descend1 which it cannot do1 being rendered buoyant1 nor to move laterally1 no lateral impulse being given1 and which it could only do by reason of a general declivity of surface1 the dilated portion occupying a higher level4 ,let us see what this declivity would amount to4 ,the equatorial surface-water has a temperature of #hd4 ,at #g1bjj feet deep the temperature is #ci1 the level of which temperature rises to the surface in latitude #ef4 ,taking the dilatability of sea-water to be the same as that of fresh1 a uniformly progressive increase of temperature1 from #ci to #hd ,fahr41 would dilate a column of #g1bjj feet by #aj feet1 to which height1 therefore1 above the spheroid of equilibrium 7or above the sea-level in lat4 #ef71 the equatorial surface is actually raised by dilatation4 ,an arc of #ef on the earth's surface measures #c1cfj geographical miles2 so that we have a slope of #a_/bhth of an inch per geographical mile1 or #a_/cbnd of an inch per statute mile for the water so raised to run down4 ,as the accelerating force corresponding to such a slope 7of #a_/ajth of a second1 #ja7 is less than one two-millionth part of gravity1 we may dismiss this as a cause capable of creating only a very trifling surface-drift1 and not worth considering1 even were it in the proper direction to form1 by concentration1 a current from east to west1 which it could not be1 but the very reverse40#ee ,it is singular how any one1 even though he regarded this conclusion as but a rough approximation to the truth1 could entertain the idea that ocean-currents can be the result of difference in specific gravity4 ,there are one or two reasons1 however1 which may be given for the above not having been generally received as conclusive4 ,herschel's calculations refer to the difference of gravity resulting from difference of temperature2 but this is only one of the causes to which ,maury appeals1 and even not the one to which he most frequently refers4 ,he insists so strongly on the effects of difference of saltness1 that many might think that1 although ,herschel may have shown that difference in specific gravity arising from difference of temperature could not account for the motion of ocean-currents1 yet nevertheless that this1 combined with the effects resulting from difference in saltness1 might be a sufficient explanation of the phenomena4 ,such1 of course1 would not be the case with those who perceived the contradictory nature of ,maury's two causes2 but probably many read the 8,physical ,geography of the ,sea0 without being aware that the one cause is destructive of the other4 ,again1 a few plausible objections1 which have never received due consideration1 have been strongly urged by ,maury and others against the theory that ocean-currents can be caused by the impulses of the winds2 and probably these objections appear to militate as strongly against this theory as ,herschel's arguments against ,maury's4 ,there is one trifling objection to ,herschel's result3 he takes #ci as the temperature of maximum density4 ,this1 however1 as we shall see1 does not materially affect his conclusions4 ,observations on the temperature of the maximum density of sea-water have been made by ,erman1 ,despretz1 ,rossetti1 ,neumann1 ,marcet1 ,hubbard1 ,horner1 and others4 ,no two of them have arrived at exactly the same conclusion4 ,this probably arises from the fact that the temperature of maximum density depends upon the amount of salt held in solution4 ,no two seas1 unless they are equal as to saltness1 have the same temperature of maximum density4 ,the following ,table of ,despretz will show how rapidly the temperature of both the freezing-point and of maximum density is lowered by additional amounts of salt3-- ---------------------------------------- ------ ,amount ,temperature of ,temperature of of salt4 freezing-point4 ,maximum density4 ---------------------------------------- ------ #jjjjabc #aba ,c4 #aai ,c4 #jjbdf #bbd #afi #jjcga #bgg #dge #jjgda #ebh #afjj ---------------------------------------- ------ ,he found the temperature of maximum density of sea-water1 whose density at #bj;,c4 was #ajbgc1 to be #cfg;,c4 7#bed;,f471 and the temperature of freezing-point #bee;,c4 7#bgd;,f474#ef ,somewhere between #be and #bf ,f4 may therefore be regarded as the temperature of maximum density of sea-water of average saltness4 ,we have no reason to believe that the ocean1 from the surface to the bottom1 even at the poles1 is at #bgd;,f41 the freezing-point4 ,the actual slope resulting from difference of specific gravity1 as we shall presently see1 does not amount to #aj feet4 ,herschel's estimate was1 however1 made on insufficient data1 both as to the rate of expansion of sea-water and that at which the temperature of the ocean at the equator decreases from the surface downwards4 ,we are happily now in the possession of data for determining with tolerable accuracy the amount of slope due to difference of temperature between the equatorial and polar seas4 ,the rate of expansion of sea-water from #j;,c4 to #ajj;,c4 has been experimentally determined by ,professor ,muncke1 of ,heidelberg4#eg ,the valuable reports of ,captain ,nares1 of ,h4,m4,s4 ,challenger1 lately published by the ,admiralty1 give the rate at which the temperature of the ,atlantic at the equator decreases from the surface downwards4 ,these observations show clearly that the super-heating effect of the sun's rays does not extend to any great depth4 ,they also prove that at the equator the temperature decreases as the depth increases so rapidly that at #fj fathoms from the surface the temperature is #fbd1 the same as at ,madeira at the same depth2 while at the depth of #aej fathoms it is only #ea1 about the same as that in the ,bay of ,biscay 7,reports1 p4 #aa74 ,here at the very outset we have broad and important facts hostile to the theory of a flow of water resulting from difference of temperature between the ocean in equatorial and temperate and polar regions4 ,through the kindness of ,staff-,captain ,evans1 ,hydrographer of the ,admiralty1 ,i have been favoured with a most valuable set of serial temperature soundings made by ,captain ,nares of the ,challenger1 close to the equator1 between long4 #ad #di ,w4 and #cb #af ,w4 ,the following ,table represents the mean of the whole of these observations3-- ----------------------- ,fathoms4 ,temperature4 ----------------------- ,surface4 #ggi #aj #ggb #bj #gga #cj #gfi #dj #gag #ej #fdj #fj #fjd #gj #eid #hj #ehj #ij #ehj #ajj #eef #aej #eaj #bjj #dff #cjj #dbb #djj #djc #ejj #chi #fjj #cib #gjj #cij #hjj #cia #ijj #chb #ajjj #cfi #aajj #cgf #abjj #cfg #acjj #ceh #adjj #cfd #aejj #cfa ,bottom4 #cdg ----------------------- ,we have in this ,table data for determining the height at which the surface of the ocean at the equator ought to stand above that of the poles4 ,assuming #cb;,f4 to be the temperature of the ocean at the poles from the surface to the bottom and the foregoing to be the rate at which the temperature of the ocean at the equator decreases from the surface downwards1 and then calculating according to ,muncke's ,table of the expansion of sea-water1 we have only #d feet #f inches as the height to which the level of the ocean at the equator ought to stand above that at the poles in order that the ocean may be in static equilibrium4 ,in other words1 the equatorial column requires to be only #d feet #f inches higher than the polar in order that the two may balance each other4 ,taking the distance from the equator to the poles at #f1bjj miles1 the force resulting from the slope of #d feet in #f1bjj will amount to only #a_/g1cdj1jjjth that of gravity1 or about #a_/ajjjth of a grain on a pound of water4 ,but1 as we shall shortly see1 there can be no permanent current resulting from difference of temperature while the two columns remain in equilibrium1 for the current is simply an effort to the retardation of equilibrium4 ,in order to have permanent circulation there must be a permanent disturbance of equilibrium4 ,or1 in other words1 the weight of the polar column must be kept in excess of that of the equatorial4 ,suppose1 then1 that the weight of the polar column exceeds that of the equatorial by #b feet of water1 the difference of level between the two columns will1 in that case1 amount to only #b feet #f inches4 ,this would give a force of only #a_/ac1bjj1jjjth that of gravity1 or not much over #a_/a1ijjth of a grain on a pound of water1 tending to draw the water down the slope from the equator to the poles1 a force which does not much exceed the weight of a grain on a ton of water4 ,but it must be observed that this force of a grain per ton would affect only the water at the surface2 a very short distance below the surface the force1 small as it is1 would be enormously reduced4 ,if water were a perfect fluid1 and offered no resistance to motion1 it would not only flow down an incline1 however small it might be1 but would flow down with an accelerated motion4 ,but water is not a perfect fluid1 and its molecules do offer considerable resistance to motion4 ,water flowing down an incline1 however steep it may be1 soon acquires a uniform motion4 ,there must therefore be a certain inclination below which no motion can take place4 ,experiments were made by ,m4 ,dubuat with the view of determining this limit4#eh ,he found that when the inclination was #a in #ejj1jjj1 the motion of the water was barely perceptible2 and he came to the conclusion that when the inclination is reduced to #a in #a1jjj1jjj1 all motion ceases4 ,but the inclination afforded by the difference of temperature between the sea in equatorial and polar regions does not amount to one-seventh of this1 and consequently it can hardly produce even that 8trifling surface-drift0 which ,sir ,john ,herschel is willing to attribute to it4 ,there is an error into which some writers appear to fall to which ,i may here refer4 ,suppose that at the equator we have to descend #aj1jjj feet before water equal in density to that at the poles is reached4 ,we have in this case a plain with a slope of #aj1jjj feet in #f1bjj miles1 forming the upper surface of the water of maximum density4 ,now this slope exercises no influence in the way of producing a current1 as some seem to think2 for it is not a case of disturbed equilibrium1 but the reverse4 ,it is the condition of static equilibrium resulting from a difference between the temperature of the water at the equator and the poles4 ,the only slope that has any tendency to produce motion is that which is formed by the surface of the ocean in the equatorial regions being higher than the surface at the poles2 but this is an inclination of only #d feet #f inches1 and is therefore wholly inadequate to produce such currents as the ,gulf-stream4 ,,chapter ,,viii4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,dr4 ,,carpenter',s ,,theory4 ,gulf-stream according to ,dr4 ,carpenter not due to ,difference of ,specific ,gravity4--,facts to be ,explained4--,the ,explanation of the ,facts4--,the ,explanation hypothetical4--,the ,cause assigned for the hypothetical ,mode of ,circulation4--,under currents account for all the ,facts better than the ,gravitation ,hypothesis4--,known ,condition of the ,ocean inconsistent with that ,hypothesis4 ,dr4 ,carpenter does not suppose1 with ,lieut4 ,maury1 that the difference of temperature between the ocean in equatorial and polar regions can account for the ,gulf-stream and other great currents of the ocean4 ,he maintains1 however1 that this difference is quite sufficient to bring about a slow general interchange of water between the polar and inter-tropical areas--to induce a general movement of the upper portion of the ocean from the equator to the poles and a counter-movement of the under portion in a contrary direction4 ,it is this general movement which1 according to that author1 is the great agent by which heat is distributed over the globe4#ei ,in attempting to estimate the adequacy of this hypothesis as an explanation of the phenomena involved1 there are obviously two questions to be considered3 namely1 7#a7 is the difference of temperature between the sea in inter-tropical and polar regions sufficiently great to produce the required movement8 and 7#b7 assuming that there is such a movement1 does it convey the amount of heat which ,dr4 ,carpenter supposes8 ,i shall begin with the consideration of the first of these two points4 ,but before doing so let us see what the facts are which this gravitation theory is intended to explain4 ,the ,facts to be ,explained4--,dr4 ,carpenter considers that the great mass of warm water proved during recent dredging expeditions to occupy the depths of the ,north ,atlantic1 must be referred1 not to the ,gulf-stream1 but to a general movement of water from the equator4 8,the inference seems inevitable10 he says1 8that the bulk of the water in the warm area must have come thither from the south-west4 ,the influence of the ,gulf-stream proper 7meaning by this the body of super-heated water which issues through the #8,narrows' from the ,gulf of ,mexico71 if it reaches this locality at all 7which is very doubtful71 could only affect the most superficial stratum2 and the same may be said of the surface-drift caused by the prevalence of south-westerly winds1 to which some have attributed the phenomena usually accounted for by the extension of the ,gulf-stream to these regions4 ,and the presence of the body of water which lies between #ajj and #fjj fathoms deep1 and the range of whose temperature is from #dh to #db1 can scarcely be accounted for on any other hypothesis than that of a great general movement of equatorial water towards the polar area1 of which movement the ,gulf-stream constitutes a peculiar case modified by local conditions4 ,in like manner the ,arctic stream which underlies the warm superficial stratum in our cold area constitutes a peculiar case1 modified by the local conditions to be presently explained1 of a great general movement of polar water towards the equatorial area1 which depresses the temperature of the deepest parts of the great oceanic basins nearly to the freezing-point40 ,it is well-known that1 wherever temperature-observations have been made in the ,atlantic1 the bottom of that ocean has been found to be occupied by water of an ice-cold temperature4 ,and this holds true not merely of the ,atlantic1 but also of the ocean in inter-tropical regions--a fact which has been proved by repeated observations1 and more particularly of late by those of ,commander ,chimmo in the ,china ,sea and ,indian ,ocean1 where a temperature as low as #cb ,fahr4 was found at a depth of #b1fef fathoms4 ,in short1 the ,north ,atlantic1 and probably the inter-tropical seas also1 may be regarded1 ,dr4 ,carpenter considers1 as divided horizontally into two great layers or strata--an upper warm1 and a lower cold stratum4 ,all these facts ,i1 of course1 freely admit2 nor am ,i aware that their truth has been called in question by any one1 no matter what his views may have been as to the mode in which they are to be explained4 ,the ,explanation of the ,facts4--,we have next the explanation of the facts1 which is simply this3--,the cold water occupying the bottom of the ,atlantic and of inter-tropical seas is to be accounted for by the supposition that it came from the polar regions4 ,this is obvious1 because the cold possessed by the water could not have been derived from the crust of the earth beneath3 neither could it have come from the surface2 for the temperature of the bottom water is far below the normal temperature of the latitude in which it is found4 ,consequently 8the inference seems irresistible that this depression must be produced and maintained by the convection of cold from the polar towards the equatorial area40 ,of course1 if we suppose a flow of water from the poles towards the equator1 we must necessarily infer a counter flow from the equator towards the poles2 and while the water flowing from equatorial to polar regions will be warm1 that flowing from polar to equatorial regions will be cold4 ,the doctrine of a mutual interchange of equatorial and polar water is therefore a necessary consequence from the admission of the foregoing facts4 ,with this explanation of the facts ,i need hardly say that ,i fully agree2 nor am ,i aware that its correctness has ever been disputed4 ,dr4 ,carpenter surely cannot charge me with overlooking the fact of a mutual interchange of equatorial and polar water1 seeing that my estimate of the thermal power of the ,gulf-stream1 from which it is proved that the amount of heat conveyed from equatorial to temperate and polar regions is enormously greater than had ever been anticipated1 was made a considerable time before he began to write on the subject of oceanic circulation4#fj ,and in my paper 8,on ,ocean-currents in relation to the ,distribution of ,heat over the ,globe0#fa 7the substance of which is reproduced in ,chapters ,,ii4 and ,,iii4 of this volume71 ,i have endeavoured to show that1 were it not for the raising of the temperature of polar and high temperate regions and the lowering of the temperature of inter-tropical regions by means of this interchange of water1 these portions of the globe would not be habitable by the present existing orders of beings4 ,the explanation goes further3--8,it is along the surface and upper portion of the ocean that the equatorial waters flow towards the poles1 and it is along the bottom and under portion of the ocean that polar waters flow towards the equator2 or1 in other words1 the warm water keeps the upper portion of the ocean and the cold water the under portion40 ,with this explanation ,i to a great extent agree4 ,it is evident that1 in reference to the northern hemisphere at least1 the most of the water which flows from inter-tropical to polar regions 7as1 for example1 the ,gulf-stream7 keeps to the surface and upper portion of the ocean2 but for reasons which ,i have already stated1 a very large proportion of this water must return in the form of under currents2 or1 which is the same thing1 the return compensating current1 whether it consist of the identical water which originally came from the equator or not1 must flow towards the equator as an under current4 ,that the cold water which is found at the bottom of the ,atlantic and of inter-tropical seas must have come as under currents is perfectly obvious1 because water which should come along the surface of the ocean from the polar regions would not be cold when it reached inter-tropical regions4 ,the ,explanation hypothetical4--,here the general agreement between us in a great measure terminates1 for ,dr4 ,carpenter is not satisfied with the explanation generally adopted by the advocates of the wind theory1 viz41 that the cold water found in temperate and inter-tropical areas comes from polar regions as compensating under currents1 but advances a hypothetical form of circulation to account for the phenomenon4 ,he assumes that there is a general set or flow of the surface and upper portion of the ocean from the equator to polar regions1 and a general set or flow of the bottom and under portion of the ocean from polar regions to the equator4 ,mr4 ,ferrel 7,nature1 ,june #ac1 #ahgb7 speaks of that 8interchanging motion of the water between the equator and the pole discovered by ,dr4 ,carpenter40 ,in this1 however1 ,mr4 ,ferrel is mistaken2 for ,dr4 ,carpenter not only makes no claim to any discovery of the kind1 but distinctly admits that none such has yet been made4 ,although in some of his papers he speaks of a 8set of warm surface-water in the southern oceans toward the ,antarctic pole0 as being well known to navigators1 yet he nowhere affirms1 as far as ,i know1 that the existence of such a general oceanic circulation as he advocates has ever been directly determined from observations4 ,this mode of circulation is simply inferred or assumed in order to account for the facts referred to above4 8,at present10 ,dr4 ,carpenter says1 8,i claim for it no higher character than that of a good working hypothesis to be used as a guide in further inquiry0 7 #af72 and lest there should be any misapprehension on this point1 he closes his memoir thus3--8,at present1 as ,i have already said1 ,i claim for the doctrine of a general oceanic circulation no higher a character than that of a good working hypothesis consistent with our present knowledge of facts1 and therefore entitled to be provisionally adopted for the purpose of stimulating and directing further inquiry40 ,i am unable to agree with him1 however1 on this latter point4 ,it seems to me that there is no necessity for adopting any hypothetical mode of circulation to account for the facts1 as they can be quite well accounted for by means of that mode of circulation which does actually exist4 ,it has been determined from direct observation that surface-currents flow from equatorial to polar regions1 and their paths have been actually mapped out4 ,but if it is established that currents flow from equatorial to polar regions1 it is equally so that return currents flow from polar to equatorial regions2 for if the one actually exists1 the other of necessity must exist4 ,we know also on physical grounds1 to which ,i have already referred1 and which fall to be considered more fully in a subsequent chapter1 that a very large portion of the water flowing from polar to equatorial regions must be in the form of under currents4 ,if there are cold under currents1 therefore1 flowing from polar to temperate and equatorial regions1 this is all that we really require to account for the cold water which is found to occupy the bed of the ocean in those regions4 ,it does not necessarily follow1 because cold water may be found at the bottom of the ocean all along the equator1 that there must be a direct flow from the polar regions to every point of the equator4 ,water brought constantly from the polar regions to various points along the equator by means of under currents will necessarily accumulate1 and in course of time spread over the bottom of the inter-tropical seas4 ,it must either do this1 or the currents on reaching the equator must bend upwards and flow to the surface in an unbroken mass4 ,considerable portions of some of those currents may no doubt do so and join surface-currents2 but probably the greater portion of the water coming from polar regions extends itself over the floor of the equatorial seas4 ,in a letter in ,nature1 ,january #aa1 #ahgb1 ,i endeavoured to show that the surface-currents of the ocean are not separate and independent of one another1 but form one grand system of circulation1 and that the impelling cause keeping up this system of circulation is not the trade-winds alone1 as is generally supposed1 but the prevailing winds of the entire globe considered also as one grand system4 ,the evidence for this opinion1 however1 will be considered more fully in the sequel4 ,although the under currents are parts of one general system of oceanic circulation produced by the impulse of the system of prevailing winds1 yet their direction and position are nevertheless1 to a large extent1 determined by different laws4 ,the water at the surface1 being moved by the force of the wind1 will follow the path of greatest pressure and traction1--the effects resulting from the general contour of the land1 which to a great extent are common to both sets of currents1 not being taken into account2 while1 on the other hand1 the under currents from polar regions 7which to a great extent are simply 8indraughts0 compensating for the water drained from equatorial regions by the ,gulf-stream and other surface currents7 will follow1 as a general rule1 the path of least resistance4 ,the ,cause assigned for the ,hypothetical ,mode of ,circulation4--,dr4 ,carpenter assigns a cause for his mode of circulation2 and that cause he finds in the difference of specific gravity between equatorial and polar waters1 resulting from the difference of temperature between these two regions4 8,two separate questions10 he says1 8have to be considered1 which have not1 perhaps1 been kept sufficiently distinct1 either by ,mr4 ,croll or by myself2--first1 whether there is adequate evidence of the existence of a general vertical oceanic circulation2 and second1 whether1 supposing its existence to be provisionally admitted1 a vera causa can be found for it in the difference of temperature between the oceanic waters of the polar and equatorial areas0 7 #ag74 ,it seems to me that the facts adduced by ,dr4 ,carpenter do not necessarily require the assumption of any such mode of circulation as that advanced by him4 ,the phenomena can be satisfactorily accounted for otherwise2 and therefore there does not appear to be any necessity for considering whether his hypothesis be sufficient to produce the required effect or not4 ,an important ,consideration overlooked4--,but there is one important consideration which seems to have been overlooked--namely1 the fact that the sea is salter in inter-tropical than in polar regions1 and that this circumstance1 so far as it goes1 must tend to neutralize the effect of difference of temperature4 ,it is probable1 indeed1 that the effect produced by difference of temperature is thus entirely neutralized1 and that no difference of density whatever exists between the sea in inter-tropical and polar regions1 and consequently that there is no difference of level nor anything to produce such a general motion as ,dr4 ,carpenter supposes4 ,this1 ,i am glad to find1 is the opinion of ,professor ,wyville ,thomson4 8,i am greatly mistaken10 says that author1 8if the low specific gravity of the polar sea1 the result of the condensation and precipitation of vapour evaporated from the inter-tropical area1 do not fully counterbalance the contraction of the superficial film by arctic cold4444 ,speaking in the total absence of all reliable data1 it is my general impression that if we were to set aside all other agencies1 and to trust for an oceanic circulation to those conditions only which are relied upon by ,dr4 ,carpenter1 if there were any general circulation at all1 which seems very problematical1 the odds are rather in favour of a warm under current travelling northwards by virtue of its excess of salt1 balanced by a surface return current of fresher though colder arctic water40#fb ,this is what actually takes place on the west and north-west of ,spitzbergen4 ,there the warm water of the ,gulf-stream flows underneath the cold polar current4 ,and it is the opinion of ,dr4 ,scoresby1 ,mr4 ,clements ,markham1 and ,lieut4 ,maury that this warm water1 in virtue of its greater saltness1 is denser than the polar water4 ,mr4 ,leigh ,smith found on the north-west of ,spitzbergen the temperature at #ejj fathoms to be #eb1 and once even #fd1 while the water on the surface was only a degree or two above freezing4#fc ,mr4 ,aitken1 of ,darroch1 in a paper lately read before the ,royal ,scottish ,society of ,arts1 showed experimentally that the polar water in regions where the ice is melting is actually less dense than the warm and more salt tropical waters4 ,nor will it help the matter in the least to maintain that difference of specific gravity is not the reason why the warm water of the ,gulf-stream passes under the polar stream--because if difference of specific gravity be not the cause of the warm water underlying the cold water in polar regions1 then difference of specific gravity may likewise not be the cause of the cold water underlying the warm at the equator2 and if so1 then there is no necessity for the gravitation hypothesis of oceanic circulation4 ,there is little doubt that the super-heated stratum at the surface of the inter-tropical seas1 which stratum1 according to ,dr4 ,carpenter1 is of no great thickness1 is less dense than the polar water3 but if we take a column extending from the surface down to the bottom of the ocean1 this column at the equator will be found to be as heavy as one of equal length in the polar area4 ,and if this be the case1 then there can be no difference of level between the equator and the poles1 and no disturbance of static equilibrium nor anything else to produce circulation4 ,under ,currents account for all the ,facts better than ,dr4 ,carpenter's ,hypothesis4--,assuming1 for the present1 the system of prevailing winds to be the true cause of oceanic currents1 it necessarily follows 7as will be shown hereafter7 that a large quantity of ,atlantic water must be propelled into the ,arctic ,ocean2 and such1 as we know1 is actually the case4 ,the ,arctic ,ocean1 however1 as ,professor ,wyville ,thomson remarks1 is a well-nigh closed basin1 not permitting of a free outflow into the ,pacific ,ocean of the water impelled into it4 ,but it is evident that the water which is thus being constantly carried from the inter-tropical to the arctic regions must somehow or other find its way back to the equator2 in other words1 there must be a return current equal in magnitude to the direct current4 ,now the question to be determined is1 what path must this return current take8 ,it appears to me that it will take the path of least resistance1 whether that path may happen to be at the surface or under the surface4 ,but that the path of least resistance will1 as a general rule1 lie at a very considerable distance below the surface is1 ,i think1 evident from the following considerations4 ,at the surface the general direction of the currents is opposite to that of the return current4 ,the surface motion of the water in the ,atlantic is from the equator to the pole2 but the return current must be from the pole to the equator4 ,consequently the surface currents will oppose the motion of any return current unless that current lie at a considerable depth below the surface currents4 ,again1 the winds1 as a general rule1 blow in an opposite direction to the course of the return current1 because1 according to supposition1 the winds blow in the direction of the surface currents4 ,from all these causes the path of least resistance to the return current will1 as a general rule1 not be at the surface1 but at a very considerable depth below it4 ,a large portion of the water from the polar regions no doubt leaves those regions as surface currents2 but a surface current of this kind1 on meeting with some resistance to its onward progress along the surface1 will dip down and continue its course as an under current4 ,we have an example of this in the case of the polar current1 which upon meeting the ,gulf-stream on the banks of ,newfoundland divides--a portion of it dipping down and pursuing its course underneath that stream into the ,gulf of ,mexico and the ,caribbean ,sea4 ,and that this under current is a real and tangible current1 in the proper sense of the term1 and not an imperceptible movement of the water1 is proved by the fact that large icebergs deeply immersed in it are often carried southward with considerable velocity against the united force of the wind and the ,gulf-stream4 ,dr4 ,carpenter refers at considerable length 7 #acd7 to ,mr4 ,mitchell's opinion as to the origin of the polar current1 which is the same as that advanced by ,maury1 viz41 that the impelling cause is difference of specific gravity4 ,but although ,dr4 ,carpenter quotes ,mr4 ,mitchell's opinion1 he nevertheless does not appear to adopt it3 for in #ijic and various other places he distinctly states that he does not agree with ,lieut4 ,maury's view that the ,gulf-stream and polar current are caused by difference of density4 ,in fact1 ,dr4 ,carpenter seems particularly anxious that it should be clearly understood that he dissents from the theory maintained by ,maury4 ,but he does not merely deny that the ,gulf-stream and polar current can be caused by difference of density2 he even goes so far as to affirm that no sensible current whatever can be due to that cause1 and adduces the authority of ,sir ,john ,herschel in support of that opinion3--8,the doctrine of ,lieut4 ,maury10 he says1 8was powerfully and convincingly opposed by ,sir ,john ,herschel2 who showed1 beyond all reasonable doubt1 first1 that the ,gulf-stream really has its origin in the propulsive force of the trade-winds1 and secondly1 that the greatest disturbance of equilibrium which can be supposed to result from the agencies invoked by ,lieut4 ,maury would be utterly inadequate to generate and maintain either the ,gulf-stream or any other sensible current0 7 #ib74 ,this being ,dr4 ,carpenter's belief1 it is somewhat singular that he should advance the case of the polar current passing under the ,gulf-stream as evidence in favour of his theory2 for in reality he could hardly have selected a case more hostile to that theory4 ,in short1 it is evident that1 if a polar current impelled by a force other than that of gravity can pass from the banks of ,newfoundland to the ,gulf of ,mexico 7a distance of some thousands of miles7 under a current flowing in the opposite direction and1 at the same time1 so powerful as the ,gulf-stream1 it could pass much more easily under comparatively still water1 or water flowing in the same direction as itself4 ,and if this be so1 then all our difficulties disappear1 and we satisfactorily explain the presence of cold polar water at the bottom of inter-tropical seas without having recourse to the hypothesis advanced by ,dr4 ,carpenter4 ,but we have an example of an under current more inexplicable on the gravitation hypothesis than even that of the polar current1 viz41 the warm under current of ,davis ,strait4 ,there is a strong current flowing north from the ,atlantic through ,davis ,strait into the ,arctic ,ocean underneath a surface current passing southwards in an opposite direction4 ,large icebergs have been seen to be carried northwards by this under current at the rate of four knots an hour against both the wind and the surface current1 ripping and tearing their way with terrific force through surface ice of great thickness4#fd ,a current so powerful and rapid as this cannot1 as ,dr4 ,carpenter admits1 be referred to difference of specific gravity4 ,but even supposing that it could1 still difference of temperature between the equatorial and polar seas would not account for it2 for the current in question flows in the wrong direction4 ,nor will it help the matter the least to adopt ,maury's explanation1 viz41 that the warm under current from the south1 in consequence of its greater saltness1 is denser than the cold one from the polar regions4 ,for if the water of the ,atlantic1 notwithstanding its higher temperature1 is in consequence of its greater saltness so much denser than the polar water on the west of ,greenland as to produce an under current of four knots an hour in the direction of the pole1 then surely the same thing to a certain extent will hold true in reference to the ocean on the east side of ,greenland4 ,thus instead of there being1 as ,dr4 ,carpenter supposes1 an underflow of polar water south into the ,atlantic in virtue of its greater density1 there ought1 on the contrary1 to be a surface flow in consequence of its lesser density4 ,the true explanation no doubt is1 that the warm under current from the south and the cold upper current from the north are both parts of one grand system of circulation produced by the winds1 difference of specific gravity having no share whatever either in impelling the currents1 or in determining which shall be the upper and which the lower4 ,the wind in ,baffin's ,bay and ,davis ,strait blows nearly always in one direction1 viz4 from the north4 ,the tendency of this is to produce a surface or upper current from the north down into the ,atlantic1 and to prevent or retard any surface current from the south4 ,the warm current from the ,atlantic1 taking the path of least resistance1 dips under the polar current and pursues its course as an under current4 ,mr4 ,clements ,markham1 in his 8,threshold of the ,unknown ,region10 is inclined to attribute the motion of the icebergs to tidal action or to counter under currents4 ,that the motion of the icebergs cannot reasonably be attributed to the tides is1 ,i think1 evident from the descriptions given both by ,midshipman ,griffin and by ,captain ,duncan1 who distinctly saw the icebergs moving at the rate of about four knots an hour against a surface current flowing southwards4 ,and ,captain ,duncan states that the bergs continued their course northwards for several days1 till they ultimately disappeared4 ,the probability is that this northward current is composed partly of ,gulf-stream water and partly of that portion of polar water which is supposed to flow round ,cape ,farewell from the east coast of ,greenland4 ,this stream1 composed of both warm and cold water1 on reaching to about latitude #fe,n41 where it encounters the strong northerly winds1 dips down under the polar current and continues its northward course as an under current4 ,we have on the west of ,spitzbergen1 as has already been noticed1 a similar example of a warm current from the south passing under a polar current4 ,a portion of the ,gulf-stream which passes round the west coast of ,spitzbergen flows under an arctic current coming down from the north2 and it does so no doubt because it is here in the region of prevailing northerly winds1 which favour the polar current but oppose the ,gulf-stream4 ,again1 we have a cold and rapid current sweeping round the east and south of ,spitzbergen1 a current of which ,mr4 ,lamont asserts that he is positive he has seen it running at the rate of seven or eight miles an hour4 ,this current1 on meeting the ,gulf-stream about the northern entrance to the ,german ,ocean1 dips down under that stream and pursues its course southwards as an under current4 ,several other cases of under currents might be adduced which cannot be explained on the gravitation theory1 and which must be referred to a system of oceanic circulation produced by the impulse of the wind2 but these will suffice to show that the assumption that the winds can produce only a mere surface-drift is directly opposed to facts4 ,and it will not do to affirm that a current which forms part of a general system of circulation produced by the impulse of the winds cannot possibly be an under current2 for in the case referred to we have proof that the thing is not only possible but actually exists4 ,this point1 however1 will be better understood after we have considered the evidence in favour of a general system of oceanic currents4 ,much of the difficulty experienced in comprehending how under currents can be produced by the wind1 or how an impulse imparted to the surface of the ocean can ever be transmitted to the bottom1 appears to me to result1 to a considerable extent at least1 from a slight deception of the imagination4 ,the thing which impresses us most forcibly in regard to the ocean is its profound depth4 ,a mean depth of1 say1 three miles produces a striking impression2 but if we could represent to the mind the vast area of the ocean as correctly as we can its depth1 shallowness rather than depth would be the impression produced4 ,if in crossing a meadow we found a sheet of water one hundred yards in diameter and only an inch in depth1 we should not call that a deep1 but a very shallow pool4 ,the probability is that we should speak of it as simply a piece of ground covered with a thin layer of water4 ,yet such a thin layer of water would be a correct representation in miniature of the ocean2 for the ocean in relation to its superficial area is as shallow as the pool of our illustration4 ,in reference to such a pool or thin film of water1 we have no difficulty in conceiving how a disturbance on its surface would be transmitted to its bottom4 ,in fact our difficulty is in conceiving how any disturbance extending over its entire surface should not extend to the bottom4 ,now if we could form as accurate a sensuous impression of the vast area of the ocean as we do of such a pool1 all our difficulty in understanding how the impulses of the wind acting on the vast area of the ocean should communicate motion down to its bottom would disappear4 ,it is certainly true that sudden commotions caused by storms do not generally extend to great depths4 ,neither will winds of short continuance produce a current extending far below the surface4 ,but prevailing winds which can produce such immense surface-flow as that of the great equatorial currents of the globe and the ,gulf-stream1 which follow definite directions1 must communicate their motion to great depths1 unless water be frictionless1 a thing which it is not4 ,suppose the upper layer of the ocean to be forced on by the direct action of the winds with a constant velocity of1 say1 four miles an hour1 the layer immediately below will be dragged along with a constant velocity somewhat less than four miles an hour4 ,the layer immediately below this second layer will in turn be also dragged along with a constant velocity somewhat less than the one above it4 ,the same will take place in regard to each succeeding layer1 the constant velocity of each layer being somewhat less than the one immediately above it1 and greater than the one below it4 ,the question to be determined is1 at what depth will all motion cease8 ,i presume that at present we have not sufficient data for properly determining this point4 ,the depth will depend1 other things being equal1 upon the amount of molecular resistance offered by the water to motion--in other words1 on the amount of the shearing-force of the one layer over the other4 ,the fact1 however1 that motion imparted to the surface will extend to great depths can be easily shown by direct experiment4 ,if a constant motion be imparted to the surface of water1 say1 in a vessel1 motion will ultimately be communicated to the bottom1 no matter how wide or how deep the vessel may be4 ,the same effect will take place whether the vessel be #e feet deep or #ejj feet deep4 ,the known ,condition of the ,ocean inconsistent with ,dr4 ,carpenter's ,hypothesis4--,dr4 ,carpenter says that he looks forward with great satisfaction to the results of the inquiries which are being prosecuted by the ,circumnavigation ,expedition1 in the hope that the facts brought to light may establish his theory of a general oceanic circulation2 and he specifies certain of these facts which1 if found to be correct1 will establish his theory4 ,it seems to me1 however1 that the facts to which he refers are just as explicable on the theory of under currents as on the theory of a general oceanic circulation4 ,he begins by saying1 8,if the views ,i have propounded be correct1 it may be expected that near the border of the great antarctic ice-barrier a temperature below #cj will be met with 7as it has been by ,parry1 ,martens1 and ,weyprecht near ,spitzbergen7 at no great depth beneath the surface1 and that instead of rising at still greater depths1 the thermometer will fall to near the freezing-point of salt water0 7 #ci74 ,dr4 ,carpenter can hardly claim this as evidence in favour of his theory2 for near the borders of the ice-barrier the water1 as a matter of course1 could not be expected to have a much higher temperature than the ice itself4 ,and if the observations be made during summer months1 the temperature of the water at the surface will no doubt be found to be higher than that of the bottom2 but if they be carried on during winter1 the surface-temperature will doubtless be found to be as low as the bottom-temperature4 ,these are results which do not depend upon any particular theory of oceanic circulation4 8,the bottom temperature of the ,north ,pacific10 he continues1 8will afford a crucial test of the truth of the doctrine4 ,for since the sole communication of this vast oceanic area with the arctic basin is a strait so shallow as only to permit an inflow of warm surface water1 its deep cold stratum must be entirely derived from the antarctic area2 and if its bottom temperature is not actually higher than that of the ,south ,pacific1 the glacial stratum ought to be found at a greater depth north of the equator than south of it0 7 #ci74 ,this may probably show that the water came from the antarctic regions1 but cannot possibly prove that it came in the manner which he supposes4 8,in the ,north ,atlantic1 again1 the comparative limitation of communication with the arctic area may be expected to prevent its bottom temperature from being reduced as low as that of the ,southern ,atlantic0 7 #ci74 ,supposing the bottom temperature of the ,south ,atlantic should be found to be lower than the bottom temperature of the ,north ,atlantic1 this fact will be just as consistent with the theory of under currents as with his theory of a general movement of the ocean4 ,i am also wholly unable to comprehend how he should imagine1 because the bottom temperature of the ,south ,atlantic happens to be lower1 and the polar water to lie nearer to the surface in this ocean than in the ,north ,atlantic1 that therefore this proves the truth of his theory4 ,this condition of matters is just as consistent1 and even more so1 as will be shown in ,chapter ,,xiii41 with my theory as with his4 ,when we consider the immense quantity of warm surface water which1 as has been shown 7,chapter ,v471 is being constantly transferred from the ,south into the ,north ,atlantic1 we readily understand how the polar water comes nearer to the surface in the former ocean than in the latter4 ,every pound of water1 of course1 passing from the southern to the northern hemisphere must be compensated by an equal amount passing from the northern to the southern hemisphere4 ,but nevertheless the warm water drained off the ,south ,atlantic is not replaced directly by water from the north1 but by that cold antarctic current1 the existence of which is1 unfortunately1 too well known to navigators from the immense masses of icebergs which it brings along with it4 ,in fact1 the whole of the phenomena are just as easily explained upon the principle of under currents as upon ,dr4 ,carpenter's theory4 ,but we shall have to return to this point in ,chapter ,,xiii41 when we come to discuss a class of facts which appear to be wholly irreconcilable with the gravitation theory4 ,indeed ,i fear that even although ,dr4 ,carpenter's expectations should eventually be realised in the results of the ,circumnavigation ,expedition1 yet the advocates of the wind theory will still remain unconverted4 ,in fact the ,director of this ,expedition has already1 on the wind theory1 offered an explanation of nearly all the phenomena on which ,dr4 ,carpenter relies2#fe and the same has also been done by ,dr4 ,petermann1#ff who1 as is well known1 is equally opposed to ,dr4 ,carpenter's theory4 ,dr4 ,carpenter directs attention to the necessity of examining the broad and deep channel separating ,iceland from ,greenland4 ,the observations which have already been made1 however1 show that nearly the entire channel is occupied1 on the surface at least1 by water flowing southward from the polar area--a direction the opposite of what it ought to be according to the gravitation theory4 ,in fact the surface of one half of the entire area of the ocean1 extending from ,greenland to the ,north ,cape1 is moving in a direction the opposite of that which it ought to take according to the theory under review4 ,the western half of this area is occupied by water which at the surface is flowing southwards2 while the eastern half1 which has hitherto been regarded by almost everybody but ,dr4 ,carpenter himself and ,mr4 ,findlay as an extension of the ,gulf-stream1 is moving polewards4 ,the motion of the western half must be attributed to the winds and not to gravity2 for it is moving in the wrong direction to be accounted for by the latter cause2 but had it been moving in the opposite direction1 no doubt its motion would have been referred to gravitation4 ,to this cause the motion of the eastern half1 which is in the proper direction1 is attributed2#fg but why not assign this motion also to the impulse of the winds1 more especially since the direction of the prevailing winds blowing over that area coincides with that of the water8 ,if the wind can produce the motion of the water in the western half1 why may not it do the same in the eastern half8 ,if there be such a difference of density between equatorial and polar waters as to produce a general flow of the upper portion of the ocean poleward1 how does it happen that one half of the water in the above area is moving in opposition to gravity8 ,how is it that in a wide open sea gravitation should act so powerfully in the one half of it and with so little effect in the other half8 ,there is probably little doubt that the ice-cold water of the western half extends from the surface down to the bottom4 ,and it is also probable that the bottom water is moving southwards in the same direction as the surface water4 ,the bottom water in such a case would be moving in harmony with the gravitation theory2 but would ,dr4 ,carpenter on this account attribute its motion to gravity8 ,would he attribute the motion of the lower half to gravity and the upper half to the wind8 ,he could not in consistency with his theory attribute the motion of the upper half to gravity3 for although the ice-cold water extended to the surface1 this could not explain how gravity should move it southward instead of polewards1 as according to theory it ought to move4 ,he might affirm1 if he chose1 that the surface water moves southwards because it is dragged forward by the bottom water2 but if this view be held1 he is not entitled to affirm1 as he does1 that the winds can only produce a mere surface drift4 ,if the viscosity and molecular resistance of water be such that1 when the lower strata of the ocean are impelled forward by gravity or by any other cause1 the superincumbent strata extending to the surface are perforce dragged after them1 then1 for the same reason1 when the upper strata are impelled forward by the wind or any other cause1 the underlying strata must also be dragged along after them4 ,if the condition of the ocean between ,greenland and the north-western shore of ,europe is irreconcilable with the gravitation theory1 we find the case even worse for that theory when we direct our attention to the condition of the ocean on the southern hemisphere2 for according to the researches of ,captain ,duperrey and others on the currents of the ,southern ,ocean1 a very large portion of the area of that ocean is occupied by water moving on the surface more in a northward than a poleward direction4 ,referring to the deep trough between the ,shetland and the ,faroe ,islands1 called by him the 8,lightning ,channel10 ,dr4 ,carpenter says1 8,if my view be correct1 a current-drag suspended in the upper stratum ought to have a perceptible movement in the ,n4,e4 direction2 whilst another1 suspended in the lower stratum1 should move ,s4,w40 7 #dj74 ,any one believing in the north-eastern extension of the ,gulf-stream and in the ,spitsbergen polar under current1 to which ,i have already referred1 would not feel surprised to learn that the surface strata have a perceptible north-eastward motion1 and the bottom strata a perceptible south-westward motion4 ,north-east and east of ,iceland there is a general flow of cold polar water in a south-east direction towards the left edge of the ,gulf-stream4 ,this water1 as ,professor ,mohn concludes1 8descends beneath the ,gulf-stream and partially finds an outlet in the lower half of the ,faroe-,shetland channel40#fh ,an ,objection ,considered4--,in ,nature1 vol4 ix4 p4 #dbc1 ,dr4 ,carpenter has advanced the following objection to the foregoing theory of under-currents3--8,according to ,mr4 ,croll's doctrine1 the whole of that vast mass of water in the ,north ,atlantic1 averaging1 say1 #a1ejj fathoms in thickness and #c1fjj miles in breadth1 the temperature of which 7from #dj downwards71 as ascertained by the ,challenger soundings1 clearly shows it to be mainly derived from a polar source1 is nothing else than the reflux of the ,gulf-stream4 ,now1 even if we suppose that the whole of this stream1 as it passes ,sandy ,hook1 were to go on into the closed arctic basin1 it would only force out an equivalent body of water4 ,and as1 on comparing the sectional areas of the two1 ,i find that of the ,gulf-stream to be about #a_/ijjth that of the ,north ,atlantic underflow2 and as it is admitted that a large part of the ,gulf-stream returns into the ,mid-,atlantic circulation1 only a branch of it going on to the north-east1 the extreme improbability 7may ,i not say impossibility87 that so vast a mass of water can be put in motion by what is by comparison a mere rivulet 7the north-east motion of which1 as a distinct current1 has not been traced eastward of #cj ,w4 long47 seems still more obvious40 ,in this objection three things are assumed3 7#a7 that the mass of cold water #a1ejj fathoms deep and #c1fjj miles in breadth is in a state of motion towards the equator2 7#b7 that it cannot be the reflux of the ,gulf-stream1 because its sectional area is #ijj times as great as that of the ,gulf-stream2 7#c7 that the immense mass of water is1 according to my views1 set in motion by the ,gulf-stream4 ,as this objection has an important bearing on the question under consideration1 ,i shall consider these three assumptions separately and in their order3 7#a7 ,that this immense mass of cold water came originally from the polar regions ,i1 of course1 admit1 but that the whole is in a state of motion ,i certainly do not admit4 ,there is no warrant whatever for any such assumption4 ,according to ,dr4 ,carpenter himself1 the heating-power of the sun does not extend to any great depth below the surface2 consequently there is nothing whatever to heat this mass but the heat coming through the earth's crust4 ,but the amount of heat derived from this source is so trifling1 that an under current from the arctic regions far less in volume than that of the ,gulf-stream would be quite sufficient to keep the mass at an ice-cold temperature4 ,taking the area of the ,north ,atlantic between the equator and the ,tropic of ,cancer1 including also the ,caribbean ,sea and the ,gulf of ,mexico1 to be #g1gjj1jjj square miles1 and the rate at which internal heat passes through the earth's surface to be that assigned by ,sir ,william ,thomson1 we find that the total quantity of heat derived from the earth's crust by the above area is equal to about #hh #ajae foot-pounds per day4 ,but this amount is equal to only #a_/hidth that conveyed by the ,gulf-stream1 on the supposition that each pound of water carries #ai1cjj foot-pounds of heat4 ,consequently an under current from the polar regions of not more than #a_/ceth the volume of the ,gulf-stream would suffice to keep the entire mass of water of that area within #a of what it would be were there no heat derived from the crust of the earth2 that is to say1 were the water conveyed by the under current at #cb1 internal heat would not maintain the mass of the ocean in the above area at more than #cc4 ,the entire area of the ,north ,atlantic from the equator to the arctic circle is somewhere about #af1jjj1jjj square miles4 ,an under current of less than #a_/agth that of the ,gulf-stream coming from the arctic regions would therefore suffice to keep the entire ,north ,atlantic basin filled with ice-cold water4 ,in short1 whatever theory we adopt regarding oceanic circulation1 it follows equally as a necessary consequence that the entire mass of the ocean below the stratum heated by the sun's rays must consist of cold water4 ,for if cold water be continually coming from the polar regions either in the form of under currents1 or in the form of a general underflow as ,dr4 ,carpenter supposes1 the entire under portion of the ocean must ultimately become occupied by cold water2 for there is no source from which this influx of water can derive heat1 save from the earth's crust4 ,but the amount thus derived is so trifling as to produce no sensible effect4 ,for example1 a polar under current one half the size of the ,gulf-stream would be sufficient to keep the entire water of the globe 7below the stratum heated by the sun's rays7 at an ice-cold temperature4 ,internal heat would not be sufficient under such circumstances to maintain the mass #a ,fahr4 above the temperature it possessed when it left the polar regions4 ,it follows therefore that the presence of the immense mass of ice-cold water in the great depths of the ocean is completely accounted for by under currents1 and there is no necessity for supposing it to be all in a state of motion towards the equator4 ,in fact1 this very state of things1 which the general oceanic circulation hypothesis was devised to explain1 results as a necessary consequence of polar under currents4 ,unless these were entirely stopped it is physically impossible that the ocean could be in any other condition4 ,but suppose that this immense mass of cold water occupying the great depths of the ocean were1 as ,dr4 ,carpenter assumes it to be1 in a state of constant motion towards the equator1 and that its sectional area were #ijj times that of the ,gulf-stream1 it would not therefore follow that the quantity of water passing through this large sectional area must be greater than that flowing through a sectional area of the ,gulf-stream2 for the quantity of water flowing through this large sectional area depends entirely on the rate of motion4 ,i am wholly unable to understand how it could be supposed that this underflow1 according to my view1 is set in motion by the ,gulf-stream1 seeing that ,i have shown that the return under current is as much due to the impulse of the wind as the ,gulf-stream itself4 ,dr4 ,carpenter lays considerable stress on the important fact established by the ,challenger expedition1 that the great depths of the sea in equatorial regions are occupied by ice-cold water1 while the portion heated by the sun's rays is simply a thin stratum at the surface4 ,it seems to me that it would be difficult to find a fact more hostile to his theory than this4 ,were it not for this upper stratum of heated water there would be no difference between the equatorial and polar columns1 and consequently nothing to produce motion4 ,but the thinner this stratum is the less is the difference1 and the less there is to produce motion4 ,,chapter ,,ix4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,the ,,mechanics ,,of ,,dr4 ,,carpenter',s ,,theory4 ,experimental ,illustration of the ,theory4--,the ,force exerted by ,gravity4--,work performed by ,gravity4--,circulation not by ,convection4--,circulation depends on ,difference in ,density of the ,equatorial and ,polar ,columns4--,absolute ,amount of ,work which can be performed by ,gravity4--,how ,underflow is produced4--,how ,vertical ,descent at the ,poles and ,ascent at the ,equator is produced4--,the ,gibraltar ,current4--,mistake in ,mechanics concerning it4--,the ,baltic ,current4 ,experiment to illustrate ,theory4--,in support of the theory of a general movement of water between equatorial and polar regions1 ,dr4 ,carpenter adduces the authority of ,humboldt and of ,prof4 ,buff4#fi ,i have been unable to find anything in the writings of either from which it can be inferred that they have given this matter special consideration4 ,humboldt merely alludes to the theory1 and that in the most casual manner2 and that ,prof4 ,buff has not carefully investigated the subject is apparent from the very illustration quoted by ,dr4 ,carpenter from the 8,physics of the ,earth40 8,the water of the ocean at great depths10 says ,prof4 ,buff1 8has a temperature1 even under the equator1 nearly approaching to the freezing-point4 ,this low temperature cannot depend on any influence of the sea-bottom4444 ,the fact1 however1 is explained by a continual current of cold water flowing from the polar regions towards the equator4 ,the following well-known experiment clearly illustrates the manner of this movement4 ,a glass vessel is to be filled with water with which some powder has been mixed1 and is then to be heated at bottom4 ,it will soon be seen1 from the motion of the particles of powder1 that currents are set up in opposite directions through the water4 ,warm water rises from the bottom up through the middle of the vessel1 and spreads over the surface1 while the colder and therefore heavier liquid falls down at the sides of the glass40 ,this illustration is evidently intended to show not merely the form and direction of the great system of oceanic circulation1 but also the mode in which the circulation is induced by heat4 ,it is no doubt true that if we apply heat 7say that of a spirit-lamp7 to the bottom of a vessel filled with water1 the water at the bottom of the vessel will become heated and rise to the surface2 and if the heat be continued an ascending current of warm water will be generated2 and this1 of course1 will give rise to a compensating under current of colder water from all sides4 ,in like manner it is also true that1 if heat were applied to the bottom of the ocean in equatorial regions1 an ascending current of hot water would be also generated1 giving rise to an under current of cold water from the polar regions4 ,but all this is the diametrically opposite of what actually takes place in nature4 ,the heat is not applied to the bottom of the ocean1 so as to make the water there lighter than the water at the surface1 and thus to generate an ascending current2 but the heat is applied to the surface of the ocean1 and the effect of this is to prevent an ascending current rather than to produce one1 for it tends to keep the water at the surface lighter than the water at the bottom4 ,in order to show how the heat of the sun produces currents in the ocean1 ,prof4 ,buff should have applied the heat1 not to the bottom of his vessel1 but to the upper surface of the water4 ,but this is not all1 the form of the vessel has something to do with the matter4 ,the wider we make the vessel in proportion to its depth1 the more difficult it is to produce currents by means of heat4 ,but in order to represent what takes place in nature1 we ought to have the same proportion between the depth and the superficial area of the water in our vessel as there is between the depth and the superficial area of the sea4 ,the mean depth of the sea may be taken roughly to be about three miles4#gj ,the distance between pole and pole we shall take in round numbers to be #ab1jjj miles4 ,the sun may therefore be regarded as shining upon a circular sea #ab1jjj miles in diameter and three miles deep4 ,the depth of the sea to its diameter is therefore as #a to #d1jjj4 ,suppose1 now1 that in our experiment we make the depth of our vessel one inch1 we shall require to make its diameter #d1jjj inches1 or #ccc feet1 say1 in round numbers1 #ajj yards in diameter4 ,let us1 then1 take a pool of water #ajj yards in diameter1 and one inch deep4 ,suppose the water to be at #cb4 ,apply heat to the upper surface of the pool1 so as to raise the temperature of the surface of the water to #hj at the centre of the pool1 the temperature diminishing towards the edge1 where it is at #cb4 ,it is found that at a depth of two miles the temperature of the water at the equator is about as low as that of the poles4 ,we must therefore suppose the water at the centre of our pool to diminish in temperature from the surface downwards1 so that at a depth of half an inch the water is at #cb4 ,we have in this case a thin layer of warm water half an inch thick at the centre1 and gradually thinning off to nothing at the edge of the pool4 ,the lightest water1 be it observed1 is at the surface1 so that an ascending or a descending current is impossible4 ,the only way whereby the heat applied can have any tendency to produce motion is this3--,the heating of the water expands it1 consequently the surface of the pool must stand at a little higher level at its centre than at its edge1 where no expansion takes place2 and therefore1 in order to restore the level of the pool1 the water at the centre will tend to flow towards the sides4 ,but what is the amount of this tendency8 ,its amount will depend upon the amount of slope1 but the slope in the case under consideration amounts to only #a in #g1cdj1jjj4 ,dr4 ,carpenter's ,experiment4--,in order to obviate the objection to ,professor ,buff's experiment ,dr4 ,carpenter has devised another mode4 ,but ,i presume his experiment was intended rather to illustrate the way in which the circulation of the ocean1 according to his theory1 takes place1 than to prove that it actually does take place4 ,at any rate1 all that can be claimed for the experiment is the proof that water will circulate in consequence of difference of specific gravity resulting from difference of temperature4 ,but this does not require proof1 for no physicist denies it4 ,the point which requires to be proved is this4 ,is the difference of specific gravity which exists in the ocean sufficient to produce the supposed circulation8 ,now his mode of experimenting will not prove this1 unless he makes his experiment agree with the conditions already stated4 ,but ,i decidedly object to the water being heated in the way in which it has been done by him in his experiment before the ,royal ,geographical ,society2 for ,i feel somewhat confident that in this experiment the circulation resulted not from difference of specific gravity1 as was supposed1 but rather from the way in which the heat was applied4 ,in that experiment the one half of a thick metallic plate was placed in contact with the upper surface of the water at one end of the trough2 the other half1 projecting over the end of the trough1 was heated by means of a spirit-lamp4 ,it is perfectly obvious that though the temperature of the great mass of the water under the plate might not be raised over #hj or so1 yet the molecules in contact with the metal would have a very high temperature4 ,these molecules1 in consequence of their expansion1 would be unable to sink into the cooler and denser water underneath1 and thus escape the heat which was being constantly communicated to them from the heated plate4 ,but escape they must1 or their temperature would continue to rise until they would ultimately burst into vapour4 ,they cannot ascend1 neither can they descend3 they therefore must be expelled by the heat from the plate in a horizontal direction4 ,the next layer of molecules from beneath would take their place and would be expelled in a similar manner1 and this process would continue so long as the heat was applied to the plate4 ,a circulation would thus be established by the direct expansive force of vapour1 and not in any way due to difference of specific gravity1 as ,dr4 ,carpenter supposes4 ,but supposing the heated bar to be replaced by a piece of ice1 circulation would no doubt take place2 but this proves nothing more than that difference of density will produce circulation1 which is what no one calls in question4 ,the case referred to by ,dr4 ,carpenter of the heating apparatus in ,london ,university is also unsatisfactory4 ,the water leaves the boiler at #abj and returns to it at #hj4 ,the difference of specific gravity between the water leaving the boiler and the water returning to it is supposed to produce the circulation4 ,it seems to me that this difference of specific gravity has nothing whatever to do with the matter4 ,the cause of the circulation must be sought for in the boiler itself1 and not in the pipes4 ,the heat is applied to the bottom of the boiler1 not to the top4 ,what is the temperature of the molecules in contact with the bottom of the boiler directly over the fire1 is a question which must be considered before we can arrive at a just determination of the causes which produce circulation in the pipes of a heating apparatus such as that to which ,dr4 ,carpenter refers4 ,but1 in addition to this1 as the heat is applied to the bottom of the boiler and not to the top1 convection comes into play1 a cause which1 as we shall find1 does not come into play in the theory of oceanic circulation at present under our consideration4 ,the ,force exerted by ,gravity4--,dr4 ,carpenter speaks of his doctrine of a general oceanic circulation sustained by difference of temperature alone1 8as one of which physical geographers could not recognise the importance1 so long as they remained under the dominant idea that the temperature of the deep sea is everywhere #ci40 ,and he affirms that 8until it is clearly apprehended that sea-water becomes more and more dense as its temperature is reduced1 the immense motive power of polar cold cannot be understood40 ,but in chap4 vii4 and also in the ,phil4 ,mag4 for ,october1 #ahgj and #ahga1 ,i proved that if we take #ci as the temperature of maximum density the force exerted by gravity tending to produce circulation is just as great as when we take #cb4 ,the reason for this is that when we take #cb as the temperature of maximum density1 although we have1 it is true1 a greater elevation of the ocean above the place of maximum density1 yet this latter occurs at the poles2 while on the other hand1 when we take #ci1 the difference of level is less--the place not being at the poles but in about lat4 #ef4 ,now the shorter slope from the equator to lat4 #ef is as steep as the larger one from the equator to the poles1 and consequently gravity exerts as much force in the production of motion in the one case as in the other4 ,sir ,john ,herschel1 taking #ci as the temperature of maximum density1 estimated the slope at #a_/cbnd of an inch per mile1 whereas we1 taking #cb as the actual temperature of maximum density of the polar seas and calculating from modern data1 find that the slope is not one-half that amount1 and that the force of gravity tending to produce circulation is much less than ,herschel concluded it to be4 ,the reason1 therefore1 why physical geographers did not adopt the theory that oceanic circulation is the result of difference of temperature could not possibly be the one assigned by ,dr4 ,carpenter1 viz41 that they had under-estimated the force of gravity by taking #ci instead of #cb as the temperature of maximum density4 ,the ,work performed by ,gravity4--,but in order clearly to understand this point1 it will be better to treat the matter according to the third method1 and consider not the mere force of gravity impelling the waters1 but the amount of work which gravitation is capable of performing4 ,let us then assume the correctness of my estimate1 that the height of the surface of the ocean at the equator above that at the poles is #d feet #f inches1 for in representing the mode in which difference of specific gravity produces circulation it is of no importance what we may fix upon as the amount of the slope4 ,in order1 therefore1 to avoid fractions of a foot1 ,i shall take the slope at #d feet instead of #d feet1 which it actually is4 ,a pound of water in flowing down this slope from the equator to either of the poles will perform #d foot-pounds of work2 or1 more properly speaking1 gravitation will4 ,now it is evident that when this pound of water has reached the pole1 it is at the bottom of the slope1 and consequently cannot descend further4 ,gravity1 therefore1 cannot perform any more work upon it2 as it can only do so while the thing acted upon continues to descend--that is1 moves under the force exerted4 ,but the water will not move under the influence of gravity unless it move downward2 it being in this direction only that gravity acts on the water4 8,but10 says ,dr4 ,carpenter1 8the effect of surface-cold upon the water of the polar basin will be to reduce the temperature of its whole mass below the freezing-point of fresh water1 the surface-stratum sinking as it is cooled in virtue of its diminished bulk and increased density1 and being replaced by water not yet cooled to the same degree40#ga ,by the cooling of the whole mass of polar water by cold and the heating of the water at the equator by the sun's rays the polar column of water1 as we have seen1 is rendered denser than the equatorial one1 and in order that the two may balance each other1 the polar column is necessarily shorter than the equatorial by #d feet2 and thus it is that the slope of #d feet is formed4 ,it is perfectly true that the water which leaves the equator warm and light1 becomes by the time it reaches the pole cold and dense4 ,but unless it be denser than the underlying polar water it will not sink down through it4#gb ,we are not told1 however1 why it should be colder than the whole mass underneath1 which1 according to ,dr4 ,carpenter1 is cooled by polar cold4 ,but that he does suppose it to sink to the bottom in consequence of its contraction by cold would appear from the following quotation3-- 8,until it is clearly apprehended that sea-water becomes more and more dense as its temperature is reduced1 and that it consequently continues to sink until it freezes1 the immense motor power of polar cold cannot be apprehended4 ,but when this has been clearly recognised1 it is seen that the application of cold at the surface is precisely equivalent as a moving power to that application of heat at the bottom by which the circulation of water is sustained in every heating apparatus that makes use of it0 7 #be74 ,the application of cold at the surface is thus held to be equivalent as a motor power to the application of heat at the bottom4 ,but heat applied to the bottom of a vessel produces circulation by convection4 ,it makes the molecules at the bottom expand1 and they1 in consequence of buoyancy1 rise through the water in the vessel4 ,consequently if the action of cold at the surface in polar regions is equivalent to that of heat1 the cold must contract the molecules at the surface and make them sink through the mass of polar water beneath4 ,but assuming this to be the meaning in the passage just quoted1 how much colder is the surface water than the water beneath8 ,let us suppose the difference to be one degree4 ,how much work1 then1 will gravity perform upon this one pound of water which is one degree colder than the mass beneath supposed to be at #cb8 ,the force with which the pound of water will sink will not be proportional to its weight1 but to the difference of weight between it and a similar bulk of the water through which it sinks4 ,the difference between the weight of a pound of water at #ca and an equal volume of water at #cb is #a_/bi1jjjth of a pound4 ,now this pound of water in sinking to a depth of #aj1jjj feet1 which is about the depth at which a polar temperature is found at the equator1 would perform only one-third of a foot-pound of work4 ,and supposing it were three degrees colder than the water beneath1 it would in sinking perform only one foot-pound4 ,this would give us only #d #a #e foot-pounds as the total amount that could be performed by gravitation on the pound of water from the time that it left the equator till it returned to the point from which it started4 ,the amount of work performed in descending the slope from the equator to the pole and in sinking to a depth of #aj1jjj feet or so through the polar water assumed to be warmer than the surface water1 comprehends the total amount of work that gravitation can possibly perform2 so that the amount of force gained by such a supposition over and above that derived from the slope is trifling4 ,it would appear1 however1 that this is not what is meant after all4 ,what ,dr4 ,carpenter apparently means is this3 when a quantity of water1 say a layer one foot thick1 flows down from the equator to the pole1 the polar column becomes then heavier than the equatorial by the weight of this additional layer4 ,a layer of water equal in quantity is therefore pressed away from the bottom of the column and flows off in the direction of the equator as an under current1 the polar column at the same time sinking down one foot until equilibrium of the polar and equatorial columns is restored4 ,another foot of water now flows down upon the polar column and another foot of water is displaced from below1 causing1 of course1 the column to descend an additional foot4 ,the same process being continually repeated1 a constant downward motion of the polar column is the result4 ,or1 perhaps1 to express the matter more accurately1 owing to the constant flow of water from the equatorial regions down the slope1 the weight of the polar column is kept always in excess of that of the equatorial2 therefore the polar column in the effort to restore equilibrium is kept in a constant state of descent4 ,hence he terms it a 8vertical0 circulation4 ,the following will show ,dr4 ,carpenter's theory in his own words3-- 8,the action of cold on the surface water of each polar area will be exerted as follows3-- 87a7 ,in diminishing the height of the polar column as compared with that of the equatorial1 so that a lowering of its level is produced1 which can only be made good by a surface-flow from the latter towards the former4 87b7 ,in producing an excess in the downward pressure of the column when this inflow has restored its level1 in virtue of the increase of specific gravity it has gained by its reduction in volume2 whereby a portion of its heavy bottom-water is displaced laterally1 causing a further reduction of level1 which draws in a further supply of the warmer and lighter water flowing towards its surface4 87c7 ,in imparting a downward movement to each new surface-stratum as its temperature undergoes reduction2 so that the entire column may be said to be in a state of constant descent1 like that which exists in the water of a tall jar when an opening is made at its bottom1 and the water which flows away through it is replaced by an equivalent supply poured into the top of the jar0 7 #bc74 ,but if this be his theory1 as it evidently is1 then the #d foot-pounds 7the amount of work performed by the descent of the water down the slope7 comprehends all the work that gravitation can perform on a pound of water in making a complete circuit from the equator to the pole and from the pole back to the equator4 ,this1 ,i trust1 will be evident from the following considerations4 ,when a pound of water has flowed down from the equator to the pole1 it has descended #d feet1 and is then at the foot of the slope4 ,gravity has therefore no more power to pull it down to a lower level4 ,it will not sink through the polar water1 for it is not denser than the water beneath on which it rests4 ,but it may be replied that although it will not sink through the polar water1 it has nevertheless made the polar column heavier than the equatorial1 and this excess of pressure forces a pound of water out from beneath and allows the column to descend4 ,suppose it may be argued that a quantity of water flows down from the equator1 so as to raise the level of the polar water by1 say1 one foot4 ,the polar column will now be rendered heavier than the equatorial by the weight of one foot of water4 ,the pressure of the one foot will thus force a quantity of water laterally from the bottom and cause the entire column to descend till the level of equilibrium is restored4 ,in other words1 the polar column will sink one foot4 ,now in the sinking of this column work is performed by gravity4 ,a certain amount of work is performed by gravity in causing the water to flow down the slope from the equator to the pole1 and1 in addition to this1 a certain amount is performed by gravity in the vertical descent of the column4 ,i freely admit this to be sound reasoning1 and admit that so much is due to the slope and so much to the vertical descent of the water4 ,but here we come to the most important point1 viz41 is there the full slope of #d feet and an additional vertical movement8 ,dr4 ,carpenter seems to conclude that there is1 and that this vertical force is something in addition to the force which ,i derive from the slope4 ,and here1 ,i venture to think1 is a radical error into which he has fallen in regard to the whole matter4 ,let it be observed that1 when water circulates from difference of specific gravity1 this vertical movement is just as real a part of the process as the flow down the slope2 but the point which ,i maintain is that there is no additional power derived from this vertical movement over and above what is derived from the full slope--or1 in other words1 that this primum mobile1 which he says ,i have overlooked1 has in reality no existence4 ,perhaps the following diagram will help to make the point still clearer3-- ,illustration3 ,fig4 #a4 ,let ,p 7fig4 #a7 be the surface of the ocean at the pole1 and ,e the surface at the equator2 ,p ,o a column of water at the pole1 and ,e ,q a column at the equator4 ,the two columns are of equal weight1 and balance each other2 but as the polar water is colder1 and consequently denser than the equatorial1 the polar column is shorter than the equatorial1 the difference in the length of the two columns being #d feet4 ,the surface of the ocean at the equator ,e is #d feet higher than the surface of the ocean at the pole ,p2 there is therefore a slope of #d feet from ,e to ,p4 ,the molecules of water at ,e tend to flow down this slope towards ,p4 ,the amount of work performed by gravity in the descent of a pound of water down this slope from ,e to ,p is therefore #d foot-pounds4 ,but of course there can be no permanent circulation while the full slope remains4 ,in order to have circulation the polar column must be heavier than the equatorial4 ,but any addition to the weight of the polar column is at the expense of the slope4 ,in proportion as the weight of the polar column increases the less becomes the slope4 ,this1 however1 makes no difference in the amount of work performed by gravity4 ,suppose now that water has flowed down till an addition of one foot of water is made to the polar column1 and the difference of level1 of course1 diminished by one foot4 ,the surface of the ocean in this case will now be represented by the dotted line ,p ,e1 and the slope reduced from #d feet to #c feet4 ,let us then suppose a pound of water to leave ,e and flow down to ,p2 #c foot-pounds will be the amount of work performed4 ,the polar column being now too heavy by the extent of the mass of water ,p ,p one foot thick1 its extra pressure causes a mass of water equal to ,p ,p to flow off laterally from the bottom of the column4 ,the column therefore sinks down one foot till ,p reaches ,p4 ,now the pound of water in this vertical descent from ,p to ,p has one foot-pound of work performed on it by gravity2 this added to the #c foot-pounds derived from the slope1 gives a total of #d foot-pounds in passing from ,e to ,p and then from ,p to ,p4 ,this is the same amount of work that would have been performed had it descended directly from ,e to ,p4 ,in like manner it can be proved that #d foot-pounds is the amount of work performed in the descent of every pound of water of the mass ,p ,p4 ,the first pound which left ,e flowed down the slope directly to ,p1 and performed #d foot-pounds of work4 ,the last pound flowed down the slope ,e ,p1 and performed only #c foot-pounds2 but in descending from ,p to ,p it performed the other one foot-pound4 ,a pound leaving at a period exactly intermediate between the two flowed down #c feet of slope and descended vertically half a foot4 ,whatever path a pound of water might take1 by the time that it reached ,p1 #d foot-pounds of work would be performed4 ,but no further work can be performed after it reaches ,p4 ,but some will ask1 in regard to the vertical movement1 is it only in the descent of the water from ,p to ,p that work is performed8 ,water cannot descend from ,p to ,p1 it will be urged1 unless the entire column ,p ,o underneath descend also4 ,but the column ,p ,o descends by means of gravity4 ,why1 then1 it will be asked1 is not the descent of the column a motive power as real as the descent of the mass of water ,p ,p8 ,that neither force nor energy can be derived from the mere descent of the polar column ,p ,o is demonstrable thus3--,the reason why the column ,p ,o descends is because1 in consequence of the mass of water ,p ,p resting on it1 its weight is in excess of the equatorial column ,e ,q4 ,but the force with which the column descends is equal1 not to the weight of the column1 but to the weight of the mass ,p ,p2 consequently as much work would be performed by gravity in the descent of the mass ,p ,p 7the one foot of water7 alone as in the descent of the entire column ,p ,o1 #aj1jjj feet in height4 ,suppose a ton weight is placed in each scale of a balance3 the two scales balance each other4 ,place a pound weight in one of the scales along with the ton weight and the scale will descend4 ,but it descends1 not with the pressure of a ton and a pound1 but with the pressure of the pound weight only4 ,in the descent of the scale1 say1 one foot1 gravity can perform only one foot-pound of work4 ,in like manner1 in the descent of the polar column1 the only work available is the work of the mass ,p ,p laid on the top of the column4 ,but it must be observed that in the descent of the column from ,p to ,p1 a distance of one foot1 each pound of water of the mass ,p ,p does not perform one foot-pound of work2 for the moment that a molecule of water reaches ,p1 it then ceases to perform further work4 ,the molecules at the surface ,p descend one foot before reaching ,p2 the molecules midway between ,p and ,p descend only half a foot before reaching ,p1 and the molecules at the bottom of the mass are already at ,p1 and therefore cannot perform any work4 ,the mean distance through which the entire mass performs work is therefore half a foot4 ,one foot-pound per pound of water represents in this case the amount of work derived from the vertical movement4 ,that such is the case is further evident from the following considerations4 ,before the polar column begins to descend1 it is heavier than the equatorial by the weight of one foot of water2 but when the column has descended half a foot1 the polar column is heavier than the equatorial by the weight of only half a foot of water2 and1 as the column continues to descend1 the force with which it descends continues to diminish1 and when it has sunk to ,p the force is zero4 ,consequently the mean pressure or weight with which the one foot of water ,p ,p descended was equal to that of a layer of half a foot of water2 in other words1 each pound of water1 taking the mass as a whole1 descended with the pressure or weight of half a pound4 ,but a half pound descending one foot performs half a foot-pound2 so that whether we consider the full pressure acting through the mean distance1 or the mean pressure acting through the full distance1 we get the same result1 viz4 a half foot-pound as the work of vertical descent4 ,now it will be found1 as we shall presently see1 that if we calculate the mean amount of work performed in descending the slope from the equator to the pole1 #c foot-pounds per pound of water is the amount4 ,the water at the bottom of the mass ,p ,p moved1 of course1 down the full slope ,e ,p #d feet4 ,the water at the top of the mass which descended from ,e to ,p descended a slope of only #c feet4 ,the mean descent of the whole mass is therefore #c feet4 ,and this gives #c foot-pounds as the mean amount of work per pound of water in descending the slope2 this1 added to the half foot-pound derived from vertical descent1 gives #d foot-pounds as the total amount of work per pound of the mass4 ,i have in the above reasoning supposed one foot of water accumulated on the polar column before any vertical descent takes place4 ,it is needless to remark that the same conclusion would have been arrived at1 viz41 that the total amount of work performed is #d foot-pounds per pound of water1 supposing we had considered #b feet1 or #c feet1 or even #d feet of water to have accumulated on the polar column before vertical motion took place4 ,i have also1 in agreement with ,dr4 ,carpenter's mode of representing the operation1 been considering the two effects1 viz41 the flowing of the water down the slope and the vertical descent of the polar column as taking place alternately4 ,in nature1 however1 the two effects take place simultaneously2 but it is needless to add that the amount of work performed would be the same whether the effects took place alternately or simultaneously4 ,i have also represented the level of the ocean at the equator as remaining permanent while the alterations of level were taking place at the pole4 ,but in representing the operation as it would actually take place in nature1 we should consider the equatorial column to be lowered as the polar one is being raised4 ,we should1 for example1 consider the one foot of water ,p ,p put upon the polar column as so much taken off the equatorial column4 ,but in viewing the problem thus we arrive at exactly the same results as before4 ,let ,p 7,fig4 #b71 as in ,fig4 #a1 be the surface of the ocean at the pole1 and ,e the surface at the equator1 there being a slope of #d feet from ,e to ,p4 ,suppose now a quantity of water1 ,e ,e1 say1 one foot thick1 to flow from off the equatorial regions down upon the polar4 ,it will thus lower the level of the equatorial column by one foot1 and raise the level of the polar column by the same amount4 ,i may1 however1 observe that the one foot of water in passing from ,e to ,p would have its temperature reduced from #hj to #cb1 and this would produce a slight contraction4 ,but as the weight of the mass would not be affected1 in order to simplify our reasoning we may leave this contraction out of consideration4 ,any one can easily satisfy himself that the assumption that ,e ,e is equal to ,p ,p does not in any way affect the question at issue--the only effect of the contraction being to increase by an infinitesimal amount the work done in descending the slope1 and to diminish by an equally infinitesimal amount the work done in the vertical descent4 ,if1 for example1 #c foot-pounds represent the amount of work performed in descending the slope1 and one foot-pound the amount performed in the vertical descent1 on the supposition that ,e ,e does not contract in passing to the pole1 then #cjjbd foot-pounds will represent the work of the slope1 and #jiigf foot-pounds the work of vertical descent when allowance is made for the contraction4 ,but the total amount of work performed is the same in both cases4 ,consequently1 to simplify our reasoning1 we may be allowed to assume ,p ,p to be equal to ,e ,e4 ,illustration3 ,fig4 #b4 ,the slope ,e ,p being #d feet1 the slope ,e ,p is consequently #b feet2 the mean slope for the entire mass is therefore #c feet4 ,the mean amount of work performed by the descent of the mass will of course be #c foot-pounds per pound of water4 ,the amount of work performed by the vertical descent of ,p ,p ought therefore to be one foot-pound per pound4 ,that this is the amount will be evident thus3--,the transference of the one foot of water from the equatorial column to the polar disturbs the equilibrium by making the equatorial column too light by one foot of water and the polar column too heavy by the same amount of water4 ,the polar column will therefore tend to sink1 and the equatorial to rise till equilibrium is restored4 ,the difference of weight of the two columns being equal to #b feet of water1 the polar column will begin to descend with a pressure of #b feet of water2 and the equatorial column will begin to rise with an equal amount of pressure4 ,when the polar column has descended half a foot the equatorial column will have risen half a foot4 ,the pressure of the descending polar column will now be reduced to one foot of water4 ,and when the polar column has descended another foot1 ,p will have reached ,p1 and ,e will have reached ,e2 the two columns will then be in equilibrium4 ,it therefore follows that the mean pressure with which the polar column descended the one foot was equal to the pressure of one foot of water4 ,consequently the mean amount of work performed by the descent of the mass was equal to one foot-pound per pound of water2 this1 added to the #c foot-pounds derived from the slope1 gives a total of #d foot-pounds4 ,in whatever way we view the question1 we are led to the conclusion that if #d feet represent the amount of slope between the equatorial and polar columns when the two are in equilibrium1 then #d foot-pounds is the total amount of work that gravity can perform upon a pound of water in overcoming the resistance to motion in its passage from the equator to the pole down the slope1 and then in its vertical descent to the bottom of the ocean4 ,but it will be replied1 not only does the one foot of water ,p ,p descend1 but the entire column ,p ,o1 #aj1jjj feet in length1 descends also4 ,what1 then1 it will be asked1 becomes of the force which gravity exerts in the descent of this column8 ,we shall shortly see that this force is entirely applied in work against gravity in other parts of the circuit2 so that not a single foot-pound of this force goes to overcome cohesion1 friction1 and other resistances2 it is all spent in counteracting the efforts which gravity exerts to stop the current in another part of the circuit4 ,i shall now consider the next part of the movement1 viz41 the under or return current from the bottom of the polar to the bottom of the equatorial column4 ,what produces this current8 ,it is needless to say that it cannot be caused directly by gravity4 ,gravitation cannot directly draw any body horizontally along the earth's surface4 ,the water that forms this current is pressed out laterally by the weight of the polar column1 and flows1 or rather is pushed1 towards the equator to supply the vacancy caused by the ascent of the equatorial column4 ,there is a constant flow of water from the equator to the poles along the surface1 and this draining of the water from the equator is supplied by the under or return current from the poles4 ,but the only power which can impel the water from the bottom of the polar column to the bottom of the equatorial column is the pressure of the polar column4 ,but whence does the polar column derive its pressure8 ,it can only press to the extent that its weight exceeds that of the equatorial column4 ,that which exerts the pressure is therefore the mass of water which has flowed down the slope from the equator upon the polar column4 ,it is in this case the vertical movement that causes this under current4 ,the energy which produces this current must consequently be derived from the #d foot-pounds resulting from the slope2 for the energy of the vertical movement1 as has already been proved1 is derived from this source2 or1 in other words1 whatever power this vertical movement may exert is so much deducted from the #d foot-pounds derived from the full slope4 ,let us now consider the fourth and last movement1 viz41 the ascent of the under current to the surface of the ocean at the equator4 ,when this cold under current reaches the equatorial regions1 it ascends to the surface to the point whence it originally started on its circuit4 ,what1 then1 lifts the water from the bottom of the equatorial column to its top8 ,this cannot be done directly1 either by heat or by gravity4 ,when heat1 for example1 is applied to the bottom of a vessel1 the heated water at the bottom expands and1 becoming lighter than the water above1 rises through it to the surface2 but if the heat be applied to the surface of the water instead of to the bottom1 the heat will not produce an ascending current4 ,it will tend rather to prevent such a current than to produce one--the reason being that each successive layer of water will1 on account of the heat applied1 become hotter and consequently lighter than the layer below it1 and colder and consequently heavier than the layer above it4 ,it therefore cannot ascend1 because it is too heavy2 nor can it descend1 because it is too light4 ,but the sea in equatorial regions is heated from above1 and not from below2 consequently the water at the bottom does not rise to the surface at the equator in virtue of any heat which it receives4 ,a layer of water can never raise the temperature of a layer below it to a higher temperature than itself2 and since it cannot do this1 it cannot make the layer under it lighter than itself4 ,that which raises the water at the equator1 according to ,dr4 ,carpenter's theory1 must be the downward pressure of the polar column4 ,when water flows down the slope from the equator to the pole1 the polar column1 as we have seen1 becomes too heavy and the equatorial column too light2 the former then sinks and the latter rises4 ,it is the sinking of the polar column which raises the equatorial one4 ,when the polar column descends1 as much water is pressed in underneath the equatorial column as is pressed from underneath the polar column4 ,if one foot of water is pressed from under the polar column1 a foot of water is pressed in under the equatorial column4 ,thus1 when the polar column sinks a foot1 the equatorial column rises to the same extent4 ,the equatorial water continuing to flow down the slope1 the polar column descends3 a foot of water is again pressed from underneath the polar column and a foot pressed in under the equatorial4 ,as foot after foot is thus removed from the bottom of the polar column while it sinks1 foot after foot is pushed in under the equatorial column while it rises2 so by this means the water at the surface of the ocean in polar regions descends to the bottom1 and the water at the bottom in equatorial regions ascends to the surface--the effect of solar heat and polar cold continuing1 of course1 to maintain the surface of the ocean in equatorial regions at a higher level than at the poles1 and thus keeping up a constant state of disturbed equilibrium4 ,or1 to state the matter in ,dr4 ,carpenter's own words1 8,the cold and dense polar water1 as it flows in at the bottom of the equatorial column1 will not directly take the place of that which has been drafted off from the surface2 but this place will be filled by the rising of the whole superincumbent column1 which1 being warmer1 is also lighter than the cold stratum beneath4 ,every new arrival from the poles will take its place below that which precedes it1 since its temperature will have been less affected by contact with the warmer water above it4 ,in this way an ascending movement will be imparted to the whole equatorial column1 and in due course every portion of it will come under the influence of the surface-heat of the sun40#gc ,but the agency which raises up the water of the under current to the surface is the pressure of the polar column4 ,the equatorial column cannot rise directly by means of gravity4 ,gravity1 instead of raising the column1 exerts all its powers to prevent its rising4 ,gravity here is a force acting against the current4 ,it is the descent of the polar column1 as has been stated1 that raises the equatorial column4 ,consequently the entire amount of work performed by gravity in pulling down the polar column is spent in raising the equatorial column4 ,gravity performs exactly as much work in preventing motion in the equatorial column as it performs in producing motion in the polar column2 so that1 so far as the vertical parts of ,dr4 ,carpenter's circulation are concerned1 gravity may be said neither to produce motion nor to prevent it4 ,and this remark1 be it observed1 applies not only to ,p ,o and ,e ,q1 but also to the parts ,p ,p and ,e ,e of the two columns4 ,when a mass of water ,e ,e1 say one foot deep1 is removed off the equatorial column and placed upon the polar column1 the latter column is then heavier than the former by the weight of two feet of water4 ,gravity then exerts more force in pulling the polar column down than it does in preventing the equatorial column from rising2 and the consequence is that the polar column begins to descend and the equatorial column to rise4 ,but as the polar column continues to descend and the equatorial to rise1 the power of gravity to produce motion in the polar column diminishes1 and the power of gravity to prevent motion in the equatorial column increases2 and when ,p descends to ,p and ,e rises to ,e1 the power of gravity to prevent motion in the equatorial column is exactly equal to the power of gravity to produce motion in the polar column1 and consequently motion ceases4 ,it therefore follows that the entire amount of work performed by the descent of ,p ,p is spent in raising ,e ,e against gravity4 ,it follows also that inequalities in the sea-bottom cannot in any way aid the circulation2 for although the cold under current should in its progress come to a deep trough filled with water less dense than itself1 it would no doubt sink to the bottom of the hollow2 yet before it could get out again as much work would have to be performed against gravity as was performed by gravity in sinking it4 ,but whilst inequalities in the bed of the ocean would not aid the current1 they would nevertheless very considerably retard it by the obstructions which they would offer to the motion of the water4 ,we have been assuming that the weight of ,p ,p is equal to that of ,e ,e2 but the mass ,p ,p must be greater than ,e ,e because ,p ,p has not only to raise ,e ,e1 but to impel the under current--to push the water along the sea-bottom from the pole to the equator4 ,so we must have a mass of water1 in addition to ,p ,p1 placed on the polar column to enable it to produce the under current in addition to the raising of the equatorial column4 ,it follows also that the amount of work which can be performed by gravity depends entirely on the difference of temperature between the equatorial and the polar waters1 and is wholly independent of the way in which the temperature may decrease from the equator to the poles4 ,suppose1 in agreement with ,dr4 ,carpenter's idea1#gd that the equatorial heat and polar cold should be confined to limited areas1 and that through the intermediate space no great difference of temperature should prevail4 ,such an arrangement as this would not increase the amount of work which gravity could perform2 it would simply make the slope steeper at the two extremes and flatter in the intervening space4 ,it would no doubt aid the surface-flow of the water near the equator and the poles1 but it would retard in a corresponding degree the flow of the water in the intermediate regions4 ,in short1 it would merely destroy the uniformity of the slope without aiding in the least degree the general motion of the water4 ,it is therefore demonstrable that the energy derived from the full slope1 whatever that slope may be1 comprehends all that can possibly be obtained from gravity4 ,it cannot be urged as an objection to what has been advanced that ,i have determined simply the amount of the force acting on the water at the surface of the ocean and not that on the water at all depths--that ,i have estimated the amount of work which gravity can perform on a given quantity of water at the surface1 but not the total amount of work which gravity can perform on the entire ocean4 ,this objection will not stand1 because it is at the surface of the ocean where the greatest difference of temperature1 and consequently of density1 exists between the equatorial and polar waters1 and therefore there that gravity exerts its greatest force4 ,and if gravity be unable to move the water at the surface1 it is much less able to do so under the surface4 ,so far as the question at issue is concerned1 any calculations as to the amount of force exerted by gravity at various depths are needless4 ,it is maintained also that the winds cannot produce a vertical current except under some very peculiar conditions4 ,we have already seen that1 according to ,dr4 ,carpenter's theory1 the vertical motion is caused by the water flowing off the equatorial column1 down the slope1 upon the polar column1 thus destroying the equilibrium between the two by diminishing the weight of the equatorial column and increasing that of the polar column4 ,in order that equilibrium may be restored1 the polar column sinks and the equatorial one rises4 ,now must not the same effect occur1 supposing the water to be transferred from the one column to the other1 by the influence of the winds instead of by the influence of gravity8 ,the vertical descent and ascent of these columns depend entirely upon the difference in their weights1 and not upon the nature of the agency which makes this difference4 ,so far as difference of weight is concerned1 #b feet of water1 propelled down the slope from the equatorial column to the polar by the winds1 will produce just the same effect as though it had been propelled by gravity4 ,if vertical motion follows as a necessary consequence from a transference of water from the equator to the poles by gravity1 it follows equally as a necessary consequence from the same transference by the winds2 so that one is not at liberty to advocate a vertical circulation in the one case and to deny it in the other4 ,gravitation ,theory of the ,gibraltar ,current4--,if difference of specific gravity fails to account for the currents of the ocean in general1 it certainly fails in a still more decided manner to account for the ,gibraltar current4 ,the existence of the submarine ridge between ,capes ,trafalgar and ,spartel1 as was shown in the ,phil4 ,mag4 for ,october1 #ahga1 p4 #bfi1 affects currents resulting from difference of specific gravity in a manner which does not seem to have suggested itself to ,dr4 ,carpenter4 ,the pressure of water and other fluids is not like that of a solid--not like that of the weight in the scale of a balance1 simply a downward pressure4 ,fluids press downwards like the solids1 but they also press laterally4 ,the pressure of water is hydrostatic4 ,if we fill a basin with water or any other fluid1 the fluid remains in perfect equilibrium1 provided the sides of the basin be sufficiently strong to resist the pressure4 ,the ,mediterranean and ,atlantic1 up to the level of the submarine ridge referred to1 may be regarded as huge basins1 the sides of which are sufficiently strong to resist all pressure4 ,it follows that1 however much denser the water of the ,mediterranean may be than that of the ,atlantic1 it is only the water above the level of the ridge that can possibly exercise any influence in the way of disturbing equilibrium1 so as to cause the level of the ,mediterranean to stand lower than that of the ,atlantic4 ,the water of the ,atlantic below the level of this ridge might be as light as air1 and that of the ,mediterranean as heavy as molten lead1 but this could produce no disturbance of equilibrium2 and if there be no difference of density between the ,atlantic and the ,mediterranean waters from the surface down to the level of the top of the ridge1 then there can be nothing to produce the circulation which ,dr4 ,carpenter infers4 ,suppose both basins empty1 and dense water to be poured into the ,mediterranean1 and water less dense into the ,atlantic1 until they are both filled up to the level of the ridge1 it is evident that the heavier water in the one basin can exercise no influence in raising the level of the lighter water in the other basin1 the entire pressure being borne by the sides of the basins4 ,but if we continue to pour in water till the surface is raised1 say one foot1 above the level of the ridge1 then there is nothing to resist the lateral pressure of this one foot of water in the ,mediterranean but the counter pressure of the one foot in the ,atlantic4 ,but as the ,mediterranean water is denser than the ,atlantic1 this one foot of water will consequently exert more pressure than the one foot of water of the ,atlantic4 ,we must therefore continue to pour more water into the ,atlantic until its lateral pressure equals that of the ,mediterranean4 ,the two seas will then be in equilibrium1 but the surface of the ,atlantic will of course be at a higher level than the surface of the ,mediterranean4 ,the difference of level will be proportionate to the difference in density of the waters of the two seas4 ,but here we come to the point of importance4 ,in determining the difference of level between the two seas1 or1 which is the same thing1 the difference of level between a column of the ,atlantic and a column of the ,mediterranean1 we must take into consideration only the water which lies above the level of the ridge4 ,if there be one foot of water above the ridge1 then there is a difference of level proportionate to the difference of pressure between the one foot of water of the two seas4 ,if there be #b feet1 #c feet1 or any number of feet of water above the level of the ridge1 the difference of level is proportionate to the #b feet1 #c feet1 or whatever number of feet there may be of water above the ridge4 ,if1 for example1 #ac should represent the density of the ,mediterranean water and #ab the density of the ,atlantic water1 then if there were one foot of water in the ,mediterranean above the level of the ridge1 there would require to be one foot one inch of water in the ,atlantic above the ridge in order that the two might be in equilibrium4 ,the difference of level would therefore be one inch4 ,if there were #b feet of water1 the difference of level would be #b inches2 if #c feet1 the difference would be #c inches1 and so on4 ,and this would follow1 no matter what the actual depth of the two basins might be2 the water below the level of the ridge exercising no influence whatever on the level of the surface4 ,taking ,dr4 ,carpenter's own data as to the density of the ,mediterranean and ,atlantic waters1 what1 then1 is the difference of density8 ,the submarine ridge comes to within #afg fathoms of the surface2 say1 in round numbers1 to within #a1jjj feet4 ,what are the densities of the two basins down to the depth of #a1jjj feet8 ,according to ,dr4 ,carpenter there is little1 if any1 difference4 ,his own words on this point are these3--8,a comparison of these results leaves no doubt that there is an excess of salinity in the water of the ,mediterranean above that of the ,atlantic2 but that this excess is slight in the surface-water1 whilst somewhat greater in the deeper water0 7 #g74 8,again1 it was found by examining samples of water taken from the surface1 from #ajj fathoms1 from #bej fathoms1 and from #djj fathoms respectively1 that whilst the first two had the characteristic temperature and density of ,atlantic water1 the last two had the characteristics and density of ,mediterranean water0 7 #ac74 ,here1 at least to the depth of #ajj fathoms or #fjj feet1 there is little difference of density between the waters of the two basins4 ,consequently down to the depth of #fjj feet1 there is nothing to produce any sensible disturbance of equilibrium4 ,if there be any sensible disturbance of equilibrium1 it must be in consequence of difference of density which may exist between the depths of #fjj feet and the surface of the ridge4 ,we have nothing to do with any difference which may exist between the water of the ,mediterranean and the ,atlantic below the ridge2 the water in the ,mediterranean basin may be as heavy as mercury below #a1jjj feet3 but this can have no effect in disturbing equilibrium4 ,the water to the depth of #fjj feet being of the same density in both seas1 the length of the two columns acting on each other is therefore reduced to #djj feet--that is1 to that stratum of water lying at a depth of from #fjj to the surface of the ridge #a1jjj feet below the surface4 ,but1 to give the theory full justice1 we shall take the ,mediterranean stratum at the density of the deep water of the ,mediterranean1 which he found to be about #ajbi1 and the density of the ,atlantic stratum at #ajbf4 ,the difference of density between the two columns is therefore #jjc4 ,consequently1 if the height of the ,mediterranean column be #djj feet1 it will be balanced by the ,atlantic column of #djab feet2 the difference of level between the ,mediterranean and the ,atlantic cannot therefore be more than #ab foot4 ,the amount of work that can be performed by gravity in the case of the ,gibraltar current is little more than one foot-pound per pound of water1 an amount of energy evidently inadequate to produce the current4 ,it is true that in his last expedition ,dr4 ,carpenter found the bottom-water on the ridge somewhat denser than ,atlantic water at the same depth1 the former being #ajbib and the latter #ajbfe2 but it also proved to be denser than ,mediterranean water at the same depth4 ,he found1 for example1 that 8the dense ,mediterranean water lies about #ajj fathoms nearer the surface over a #cjj-;fathoms bottom1 than it does where the bottom sinks to more than #ejj fathoms0 7 #ea74 ,but any excess of density which might exist at the ridge could have no tendency whatever to make the ,mediterranean column preponderate over the ,atlantic column1 any more than could a weight placed over the fulcrum of a balance have a tendency to make the one scale weigh down the other4 ,if the objection referred to be sound1 it shows the mechanical impossibility of the theory4 ,it proves that whether there be an under current or not1 or whether the dense water lying in the deep trough of the ,mediterranean be carried over the submarine ridge into the ,atlantic or not1 the explanation offered by ,dr4 ,carpenter is one which cannot be admitted4 ,it is incumbent on him to explain either 7#a7 how the almost infinitesimal difference of density which exists between the ,atlantic and ,mediterranean columns down to the level of the ridge can produce the upper and under currents carrying the deep and dense water of the ,mediterranean over the ridge1 or 7#b7 how all this can be done by means of the difference of density which exists below the level of the ridge4#ge ,what the true cause of the ,gibraltar current really is will be considered in ,chap4 ,,xiii4 ,the ,baltic ,current4--,the entrance to the ,baltic ,sea is in some places not over #ej or #fj feet deep4 ,it follows1 therefore1 from what has already been proved in regard to the ,gibraltar current1 that the influence of gravity must be even still less in causing a current in the ,baltic strait than in the ,gibraltar strait4 ,,chapter ,x4 ,,examination ,,of ,,the ,,gravitation ,,theory ,,of ,,oceanic ,,circulation4--,,dr4 ,,carpenter',s ,,theory4--,,objections ,,considered4 ,modus ,operandi of the ,matter4--,polar ,cold considered by ,dr4 ,carpenter the ,primum ,mobile4--,supposed ,influence of ,heat derived from the ,earth's ,crust4--,circulation without ,difference of ,level4--,a ,confusion of ,ideas in ,reference to the supposed ,agency of ,polar ,cold4--,m4 ,dubuat's ,experiments4--,a ,begging of the ,question at ,issue4--,pressure as a ,cause of ,circulation4 ,in the foregoing chapter1 the substance of which appeared in the ,phil4 ,mag4 for ,october1 #ahga1 ,i have represented the manner in which difference of specific gravity produces circulation4 ,but ,dr4 ,carpenter appears to think that there are some important points which ,i have overlooked4 ,these ,i shall now proceed to consider in detail4 8,mr4 ,croll's whole manner of treating the subject10 he says1 8is so different from that which it appears to me to require1 and he has so completely misapprehended my own view of the question1 that ,i feel it requisite to present this in fuller detail in order that physicists and mathematicians1 having both sides fully before them1 may judge between us0 7 #bf74gf ,he then refers to a point so obvious as hardly to require consideration1 viz41 the effect which results when the surface of the entire area of a lake or pond of water is cooled4 ,the whole of the surface-film1 being chilled at the same time1 sinks through the subjacent water1 and a new film from the warmer layer immediately beneath the surface rises into its place4 ,this being cooled in its turn1 sinks1 and so on4 ,he next considers what takes place when only a portion of the surface of the pond is cooled1 and shows that in this case the surface-film which descends is replaced not from beneath1 but by an inflow from the neighbouring area4 8,that such must be the case10 says ,dr4 ,carpenter1 8appears to me so self-evident that ,i am surprised that any person conversant with the principles of physical science should hesitate in admitting it1 still more that he should explicitly deny it4 ,but since others may feel the same difficulty as ,mr4 ,croll1 it may be worth while for me to present the case in a form of yet more elementary simplicity0 7 #bi74 ,then1 in order to show the mode in which the general oceanic circulation takes place1 he supposes two cylindrical vessels1 ,w and ,c1 of equal size1 to be filled with sea-water4 ,cylinder ,w represents the equatorial column1 and the water contained in it has its temperature maintained at #fj2 whilst the water in the other cylinder ,c1 representing the polar column1 has its temperature maintained at #cj by means of the constant application of cold at the top4 ,free communication is maintained between the two cylinders at top and bottom2 and the water in the cold cylinder being1 in virtue of its low temperature1 denser than the water in the warm cylinder1 the two columns are therefore not in static equilibrium4 ,the cold1 and hence heavier column tends to produce an outflow of water from its bottom to the bottom of the warm column1 which outflow is replaced by an inflow from the top of the warm column to the top of the cold column4 ,in fact1 we have just a simple repetition of what he has given over and over again in his various memoirs on the subject4 ,but why so repeatedly enter into the modus operandi of the matter8 ,who feels any difficulty in understanding how the circulation is produced8 ,polar ,cold considered by ,dr4 ,carpenter the ,primum ,mobile4--,it is evident that ,dr4 ,carpenter believes that he has found in polar cold an agency the potency of which1 in producing a general oceanic circulation1 has been overlooked by physicists2 and it is with the view of developing his ideas on this subject that he has entered so fully and so frequently into the exposition of his theory4 8,if ,i have myself done anything10 he says1 8to strengthen the doctrine1 it has been by showing that polar cold1 rather than equatorial heat1 is the primum mobile of this circulation40#gg ,the influence of the sun in heating the waters of the inter-tropical seas is1 in ,dr4 ,carpenter's manner of viewing the problem1 of no great importance4 ,the efficient cause of motion he considers resides in cold rather than in heat4 ,in fact1 he even goes the length of maintaining that1 as a power in the production of the general interchange of equatorial and polar water1 the effect of polar cold is so much superior to that of inter-tropical heat1 that the influence of the latter may be practically disregarded4 8,suppose two basins of ocean-water10 he says1 8connected by a strait to be placed under such different climatic conditions that the surface of one is exposed to the heating influence of tropical sunshine1 whilst the surface of the other is subjected to the extreme cold of the sunless polar winter4 ,the effect of the surface-heat upon the water of the tropical basin will be for the most part limited 7as ,i shall presently show7 to its uppermost stratum1 and may here be practically disregarded40#gh ,dr4 ,carpenter's idea regarding the efficiency of cold in producing motion seems to me to be not only opposed to the generally received views on the subject1 but wholly irreconcilable with the ordinary principles of mechanics4 ,in fact1 there are so many points on which ,dr4 ,carpenter's theory of a 8,general ,vertical ,oceanic ,circulation0 differs from the generally received views on the subject of circulation by means of difference of specific gravity1 that ,i have thought it advisable to enter somewhat minutely into the consideration of the mechanics of that theory1 the more so as he has so repeatedly asserted that eminent physicists agree with what he has advanced on the subject4 ,according to the generally received theory1 the circulation is due to the difference of density between the sea in equatorial and polar regions4 ,the real efficient cause is gravity2 but gravity cannot act when there is no difference of specific gravity4 ,if the sea were of equal density from the poles to the equator1 gravity could exercise no influence in the production of circulation2 and the influence which it does possess is in proportion to the difference of density4 ,but the difference of density between equatorial and polar waters is in turn due not absolutely either to polar cold or to tropical heat1 but to both--or1 in other words1 to the difference of temperature between the polar and equatorial seas4 ,this difference1 in the very nature of things1 must be as much the result of equatorial heat as of polar cold4 ,if the sea in equatorial regions were not being heated by the sun as rapidly as the sea in polar regions is being cooled1 the difference of temperature between them1 and consequently the difference of density1 would be diminishing1 and in course of time would disappear altogether4 ,as has already been shown1 it is a necessary consequence that the water flowing from equatorial to polar regions must be compensated by an equal amount flowing from polar to equatorial regions4 ,now1 if the water flowing from polar to equatorial regions were not being heated as rapidly as the water flowing from equatorial to polar regions is being cooled1 the equatorial seas would gradually become colder and colder until no sensible difference of temperature existed between them and the polar oceans4 ,in fact1 equality of the two rates is necessary to the very existence of such a general circulation as that advocated by ,dr4 ,carpenter4 ,if he admits that the general interchange of equatorial and polar water advocated by him is caused by the difference of density between the water at the equator and the poles1 resulting from difference of temperature1 then he must admit also that this difference of density is just as much due to the heating of the equatorial water by the sun as it is to the cooling of the polar water by radiation and other means--or1 in other words1 that it is as much due to equatorial heat as to polar cold4 ,and if so1 it cannot be true that polar cold rather than equatorial heat is the 8primum mobile0 of this circulation2 and far less can it be true that the heating of the equatorial water by the sun is of so little importance that it may be 8practically disregarded40 ,supposed ,influence of ,heat derived from the ,earth's ,crust4--,there is1 according to ,dr4 ,carpenter1 another agent concerned in the production of the general oceanic circulation1 viz41 the heat derived by the bottom of the ocean from the crust of the earth4#gi ,we have no reason to believe that the quantity of internal heat coming through the earth's crust is greater in one part of the globe than in another2 nor have we any grounds for concluding that the bottom of inter-tropical seas receives more heat from the earth's crust than the bottom of those in polar regions4 ,but if the polar seas receive as much heat from this source as the seas within the tropics1 then the difference of density between the two cannot possibly be due to heat received from the earth's crust2 and this being so1 it is mechanically impossible that internal heat can be a cause in the production of the general oceanic circulation4 ,circulation without ,difference of ,level4--,there is another part of the theory which appears to me irreconcilable with mechanics4 ,it is maintained that this general circulation takes place without any difference of level between the equator and the poles4 ,referring to the case of the two cylinders ,w and ,c1 which represent the equatorial and polar columns respectively1 ,dr4 ,carpenter says3-- 8,the force which will thus lift up the entire column of water in ,w is that which causes the descent of the entire column in ,c1 namely1 the excess of gravity constantly acting in ,c1--the levels of the two columns1 and consequently their heights1 being maintained at a constant equality by the free passage of surface-water from ,w to ,c40 8,the whole of ,mr4 ,croll's discussion of this question1 however10 he continues1 8proceeds upon the assumption that the levels of the polar and equatorial columns are not kept at an equality1 c40 7 #cj47 ,and again1 8,now1 so far from asserting 7as ,captain ,maury has done7 that the trifling difference of level arising from inequality of temperature is adequate to the production of ocean-currents1 ,i simply affirm that as fast as the level is disturbed by change of temperature it will be restored by gravity40 7 #bc47hj ,illustration3 ,fig4 #c4 ,in order to understand more clearly how the circulation under consideration cannot take place without a difference of level1 let ,w ,e 7,fig4 #c7 represent the equatorial column1 and ,c ,p the polar column4 ,the equatorial column is warmer than the polar column because it receives more heat from the sun than the latter2 and the polar is colder than the equatorial column because it receives less4 ,the difference in the density of the two columns results from their difference of temperature2 and the difference of temperature results in turn from the difference in the quantity of heat received from the sun by each4 ,or1 to express the matter in other words1 the difference of density 7and consequently the circulation under consideration7 is due to the excess of heat received from the sun by the equatorial over that received by the polar column2 so that to leave out of account the super-heating of the inter-tropical waters by the sun is to leave out of account the very thing of all others that is absolutely essential to the existence of the circulation4 ,the water being assumed to be the same in both columns and differing only as regards temperature1 and the equatorial column possessing more heat than the polar1 and being therefore less dense than the latter1 it follows1 in order that the two columns may be in static equilibrium1 that the surface of the equatorial column must stand at a higher level than that of the polar4 ,this produces the slope ,w ,c from the equator to the pole4 ,the extent of the slope will of course depend upon the extent of the difference of their temperatures4 ,but1 as was shown on a former occasion1#ha it is impossible that static equilibrium can ever be fully obtained1 because the slope occasioned by the elevation of the equatorial column above the polar produces what we may be allowed to call a molecular disturbance of equilibrium4 ,the surface of the ocean1 or the molecules of water lying on the slope1 are not in a position of equilibrium1 but tend1 in virtue of gravity1 to roll down the slope in the direction of the polar column ,c4 ,it will be observed that the more we gain of static equilibrium of the entire ocean the greater is the slope1 and consequently the greater is the disturbance of molecular equilibrium2 and1 vice vers1 the more molecular equilibrium is restored by the reduction of the slope1 the greater is the disturbance of static equilibrium4 ,it is therefore absolutely impossible that both conditions of equilibrium can be fulfilled at the same time so long as a difference of temperature exists between the two columns4 ,and this conclusion holds true even though we should assume water to be a perfect fluid absolutely devoid of viscosity4 ,it follows1 therefore1 that a general oceanic circulation without a difference of level is a mechanical impossibility4 ,in a case of actual circulation due to difference of gravity1 there is always a constant disturbance of both static and molecular equilibrium4 ,column ,c is always higher and column ,w always lower than it ought to be were the two in equilibrium2 but they never can be at the same level4 ,it is quite conceivable1 of course1 that the two conditions of equilibrium may be fulfilled alternately4 ,we can conceive column ,c remaining stationary till the water flowing from column ,w has restored the level4 ,and after the level is restored we can conceive the polar column ,c sinking and the equatorial column ,w rising till the two perfectly balance each other4 ,such a mode of circulation1 consisting of an alternate surface-flow and vertical descent and ascent of the columns1 though conceivable1 is in reality impossible in nature2 for there are no means by which the polar column ,c could be supported from sinking till the level had been restored4 ,but ,dr4 ,carpenter does not assume that the general oceanic circulation takes place in this intermitting manner2 according to him1 the circulation is constant4 ,he asserts that there is a 8continual transference of water from the bottom of ,c to the bottom of ,w1 and from the top of ,w to the top of ,c1 with a constant descending movement in ,c and a constant ascending movement in ,w0 7 #bi74 ,but such a condition of things is irreconcilable with the idea of 8the levels of the two columns1 and consequently their heights1 being maintained at a constant equality0 7 #bi74 ,although ,dr4 ,carpenter does not admit the existence of a permanent difference of level between the equator and the pole1 he nevertheless speaks of a depression of level in the polar basin resulting from the contraction by cooling of the water flowing into it4 ,this reduction of level induces an inflow of water from the surrounding area2 8and since what is drawn away10 to quote his own words1 8is supplied from a yet greater distance1 the continued cooling of the surface-stratum in the polar basin will cause a #8set' of waters towards it1 to be propagated backwards through the whole intervening ocean in communication with it until it reaches the tropical area40 ,the slope produced between the polar basin and the surrounding area1 if sufficiently great1 will enable the water in the surrounding area to flow polewards2 but unless this slope extend to the equator1 it will not enable the tropical waters also to flow polewards4 ,one of two things necessarily follows3 either the slope extends from the equator to the pole1 or water can flow from the equator to the pole without a slope4 ,if ,dr4 ,carpenter maintains the former1 he contradicts himself2 and if he adopts the latter1 he contradicts an obvious principle of mechanics4 ,a ,confusion of ,ideas in ,reference to the supposed ,agency of ,polar ,cold4--,it seems to me that ,dr4 ,carpenter has been somewhat misled by a slight confusion of ideas in reference to the supposed agency of polar cold4 ,this is brought out forcibly in the following passage from his memoir in the ,proceedings of the ,royal ,geographical ,society1 vol4 xv4 8,mr4 ,croll1 in arguing against the doctrine of a general oceanic circulation sustained by difference of temperature1 and justly maintaining that such a circulation cannot be produced by the application of heat at the surface1 has entirely ignored the agency of cold40 ,it is here supposed that there are two agents at work in the production of the general oceanic circulation4 ,the one agent is heat1 acting at the equatorial regions2 and the other agent is cold1 acting at the polar regions4 ,it is supposed that the agency of cold is far more powerful than that of heat4 ,in fact so trifling is the agency of equatorial heat in comparison with that of polar cold that it may be 8practically disregarded0--left out of account altogether1--polar cold being the primum mobile of the circulation4 ,it is supposed also that ,i have considered the efficiency of one of the agents1 viz41 heat1 and found it totally inadequate to produce the circulation in question2 and it is admitted also that my conclusions are perfectly correct4 ,but then ,i am supposed to have left out of account the other agent1 viz41 polar cold1 the only agent possessing real potency4 ,had ,i taken into account polar cold1 it is supposed that ,i should have found at once a cause perfectly adequate to produce the required effect4 ,this is a fair statement of ,dr4 ,carpenter's views on the subject2 ,i am unable1 at least1 to attach any other meaning to his words4 ,and ,i have no doubt they are also the views which have been adopted by those who have accepted his theory4 ,it must be sufficiently evident from what has already been stated1 that the notion of there being two separate agents at work producing circulation1 namely heat and cold1 the one of which is assumed to have much more potency than the other1 is not only opposed to the views entertained by physicists1 but is also wholly irreconcilable with the ordinary principles of mechanics4 ,but more than this1 if we analyze the subject a little so as to remove some of the confusion of ideas which besets it1 we shall find that these views are irreconcilable with even ,dr4 ,carpenter's own explanation of the cause of the general oceanic circulation4 ,cold is not a something positive imparted to the polar waters giving them motion1 and of which the tropical waters are deprived4 ,if1 dipping one hand into a basin filled with tropical water at #hj and the other into one filled with polar water at #cb1 we refer to our sensations1 we call the water in the one hot and that in the other cold2 but so far as the water itself is concerned heat and cold simply mean difference in the amounts of heat possessed4 ,both the polar and the tropical water possess a certain amount of energy in the form of heat1 only the polar water does not possess so much of it as the tropical4 ,how1 then1 according to ,dr4 ,carpenter1 does polar cold impart motion to the water8 ,the warm water flowing in upon the polar column becomes chilled by cold1 but it is not cooled below that of the water underneath2 for1 according to ,dr4 ,carpenter1 the ocean in polar regions is as cold and as dense underneath as at the surface4 ,the cooled surface-water does not sink through the water underneath1 like the surface-water of a pond chilled during a frosty night4 8,the descending motion in column ,c will not consist10 he says1 8in a successional descent of surface-films from above downwards1 but it will be a downward movement of the entire mass1 as if water in a tall jar were being drawn off through an orifice at the bottom0 7 #bi74 ,there is a downward motion of the entire column1 producing an outflow of water at the bottom towards the equatorial column ,w1 which outflow is compensated by an inflow from the top of the equatorial column to the top of the polar column ,c4 ,but what causes column ,c to descend8 ,the cause of the descent is its excess of weight over that of column ,w4 ,column ,c descends and column ,w ascends1 for the same reason that in a balance the heavy scale descends and the light scale rises4 ,column ,c descends not simply because it is cold1 but because it is colder than column ,w4 ,column ,c descends not simply because in consequence of being cold it is dense and therefore heavy1 but because in consequence of being cold it is denser and therefore heavier than column ,w4 ,it might be as cold as frozen mercury and as heavy as lead2 but it would not on that account descend unless it were heavier than column ,w4 ,the descent of column ,c and ascent of column ,w1 and consequently the general oceanic circulation1 results1 therefore1 according to ,dr4 ,carpenter's explanation1 from the difference in the weights of the two columns2 and the difference in the weights of the two columns results from their difference of density2 and the difference of density of the two columns in turn results from their difference of temperature4 ,but it has already been proved that the difference of temperature between the polar and equatorial columns depends wholly on the difference in the amount of heat received by each from the sun4 ,the equatorial column ,w possesses more heat than the polar column ,c1 solely because it receives more heat from the sun than column ,c4 ,consequently ,dr4 ,carpenter's statement that the circulation is produced by polar cold rather than by equatorial heat1 is just as much in contradiction to his own theory as it is to the principles of mechanics4 ,again1 his admission that the general oceanic circulation 8cannot be produced by the application of heat to the surface10 is virtually a giving up the whole point in debate2 for according to his gravitation theory1 and every form of that theory1 the circulation results from difference of temperature between equatorial and polar seas2 but this difference1 as we have seen1 is entirely owing to the difference in the amount of heat received from the sun at these two places4 ,the heat received1 however1 is 8surface-heat20 for it is at the surface that the ocean receives all its heat from the sun2 and consequently if surface-heat cannot produce the effect required1 nothing else can4 ,m4 ,dubuat's ,experiments4--,referring to the experiments of ,m4 ,dubuat adduced by me to show that water would not run down a slope of #a in #a1hbj1jjj1hb he says1 8,now the experiments of ,m4 ,dubuat had reference1 not to the slow restoration of level produced by the motion of water on itself1 but to the sensible movement of water flowing over solid surfaces and retarded by its friction against them0 7 #bb74 ,dr4 ,carpenter's meaning1 ,i presume1 is that if the incline consist of any solid substance1 water will not flow down it2 but if it be made of water itself1 water will flow down it4 ,but in ,m4 ,dubuat's experiments it was only the molecules in actual contact with the solid incline that could possibly be retarded by friction against it4 ,the molecules not in contact with the solid incline evidently rested upon an incline of water1 and were at perfect liberty to roll down that incline if they chose2 but they did not do so2 and consequently ,m4 ,dubuat's experiment proved that water will not flow over itself on an incline of #a in #a1jjj1jjj4 ,a ,begging of the ,question at ,issue4--8,it is to be remembered10 says ,dr4 ,carpenter1 8that1 however small the original amount of movement may be1 a momentum tending to its continuance must be generated from the instant of its commencement2 so that if the initiating force be in constant action1 there will be a progressive acceleration of its rate1 until the increase of resistance equalises the tendency to further acceleration4 ,now1 if it be admitted that the propagation of the disturbance of equilibrium from one column to another is simply retarded1 not prevented1 by the viscosity of the liquid1 ,i cannot see how the conclusion can be resisted1 that the constantly maintained difference of gravity between the polar and equatorial columns really acts as a vis viva in maintaining a circulation between them0 7 #ce74 ,if it be true1 as ,dr4 ,carpenter asserts1 that in the case of the general oceanic circulation advocated by him 8viscosity0 simply retards motion1 but does not prevent it1 ,i certainly agree with him 8that the constantly maintained difference of gravity between the polar and equatorial columns really acts as a vis viva in maintaining a circulation between them40 ,but to assert that it merely retards1 but does not prevent1 motion1 is simply begging the question at issue4 ,it is an established principle that if the force resisting motion be greater than the force tending to produce it1 then no motion can take place and no work can be performed4 ,the experiments of ,m4 ,dubuat prove that the force of the molecular resistance of water to motion is greater than the force derived from a slope of #a in #a1jjj1jjj2 and therefore it is simply begging the question at issue to assert that it is less4 ,the experiments of ,,mm4 ,barlow1 ,rainey1 and others1 to which he alludes1 are scarcely worthy of consideration in relation to the present question1 because we know nothing whatever regarding the actual amount of force producing motion of the water in these experiments1 further than that it must have been enormously greater than that derived from a slope of #a in #a1jjj1jjj4 ,supposed ,argument from the ,tides4--,dr4 ,carpenter advances ,mr4 ,ferrel's argument in regard to the tides4 ,the power of the moon to disturb the earth's water1 he asserts1 is1 according to ,herschel1 only #a_/aa1djj1jjjth part of gravity1 and that of the sun not over #a_/be1gcf1djjth part of gravity2 yet the moon's attractive force1 even when counteracted by the sun1 will produce a rise of the ocean4 ,but as the disturbance of gravity produced by difference of temperature is far greater than the above1 it ought to produce circulation4 ,it is here supposed that the force exerted by gravity on the ocean1 resulting from difference of temperature1 tending to produce the general oceanic circulation1 is much greater than the force exerted on the ocean by the moon in the production of the tides4 ,but if we examine the subject we shall find that the opposite is the case4 ,the attraction of the moon tending to lift the waters of the ocean acts directly on every molecule from the surface to the bottom2 but the force of gravity tending to produce the circulation in question acts directly on only a portion of the ocean4 ,gravity can exercise no direct force in impelling the underflow from the polar to the equatorial regions1 nor in raising the water to the surface when it reaches the equatorial regions4 ,gravity can exercise no direct influence in pulling the water horizontally along the earth's surface1 nor in raising it up to the surface4 ,the pull of gravity is always downwards1 never horizontally nor upwards4 ,gravity will tend to pull the surface-water from the equator to the poles because here we have descent4 ,gravity will tend to sink the polar column because here also we have descent4 ,but these are the only parts of the circuit where gravity has any tendency to produce motion4 ,motion in the other parts of the circuit1 viz41 along the bottom of the ocean from the poles to the equator and in raising the equatorial column1 is produced by the pressure of the polar column2 and consequently it is only indirectly that gravity may be said to produce motion in those parts4 ,it is true that on certain portions of the ocean the force of gravity tending to produce motion is greater than the force of the moon's attraction1 tending to produce the tides2 but this portion of the ocean is of inconsiderable extent4 ,the total force of gravity acting on the entire ocean tending to produce circulation is in reality prodigiously less than the total force of the moon tending to produce the tides4 ,it is no doubt a somewhat difficult problem to determine accurately the total amount of force exercised by gravity on the ocean2 but for our present purpose this is not necessary4 ,all that we require at present is a very rough estimate indeed4 ,and this can be attained by very simple considerations4 ,suppose we assume the mean depth of the sea to be1 say1 three miles4 ,the mean depth may yet be found to be somewhat less than this1 or it may be found to be somewhat greater2 a slight mistake1 however1 in regard to the mass of the ocean will not materially affect our conclusions4 ,taking the depth at #c miles1 the force or direct pull of gravity on the entire waters of the ocean tending to the production of the general circulation will not amount to more than #a_/bd1jjj1jjj1jjjth that of gravity1 or only about #a_/b1ajjth that of the attraction of the moon in the production of the tides4 ,let it be observed that ,i am referring to the force or pull of gravity1 and not to hydrostatic pressure4 ,the moon1 by raising the waters of the ocean1 will produce a slope of #b feet in a quadrant2 and because the raised water sinks and the level is restored1 ,mr4 ,ferrel concludes that a similar slope of #b feet produced by difference of temperature will therefore be sufficient to produce motion and restore level4 ,but it is overlooked that the restoration of level in the case of the tides is as truly the work of the moon as the disturbance of that level is4 ,for the water raised by the attraction of the moon at one time is again1 six hours afterwards1 pulled down by the moon when the earth has turned round a quadrant4 ,no doubt the earth's gravity alone would in course of time restore the level2 but this does not follow as a logical consequence from ,mr4 ,ferrel's premises4 ,if we suppose a slope to be produced in the ocean by the moon and the moon's attraction withdrawn so as to allow the water to sink to its original level1 the raised side will be the heaviest and the depressed side the lightest2 consequently the raised side will tend to sink and the depressed side will tend to rise1 in order that the ocean may regain its static equilibrium4 ,but when a difference of level is produced by difference of temperature1 the raised side is always the lightest and the depressed side is always the heaviest2 consequently the very effort which the ocean makes to maintain its equilibrium tends to prevent the level being restored4 ,the moon produces the tides chiefly by means of a simple yielding of the entire ocean considered as a mass2 whereas in the case of a general oceanic circulation the level is restored by a flow of water at or near the surface4 ,consequently the amount of friction and molecular resistance to be overcome in the restoration of level in the latter case is much greater than in the former4 ,the moon1 as the researches of ,sir ,william ,thomson show1 will produce a tide in a globe composed of a substance where no currents or general flow of the materials could possibly take place4 ,pressure as a ,cause of ,circulation4--,we shall now briefly refer to the influence of pressure 7the indirect effects of gravity7 in the production of the circulation under consideration4 ,that which causes the polar column ,c to descend and the equatorial column ,w to ascend1 as has repeatedly been remarked1 is the difference in the weight of the two columns4 ,the efficient cause in the production of the movement is1 properly speaking1 gravity2 cold at the poles and heat at the equator1 or1 what is the same thing1 the excess of heat received by the equator over that received by the poles is what maintains the difference of temperature between the two columns1 and consequently is that also which maintains the difference of weight between them4 ,in other words1 difference of temperature is the cause which maintains the state of disturbed equilibrium4 ,but the efficient cause of the circulation in question is gravity4 ,gravity1 however1 could not act without this state of disturbed equilibrium2 and difference of temperature may therefore be called1 in relation to the circulation1 a necessary condition1 while gravity may be termed the cause4 ,gravity sinks column ,c directly1 but it raises column ,w indirectly by means of pressure4 ,the same holds true in regard to the motion of the bottom-waters from ,c to ,w1 which is likewise due to pressure4 ,the pressure of the excess of the weight of column ,c over that of column ,w impels the bottom-water equatorwards and lifts the equatorial column4 ,but on this point ,i need not dwell1 as ,i have in the preceding chapter entered into a full discussion as to how this takes place4 ,we come now to the most important part of the inquiry1 viz41 how is the surface-water impelled from the equator to the poles8 ,is pressure from behind the impelling force here as in the case of the bottom-water of the ocean8 ,it seems to me that1 in attempting to account for the surface-flow from the equator to the poles1 ,dr4 ,carpenter's theory signally fails4 ,the force to which he appeals appears to be wholly inadequate to produce the required effect4 ,the experiments of ,m4 ,dubuat1 as already noticed1 prove that1 any slope which can possibly result from the difference of temperature between the equator and the poles is wholly insufficient to enable gravity to move the waters2 but it does not necessarily prove that the pressure resulting from the raised water at the equator may not be sufficient to produce motion4 ,this point will be better understood from the following figure1 where1 as before1 ,p ,c represents the polar column and ,e ,w the equatorial column4 ,illustration3 ,fig4 #d4 ,it will be observed that the water in that wedge-shaped portion ,w ,c ,w forming the incline cannot be in a state of static equilibrium4 ,a molecule of water at ,o1 for example1 will be pressed more in the direction of ,c than in the direction of ,w1 and the amount of this excess of pressure towards ,c will depend upon the height of ,w above the line ,c ,w4 ,it is evident that the pressure tending to move the molecule at ,o towards ,c will be far greater than the direct pull of gravity tending to draw a molecule at ,o lying on the surface of the incline towards ,c4 ,the experiments of ,m4 ,dubuat prove that the direct force of gravity will not move the molecule at ,o--that is1 cause it to roll down the incline ,w ,c2 but they do not prove that it may not yield to pressure from above1 or that the pressure of the column ,w ,w will not move the molecule at ,o4 ,the pressure is caused by gravity1 and cannot1 of course1 enable gravity to perform more work than what is derived from the energy of gravity2 it will enable gravity1 however1 to overcome resistance1 which it could not do by direct action4 ,but whether the pressure resulting from the greater height of the water at the equator due to its higher temperature be actually sufficient to produce displacement of the water is a question which ,i am wholly unable to answer4 ,if we suppose #d feet #f inches to be the height of the equatorial surface above the polar required to make the two columns balance each other1 the actual difference of level between the two columns will certainly not be more than one-half that amount1 because1 if a circulation exist1 the weight of the polar column must always be in excess of that of the equatorial4 ,but this excess can only be obtained at the expense of the surface-slope1 as has already been shown at length4 ,the surface-slope probably will not be more than #b feet or #b feet #f inches4 ,suppose the ocean to be of equal density from the poles to the equator1 and that by some means or other the surface of the ocean at the equator is raised1 say1 #b feet above that of the poles1 then there can be little doubt that in such a case the water would soon regain its level2 for the ocean at the equator being heavier than at the poles by the weight of a layer #b feet in thickness1 it would sink at the former place and rise at the latter until equilibrium was restored1 producing1 of course1 a very slight displacement of the bottom-waters towards the poles4 ,it will be observed1 however1 that restoration of level in this case takes place by a simple yielding1 as it were1 of the entire mass of the ocean without displacement of the molecules of the water over each other to any great extent4 ,in the case of a slope produced by difference of temperature1 however1 the raised portion of the ocean is not heavier but lighter than the depressed portion1 and consequently has no tendency to sink4 ,any movement which the ocean as a mass makes in order to regain equilibrium tends1 as we have seen1 rather to increase the difference of level than to reduce it4 ,restoration of level can only be produced by the forces which are in operation in the wedge-shaped mass ,w ,c ,w1 constituting the slope itself4 ,but it will be observed by a glance at the ,figure that1 in order to the restoration of level1 a large portion of the water ,w ,w at the equator will require to flow to ,c1 the pole4 ,according to the general vertical oceanic circulation theory1 pressure from behind is not one of the forces employed in the production of the flow from the equator to the poles4 ,this is evident2 for there can be no pressure from behind acting on the water if there be no slope existing between the equator and the poles4 ,dr4 ,carpenter not only denies the actual existence of a slope1 but denies the necessity for its existence4 ,but to deny the existence of a slope is to deny the existence of pressure1 and to deny the necessity for a slope is to deny the necessity for pressure4 ,that in ,dr4 ,carpenter's theory the surface-water is supposed to be drawn from the equator to the poles1 and not pressed forward by a force from behind1 is further evident from the fact that he maintains that the force employed is not vis a tergo but vis a fronte4#hc ,,chapter ,,xi4 ,,the ,,inadequacy ,,of ,,the ,,gravitation ,,theory ,,proved ,,by ,,another ,,method4 ,quantity of ,heat which can be conveyed by the ,general ,oceanic ,circulation trifling4--,tendency in the ,advocates of the ,gravitation ,theory to under-estimate the ,volume of the ,gulf-stream4--,volume of the ,stream as determined by the ,challenger4--,immense ,volume of ,warm ,water discovered by ,captain ,nares4--,condition of ,north ,atlantic inconsistent with the ,gravitation ,theory4--,dr4 ,carpenter's ,estimate of the ,thermal ,work of the ,gulf-stream4 ,i shall now proceed by another method to prove the inadequacy of such a general oceanic circulation as that which ,dr4 ,carpenter advocates4 ,by contrasting the quantity of heat carried by the ,gulf-stream from inter-tropical to temperate and polar regions with such amount as can possibly be conveyed in the same direction by means of a general oceanic circulation1 it will become evident that the latter sinks into utter insignificance before the former4 ,in my earlier papers on the amount of heat conveyed by the ,gulf-stream1#hd ,i estimated the volume of that stream as equal to that of a current #ej miles broad and #a1jjj feet deep1 flowing 7from the surface to the bottom7 at #d miles an hour4 ,of course ,i did not mean1 as ,dr4 ,carpenter seems to suppose1 that the stream at any particular place is #ej miles broad and #a1jjj feet deep1 or that it actually flows at the uniform rate of #d miles an hour at surface and bottom4 ,all ,i meant was1 that the ,gulf-stream is equal to that of a current of the above size and velocity4 ,but in my recent papers on ,ocean-currents1 the substance of which appears in the present volume1 to obviate any objections on the grounds of having over-estimated the volume1 ,i have taken that at one half this estimate1 viz41 equal to a current #ej miles broad and #a1jjj feet deep flowing at the rate of #b miles an hour4 ,i have estimated the mean temperature of the stream as it passes the ,straits of ,florida to be #fe1 and have supposed that the water in its course becomes ultimately cooled down on an average to #dj4 ,in this case each pound of water conveys #ai1cjj foot-pounds of heat from the ,gulf of ,mexico1 to be employed in warming temperate and polar regions4 ,assuming these data to be correct1 it follows that the amount of heat transferred from the ,gulf of ,mexico by this stream per day amounts to #gg1dgi1fej1jjj1jjj1jjj1jjj foot-pounds4 ,this enormous quantity of heat is equal to one-fourth of all that is received from the sun by the whole of the ,atlantic ,ocean from the ,tropic of ,cancer up to the ,arctic ,circle4 ,this is the amount of heat conveyed from inter-tropical to temperate and polar regions by the ,gulf-stream4 ,what now is the amount conveyed by means of the ,general ,oceanic ,circulation8 ,according to this theory there ought to be as much warm water flowing from inter-tropical regions towards the ,antarctic as towards the ,arctic ,circle4 ,we may1 therefore1 in our calculations1 consider that the heat which is received in tropical regions to the south of the equator goes to warm the southern hemisphere1 and that received on the north side of the equator to warm the northern hemisphere4 ,the warm currents found in the ,north ,atlantic in temperate regions we may conclude came from the regions lying to the north of the equator1--or1 in other words1 from that part of the ,atlantic lying between the equator and the ,tropic of ,cancer4 ,at least1 according to the gravitation theory1 we have no reason to believe that the quantity of warm water flowing from tropical to temperate and polar regions in the ,atlantic is greater than the area between the equator and the ,tropic of ,cancer can supply--because it is affirmed that a very large proportion of the cold water found in the ,north ,atlantic comes1 not from the arctic1 but from the antarctic regions4 ,but if the ,north ,atlantic is cooled by a cold stream from the southern hemisphere1 the southern hemisphere in turn must be heated by a warm current from the ,north ,atlantic--unless we assume that the compensating current flowing from the ,atlantic into the southern hemisphere is as cold as the antarctic current1 which is very improbable4 ,but ,dr4 ,carpenter admits that the quantity of warm water flowing from the ,atlantic in equatorial regions towards the south is even greater than that flowing northwards4 8,the unrestricted communication10 he says1 8which exists between the antarctic area and the great ,southern ,ocean-basins would involve1 if the doctrine of a general oceanic circulation be admitted1 a much more considerable interchange of waters between the antarctic and the equatorial areas than is possible in the northern hemisphere40#he ,we have already seen that1 were it not for the great mass of warm water which finds its way to the polar regions1 the temperature of these regions would be enormously lower than they really are4 ,it has been shown likewise that the comparatively high temperature of north-western ,europe is due to the same cause4 ,but if it be doubtful whether the ,gulf-stream reaches our shores1 and if it be true that1 even supposing it did1 it 8could only affect the most superficial stratum10 and that the great mass of warm water found by ,dr4 ,carpenter in his dredging expeditions came directly from the equatorial regions1 and not from the ,gulf-stream1 then the principal part of the heating-effect must be attributed1 not to the ,gulf-stream1 but to the general flow of water from the equatorial regions4 ,it surely would not1 then1 be too much to assume that the quantity of heat conveyed from equatorial regions by this general flow of water into the ,north ,atlantic is at least equal to that conveyed by the ,gulf-stream4 ,if we assume this to be the amount of heat conveyed by the two agencies into the ,atlantic from inter-tropical regions1 it will1 of course1 be equal to twice that conveyed by the ,gulf-stream alone4 ,we shall now consider whether the area of the ,atlantic to the north of the equator is sufficient to supply the amount of heat demanded by ,dr4 ,carpenter's theory4 ,the entire area of the ,atlantic1 extending from the equator to the ,tropic of ,cancer1 including the ,caribbean ,sea and the ,gulf of ,mexico1 is about #g1gjj1jjj square miles4 ,the quantity of heat conveyed by the ,gulf-stream through the ,straits of ,florida is1 as we have already endeavoured to show1 equal to all the heat received from the sun by #a1efj1ice square miles at the equator4 ,the annual quantity of heat received from the sun by the torrid zone per unit surface1 taking the mean of the whole zone1 is to that received by the equator as #ci to #dj1 consequently the quantity of heat conveyed by the ,gulf-stream is equal to all the heat received by #a1fjj1ifj square miles of the ,atlantic in the torrid zone4 ,but if1 according to ,dr4 ,carpenter's views1 the quantity of heat conveyed from the tropical regions is double that conveyed by the ,gulf-stream1 the amount of heat in this case conveyed into the ,atlantic in temperate regions will be equal to all the heat received from the sun by #c1bja1ibj square miles of the ,atlantic between the equator and the ,tropic of ,cancer4 ,this is #cb_/ggths of all the heat received from the sun by that area4 ,taking the annual quantity received per unit surface at the equator at #a1jjj1 the quantities received by the three zones would be respectively as follows3-- ,equator #ajjj ,torrid zone #ige ,temperate zone #geg ,frigid zone #ded ,now1 if we remove from the ,atlantic in tropical regions #cb_/ggths of the heat received from the sun1 we remove #dje parts from every #ige received from the sun1 and consequently only #egj parts per unit surface remain4 ,it has been shown#hf that the quantity of heat conveyed by the ,gulf-stream from the equatorial regions into the temperate regions is equal to #ajj_/dabths of all the heat received by the ,atlantic in temperate regions4 ,but according to the theory under consideration the quantity removed is double this1 or equal to #ajj_/bjfths of all the heat received from the sun4 ,but the amount received from the sun is equal to #geg parts per unit surface2 add then to this #ajj_/bjfths of #geg1 or #cfg1 and we have #a1abd parts of heat per unit surface as the amount possessed by the ,atlantic in temperate regions4 ,the ,atlantic should in this case be much warmer in temperate than in tropical regions2 for in temperate regions it would possess #a1abd parts of heat per unit surface1 whereas in tropical regions it would possess only #egj parts per unit surface4 ,of course the heat conveyed from tropical regions does not all remain in temperate regions2 a very considerable portion of it must pass into the arctic regions4 ,let us1 then1 assume that one half goes to warm the ,arctic ,ocean1 and the other half remains in the temperate regions4 ,in this case #ahce parts would remain1 and consequently #geg #ahce #idje parts would be the quantity possessed by the ,atlantic in temperate regions1 a quantity which still exceeds by no less than #cgje parts the heat possessed by the ,atlantic in tropical regions4 ,as one half of the amount of heat conveyed from the tropical regions is assumed to go into the ,arctic ,ocean1 the quantity passing into that ocean would therefore be equal to that which passes through the ,straits of ,florida1 an amount which1 as we have found1 is equal to all the heat received from the sun by #c1dcf1ijj square miles of the ,arctic ,ocean4#hg ,the entire area covered by sea beyond the ,arctic ,circle is under #e1jjj1jjj square miles2 but taking the ,arctic ,ocean in round numbers at #e1jjj1jjj square miles1 the quantity of heat conveyed into it by currents to that received from the sun would therefore be as #c1dcf1ijj to #e1jjj1jjj4 ,the amount received on the unit surface of the arctic regions we have seen to be #ded parts4 ,the amount received from the currents would therefore be #cab parts4 ,this gives #gff parts of heat per unit surface as the quantity possessed by the ,arctic ,ocean4 ,thus the ,arctic ,ocean also would contain more heat than the ,atlantic in tropical regions2 for the ,atlantic in these regions would1 in the case under consideration1 possess only #egj parts1 while the ,arctic ,ocean would possess #gff parts4 ,it is true that more rays are cut off in arctic regions than in tropical2 but still1 after making due allowance for this1 the ,arctic ,ocean1 if the theory we are considering were true1 ought to be as warm as1 if not warmer than1 the ,atlantic in tropical regions4 ,the relative quantities of heat possessed by the three zones would therefore be as follows3-- ,atlantic1 in torrid zone #egj in temperate zone #idj in frigid zone #gff ,it is here assumed1 however1 that none of the heat possessed by the ,gulf-stream is derived from the southern hemisphere1 which1 we know1 is not the case4 ,but supposing that as much as one half of the heat possessed by the stream came from the southern hemisphere1 and that the other half was obtained from the seas lying between the equator and the ,tropic of ,cancer1 the relative proportions of heat possessed by the three zones per given area would be as follows3-- ,atlantic1 in torrid zone #fga in temperate zone #idj in frigid zone #gff ,this proves incontestably that1 supposing there is such a general oceanic circulation as is maintained1 the quantity of heat conveyed by means of it into the ,north ,atlantic and ,arctic ,oceans must be trifling in comparison with that conveyed by the ,gulf-stream2 for if it nearly equalled that conveyed by the ,gulf-stream1 then not only the ,north ,atlantic in temperate regions1 but even the ,arctic ,ocean itself would be much warmer than the inter-tropical seas4 ,in fact1 so far as the distribution of heat over the globe is concerned1 it is a matter of indifference whether there really is or is not such a thing as this general oceanic circulation4 ,the enormous amount of heat conveyed by the ,gulf-stream alone puts it beyond all doubt that ocean-currents are the great agents employed in distributing over the globe the excess of heat received by the sea in inter-tropical regions4 ,it is therefore1 so far as concerns the theory of a ,general ,oceanic ,circulation1 of the utmost importance that the advocates of that theory should prove that ,i have over-estimated the thermal power of the ,gulf-stream4 ,this1 however1 can only be done by detecting some error either in my computation or in the data on which it is based2 yet neither ,dr4 ,carpenter nor any one else1 as far as ,i know1 has challenged the accuracy of my figures4 ,the question at issue is the correctness of the data2 but the only part of the data which can possibly admit of being questioned is my estimate of the volume and temperature of the stream4 ,dr4 ,carpenter1 however1 does not maintain that ,i have over-estimated the temperature of the stream2 on the contrary1 he affirms that ,i have really under-estimated it4 8,if we assume10 he remarks1 8the limit of the stratum above #fj as that of the real ,gulf-stream current1 we shall find its average temperature to be somewhat higher than it has been stated by ,mr4 ,croll1 who seems to have taken #fe as the average of the water flowing through the entire channel4 ,the average surface temperature of the ,florida channel for the whole year is #hj2 and we may fairly set the average of the entire outgoing stream1 down to the plane of #fj1 at #gj1 instead of #fe as estimated by ,mr4 ,croll0 7 #ada74 ,it follows1 then1 that every pound of water of the ,gulf-stream actually conveys #e units of heat more than ,i have estimated it to do--the amount conveyed being #cj units instead of #be units as estimated by me4 ,consequently1 if the ,gulf-stream be equal to that of a current of merely #da miles broad and #a1jjj feet deep1 flowing at the rate of #b miles an hour1 it will still convey the estimated quantity of heat4 ,but this estimate of the volume of the stream1 let it be observed1 barely exceeds one-third of that given by ,herschel1 ,maury1 and ,colding1#hh and is little more than one-half that assigned to it by ,mr4 ,laughton1 while it very little exceeds that given by ,mr4 ,findlay1#hi an author whom few will consider likely to overrate either the volume or heating-power of the stream4 ,the important results obtained during the ,challenger expedition have clearly proved that ,i have neither over-estimated the temperature nor the volume of the ,gulf-stream4 ,between ,bermuda and ,sandy ,hook the stream is #fj miles broad and #fjj feet deep1 with a maximum velocity of from #c to #d miles an hour4 ,if the mean velocity of the entire section amounts to #b miles an hour1 which it probably does1 the volume of the stream must equal that given in my estimate4 ,but we have no evidence that all the water flowing through the ,straits of ,florida passes through the section examined by the officers of the ,challenger4 ,be this1 however1 as it may1 the observations made between ,st4 ,thomas and ,sandy ,hook reveal the existence of an immense flow of warm water1 #b1cjj feet deep1 entirely distinct from the water included in the above section of the ,gulf-stream proper4 ,as the thickest portion of this immense body of water joins the warm water of the ,gulf-stream1 ,captain ,nares considers that 8it is evidently connected with it1 and probably as an offshoot40 ,at ,sandy ,hook1 according to him1 it extends #a1bjj feet deeper than the ,gulf-stream itself1 but off ,charleston1 #fjj miles nearer the source1 the same temperature is found at the same depth4 ,but whether it be an offshoot of the ,gulf-stream or not1 one thing is certain1 it can only come from the ,gulf of ,mexico or from the ,caribbean ,sea4 ,this mass of water1 after flowing northwards for about #a1jjj miles1 turns to the right and crosses the ,atlantic in the direction of the ,azores1 where it appears to thin out4 ,if1 therefore1 we take into account the combined heat conveyed by both streams1 my estimate of the heat transferred from inter-tropical regions into the ,north ,atlantic will be found rather under than above the truth4 ,dr4 ,carpenter's ,estimate of the ,thermal ,work of the ,gulf-stream4--,in the appendix to an elaborate memoir on ,oceanic ,circulation lately read before the ,geographical ,society1 ,dr4 ,carpenter endeavours to show that ,i have over-estimated the thermal work of the ,gulf-stream4 ,in that memoir#ij he has also favoured us with his own estimate of the sectional area1 rate of flow1 and temperature of the stream4 ,even adopting his data1 however1 ,i find myself unable to arrive at his conclusions4 ,let us consider first his estimate of the sectional area of the stream4 ,he admits that 8it is impossible1 in the present state of our knowledge1 to arrive at any exact estimate of the sectional area of the stream2 since it is for the most part only from the temperatures of its different strata that we can judge whether they are1 or are not1 in movement1 and what is the direction of their movement40 ,now it is perfectly evident that our estimate of the sectional area of the stream will depend upon what we assume to be its bottom temperature4 ,if1 for example1 we assume #gj to be the bottom temperature1 we shall have a small sectional area4 ,taking the temperature at #fj1 the sectional area will be larger1 and if #ej be assumed to be the temperature1 the sectional area will be larger still1 and so on4 ,now the small sectional area obtained by ,dr4 ,carpenter arises from the fact of his having assumed the high temperature of #fj to be that of the bottom of the stream4 ,he concludes that all the water below #fj has an inward flow1 and that it is only that portion from #fj and upwards which constitutes the ,gulf-stream4 ,i have been unable to find any satisfactory evidence for assuming so high a temperature for the bottom of the stream4 ,it must be observed that the water underlying the ,gulf-stream is not the ordinary water of the ,atlantic1 but the cold current from the arctic regions4 ,in fact1 it is the same water which reaches the equator at almost every point with a temperature not much above the freezing-point4 ,it is therefore highly improbable that the under surface of the ,gulf-stream has a temperature so high as #fj4 ,dr4 ,carpenter's method of measuring the mean velocity of the ,gulf-stream is equally objectionable4 ,he takes the mean annual rate at the surface in the 8,narrows0 to be two miles an hour and the rate at the bottom to be zero1 and he concludes from this that the average rate of the whole is one mile an hour--the arithmetical mean between these two extremes4 ,now it will be observed that this conclusion only holds true on the supposition that the breadth of the stream is as great at the bottom as at the surface1 which of course it is not4 ,all admit that the sides of the ,gulf-stream are not perpendicular1 but slope somewhat in the manner of the banks of a river4 ,the stream is broad at the surface and narrows towards the bottom4 ,it is therefore evident that the upper half of the section has a much larger area than the lower2 the quantity of water flowing through the upper half with a greater velocity than one mile an hour must be much larger than the quantity flowing through the lower half with a less velocity than one mile an hour4 ,his method of estimating the mean temperature of the stream is even more objectionable4 ,he says1 8,the average surface temperature of the ,florida ,channel for the whole year is #hj1 and we may set the average of the entire outgoing stream down to the plane of #fj at #gj1 instead of #fe1 as estimated by ,mr4 ,croll40 ,if #hj be the surface and #fj be the bottom temperature1 temperature and rate of velocity being assumed of course to decrease uniformly from the surface downwards1 how is it possible that #gj can be the average temperature8 ,the amount of water flowing through the upper half of the section1 with a temperature above #gj1 is far more than the amount flowing through the under half of the section1 with a temperature below #gj4 ,supposing the lower half of the section to be as large as the upper half1 which it is not1 still the quantity of water flowing through it would only equal one-third of that flowing through the upper half1 because the mean velocity of the water in the lower half would be only half a mile per hour1 whereas the mean velocity of that in the upper half would be a mile and a half an hour4 ,but the area of the lower half is much less than that of the upper half1 consequently the amount of water whose temperature is under #gj must be even much under one-third of that1 the temperature of which is above #gj4 ,had ,dr4 ,carpenter taken the proper method of estimating the mean temperature1 he would have found that #ge1 even according to his own data1 was much nearer the truth than #gj4 ,i pointed out1 several years ago1#ia the fallacy of estimating the mean temperature of a stream in this way4 ,so high a mean temperature as #ge for the ,gulf-stream1 even in the ,florida ,channel1 is manifestly absurd1 but if #fj be the bottom temperature of the stream1 the mean temperature cannot possibly be much under that amount4 ,it is1 of course1 by under-estimating the sectional area of the stream that its mean temperature is over-estimated4 ,we cannot reduce the mean temperature without increasing the sectional area4 ,if my estimate of #fe be taken as the mean temperature1 which ,i have little doubt will yet be found to be not far from the truth1 ,dr4 ,carpenter's estimate of the sectional area must be abandoned4 ,for if #fe be the mean temperature of the stream1 its bottom temperature must be far under #fj1 and if the bottom temperature be much under #fj1 then the sectional area must be greater than he estimates it to be4 ,be this1 however1 as it may2 even if we suppose that #fj will eventually be found to be the actual bottom temperature of the ,gulf-stream1 nevertheless1 if the total quantity of heat conveyed by the stream from inter-tropical regions be estimated in the proper way1 we shall still find that amount to be so enormous1 that there is not sufficient heat remaining in those regions to supply ,dr4 ,carpenter's oceanic circulation with a quantity as great for distribution in the ,north ,atlantic4 ,it therefore follows 7and so far as regards the theory of ,secular changes of climate1 this is all that is worth contending for7 that ,ocean-currents and not a ,general ,oceanic ,circulation resulting from gravity1 are the great agents employed in the distribution of heat over the globe4 ,,chapter ,,xii4 ,,mr4 ,a4 ,g4 ,,findlay',s ,,objections ,,considered4 ,mr4 ,findlay's ,estimate of the ,volume of the ,gulf-stream4--,mean ,temperature of a ,cross ,section less than ,mean ,temperature of ,stream4--,reason of such ,diversity of ,opinion regarding ,ocean-currents4--,more rigid ,method of ,investigation necessary4 ,at the conclusion of the reading of ,dr4 ,carpenter's paper before the ,royal ,geographical ,society1 on ,january #ith1 #ahga1 ,mr4 ,findlay made the following remarks3-- 8,when1 by the direction of the ,united ,states ,government1 ten or eleven years ago1 the narrowest part of the ,gulf-stream was examined1 figures were obtained which shut out all idea of its ever reaching our shores as a heat-bearing current4 ,in the narrowest part1 certainly not more than from #bej to #cjj cubic miles of water pass per diem4 ,six months afterwards that water reaches the banks of ,newfoundland1 and nine or twelve months afterwards the coast of ,england1 by which time it is popularly supposed to cover an area of #a1ejj1jjj square miles4 ,the proportion of the water that passes through the ,gulf of ,florida will not make a layer of water more than #f inches thick per diem over such a space4 ,every one knows how soon a cup of tea cools2 and yet it is commonly imagined that a film of only a few inches in depth1 after the lapse of so long a time1 has an effect upon our climate4 ,there is no need for calculations2 the thing is self-evident40#ib ,about five years ago1 ,mr4 ,findlay objected to the conclusions which ,i had arrived at regarding the enormous heating-power of the ,gulf-stream on the ground that ,i had over-estimated the volume of the stream4 ,he stated that its volume was only about the half of what ,i had estimated it to be4 ,to obviate this objection1 ,i subsequently reduced the volume to one-half of my former estimate4#ic ,but taking the volume at this low estimate1 it was nevertheless found that the quantity of heat conveyed into the ,atlantic through the ,straits of ,florida by means of the stream was equal to about one-fourth of all the heat received from the sun by the ,atlantic from the latitude of the ,strait of ,florida up to the ,arctic ,circle4 ,mr4 ,findlay1 in his paper read before the ,british ,association1 affirmed that the volume of the stream is somewhere from #bid to #ccc cubic miles per day2 but in his remarks at the close of ,dr4 ,carpenter's address1 he stated it to be not greater than from #bej to #cjj cubic miles per day4 ,i am unable to reconcile any of those figures with the data from which he appears to have derived them4 ,in his paper to the ,british ,association1 he remarks that 8the ,gulf-stream at its outset is not more than #ci miles wide1 and #a1bjj feet deep40 ,from all attainable data1 he computes the mean annual rate of motion to be #fed miles per day2 but as the rate decreases with the depth1 the mean velocity of the whole mass does not exceed #did miles per day4 ,when he speaks of the mean velocity of the ,gulf-stream being so and so1 he must refer to the mean velocity at some particular place4 ,this is evident2 for the mean velocity entirely depends upon the sectional area of the stream4 ,the place where the mean velocity is #did miles per day must be the place where it is #ci miles broad and #a1bjj feet deep2 for he is here endeavouring to show us how small the volume of the stream actually is4 ,now1 unless the mean velocity refers to the place where he gives us the breadth and depth of the stream1 his figures have no bearing on the point in question4 ,but a stream #ci miles broad and #a1bjj feet deep has a sectional area of #hig square miles1 and this1 with a mean velocity of #did miles per day1 will give #ddc cubic miles of water4 ,the amount1 according to my estimate1 is #dei cubic miles per day2 it therefore exceeds ,mr4 ,findlay's estimate by only #af cubic miles4 ,mr4 ,findlay does not1 as far as ,i know1 consider that ,i have over-estimated the mean temperature of the stream4 ,he states#id that between ,sand ,key and ,havana the ,gulf-stream is about #a1bjj feet deep1 and that it does not reach the summit of a submarine ridge1 which he states has a temperature of #fj4 ,it is evident1 then1 that the bottom of the stream has a temperature of at least #fj1 which is within #e of what ,i regard as the mean temperature of the mass4 ,but the surface of the stream is at least #ag above this mean4 ,now1 when we consider that it is at the upper parts of the stream1 the place where the temperature is so much above #fe1 that the motion is greatest1 it is evident that the mean temperature of the entire moving mass must1 according to ,mr4 ,findlay1 be considerably over #fe4 ,it therefore follows1 according to his own data1 that the ,gulf-stream conveys into the ,atlantic an amount of heat equal to one-fourth of all the heat which the ,atlantic1 from the latitude of the ,straits of ,florida up to the arctic regions1 derives from the sun4 ,but it must be borne in mind that although the mean temperature of the cross section should be below #fe1 it does not therefore follow that the mean temperature of the water flowing through this cross section must be below that temperature1 for it is perfectly obvious that the mean temperature of the mass of water flowing through the cross section in a given time must be much higher than that of the cross section itself4 ,the reason is very simple4 ,it is in the upper half of the section where the high temperature exists2 but as the velocity of the stream is much greater in its upper than in its lower half1 the greater portion of the water passing through this cross section is water of high temperature4 ,but even supposing we were to halve ,mr4 ,findlay's own estimate1 and assume that the volume of the stream is equal to only #bbb cubic miles of water per day instead of #ddc1 still the amount of heat conveyed would be equal to one-eighth part of the heat received from the sun by the ,atlantic4 ,but would not the withdrawal of an amount of heat equal to one-eighth of that received from the sun greatly affect the climate of the ,atlantic8 ,supposing we take the mean temperature of the ,atlantic at1 say1 #ef2 this will make its temperature #bie above that of space4 ,extinguish the sun and stop the ,gulf-stream1 and the temperature ought to sink #bie4 ,how far1 then1 ought the temperature to sink1 supposing the sun to remain and the ,gulf-stream to stop8 ,would not the withdrawal of the stream cause the temperature to sink some #cj8 ,of course1 if the ,gulf-stream were withdrawn and everything else were to remain the same1 the temperature of the ,atlantic would not actually remain #cj lower than at present2 for heat would flow in from all sides and partly make up for the loss of the stream4 ,but nevertheless #cj represents the amount of temperature maintained by means of the heat from the stream4 ,and this1 be it observed1 is taking the volume of the stream at a lower estimate than even ,mr4 ,findlay himself would be willing to admit4 ,mr4 ,findlay says that1 by the time the ,gulf-stream reaches the shores of ,england1 it is supposed to cover a space of #a1ejj1jjj square miles4 8,the proportion of water that passes through the ,straits of ,florida will not make10 according to him1 8a layer of water more than #f inches thick per diem over such a space40 ,but a layer of water #f inches thick cooling #be will give out #egi1jjj foot-pounds of heat per square foot4 ,if1 therefore1 the ,gulf-stream1 as he asserts1 supplies #f inches per day to that area1 then every square foot of the area gives off per day #egi1jjj foot-pounds of heat4 ,the amount of heat received from the sun per square foot in latitude #ee1 which is not much above the mean latitude of ,great ,britain1 is #a1jdg1gcj foot-pounds per day1 taking1 of course1 the mean of the whole year2 consequently this layer of water gives out an amount of heat equal to more than one-half of all that is received from the sun4 ,but assuming that the stream should leave the half of its heat on the ,american shores and carry to the shores of ,britain only #ab of heat1 still we should have #bhi1ejj foot-pounds per square foot1 which notwithstanding is more than equal to one-fourth of that received from the sun4 ,if an amount of heat so enormous cannot affect climate1 what can8 ,i shall just allude to one other erroneous notion which prevails in regard to the ,gulf-stream2 but it is an error which ,i by no means attribute either to ,mr4 ,findlay or to ,dr4 ,carpenter4 ,the error to which ,i refer is that of supposing that when the ,gulf-stream widens out to hundreds of miles1 as it does before it reaches our shores1 its depth must on this account be much less than when it issues from the ,gulf of ,mexico4 ,although the stream may be hundreds of miles in breadth1 there is no necessity why it should be only #f inches1 or #f feet1 or #fj feet1 or even #fjj feet in depth4 ,it may just as likely be #f1jjj feet deep as #f inches4 ,the ,reason why such ,diversity of ,opinion prevails in ,regard to ,ocean-currents4--,in conclusion ,i venture to remark that more than nine-tenths of all the error and uncertainty which prevail1 both in regard to the cause of ocean-currents and to their influence on climate1 is due1 not1 as is generally supposed1 to the intrinsic difficulties of the subject1 but rather to the defective methods which have hitherto been employed in its investigation--that is1 in not treating the subject according to the rigid methods adopted in other departments of physics4 ,what ,i most particularly allude to is the disregard paid to the modern method of determining the amount of effects in absolute measure4 ,but let me not be misunderstood on this point4 ,i by no means suppose that the absolute quantity is the thing always required for its own sake4 ,it is in most cases required simply as a means to an end2 and very often that end is the knowledge of the relative quantity4 ,take1 for example1 the ,gulf-stream4 ,suppose the question is asked1 to what extent does the heat conveyed by that stream influence the climate of the ,north ,atlantic8 ,in order to the proper answering of this question1 the principal thing required is to know what proportion the amount of heat conveyed by the stream into the ,atlantic bears to that received from the sun by that area4 ,we want the relative proportions of these two quantities4 ,but how are we to obtain them8 ,we can only do so by determining first the absolute quantity of each4 ,we must first measure each before we can know how much the one is greater than the other1 or1 in other words1 before we can know their relative proportions4 ,we have the means of determining the absolute amount of heat received from the sun by a given area at any latitude with tolerable accuracy2 but the same cannot be done with equal accuracy in regard to the amount of heat conveyed by the ,gulf-stream1 because the volume and mean temperature of the stream are not known with certainty4 ,nevertheless we have sufficient data to enable us to fix upon such a maximum and minimum value to these quantities as will induce us to admit that the truth must lie somewhere between them4 ,in order to give full justice to those who maintain that the ,gulf-stream exercises but little influence on climate1 and to put an end to all further objections as to the uncertainty of my data1 ,i shall take a minimum to which none of them surely can reasonably object1 viz4 that the volume of the stream is not over #bcj cubic miles per day1 and the heat conveyed per pound of water not over #ab units4 ,calculating from these data1 we find that the amount of heat carried into the ,north ,atlantic is equal to one-sixteenth of all the heat received from the sun by that area4 ,there are1 ,i presume1 few who will not admit that the actual proportion is much higher than this1 probably as high as #a to #c1 or #a to #d4 ,but1 who1 without adopting the method ,i have pursued1 could ever have come to the conclusion that the proportion was even #a to #af8 ,he might have guessed it to be #a to #ajj or #a to #ajjj1 but he never would have guessed it to be #a to #af4 ,hence the reason why the great influence of the ,gulf-stream as a heating agent has been so much under-estimated4 ,the same remarks apply to the gravitation theory of the cause of currents4 ,viewed simply as a theory it looks very reasonable4 ,there is no one acquainted with physics but will admit that the tendency of the difference of temperature between the equator and the poles is to cause a surface current from the equator towards the poles1 and an under current from the poles to the equator4 ,but before we can prove that this tendency does actually produce such currents1 another question must be settled1 viz4 is this force sufficiently great to produce the required motion8 ,now when we apply the method to which ,i refer1 and determine the absolute amount of the force resulting from the difference of specific gravity1 we discover that not to be the powerful agent which the advocates of the gravitation theory suppose1 but a force so infinitesimal as not to be worthy of being taken into account when considering the causes by which currents are produced4 ,,chapter ,,xiii4 ,,the ,,wind ,,theory ,,of ,,oceanic ,,circulation4 ,ocean-currents not due alone to the ,trade-winds4--,an ,objection by ,maury4--,trade-winds do not explain the ,great ,antarctic ,current4--,ocean-currents due to the ,system of ,winds4--,the ,system of ,currents agrees with the ,system of the ,winds4--,chart showing the ,agreement between the ,system of ,currents and ,system of ,winds4--,cause of the ,gibraltar ,current4--,north ,atlantic an immense ,whirlpool4--,theory of ,under ,currents4--,difficulty regarding ,under ,currents obviated4--,work performed by the ,wind in impelling the ,water forward4--,the ,challenger's crucial ,test of the ,wind and ,gravitation ,theories4--,north ,atlantic above the ,level of ,equator4--,thermal ,condition of the ,southern ,ocean irreconcilable with the ,gravitation ,theory4 ,ocean-currents not due alone to the ,trade-winds4--,the generally received opinion amongst the advocates of the wind theory of oceanic circulation is that the ,gulf-stream and other currents of the ocean are due to the impulse of the trade-winds4 ,the tendency of the trade-winds is to impel the inter-tropical waters along the line of the equator from east to west2 and were those regions not occupied in some places by land1 this equatorial current would flow directly round the globe4 ,its westward progress1 however1 is arrested by the two great continents1 the old and the new4 ,on approaching the land the current bifurcates1 one portion trending northwards and the other southwards4 ,the northern branch of the equatorial current of the ,atlantic passes into the ,caribbean ,sea1 and after making a circuit of the ,gulf of ,mexico1 flows northward and continues its course into the ,arctic ,ocean4 ,the southern branch1 on the other hand1 is deflected along the ,south-,american coast1 constituting what is known as the ,brazilian current4 ,in the ,pacific a similar deflection occurs against the ,asiatic coast1 forming a current somewhat resembling the ,gulf-stream1 a portion of which 7,kamtschatka current7 in like manner passes into the arctic regions4 ,in reference to all these various currents1 the impelling cause is supposed to be the force of the trade-winds4 ,it is1 however1 urged as an objection by ,maury and other advocates of the gravitation theory1 that a current like the ,gulf-stream1 extending as far as the arctic regions1 could not possibly be impelled and maintained by a force acting at the equatorial regions4 ,but this is a somewhat weak objection4 ,it seems to be based upon a misconception of the magnitude of the force in operation4 ,it does not take into account that this force acts on nearly the whole area of the ocean in inter-tropical regions4 ,if1 in a basin of water1 say three feet in diameter1 a force is applied sufficient to produce a surface-flow one foot broad across the centre of the basin1 the water impelled against the side will be deflected to the extremes of the vessel4 ,and this result does not in any way depend upon the size of the basin4 ,the same effect which occurs in a small basin will occur in a large one1 provided the proportion between the breadth of the belt of water put in motion and the size of the vessel be the same in both cases4 ,it does not matter1 therefore1 whether the diameter of the basin be supposed to be three feet1 or three thousand miles1 or ten thousand miles4 ,there is a more formidable objection1 however1 to the theory4 ,the trade-winds will account for the ,gulf-stream1 ,brazil1 ,japan1 ,mozambique1 and many other currents2 but there are currents1 such as some of the polar currents1 which cannot be so accounted for4 ,take1 for example1 the great antarctic current flowing northward into the ,pacific4 ,this current does not bend to the left under the influence of the earth's rotation and continue its course in a north-westerly direction1 but actually bends round to the right and flows eastward against the ,south-,american coast1 in direct opposition both to the influence of rotation and to the trade-winds4 ,the trade-wind theory1 therefore1 is insufficient to account for all the facts4 ,but there is yet another explanation1 which satisfactorily solves our difficulties4 ,the currents of the ocean owe their origin1 not to the trade-winds alone1 but to the prevailing winds of the globe 7including1 of course1 the trade-winds74 ,ocean-currents due to the ,system of ,winds4--,if we leave out of account a few small inland sheets of water1 the globe may be said to have but one sea1 just as it possesses only one atmosphere4 ,we have accustomed ourselves1 however1 to speak of parts or geographical divisions of the one great ocean1 such as the ,atlantic and the ,pacific1 as if they were so many separate oceans4 ,and we have likewise come to regard the currents of the ocean as separate and independent of one another4 ,this notion has no doubt to a considerable extent militated against the acceptance of the theory that the currents are caused by the winds1 and not by difference of specific gravity2 for it leads to the conclusion that currents in a sea must flow in the direction of the prevailing winds blowing over that particular sea4 ,the proper view of the matter1 as ,i hope to be able to show1 is that which regards the various currents merely as members of one grand system of circulation produced1 not by the trade-winds alone1 nor by the prevailing winds proper alone1 but by the combined action of all the prevailing winds of the globe1 regarded as one system of circulation4 ,if the winds be the impelling cause of currents1 the direction of the currents will depend upon two circumstances1 viz43--7#a7 the direction of the prevailing winds of the globe1 including1 of course1 under this term the prevailing winds proper and the trade-winds2 and 7#b7 the conformation of land and sea4 ,it follows1 therefore1 that as a current in any given sea is but a member of a general system of circulation1 its direction is determined1 not alone by the prevailing winds blowing over the sea in question1 but by the general system of prevailing winds4 ,it may consequently sometimes happen that the general system of winds may produce a current directly opposite to the prevailing wind blowing over the current4 ,the accompanying ,chart 7,plate ,i47 shows how exactly the system of ocean-currents agrees with the system of the prevailing winds4 ,the fine lines indicate the paths of the prevailing winds1 and the fine arrows the direction in which the wind blows along those paths4 ,the large arrows show the direction of the principal ocean-currents4 ,illustration3 ,,plate ,i4 ,,chart ,,showing ,,the ,,general ,,agreement ,,between ,,the ,,system ,,of ,,ocean ,,currents ,,and ,,winds4 ,w4 ,a4 ,k4 ,johnston1 ,edinbr4 and ,london4 ,the directions and paths of the prevailing winds have been taken from ,messrs4 ,johnston's small physical ,atlas1 which1 ,i find1 agrees exactly with the direction of the prevailing winds as deduced from the four quarterly wind charts lately published by the ,hydrographic ,department of the ,admiralty4 ,the direction of the ocean-currents has been taken from the ,current-chart published by the ,admiralty4 ,in every case1 without exception1 the direction of the main currents of the globe agrees exactly with the direction of the prevailing winds4 ,there could not possibly be a more convincing proof that those winds are the cause of the ocean-currents than this general agreement of the two systems as indicated by the chart4 ,take1 for example1 the ,north ,atlantic4 ,the ,gulf-stream follows exactly the path of the prevailing winds4 ,the ,gulf-stream bifurcates in mid-,atlantic2 so does the wind4 ,the left branch of the stream passes north-eastwards into the arctic regions1 and the right branch south-eastwards by the ,azores2 so does the wind4 ,the south-eastern branch of the stream1 after passing the ,canaries1 re-enters the equatorial current and flows into the ,gulf of ,mexico2 the same1 it will be observed1 holds true of the wind4 ,a like remarkable agreement exists in reference to all the other leading currents of the ocean4 ,this is particularly seen in the case of the great antarctic current between long4 #adj ,w4 and #afj ,w4 ,this current1 flowing northwards from the antarctic regions1 instead of bending to the left under the influence of rotation1 turns to the right when it enters the regions of the westerly winds1 and flows eastwards towards the ,south-,american shores4 ,in fact1 all the currents in this region of strong westerly winds flow in an easterly or north-easterly direction4 ,taking into account the effects resulting from the conformation of sea and land1 the system of ocean-currents agrees precisely with the system of the winds4 ,all the principal currents of the globe are in fact moving in the exact direction in which they ought to move1 assuming the winds to be the sole impelling cause4 ,in short1 so perfect is the agreement between the two systems1 that1 given the system of winds and the conformation of sea and land1 and the direction of all the currents of the ocean1 or more properly the system of oceanic circulation1 might be determined priori4 ,or given the system of the ocean-currents together with the conformation of sea and land1 and the direction of the prevailing winds could also be determined priori4 ,or1 thirdly1 given the system of winds and the system of currents1 and the conformation of sea and land might be roughly determined4 ,for example1 it can be shown by this means that the antarctic regions are probably occupied by a continent and not by a number of separate islands1 nor by sea4 ,while holding that the currents of the ocean form one system of circulation1 we must not be supposed to mean that the various currents are connected end to end1 having the same water flowing through them all in succession like that in a heating apparatus4 ,all that is maintained is simply this1 that the currents are so mutually related that any great change in one would modify the conditions of all the others4 ,for example1 a great increase or decrease in the easterly flow of antarctic water in the ,southern ,ocean would decrease or increase1 as the case might be1 the strength of the ,west ,australian current2 and this change would modify the equatorial current of the ,indian ,ocean1 a modification which in like manner would affect the ,agulhas current and the ,southern ,atlantic current--this last leading in turn to a modification of the equatorial current of the ,atlantic1 and consequently of the ,brazilian current and the ,gulf-stream4 ,furthermore1 since a current impelled by the winds1 as ,mr4 ,laughton in his excellent paper on ,ocean-currents justly remarks1 tends to leave a vacancy behind1 it follows that a decrease or increase in the ,gulf-stream would affect the equatorial current1 the ,agulhas current1 and all the other currents back to the antarctic currents4 ,again1 a large modification in the great antarctic drift-current would in like manner affect all the currents of the ,pacific4 ,on the other hand1 any great change in the currents of the ,pacific would ultimately affect the currents of the ,atlantic and ,indian ,oceans1 through its influence on the ,cape ,horn current1 the ,south ,australian current1 and the current passing through the ,asiatic archipelago2 and vice vers1 any changes in the currents of the ,atlantic or ,indian ,oceans would modify the currents of the ,pacific4 ,cause of ,gibraltar ,current4--,i may now consider the cause of the ,gibraltar current4 ,there can be little doubt that this current owes its origin 7as ,mr4 ,laughton points out7 to the ,gulf-stream4 8,i conceive10 that author remarks1 8that the ,gibraltar current is distinctly a stream formed by easterly drift of the ,north ,atlantic1 which1 although it forms a southerly current on the coast of ,portugal1 is still strongly pressed to the eastward and seeks the first escape it can find4 ,so great indeed does this pressure seem to be1 that more water is forced through the ,straits than the ,mediterranean can receive1 and a part of it is ejected in reverse currents1 some as lateral currents on the surface1 some1 it appears1 as an under current at a considerable depth40#ie ,the funnel-shaped nature of the strait through which the water is impelled helps to explain the existence of the under current4 ,the water being pressed into the narrow neck of the channel tends to produce a slight banking up2 and as the pressure urging the water forward is greatest at the surface and diminishes rapidly downwards1 the tendency to the restoration of level will cause an underflow towards the ,atlantic1 because below the surface the water will find the path of least resistance4 ,it is evident indeed that this underflow will not take place toward the ,mediterranean1 from the fact that that sea is already filled to overflowing by the current received from the outside ocean4 ,if we examine the ,current-chart published by the ,hydrographic ,department of the ,admiralty1 we shall find the ,gibraltar current represented as merely a continuation of the ,s4,e4 flow of ,gulf-stream water4 ,now1 if the arrows shown upon this chart indicate correctly the direction of the flow1 we must become convinced that the ,gulf-stream water cannot possibly avoid passing through the ,gibraltar ,strait4 ,of course the excess of evaporation over that of precipitation within the ,mediterranean area would alone suffice to produce a considerable current through the ,strait2 but this of itself would not fill that inland sea to overflowing4#if ,the ,atlantic may1 in fact1 be regarded as an immense whirlpool with the ,saragossa ,sea as its vortex2 and although it is true1 as will be seen from an inspection of the ,chart1 that the wind blows round the ,atlantic along the very path taken by the water1 impelling the water forward along every inch of its course1 yet nevertheless it must hold equally true that the water has a tendency to flow off in a straight line at a tangent to the circular course in which it is moving4 ,but the water is so hemmed in on all sides that it cannot leave this circular path except only at two points2 and at these two points it actually does flow outwards4 ,on the east and west sides the land prevents any such outflow4 ,similarly1 in the south the escape of the water is frustrated by the pressure of the opposing currents flowing from that quarter2 while in the north it is prevented by the pressure exerted by polar currents from ,davis ,strait and the ,arctic ,ocean4 ,but in the ,strait of ,gibraltar and in the north-eastern portion of the ,atlantic between ,iceland and the north-eastern shores of ,europe there is no resistance offered3 and at these two points an outflow does actually take place4 ,in both cases1 however1 especially the latter1 the outflow is greatly aided by the impulse of the prevailing winds4 ,no one1 who will glance at the accompanying chart 7,plate ,i47 showing how the north-eastern branch of the ,gulf-stream bends round and1 of course1 necessarily presses against the coast1 can fail to understand how the ,atlantic water should be impelled into the ,gibraltar ,strait1 even although the loss sustained by the ,mediterranean from evaporation did not exceed the gain from rain and rivers4 ,theory of ,under ,currents4--,the consideration that ocean-currents are simply parts of a system of circulation produced by the system of prevailing winds1 and not by the impulse of the trade-winds alone1 helps to remove the difficulty which some have in accounting for the existence of under currents without referring them to difference of specific gravity4 ,take the case of the ,gulf-stream1 which passes under the polar stream on the west of ,spitzbergen1 this latter stream passing in turn under the ,gulf-stream a little beyond ,bear ,island4 ,the polar streams have their origin in the region of prevailing northerly winds1 which no doubt extends to the pole4 ,the current flowing past the western shores of ,spitzbergen1 throughout its entire course up to near the point where it disappears under the warm waters of the ,gulf-stream1 lies in the region of these same northerly winds4 ,now why should this current cease to be a surface current as soon as it passes out of the region of northerly into that of south-westerly winds8 ,the explanation seems to be this3 when the stream enters the region of prevailing south-westerly winds1 its progress southwards along the surface of the ocean is retarded both by the wind and by the surface water moving in opposition to its course2 but being continually pressed forward by the impulse of the northerly winds acting along its whole course back almost to the pole1 perhaps1 or as far north at least as the sea is not wholly covered with ice1 the polar current cannot stop when it enters the region of opposing winds and currents2 it must move forward4 ,but the water thus pressed from behind will naturally take the path of least resistance4 ,now in the present case this path will necessarily lie at a considerable distance below the surface4 ,had the polar stream simply to contend with the ,gulf-stream flowing in the opposite direction1 it would probably keep the surface and continue its course along the side of that stream2 but it is opposed by the winds1 from which it cannot escape except by dipping down under the surface2 and the depth to which it will descend will depend upon the depth of the surface current flowing in the opposite direction4 ,there is no necessity for supposing a heaping up of the water in order to produce by pressure a force sufficient to impel the under current4 ,the pressure of the water from behind is of itself enough4 ,the same explanation1 of course1 applies to the case of the ,gulf-stream passing under the polar stream4 ,and if we reflect that these under currents are but parts of the general system of circulation1 and that in most cases they are currents compensating for water drained off at some other quarter1 we need not wonder at the distance which they may in some cases flow1 as1 for example1 from the banks of ,newfoundland to the ,gulf of ,mexico4 ,the under currents of the ,gulf-stream are necessary to compensate for the water impelled southwards by the northerly winds2 and again1 the polar under currents are necessary to compensate for the water impelled northward by the south and south-westerly winds4 ,but it may be asked1 how do the opposing currents succeed in crossing each other8 ,it is evident that the ,gulf-stream must plunge through the whole thickness of the polar stream before it can become an under current1 and so likewise must the cold water of the polar-flow pass through the genial water of the ,gulf-stream in order to get underneath it and continue on its course towards the south4 ,the accompanying diagram 7,plate ,,ii41 ,fig4 #a7 will render this sufficiently intelligible4 ,illustration3 ,fig4 #c ,,plate ,,ii4 ,map shewing meeting of the ,gulf-stream and ,polar ,current 7from ,dr4 ,petermann's ,geographische ,mittheilungen47 ,the curved lines are ,isotherms2 temperatures are in ,fahrenheit4 ,illustration3 ,fig4 #a ,diagram to shew how two opposing currents intersect each other ,illustration3 ,surface ,plan to shew how two opposing currents meet each other ,w4 ,a4 ,k4 ,johnston1 ,edinbr4 and ,london4 ,fig4 #b ,now these two great ocean-currents are so compelled to intersect each other for the simple reason that they cannot turn aside1 the one to the left and the other to the right4 ,when two broad streams like those in question are pressed up against each other1 they succeed in mutually intersecting each other's path by breaking up into bands or belts--the cold water being invaded and pierced as it were by long tongues of warm water1 while at the same time the latter is similarly intersected by corresponding protrusions of cold water4 ,the two streams become in a manner interlocked1 and the one passes through the other very much as we pass the fingers of one hand between the fingers of the other4 ,the diagram 7,plate ,,ii41 ,fig4 #b71 representing the surface of the ocean at the place of meeting of two opposing currents1 will show this better than description4 ,at the surface the bands necessarily assume the tongue-shaped appearance represented in the diagram1 but when they have succeeded in mutually passing down through the whole thickness of the opposing currents1 they then unite and form two definite under currents1 flowing in opposite directions4 ,the polar bands1 after penetrating the ,gulf-stream1 unite below to form a southward-flowing under current1 and in the same way the ,gulf-stream bands1 uniting underneath the polar current1 continue in their northerly course as a broad under current of warm water4 ,that this is a correct representation of what actually occurs in nature becomes evident from an inspection of the current charts4 ,thus in the chart of the ,north ,atlantic which accompanies ,dr4 ,petermann's ,memoir on the ,gulf-stream1 we observe that south of ,spitzbergen the polar current and the ,gulf-stream are mutually interpenetrated--long tongues invading and dipping down underneath the ,gulf-stream1 while in like manner the polar current becomes similarly intersected by well-marked protrusions of warm water flowing from the south4 7,see ,plate ,,ii41 ,fig4 #c47 ,no accurate observations1 as far as ,i know1 have been made regarding the amount of work performed by the wind in impelling the water forward2 but when we consider the great retarding effect of objects on the earth's surface1 it is quite apparent that the amount of work performed on the surface of the ocean must be far greater than is generally supposed4 ,for example1 ,mr4 ,buchan1 ,secretary to the ,scottish ,meteorological ,society1 has shown#ig that a fence made of slabs of wood three inches in width and three inches apart from each other is a protection even during high winds to objects on the lee side of it1 and that a wire screen with meshes about an inch apart affords protection during a gale to flower-pots4 ,the same writer was informed by ,mr4 ,addie that such a screen put up at ,rockville was torn to pieces by a storm of wind1 the wire screen giving way much in the same way as sails during a hurricane at sea4 ,the 8,challenger's0 ,crucial ,test of the ,wind and ,gravitation ,theories of ,oceanic ,circulation4--,it has been shown in former chapters that all the facts which have been adduced in support of the gravitation theory are equally well explained by the wind theory4 ,we may now consider a class of facts which do not appear to harmonize with either theory4 ,the recent investigations of the ,challenger ,expedition into the thermal state of the ocean reveal a condition of things which appears to me utterly irreconcilable with the gravitation theory4 ,it is a condition absolutely essential to the gravitation theory that the surface of the ocean should be highest in equatorial regions and slope downwards to either pole4 ,were water absolutely frictionless1 an incline1 however small1 would be sufficient to produce a surface-flow from the equator to the poles1 but to induce such an effect some slope there must be1 or gravitation could exercise no power in drawing the surface-water polewards4 ,the researches of the ,challenger ,expedition bring to light the striking and important fact that the general surface of the ,north ,atlantic in order to produce equilibrium must stand at a higher level than at the equator4 ,in other words the surface of the ,atlantic is lowest at the equator1 and rises with a gentle slope to well-nigh the latitude of ,england4 ,if this be the case1 then it is mechanically impossible that1 as far as the ,north ,atlantic is concerned1 there can be any such general movement as ,dr4 ,carpenter believes4 ,gravitation can no more cause the surface-water of the ,atlantic to flow towards the arctic regions than it can compel the waters of the ,gulf of ,mexico up the ,mississippi into the ,missouri4 ,the impossibility is equally great in both cases4 ,in order to prove what has been stated1 let us take a section of the mid-,atlantic1 north and south1 across the equator2 and1 to give the gravitation theory every advantage1 let us select that particular section adopted by ,dr4 ,carpenter as the one of all others most favourable to his theory1 viz41 ,section marked ,no4 ,,viii4 in his memoir lately read before the ,royal ,geographical ,society4#ih ,the fact that the polar cold water comes so near the surface at the equator is regarded by ,dr4 ,carpenter as evidence in favour of the gravitation theory4 ,on first looking at ,dr4 ,carpenter's section it forcibly struck me that if it was accurately drawn1 the ocean to be in equilibrium would require to stand at a higher level in the ,north ,atlantic than at the equator4 ,in order1 therefore1 to determine whether this is the case or not ,i asked the hydrographer of the ,admiralty to favour me with the temperature soundings indicated in the section1 a favour which was most obligingly granted4 ,the following are the temperature soundings at the three stations ,a1 ,b1 and ,c4 ,the temperature of ,c are the mean of six soundings taken along near the equator3-- ---------------------------------------- ---------------------- ,a ,b ,c ,depth ,lat4 #cg #ed ,n4 ,lat4 #bc #aj ,n4 ,mean of six in ,long4 #da #dd ,w4,long4 #ch #db ,w4temperature soundings ,fathoms4 near equator4 --------------------- ,temperature4 ,temperature4 ,depth in,temperature4 ,fathoms4 ---------------------------------------- --------------------- ,surface4 #gjj #gbj ,surface4 #ggi #ajj #fce #fgj #aj #ggb #bjj #fjf #egf #bj #gga #cjj #fjj #ebe #cj #gfi #djj #edh #dgg #dj #gag #ejj #dfg #dcg #ej #fdj #fjj #daf #dag #fj #fjd #gjj #djf #djf #gj #eid #hjj #cha #cid #hj #ehj #ijj #cgh #cib #ij #ehj #ajjj #cgi #chc #ajj #eef #aajj #cga #chj #aej #eaj #abjj #cga #cgf #bjj #dff #acjj #cgb #cfg #cjj #dbb #adjj #cga #cfi #djj #djc #aejj 44 #cfg #ejj #chi #bgjj #ceb 44 #fjj #cib #bgbj 44 #ced #gjj #cij #hjj #cia #ijj #chb #ajjj #cfi #aajj #cgf #abjj #cfg #acjj #ceh #adjj #cfd #aejj #cfa ,bottom4 #cdg ---------------------------------------- --------------------- ,on computing the extent to which the three columns ,a1 ,b1 and ,c are each expanded by heat according to ,muncke's table of the expansion of sea water for every degree ,fahrenheit1 ,i found that column ,b1 in order to be in equilibrium with ,c 7the equatorial column71 would require to have its surface standing fully #b feet #f inches above the level of column ,c1 and column ,a fully #c feet #f inches above that column4 ,in short1 it is evident that there must be a gradual rise from the equator to latitude #ch ,n4 of #c feet4 ,any one can verify the accuracy of these results by making the necessary computations for himself4#ii ,illustration3 ,,plate ,,iii4 ,w4 ,a4 ,k4 ,johnston1 ,edinbr4 and ,london4 ,,section ,,of ,,the ,,atlantic nearly ,north and ,south1 between ,,lat4 #ch ,n4 ,,lat4 #ch ,s4 ,i may observe that1 had column ,c extended to the same depth as columns ,a and ,b1 the difference of level would be considerably greater1 for column ,c requires to balance only that portion of columns ,a and ,b which lies above the level of its base4 ,suppose a depth of ocean equal to that of column ,c to extend to the north pole1 and the polar water to have a uniform temperature of #cb from the surface to the bottom1 then1 in order to produce equilibrium1 the surface of the ocean at the equator would require to be #d feet #f inches above that at the pole4 ,but the surface of the ocean at ,b would be #g feet1 and at ,a #h feet1 above the poles4 ,gravitation never could have caused the ocean to assume this form4 ,it is impossible that this immense mass of warm water1 extending to such a depth in the ,north ,atlantic1 could have been brought from equatorial regions by means of gravitation4 ,and1 even if we suppose this accumulation of warm water can be accounted for by some other means1 still its presence precludes the possibility of any such surface-flow as that advocated by ,dr4 ,carpenter4 ,for so long as the ,north ,atlantic stands #c feet above the level of the equator1 gravitation can never move the equatorial waters polewards4 ,there is another feature of this section irreconcilable with the gravitation theory4 ,it will be observed that the accumulation of warm water is all in the ,north ,atlantic1 and that there is little or none in the south4 ,but according to the gravitation theory it ought to have been the reverse4 ,for owing to the unrestricted communication between the equatorial and antarctic regions1 the general flow of water towards the south pole is1 according to that theory1 supposed to be greater than towards the north1 and consequently the quantity of warm equatorial water in the ,south ,atlantic ought also to be greater4 ,dr4 ,carpenter himself seems to be aware of this difficulty besetting the theory1 and meets it by stating that 8the upper stratum of the ,north ,atlantic is not nearly as much cooled down by its limited polar underflow1 as that of the ,south ,atlantic is by the vast movement of antarctic water which is constantly taking place towards the equator40 ,but this 8vast movement of antarctic water0 necessarily implies a vast counter-movement of warm surface-water4 ,so that if there is more polar water in the ,south ,atlantic to produce the cooling effect1 there should likewise be more warm water to be cooled4 ,according to the wind theory of oceanic circulation the explanation of the whole phenomena is simple and obvious4 ,it has already been shown that owing to the fact that the ,s4 ,e4 trades are stronger than the ,n4 ,e41 and blow constantly over upon the northern hemisphere1 the warm surface-water of the ,south ,atlantic is drifted across the equator4 ,it is then carried by the equatorial current into the ,gulf of ,mexico1 and afterwards of course forms a part of the ,gulf-stream4 ,the ,north ,atlantic1 on the other hand1 not only does not lose its surface heat like the equatorial and ,south ,atlantic1 but it receives from the ,gulf-stream in the form of warm water an amount of heat1 as we have seen1 equal to one-fourth of all the heat which it receives from the sun4 ,the reason why the warm surface strata are so much thicker on the ,north ,atlantic than on the equatorial regions is perfectly obvious4 ,the surface-water at the equator is swept into the ,gulf of ,mexico by the trade-winds and the equatorial current1 as rapidly as it is heated by the sun1 so that it has not time to gather to any great depth4 ,but all this warm water is carried by the ,gulf-stream into the ,north ,atlantic1 where it accumulates4 ,that this great depth of warm water in the ,north ,atlantic1 represented in the section1 is derived from the ,gulf-stream1 and not from a direct flow from the equator due to gravitation1 is further evident from the fact that temperature sounding ,a in latitude #ch ,n4 is made through that immense body of warm water1 upwards of #cjj fathoms thick1 extending from ,bermuda to near the ,azores1 discovered by the ,challenger ,expedition1 and justly regarded by ,captain ,nares as an offshoot of the ,gulf-stream4 ,this1 in ,captain ,nares's ,report1 is ,no4 #h 8temperature sounding10 between ,bermuda and the ,azores2 sounding ,b is ,no4 #f 8temperature curve10 between ,teneriffe and ,st4 ,thomas4 ,there is an additional reason to the one already stated why the surface temperature of the ,south ,atlantic should be so much below that of the ,north4 ,it is perfectly true that whatever amount of water is transferred from the southern hemisphere to the northern must be compensated by an equal amount from the northern to the southern hemisphere1 nevertheless the warm water which is carried off the ,south ,atlantic by the winds is not directly compensated by water from the north1 but by that cold antarctic current whose existence is so well known to mariners from the immense masses of ice which it brings from the ,southern ,ocean4 ,thermal ,condition of ,southern ,ocean4----,the thermal condition of the ,southern ,ocean1 as ascertained by the ,challenger ,expedition1 appears to me to be also irreconcilable with the gravitation theory4 ,between the parallels of latitude #fe #db ,s4 and #ej #a ,s41 the ocean1 with the exception of a thin stratum at the surface heated by the sun's rays1 was found1 down to the depth of about #bjj fathoms1 to be several degrees colder than the water underneath4#ajj ,the cold upper stratum is evidently an antarctic current1 and the warm underlying water an equatorial under current4 ,but1 according to the gravitation theory1 the colder water should be underneath4 ,the very fact of a mass of water1 #bjj fathoms deep and extending over fifteen degrees of latitude1 remaining above water of three or four degrees higher temperature shows how little influence difference of temperature has in producing motion4 ,if it had the potency which some attribute to it1 one would suppose that this cold stratum should sink down and displace the warm water underneath4 ,if difference of density is sufficient to move the water horizontally1 surely it must be more than sufficient to cause it to sink vertically4 ,,chapter ,,xiv4 ,,the ,,wind ,,theory ,,of ,,oceanic ,,circulation ,,in ,,relation ,,to ,,change ,,of ,,climate4 ,direction of ,currents depends on ,direction of the ,winds4--,causes which affect the ,direction of ,currents will affect ,climate4--,how ,change of ,eccentricity affects the ,mode of ,distribution of the ,winds4--,mutual ,reaction of ,cause and ,effect4--,displacement of the ,great ,equatorial ,current4--,displacement of the ,median ,line between the ,trades1 and its ,effect on ,currents4--,ocean-currents in ,relation to the ,distribution of ,plants and ,animals4--,alternate ,cold and ,warm ,periods in ,north and ,south4--,mr4 ,darwin's ,views quoted4--,how ,glaciers at the ,equator may be accounted for4--,migration across the ,equator4 ,ocean-currents in ,relation to ,change of ,climate4--,in my attempts to prove that oceanic circulation is produced by the winds and not by difference of specific gravity1 and that ocean-currents are the great distributors of heat over the globe1 my chief aim has been to show the bearing which these points have on the grand question of secular changes of climate during geological epochs1 more particularly in reference to that mystery the cause of the glacial epoch4 ,in concluding this discussion regarding oceanic circulation1 ,i may therefore be allowed briefly to recapitulate those points connected with the subject which seem to shed most light on the question of changes of climate4 ,the complete agreement between the systems of ocean-currents and winds not only shows that the winds are the impelling cause of the currents1 but it also indicates to what an extent the directions of the currents are determined by the winds1 or1 more properly1 to what an extent their directions are determined by the direction of the winds4 ,we have seen in ,chapter ,,ii4 to what an enormous extent the climatic conditions of the globe are dependent on the distribution of heat effected by means of ocean-currents4 ,it has been there pointed out that1 if the heat conveyed from inter-tropical to temperate and polar regions by oceanic circulation were restored to the former1 the equatorial regions would then have a temperature about #ee warmer1 and the high polar regions a climate #hc colder than at present4 ,it follows1 therefore1 that any cause which will greatly affect the currents or greatly change their paths and mode of distribution1 will of necessity seriously affect the climatic condition of the globe4 ,but as the existence of these currents depends on the winds1 and their direction and form of distribution depend upon the direction and form of distribution of the winds1 any cause which will greatly affect the winds will also greatly affect the currents1 and consequently will influence the climatic condition of the globe4 ,again1 as the existence of the winds depends mainly on the difference of temperature between equatorial and polar regions1 any cause which will greatly affect this difference of temperature will likewise greatly affect the winds2 and these will just as surely react on the currents and climatic conditions of the globe4 ,a simple increase or decrease in the difference of temperature between equatorial and polar regions1 though it would certainly produce an increase or a decrease1 as the case might be1 in the strength of the winds1 and consequently in the strength of the currents1 would not1 however1 greatly affect the mode of distribution of the winds1 nor1 as a consequence1 the mode of distribution of the currents4 ,but although a simple change in the difference of temperature between the equator and the poles would not produce a different distribution of arial1 and consequently of ocean-currents1 nevertheless a difference in the difference of temperature between the equator and the two poles would do so2 that is to say1 any cause that should increase the difference of temperature between the equator and the pole on the one hemisphere1 and decrease that difference on the other1 would effect a change in the distribution of the arial currents1 which change would in turn produce a corresponding change in the distribution of ocean-currents4 ,it has been shown#aja that an increase in the eccentricity of the earth's orbit tends to lower the temperature of the one hemisphere and to raise the temperature of the other4 ,it is true that an increase of eccentricity does not afford more heat to the one hemisphere than to the other2 nevertheless it brings about a condition of things which tends to lower the temperature of the one hemisphere and to raise the temperature of the other4 ,let us imagine the eccentricity to be at its superior limit1 #jjggge1 and the winter solstice in the aphelion4 ,the midwinter temperature1 owing to the increased distance of the sun1 would be lowered enormously2 and the effect of this would be to cause all the moisture which now falls as rain during winter in temperate regions to fall as snow4 ,nor is this all2 the winters would not merely be colder than now1 but they would also be much longer4 ,at present the summer half-year exceeds the winter half year by nearly eight days2 but at the period in question the winters would be longer than the summers by upwards of thirty-six days4 ,the heat of the sun during the short summer1 for reasons which have already been explained1 would not be sufficient to melt the snow of winter2 so that gradually1 year by year1 the snow would continue to accumulate on the ground4 ,on the southern hemisphere the opposite condition of things would obtain4 ,owing to the nearness of the sun during the winter of that hemisphere1 the moisture of the air would be precipitated as rain in regions where at present it falls as snow4 ,this and the shortness of the winter would tend to produce a decrease in the quantity of snow4 ,the difference of temperature between the equatorial and the temperate and polar regions would therefore be greater on the northern than on the southern hemisphere2 and1 as a consequence1 the arial currents of the former hemisphere would be stronger than those of the latter4 ,this would be more especially the case with the trade-winds4 ,the ,n4,e4 trades being stronger than the ,s4,e4 trades would blow across the equator1 and the median line between them would therefore be at some distance to the south of the equator4 ,thus the equatorial waters would be impelled more to the southern than to the northern hemisphere2 and the warm water carried over in this manner to the southern hemisphere would tend to increase the difference of temperature between the two hemispheres4 ,this change1 again1 would in turn tend to strengthen the ,n4,e4 and to weaken the ,s4,e4 trades1 and would thus induce a still greater flow of equatorial waters into the southern hemisphere--a result which would still more increase the difference of temperature between the northern and southern hemisphere1 and so on--the one cause so reacting on the other as to increase its effects1 as was shown at length in ,chapter ,,iv4 ,it was this mutual reaction of those physical agents which led1 as was pointed out in ,chapter ,,iv41 to that extraordinary condition of climate which prevailed during the glacial epoch4 ,there is another circumstance to be considered which perhaps more than any thing else would tend to lower the temperature of the one hemisphere and to raise the temperature of the other2 and this is the displacement of the great equatorial current4 ,during a glacial period in the northern hemisphere the median line between the trades would be shifted very considerably south of the equator2 and the same would necessarily be the case with the great equatorial currents1 the only difference being that the equatorial currents1 other things being equal1 would be deflected farther south than the median line4 ,for the water impelled by the strong ,n4,e4 trades would be moving with greater velocity than the waters impelled by the weaker ,s4,e4 trades1 and1 of course1 would cross the median line of the trades before its progress southwards could be arrested by the counteracting influence of the ,s4,e4 trades4 ,let us glance briefly at the results which would follow from such a condition of things4 ,in the first place1 as was shown on former occasions1#ajb were the equatorial current of the ,atlantic 7the feeder of the ,gulf-stream7 shifted considerably south of its present position1 it would not bifurcate1 as it now does1 off ,cape ,st4 ,roque1 owing to the fact that the whole of the waters would strike obliquely against the ,brazilian coast and thus be deflected into the ,southern ,ocean4 ,the effect produced on the climate of the ,north ,atlantic and ,north-,western ,europe by the withdrawal of the water forming the ,gulf-stream1 may be conceived from what has already been stated concerning the amount of heat conveyed by that stream4 ,the heat thus withdrawn from the ,north ,atlantic would go to raise the temperature of the ,southern ,ocean and antarctic regions4 ,a similar result would take place in the ,pacific ,ocean4 ,were the equatorial current of that ocean removed greatly to the south of its present position1 it would not then impinge and be deflected upon the ,asiatic coast1 but upon the continent of ,australia2 and the greater portion of its waters would then pass southward into the ,southern ,ocean1 while that portion passing round the north of ,australia 7owing to the great strength of the ,n4,e4 trades7 would rather flow into the ,indian ,ocean than turn round1 as now1 along the east coast of ,asia by the ,japan ,islands4 ,the stoppage of the ,japan current1 combined with the displacement of the equatorial current to the south of the equator1 would greatly lower the temperature of the whole of the ,north ,pacific and adjoining continents1 and raise to a corresponding degree the temperature of the ,south ,pacific and ,southern ,ocean4 ,again1 the waters of the equatorial current of the ,indian ,ocean 7owing to the opposing ,n4,e4 trades71 would not1 as at present1 find their way round the ,cape of ,good ,hope into the ,north ,atlantic1 but would be deflected southwards into the ,antarctic ,sea4 ,we have in the present state of things a striking example of the extent to which the median line between the two trades may be shifted1 and the position of the great equatorial currents of the ocean may be affected1 by a slight difference in the relative strength of the two arial currents4 ,the ,s4,e4 trades are at present a little stronger than the ,n4,e42 and the consequence is that they blow across the equator into the northern hemisphere to a distance sometimes of #aj or #ae1 so that the mean position of the median line lies at least #f or #g degrees north of the equator4 ,and it is doubtless owing to the superior strength of the ,s4,e4 trades that so much warm water crosses the equator from the ,south to the ,north ,atlantic1 and that the main portion of the equatorial current flows into the ,caribbean ,sea rather than along the ,brazilian coast4 ,were the two trades of equal strength1 the transference of heat into the ,north ,atlantic from the southern hemisphere by means of the ,southern ,atlantic and equatorial currents would be much less than at present4 ,the same would also hold true in regard to the ,pacific4 ,ocean-currents in ,relation to the ,distribution of ,plants and ,animals4--,in the fifth and last editions of the 8,origin of ,species10 ,mr4 ,darwin has done me the honour to express his belief that the foregoing view regarding alternate cold and warm periods in north and south during the glacial epoch explains a great many facts in connection with the distribution of plants and animals which have always been regarded as exceedingly puzzling4 ,there are certain species of plants which occur alike in the temperate regions of the southern and northern hemispheres4 ,at the equator these same temperate forms are found on elevated mountains1 but not on the lowlands4 ,how1 then1 did these temperate forms manage to cross the equator from the northern temperate regions to the southern1 and vice vers8 ,mr4 ,darwin's solution of the problem is 7in his own words7 as follows3-- 8,as the cold became more and more intense1 we know that arctic forms invaded the temperate regions2 and from the facts just given1 there can hardly be a doubt that some of the more vigorous1 dominant1 and widest-spreading temperate forms invaded the equatorial lowlands4 ,the inhabitants of these hot lowlands would at the same time have migrated to the tropical and subtropical regions of the south2 for the southern hemisphere was at this period warmer4 ,on the decline of the glacial period1 as both hemispheres gradually recovered their former temperatures1 the northern temperate forms living on the lowlands under the equator would have been driven to their former homes or have been destroyed1 being replaced by the equatorial forms returning from the south4 ,some1 however1 of the northern temperate forms would almost certainly have ascended any adjoining high land1 where1 if sufficiently lofty1 they would have long survived like the arctic forms on the mountains of ,europe40 8,in the regular course of events the southern hemisphere would in its turn be subjected to a severe glacial period1 with the northern hemisphere rendered warmer2 and then the southern temperate forms would invade the equatorial lowlands4 ,the northern forms which had before been left on the mountains would now descend and mingle with the southern forms4 ,these latter1 when the warmth returned1 would return to their former homes1 leaving some few species on the mountains1 and carrying southward with them some of the northern temperate forms which had descended from their mountain fastnesses4 ,thus we should have some few species identically the same in the northern and southern temperate zones and on the mountains of the intermediate tropical regions0 7p4 #cci1 sixth edition74 ,additional light is cast on this subject by the results already stated in regard to the enormous extent to which the temperature of the equator is affected by ocean-currents4 ,were there no transferrence of heat from equatorial to temperate and polar regions1 the temperature of the equator1 as has been remarked1 would probably be about #ee warmer than at present4 ,in such a case no plant existing on the face of the globe could live at the equator unless on some elevated mountain region4 ,on the other hand1 were the quantity of warm water which is being transferred from the equator to be very much increased1 the temperature of inter-tropical latitudes might be so lowered as easily to admit of temperate species of plants growing at the equator4 ,a lowering of the temperature at the equator some #bj or #cj is all that would be required2 and only a moderate increase in the volume of the currents proceeding from the equator1 taken in connection with the effects flowing from the following considerations1 might suffice to produce that result4 ,during the glacial epoch1 when the one hemisphere was under ice and the other enjoying a warm and equable climate1 the median line between the trades may have been shifted to almost the tropical line of the warm hemisphere4 ,under such a condition of things the warmest part would probably be somewhere about the tropic of the warm hemisphere1 and not1 as now1 at the equator2 for since all1 or nearly all1 the surface-water of the equator would then be impelled over to the warm hemisphere1 the tropical regions of that hemisphere would be receiving nearly double their present amount of warm water4 ,again1 as the equatorial current at this time would be shifted towards the tropic of the warm hemisphere1 the surface-water would not1 as at present1 be flowing in equatorial regions parallel to the equator1 but obliquely across it from the cold to the warm hemisphere4 ,this of itself would tend greatly to lower the temperature of the equator4 ,it follows1 therefore1 as a necessary consequence1 that during the glacial epoch1 when the one hemisphere was under snow and ice and the other enjoying a warm and equable climate1 the temperature of the equator would be lower than at present4 ,but when the glaciated hemisphere 7which we may assume to be the northern7 began to grow warmer and the climate of the southern or warm hemisphere to get colder1 the median line of the trades and the equatorial currents of the ocean also would begin to move back from the southern tropic towards the equator4 ,this would cause the temperature of the equator to rise and to continue rising until the equatorial currents reached their normal position4 ,when the snow began to accumulate on the southern hemisphere and to disappear on the northern1 the median line of the trades and the equatorial currents of the ocean would then begin to move towards the northern tropic as they had formerly towards the southern4 ,the temperature of the equator would then again begin to sink1 and continue to do so until the glaciation of the southern hemisphere reached its maximum4 ,this oscillation of the thermal equator to and fro across the geographical equator would continue so long as the alternate glaciation of the two hemispheres continued4 ,this lowering of the temperature of the equator during the severest part of the glacial epoch will help to explain the former existence of glaciers in inter-tropical regions at no very great elevation above the sea-level1 evidence of which appears recently to have been found by ,professor ,agassiz1 ,mr4 ,belt1 and others4 ,the glacial epoch may be considered as contemporaneous in both hemispheres4 ,but the epoch consisted of a succession of cold and warm periods1 the cold periods of one hemisphere coinciding with the warm periods of the other1 and vice vers4 ,migration across the ,equator4--,mr4 ,belt#ajc and others have felt some difficulty in understanding how1 according to theory1 the plants and animals of temperate regions could manage to migrate from one hemisphere to the other1 seeing that in their passage they would have to cross the thermal equator4 ,the oscillation to and fro of the thermal equator across the geographical1 removes every difficulty in regard to how the migration takes place4 ,when1 for example1 a cold period on the northern hemisphere and the corresponding warm one on the southern were at their maximum1 the thermal equator would by this time have probably passed beyond the ,tropic of ,capricorn4 ,the geographical equator would then be enjoying a subtropical1 if not a temperate condition of climate1 and the plants and animals of the northern hemisphere would manage then to reach the equator4 ,when the cold began to abate on the northern and to increase on the southern hemisphere1 the thermal equator would commence its retreat towards the geographical4 ,the plants and animals from the north1 in order to escape the increasing heat as the thermal equator approached them1 would begin to ascend the mountain heights2 and when that equator had passed to its northern limit1 and the geographical equator was again enjoying a subtropical condition of climate1 the plants and animals would begin to descend and pursue their journey southwards as the cold abated on the southern hemisphere4 ,,chapter ,,xv4 ,,warm ,,inter-,,glacial ,,periods4 ,alternate ,cold and ,warm ,periods4--,warm ,inter-glacial ,periods a ,test of ,theories4--,reason why their ,occurrence has not been hitherto recognised4--,instances of ,warm ,inter-glacial ,periods4--,dranse1 ,drnten1 ,hoxne1 ,chapelhall1 ,craiglockhart1 ,leith ,walk1 ,redhall ,quarry1 ,beith1 ,crofthead1 ,kilmaurs1 ,sweden1 ,ohio1 ,cromer1 ,mundesley1 c41 c4--,cave and ,river ,deposits4--,occurrence of ,arctic and ,warm ,animals in some ,beds accounted for4--,mr4 ,boyd ,dawkins's ,objections4--,occurrence of ,southern ,shells in ,glacial ,deposits4--,evidence of ,warm ,inter-glacial ,periods from ,mineral ,borings4--,striated ,pavements4--,reason why ,inter-glacial ,land-surfaces are so rare4 ,alternate ,cold and ,warm ,periods4--,if the theory developed in the foregoing chapters in reference to the cause of secular changes of climate be correct1 it follows that that long age known as the glacial epoch did not1 as has hitherto been generally supposed1 consist of one long unbroken period of cold and ice4 ,neither did it consist1 as some have concluded1 of two long periods of ice with an intervening mild period1 but it must have consisted of a long succession of cold and warm periods2 the warm periods of the one hemisphere corresponding in time with the cold periods of the other and vice vers4 ,it follows also from theory that as the cold periods became more and more severe1 the warm intervening periods would become more and more warm and equable4 ,as the ice began to accumulate during the cold periods in subarctic and temperate regions in places where it previously did not exist1 so in like manner during the corresponding warm periods it would begin to disappear in arctic regions where it had held enduring sway throughout the now closing cycle4 ,as the cold periods in the southern hemisphere became more and more severe1 the ice would continue to advance northwards in the temperate regions2 but at that very same time the intervening warm periods in the northern hemisphere would become warmer and warmer and more equable1 and the ice of the arctic regions would continue to disappear farther and farther to the north1 till by the time that the ice had reached a maximum during the cold antarctic periods1 ,greenland and the arctic regions would1 during the warm intervening periods1 be probably free of ice and enjoying a mild and equable climate4 ,or we may say that as the one hemisphere became cold the other became warm1 and when the cold reached a maximum in the one hemisphere1 the warmth would reach a maximum in the other4 ,the time when the ice had reached its greatest extension on the one hemisphere would be the time when it had disappeared from the other4 ,inter-glacial ,periods a ,test of ,theories4--,here we have the grand crucial test of the truth of the foregoing theory of the cause of the glacial epoch4 ,that the glacial epoch should have consisted of a succession of cold and warm periods is utterly inconsistent with all previous theories which have been advanced to account for it4 ,what1 then1 is the evidence of geology on this subject8 ,if the glacial epoch can be proved from geological evidence to have consisted of such a succession of cold and warm periods1 then ,i have little doubt but the theory will soon be generally accepted4 ,but at the very outset an objection meets us1 viz41 why call an epoch1 which consisted as much of warm periods as of cold1 a glacial epoch1 or an 8,ice ,age10 as ,mr4 ,james ,geikie tersely expresses it8 ,why not as well call it a warm epoch as a cold one1 seeing that1 according to theory1 it was just as much a warm as a cold epoch8 ,the answer to this objection will be fully discussed in the chapter on the ,reason of the ,imperfection of ,geological ,records4 ,but in the meantime1 ,i may remark that it will be shown that the epoch known as the glacial has been justly called the glacial epoch or 8,ice ,age10 because the geological evidences of the cold periods remain in a remarkably perfect state1 whilst the evidences of the warm periods have to a great extent disappeared4 ,the reason of this difference in the two cases will be discussed in the chapter to which ,i have referred4 ,besides1 the condition of things during the cold periods was so extraordinary1 so exceptional1 so totally different from those now prevailing1 that even supposing the geological records of the warm periods had been as well preserved as those of the cold1 nevertheless we should have termed the epoch in question a glacial epoch4 ,there is yet another reason1 however1 for our limited knowledge of warm inter-glacial periods4 ,till very lately1 little or no attention was paid by geologists to this part of the subject in the way of keeping records of cases of inter-glacial deposits which1 from time to time1 have been observed4 ,few geologists ever dreamt of such a thing as warm periods during the age of ice1 so that when intercalated beds of sand and gravel1 beds of peat1 roots1 branches1 trunks1 leaves1 and fruits of trees were found in the boulder clay1 no physical importance was attached to them1 and consequently no description or record of them ever kept4 ,in fact1 all such examples were regarded as purely accidental and exceptional1 and were considered not worthy of any special attention4 ,a case which came under my own observation will illustrate my meaning4 ,an intelligent geologist1 some years ago1 read a paper before one of our local geological societies1 giving an account of a fossiliferous bed of clay found intercalated between two distinct beds of till4 ,in this intercalated bed were found rootlets and stems of trees1 nuts1 and other remains1 showing that it had evidently been an old inter-glacial land surface4 ,in the transactions of the society a description of the two beds of till was given1 but no mention whatever was made of the intercalated bed containing the organic remains1 although this was the only point of any real importance4 ,since the theory that the glacial epoch resulted from a high state of eccentricity of the earth's orbit began to receive some little acceptance1 geologists have paid a good deal of attention to cases of intercalated beds in the till containing organic remains1 and the result is that we have already a great body of evidence of a geological nature in favour of warm inter-glacial periods1 and ,i have little doubt that in the course of a few years the former occurrence of warm inter-glacial periods will be universally admitted4 ,i shall now proceed to give a very brief outline of the evidence bearing on the subject4 ,but the cases to which ,i shall have to refer are much too numerous to allow me to enter into details4 ,inter-glacial ,beds of ,switzerland4--,the first geologist1 so far as ,i am aware1 who directed attention to evidence of a break in the cold of the glacial epoch was ,m4 ,morlot4 ,it is now twenty years ago since he announced the existence of a warm period during the glacial epoch from geological evidence connected with the glacial drift of the ,alps4#ajd ,the rivers of ,switzerland1 he found1 show on their banks three well-marked terraces of regularly stratified and well-rounded shingle1 identical with the modern deposits of the rivers4 ,they stand at #ej1 #ajj1 and #aej feet above the present level of the rivers4 ,these terraces were evidently formed by the present system of rivers when these flowed at a higher level1 and extend up the ,alps to a height of from #c1jjj to #d1jjj feet above the level of the sea4 ,there is a terrace bordering the ,rhine at ,camischollas1 above ,disentis1 #d1djj feet above the level of the sea1 proving that during the period of its formation the ,alps were free of ice up to the height of #d1djj feet above the sea-level4 ,it is well known that a glacial period must have succeeded the formation of these drifts1 for they are in many places covered with erratics4 ,at ,geneva1 for example1 an erratic drift nearly #ej feet thick is seen to rest on the drift of the middle terrace1 which rises #ajj feet above the level of the lake4 ,but it is also evident that a glacial period must have preceded the formation of the drift beds1 for they are found to lie in many places upon the unstratified boulder clay or till4 ,m4 ,morlot observed in the neighbourhood of ,clareus1 from #g to #i feet of drift resting upon a bed of true till #dj feet thick2 the latter was composed of a compact blue clay1 containing worn and scratched alpine boulders and without any trace of stratification4 ,in the gorge of ,dranse1 near ,thoron1 ,m4 ,morlot found the whole three formations in a direct superimposed series4 ,at the bottom was a mass of compact till or boulder clay1 #ab feet thick1 containing boulders of alpine limestone4 ,over this mass came regularly stratified beds #aej feet thick1 made up of rounded pebbles in horizontal beds4 ,above this again lay a second formation of unstratified boulder clay1 with erratic blocks and striated pebbles1 which constituted the left lateral moraine of the great glacier of the ,rhone1 when it advanced for the second time to the ,lake of ,geneva4 ,a condition of things somewhat similar was observed by ,m4 ,ischer in the neighbourhood of ,berne4 ,these facts1 ,m4 ,morlot justly considers1 prove the existence of two glacial periods separated by an intermediate one1 during which the ice1 which had not only covered ,switzerland1 but the greater part of ,europe1 disappeared even in the principal valleys of the ,alps to a height of more than #d1djj feet above the present level of the sea4 ,this warm period1 after continuing for long ages1 was succeeded by a second glacial period1 during which the country was again covered with ice as before4 ,m4 ,morlot even suggests the possibility of these alternations of cold and warm periods depending upon a cosmical cause4 8,wild as it may have appeared10 he says1 8when first started1 the idea of general and periodical eras of refrigeration for our planet1 connected perhaps with some cosmic agency1 may eventually prove correct40#aje ,shortly afterwards1 evidence of a far more remarkable character was found in the glacial drift of ,switzerland1 namely1 the famous lignite beds of ,drnten4 ,in the vicinity of ,utznach and ,drnten1 on the ,lake of ,zurich1 and near ,mrschwyl1 on the ,lake of ,constance1 there are beds of coal or lignite1 nearly #ab feet thick1 lying directly on the boulder clay4 ,overlying these beds is another mass of drift and clay #cj feet in thickness1 with rounded blocks1 and on the top of this upper drift lie long angular erratics1 which evidently have been transported on the back of glaciers4#ajf ,professor ,vogt attributes their transport to floating ice2 but he evidently does so to avoid the hypothesis of a warm period during the glacial epoch4 ,here we have proof not merely of the disappearance of the ice during the glacial epoch1 but of its absence during a period of sufficient length to allow of the growth of #aj or #ab feet of coal4 ,professor ,heer thinks that this coal-bed1 when in the condition of peat1 must have been #fj feet thick2 and assuming that one foot of peat would be formed in a century1 he concludes that #f1jjj years must have been required for the growth of the coal plants4 ,according to ,liebig1 #i1fjj years would be required4 ,this1 as we have already seen1 is about the average duration of a warm period4 ,in these beds have been found the bones of the elephant 7,e4 ,merkii71 stag1 cave-bear1 and other animals4 ,numerous insects have also been met with1 which further prove the warm1 mild condition of climate which must have prevailed at the time of the formation of the lignite4 ,at ,hoxne1 near ,diss1 in ,suffolk1 a black peaty mass several feet thick1 containing fragments of wood of the oak1 yew1 and fir1 was found1 overlying the boulder clay4#ajg ,professor ,vogt believes that this peat bed is of the same age as the lignite beds of ,switzerland4 ,in the glacial drift of ,north ,america1 particularly about ,lake ,champlain and the valley of the ,st4 ,lawrence1 there is similar evidence of two glacial periods with an intervening non-glacial or warm period4#ajh ,glacial and ,inter-glacial ,periods of the ,southern ,hemisphere--7,south ,africa74--,mr4 ,g4 ,w4 ,stow1 in a paper on the 8,geology of ,south ,africa10#aji describes a recent glaciation extending over a large portion of ,natal1 ,british ,kaffraria1 the ,kaga and ,krome mountains1 which he attributes to the action of land-ice4 ,he sums up the phenomena as follows3--8,the rounding off of the hills in the interiors of the ancient basins2 the numerous dome-shaped 7roches moutonne7 rocks2 the enormous erratic boulders in positions where water could not have carried them2 the frequency of unstratified clays--clays with imbedded angular boulders2 drift and lofty mounds of boulders2 large tracts of country thickly spread over with unstratified clays and superimposed fragments of rock2 the ,oliphant's-,hoek clay1 and the vast piles of ,enon conglomerate40 ,in addition to these results of ice-action1 he records the discovery by himself of distinct ice-scratches or groovings on the surface of the rocks at ,reit-,poort in the ,tarka1 and subsequently#aaj the discovery by ,mr4 ,g4 ,gilfillan of a large boulder at ,pniel with stri distinctly marked upon it1 and also that the same observer found that almost every boulder in the gravel at 8,moonlight ,rush0 had unmistakable stri on one or more sides4 ,in ,south ,africa there is evidence not only of a glacial condition during the ,pliocene period1 but also of a warmer climate than now prevails in that region4 8,the evidence10 says ,mr4 ,stow1 8of the ,pliocene shells of the superficial limestone of the ,zwartkops heights1 and elsewhere1 leads us to believe that the climate of ,south ,africa must have been of a far more tropical character than at present4 8,take1 for instance1 the characteristic ,venericardia of that limestone4 ,this has migrated along the coast some #bi or #cj and is now found within a few degrees of the equator1 near ,zanzibar1 gradually driven1 as ,i presume it must have been1 further and further north by a gradual lowering of the temperature of the more southern parts of this coast since the limestone was deposited40 8,during the formation of the shell-banks in the ,zwartkops estuary1 younger than the ,pliocene limestone1 the immense number of certain species of shells1 which have as yet been found living only in latitudes nearer the equator1 point to a somewhat similar though a more modified change of temperature40 ,inter-glacial ,beds of ,scotland4--,upwards of a dozen years ago1 ,professor ,geikie arrived1 from his own observations of the glacial drift of ,scotland1 at a similar conclusion to that of ,m4 ,morlot regarding the intercalation of warm periods during the glacial epoch2 and the facts on which ,professor ,geikie's conclusions were based are briefly as follows4 ,in a cliff of boulder clay on the banks of the ,slitrig ,water1 near the town of ,hawick1 he observed a bed of stones or shingle4 ,over the lower stratum of stones lay a few inches of well-stratified sand1 silt1 and clay1 some of the layers being black and peaty1 with enclosed vegetable fibres in a crumbling state4#aaa ,there were some #cj or #dj feet of boulder clay above these stratified beds1 and #ae or #bj feet under them4 ,the stones in the shingle band were identical with those of the boulder clay1 but they showed no striations1 and were more rounded and water-worn1 and resembled in every respect the stones now lying in the bed of the ,slitrig4 ,the section of the cliff stood as under3-- #a4 ,vegetable soil4 #b4 ,boulder clay1 thirty to forty feet4 #c4 ,yellowish gravelly sand4 ,stratified beds #d4 ,peaty silt and clay4 #e4 ,fine ferruginous sand4 #f4 ,coarse shingle1 two to three feet4 #g4 ,coarse1 stiff boulder clay1 fifteen to twenty feet4 ,a few more cases of intercalation of stratified materials in the true till were also found in the same valley4 ,in a cliff of stiff brown boulder clay1 about #bj feet high1 on the banks of the ,carmichael ,water1 ,lanarkshire1 ,professor ,geikie observed a stratified bed of clay about #c or #d inches in thickness4 ,about a mile higher up the stream1 he found a series of beds of gravel1 sand1 and clay in the true till4 8,a thin seam of peaty matter10 he says1 8was observed to run for a few inches along the bottom of a bed of clay and then disappear1 while in a band of fine laminated clay with thin sandy partings occasional fragments of mouldering wood were found40#aab ,at ,chapelhall1 near ,airdrie1 a sand-bed has been extensively mined under about #aad feet of till4 ,this bed of finely stratified sand is about #bj feet thick4 ,in it were found lenticular beds of fine pale-coloured clay containing layers of peat and decaying twigs and branches4 ,professor ,geikie found the vegetable fibres1 though much decayed1 still distinct1 and the substance when put into the fire burned with a dull lambent flame4 ,underlying these stratified beds1 and forming the floor of the mine1 is a deposit of the true till about #bd feet in thickness4 ,in another pit adjoining1 the till forming the floor is #cj feet thick1 but it is sometimes absent altogether1 so as to leave the sand beds resting directly on the sandstone and shale of the coal-measures4 ,at some distance from this sand-pit an old buried river channel was met with in one of the pit workings4 ,this channel was found to contain a coating of boulder clay1 on which the laminated sands and clays reposed1 showing1 as ,professor ,geikie has pointed out1 that this old channel had been filled with boulder clay1 and then re-excavated to allow of the deposition of the stratified deposits4 ,over all lay a thick mantle of boulder clay which buried the whole4 ,a case somewhat similar was found by ,professor ,nicol in a cutting on the ,edinburgh and ,leith ,railway4 ,in many places the till had been worn into hollows as if part of it had been removed by the action of running water4#aac ,one of these hollows1 about #e or #f feet wide by #c or #d feet deep1 closely resembled the channel of a small stream4 ,it was also filled with gravel and sand1 in all respects like that found in such a stream at the present day4 ,it was seen to exhibit the same characters on both sides of the cutting1 but ,professor ,nicol was unable to determine how far it may have extended beyond2 but he had no doubt whatever that it had been formed by a stream of water4 ,over this old watercourse was a thick deposit of true till4 ,in reference to the foregoing cases1 ,professor ,geikie makes the following pertinent remarks3--8,here it is evident that the scooping out of this channel belongs to the era of the boulder clay4 ,it must have been effected during a pause in the deposition of the clay1 when a run of water could find its way along the inequalities of the surface of the clay4 ,this pause must have been of sufficient duration to enable the runnel to excavate a capacious channel for itself1 and leave in it a quantity of sand and shingle4 ,we can scarcely doubt that when this process was going on the ground must have been a land surface1 and could not have been under the sea4 ,and lastly1 we see from the upper boulder clay that the old conditions returned1 the watercourse was choked up1 and another mass of chaotic boulder clay was tumbled down upon the face of the country4 ,this indicates that the boulder clay is not the result of one great catastrophe1 but of slow and silent1 yet mighty1 forces acting sometimes with long pauses throughout a vast cycle of time40#aad ,at ,craiglockhart ,hill1 about a mile south of ,edinburgh1 an extensive bed of fine sand of from one to three feet in thickness was found between two distinct masses of true boulder clay or till4 ,the sand was extensively used for building purposes during the erection of the city poorhouse a few years ago4 ,in this sand-bed ,i found a great many tree roots in the position in which they had grown4 ,during the time of the excavations ,i visited the place almost daily1 and had every opportunity of satisfying myself that this sand-bed1 prior to the time of the formation of the upper boulder clay1 must have been a land surface on which the roots had grown4 ,in no case did ,i find them penetrating into the upper boulder clay1 and in several places ,i found stones of the upper clay resting directly on the broken ends of the roots4 ,these roots were examined by ,professor ,balfour1 but they were so decayed that he was unable to determine their character4 ,in digging a foundation for a building in ,leith ,walk1 ,edinburgh1 a few years ago1 two distinct beds of sand were passed through1 the upper1 about #aj feet in thickness1 rested upon what appeared to be a denuded surface of the lower bed4 ,in this lower bed1 which evidently had been a land surface1 numbers of tree roots were found4 ,i had the pleasure of examining them along with my friend ,mr4 ,c4 ,w4 ,peach1 who first directed my attention to them4 ,in no instance were the roots found in the upper bed4 ,that these roots did not belong to trees which had grown on the present surface and penetrated to that depth1 was further evident from the fact that in one or two cases we found the roots broken off at the place where they had been joined to the trunk1 and there the upper sand-bed over them was more than #aj feet in thickness4 ,if we assume that the roots belonged to trees which had grown on the present surface1 then we must also assume1 what no one would be willing to admit1 that the trunks of the trees had grown downwards into the earth to a depth of upwards of ten feet4 ,i have shown these roots to several botanists1 but none of them could determine to what trees they belonged4 ,the surface of the ground at the spot in question is #de feet above sea-level4 ,mr4 ,peach and ,i have found similar roots in the under sand-bed at several other places in the same neighbourhood4 ,that they belong to an inter-glacial period appears probable for the following reasons3--7#a47 ,this upper sand-bed is overlaid by a tough clay1 which in all respects appears to be the same as the ,portobello clay1 which we know belongs to the glacial series4 ,in company with ,mr4 ,bennie1 ,i found the clay in some places to be contorted in a similar manner to the ,portobello clays4 7#b47 ,in a sand-pit about one or two hundred yards to the west of where the roots were found1 the sand-bed was found contorted in the most extraordinary manner to a depth of about #ae feet4 ,in fact1 for a space of more than #cj feet1 the bedding had been completely turned up on end without the fine layers being in the least degree broken or disarranged1 showing that they had been upturned by some enormous powers acting on a large mass of the sand4 ,one of the best examples of true till to be met with in the neighbourhood of ,edinburgh is at ,redhall ,quarry1 about three miles to the south-west of the city4 ,in recently opening up a new quarry near the old one a bed of peat was found intercalated in the thick mass of till overlying the rock4 ,the clay overlying and underlying the peat-bed was carefully examined by ,mr4 ,john ,henderson1#aae and found to be true till4 ,in a quarry at ,overtown1 near ,beith1 ,ayrshire1 a sedimentary bed of clay1 intercalated between two boulder clays1 was some years ago observed by ,mr4 ,robert ,craig1 of the ,glasgow ,geological ,society4 ,this bed filled an elliptical basin about #acj yards long1 and about #cj yards broad4 ,its thickness averaged from one to two feet4 ,this sedimentary bed rested on the till on the north-east end of the basin1 and was itself overlaid on the south-west end by the upper bed of till4 ,the clay bed was found to be full of roots and stems of the common hazel4 ,that these roots had grown in the position in which they were found was evident from the fact that they were in many places found to pass into the 8cutters0 or fissures of the limestone1 and were here found in a flattened form1 having in growing accommodated themselves to the size and shape of the fissures4 ,nuts of the hazel were plentifully found4#aaf ,at ,hillhead1 some distance from ,overtown1 there is a similar intercalated bed full of hazel remains1 and a species of freshwater ,ostracoda was detected by ,mr4 ,david ,robertson4 ,in a railway cutting a short distance from ,beith1 ,mr4 ,craig pointed out to my colleague1 ,mr4 ,jack1 and myself1 a thin layer of peaty matter1 extending for a considerable distance between an upper and lower mass of till2 and at one place we found a piece of oak about four feet in length and about seven or eight inches in thickness4 ,this oak boulder was well polished and striated4 ,not far from this place is the famous ,crofthead inter-glacial bed1 so well known from the description given by ,mr4 ,james ,geikie and others that ,i need not here describe it4 ,i had the pleasure of visiting the section twice while it was well exposed1 once1 in company with ,mr4 ,james ,geikie1 and ,i do not entertain the shadow of a doubt as to its true inter-glacial character4 ,in the silt1 evidently the mud of an inter-glacial lake1 were found the upper portion of the skull of the great extinct ox 7,bos primigenius71 horns of the ,irish elk or deer1 and bones of the horse4 ,in the detailed list of the lesser organic remains found in the intercalated peat-bed by ,mr4 ,j4 ,a4 ,mahony1#aag are the following1 viz41 three species of ,desmidace1 thirty-one species of ,diatomace1 eleven species of mosses1 nine species of phanerogamous plants1 and several species of annelids1 crustacea1 and insects4 ,this list clearly shows that the inter-glacial period1 represented by these remains1 was not only mild and warm1 but of considerable duration4 ,mr4 ,david ,robertson found in the clay under the peat several species of ,ostracoda4 ,the well-known ,kilmaurs bed of peaty matter in which the remains of the mammoth and reindeer were found1 has now by the researches of the ,geological ,survey been proved to be of inter-glacial age4#aah ,in ,ireland1 as shown by ,professors ,hull and ,harkness1 the inter-glacial beds1 called by them the 8manure gravels10 contain numerous fragments of shells indicating a more genial climate than prevailed when the boulder clays lying above and below them were formed4#aai ,in ,sweden inter-glacial beds of freshwater origin1 containing plants1 have been met with by ,herr ,nathorst and also by ,herr ,holmstrm4#abj ,in ,north ,america ,mr4 ,whittlesey describes inter-glacial beds of blue clay enclosing pieces of wood1 intercalated with beds of hard pan 7till74 ,professor ,newberry found at ,germantown1 ,ohio1 an immense bed of peat1 from #ab to #bj feet in thickness1 underlying1 in some places #cj feet1 and in other places as much as #hj feet1 of till1 and overlying drift beds4 ,the uppermost layers of the peat contain undecomposed sphagnous mosses1 grasses1 and sedges1 but in the other portions of the bed abundant fragments of coniferous wood1 identified as red cedar 7,juniperus virginiana71 have been found4 ,ash1 hickory1 sycamore1 together with grape-vines and beech-leaves1 were also met with1 and with these the remains of the mastodon and great extinct beaver4#aba ,inter-glacial ,beds of ,england4--,scotland has been so much denuded by the ice sheet with which it was covered during the period of maximum glaciation that little can be learned in this part of the island regarding the early history of the glacial epoch4 ,but in ,england1 and more especially in the south-eastern portion of it1 matters are somewhat different4 ,we have1 in the ,norwich ,crag and ,chillesford beds1 a formation pretty well developed1 which is now generally regarded as lying at the base of the ,glacial ,series4 ,that this formation is of a glacial character is evident from the fact of its containing shells of a northern type1 such as ,leda lanceolata1 ,cardium ,gronlandicum1 ,lucina borealis1 ,cyprina ,islandica1 ,panopa ,norvegica1 and ,mya truncata4 ,but the glacial character of the formation is more strikingly brought out1 as ,sir ,charles ,lyell remarks1 by the predominance of such species as ,rhynchonella psittacea1 ,tellina calcarea1 ,astarte borealis1 ,scalaria ,gronlandica1 and ,fusus carinatus4 ,the 8,forest ,beds40--,immediately following this in the order of time comes the famous 8,forest ,bed0 of ,cromer4 ,this buried forest has been traced for more than forty miles along the coast from ,cromer to near ,kessengland1 and consists of stumps of trees standing erect1 attached to their roots1 penetrating the original soil in which they grew4 ,here and in the overlying fluvio-marine beds we have the first evidence of at least a temperate1 if not a warm1 inter-glacial period4 ,this is evident from the character of the flora and fauna belonging to these beds4 ,among the trees we have1 for example1 the ,scotch and spruce fir1 the yew1 the oak1 birch1 the alder1 and the common sloe4 ,there have also been found the white and yellow water-lilies1 the pond-weed1 and others4 ,amongst the mammalia have been met with the ,elephas meridionalis1 also found in the ,lower ,pliocene beds of the ,val d',arno1 near ,florence2 ,elephas antiquus1 ,hippopotamus major1 ,rhinoceros ,etruscus1 the two latter ,val d',arno species1 the roebuck1 the horse1 the stag1 the ,irish elk1 the ,cervus ,polignacus1 found also at ,mont ,perrier1 ,france1 ,c4 verticornis1 and ,c4 carnutorum1 the latter also found in ,pliocene strata of ,st4 ,prest1 ,france4 ,in the fluvio-marine series have been found the ,cyclas omnica and the ,paludina marginata1 a species of mollusc still found in the ,south of ,france1 but no longer inhabiting the ,british ,isles4 ,above the forest bed and fluvio-marine series comes the well-known unstratified ,norwich boulder till1 containing immense blocks #f or #h feet in diameter1 many of which must have come from ,scandinavia1 and above the unstratified till are a series of contorted beds of sand and gravel4 ,this series may be considered to represent a period of intense glaciation4 ,above this again comes the middle drift of ,mr4 ,searles ,wood1 junior1 yielding shells which indicate1 as is now generally admitted1 a comparatively mild condition of climate4 ,upon this middle drift lies the upper boulder clay1 which is well developed in ,south ,norfolk and ,suffolk1 and which is of unmistakable glacial origin4 ,newer than all these are the ,mundesley freshwater beds1 which lie in a hollow denuded out of the foregoing series4 ,in this formation a black peaty deposit containing seeds of plants1 insects1 shells1 and scales and bones of fishes1 has been found1 all indicating a mild and temperate condition of climate4 ,among the shells there is1 as in the forest bed1 the ,paludina marginata4 ,and that an arctic condition of things in ,england followed is believed by ,mr4 ,fisher and others1 on the evidence of the 8,trail0 described by the former observer4 ,cave and ,river ,deposits4--,evidence of the existence of warm periods during the glacial epoch is derived from a class of facts which have long been regarded by geologists as very puzzling1 namely1 the occurrence of mollusca and mammalia of a southern type associated in ,england and on the continent with those of an extremely arctic character4 ,for example1 ,cyrena fluminalis is a shell which does not live at present in any ,european river1 but inhabits the ,nile and parts of ,asia1 especially ,cashmere4 ,unio littoralis1 extinct in ,britain1 is still abundant in the ,loire2 ,paludina marginata does not exist in this country4 ,these shells of a southern type have been found in post-tertiary deposits at ,gray's ,thurrock1 in ,essex2 in the valley of the ,ouse1 near ,bedford2 and at ,hoxne1 in ,suffolk1 associated with a ,hippopotamus closely allied to that now inhabiting the ,nile1 and ,elephas antiquus1 an animal remarkable for its southern range4 ,amongst other forms of a southern type which have been met with in the cave and river deposits1 are the spotted hyna from ,africa1 an animal1 says ,mr4 ,dawkins1 identical1 except in size1 with the cave hyna1 the ,african elephant 7,e4 ,africanus71 and the ,elephas meridionalis1 the great beaver 7,trogontherium71 the cave hyna 7,hyna spela71 the cave lion 7,felis leo1 var4 spela71 the lynx 7,felis lynx71 the sabre-toothed tiger 7,machairodus latidens71 the rhinoceros 7,rhinoceros megarhinus and ,r4 leptorhinus74 ,but the most extraordinary thing is that along with these1 associated in the same beds1 have been found the remains of such animals of an arctic type as the glutton 7,gulo luscus71 the ermine 7,mustela erminea71 the reindeer 7,cervus tarandus71 the musk-ox or musk-sheep 7,ovibos moschatus71 the aurochs 7,bison priscus71 the woolly rhinoceros 7,rhinoceros tichorhinus71 the mammoth 7,elephas primigenius71 and others of a like character4 ,according to ,mr4 ,boyd ,dawkins1 these southern animals extended as far north as ,yorkshire in ,england1 and the northern animals as far south as the latitude of the ,alps and ,pyrenees4#abb ,the ,explanation of the ,difficulty4--,as an explanation of these puzzling phenomena1 ,i suggested1 in the ,philosophical ,magazine for ,november1 #ahfh1 that these southern animals lived in our island during the warm periods of the glacial epoch1 while the northern animals lived during the cold periods4 ,this view ,i am happy to find has lately been supported by ,sir ,john ,lubbock2 further1 ,mr4 ,james ,geikie1 in his 8,great ,ice ,age10 and also in the ,geological ,magazine1 has entered so fully into the subject and brought forward such a body of evidence in support of it1 that1 in all probability1 it will1 ere long1 be generally accepted4 ,the only objection which has been advanced1 so far as ,i am aware1 deserving of serious consideration1 is that by ,mr4 ,boyd ,dawkins1 who holds that if these migrations had been secular instead of seasonal1 as is supposed by ,sir ,charles ,lyell and himself1 the arctic and southern animals would now be found in separate deposits4 ,it is perfectly true that if there had been only one cold and one warm period1 each of geologically immense duration1 the remains might1 of course1 be expected to have been found in separate beds2 but when we consider that the glacial epoch consisted of a long succession of alternate cold and warm periods1 of not more than ten or twelve thousand years each1 we can hardly expect that in the river deposits belonging to this long cycle we should be able to distinguish the deposits of the cold periods from those of the warm4 ,shell ,beds4--,evidence of warm inter-glacial periods may be justly inferred from the presence of shells of a southern type which have been found in glacial beds1 of which some illustrations follow4 ,in the southern parts of ,norway1 from the present sea-level up to #ejj feet1 are found glacial shell beds1 similar to those of ,scotland4 ,in these beds ,trochus magus1 ,tapes decussata1 and ,pholas candida have been found1 shells which are distributed between the ,mediterranean and the shores of ,england1 but no longer live round the coasts of ,norway4 ,at ,capellbacken1 near ,udevalla1 in ,sweden1 there is an extensive bed of shells #bj to #cj feet in thickness4 ,this formation has been described by ,mr4 ,gwyn ,jeffreys4#abc ,it consists of several distinct layers1 apparently representing many epochs and conditions4 ,its shells are of a highly arctic character1 and several of the species have not been found living south of the arctic circle4 ,but the remarkable circumstance is that it contains ,cypra lurida1 a ,mediterranean shell1 which ,mr4 ,jeffreys1 after some hesitation1 believed to belong to the bed4 ,again1 at ,lilleherstehagen1 a short distance from ,capellbacken1 another extensive deposit is exposed4 8,here the upper layer10 says ,mr4 ,jeffreys1 8gives a singular result4 ,mixed with the universal ,trophon clathratus 7which is a high northern species1 and found living only within the arctic circle7 are many shells of a southern type1 such are ,ostrea edulis1 ,tapes pullastra1 ,corbula gibba1 and ,aporrhais pes-pelicani40 ,at ,kempsey1 near ,worcester1 a shell bed is described by ,sir ,r4 ,murchison in his 8,silurian ,system0 7p4 #ecc71 in which ,bulla ampulla and a species of ,oliva1 shells of a southern type1 have been found4 ,a case somewhat similar to the above is recorded by the ,rev4 ,mr4 ,crosskey as having been met with in ,scotland at the ,kyles of ,bute4 8,among the ,clyde beds1 ,i have found10 he says1 8a layer containing shells1 in which those of a more southern type appear to exist in greater profusion and perfection than even in our present seas4 ,it is an open question10 he continues1 8whether our climate was not slightly warmer than it is now between the glacial epoch and the present day40#abd ,in a glacial bed near ,greenock1 ,mr4 ,a4 ,bell found the fry of living ,mediterranean forms1 viz41 ,conus ,mediterraneus and ,cardita trapezia4 ,although deposits containing shells of a temperate or of a southern type in glacial beds have not been often recorded1 it by no means follows that such deposits are actually of rare occurrence4 ,that glacial beds should contain deposits indicating a temperate or a warm condition of climate is a thing so contrary to all preconceived opinions regarding the sequence of events during the glacial epoch1 that most geologists1 were they to meet with a shell of a southern type in one of those beds1 would instantly come to the conclusion that its occurrence there was purely accidental1 and would pay no special attention to the matter4 ,evidence derived from 8,borings40--,with the view of ascertaining if additional light would be cast on the sequence of events1 during the formation of the boulder clay1 by an examination of the journals of bores made through a great depth of surface deposits1 ,i collected1 during the summer of #ahfg1 about two hundred and fifty such records1 put down in all parts of the mining districts of ,scotland4 ,an examination of these bores shows most conclusively that the opinion that the boulder clay1 or lower till1 is one great undivided formation1 is wholly erroneous4 ,these two hundred and fifty bores represent a total thickness of #ba1cdh feet1 giving #hf feet as the mean thickness of the deposits passed through4 ,twenty of these have one boulder clay1 with beds of stratified sand or gravel beneath the clay2 twenty-five have two boulder clays1 with stratified beds of sand and gravel between2 ten have three boulder clays2 one has four boulder clays2 two have five boulder clays2 and no one has fewer than six separate masses of boulder clay1 with stratified beds of sand and gravel between2 sixteen have two or three separate boulder clays1 differing altogether in colour and hardness1 without any stratified beds between4 ,we have1 therefore1 out of two hundred and fifty bores1 seventy-five of them representing a condition of things wholly different from that exhibited to the geologist in ordinary sections4 ,the full details of the character of the deposits passed through by these bores1 and their bearing on the history of the glacial epoch1 have been given by ,mr4 ,james ,bennie1 in an interesting paper read before the ,glasgow ,geological ,society1#abe to which ,i would refer all those interested in the subject of surface geology4 ,the evidence afforded by these bores of the existence of warm inter-glacial periods will1 however1 fall to be considered in a subsequent chapter4#abf ,another important and unexpected result obtained from these bores to which we shall have occasion to refer1 was the evidence which they afforded of a ,continental ,period4 ,striated ,pavements4--,it has been sometimes observed that in horizontal sections of the boulder clay1 the stones and boulders are all striated in one uniform direction1 and this has been effected over the original markings on the boulders4 ,it has been inferred from this that a pause of long duration must have taken place in the formation of the boulder clay1 during which the ice disappeared and the clay became hardened into a solid mass4 ,after which the old condition of things returned1 glaciers again appeared1 passed over the surface of the hardened clay with its imbedded boulders1 and ground it down in the same way as they had formerly done the solid rocks underneath the clay4 ,an instance of striated pavements in the boulder clay was observed by ,mr4 ,robert ,chambers in a cliff between ,portobello and ,fisherrow4 ,at several places a narrow train of blocks was observed crossing the line of the beach1 somewhat like a quay or mole1 but not more than a foot above the general level4 ,all the blocks had flat sides uppermost1 and all the flat sides were striated in the same direction as that of the rocky surface throughout the country4 ,a similar instance was also observed between ,leith and ,portobello4 8,there is1 in short10 says ,mr4 ,chambers1 8a surface of the boulder clay1 deep down in the entire bed1 which1 to appearance1 has been in precisely the same circumstances as the fast rock surface below had previously been4 ,it has had in its turn to sustain the weight and abrading force of the glacial agent1 in whatever form it was applied2 and the additional deposits of the boulder clay left over this surface may be presumed to have been formed by the agent on that occasion40#abg ,several cases of a similar character were observed by ,mr4 ,james ,smith1 of ,jordanhill1 on the beach at ,row1 and on the shore of the ,gareloch4#abh ,between ,dunbar and ,cockburnspath1 ,professor ,geikie found along the beach1 for a space of #cj or #dj square yards1 numbers of large blocks of limestone with flattened upper sides1 imbedded in a stiff red clay1 and all striated in one direction4 ,on the shores of the ,solway he found another example4#abi ,the cases of striated pavements recorded are1 however1 not very numerous4 ,but this by no means shows that they are of rare occurrence in the boulder clay4 ,these pavements1 of course1 are to be found only in the interior of the mass1 and even there they can only be seen along a horizontal section4 ,but sections of this kind are rarely to be met with1 for river channels1 quarries1 railway cuttings1 and other excavations of a similar character which usually lay open the boulder clay1 exhibit vertical sections only4 ,it is therefore only along the sea-shore1 as ,professor ,geikie remarks1 where the surface of the clay has been worn away by the action of the waves1 that opportunities have hitherto been presented to the geologist for observing them4 ,there can be little doubt that during the warm periods of the glacial epoch our island would be clothed with a luxuriant flora4 ,at the end of a cold period1 when the ice had disappeared1 the whole face of the country would be covered over to a considerable depth with a confused mass of stones and boulder clay4 ,a surface thus wholly destitute of every seed and germ would probably remain for years without vegetation4 ,but through course of time life would begin to appear1 and during the thousands of years of perpetual summer which would follow1 the soil1 uncongenial as it no doubt must have been1 would be forced to sustain a luxuriant vegetation4 ,but although this was the case1 we need not wonder that now scarcely a single vestige of it remains2 for when the ice sheet again crept over the island everything animate and inanimate would be ground down to powder4 ,we are certain that prior to the glacial epoch our island must have been covered with life and vegetation4 ,but not a single vestige of these are now to be found2 no1 not even of the very soil on which the vegetation grew4 ,the solid rock itself upon which the soil lay has been ground down to mud by the ice sheet1 and1 to a large extent1 as ,professor ,geikie remarks1 swept away into the adjoining seas4#acj ,it is now even more difficult to find a trace of the ancient soil under the boulder clay than it is to find remains of the soil of the warm periods in that clay4 ,as regards ,scotland1 cases of old land surfaces under the boulder clay are as seldom recorded as cases of old land surfaces in it4 ,in so far as geology is concerned1 there is as much evidence to show that our island was clothed with vegetation during the glacial epoch as there is that it was so clothed prior to that epoch4 ,,chapter ,,xvi4 ,,warm ,,inter-,,glacial ,,periods ,,in ,,arctic ,,regions4 ,cold ,periods best marked in ,temperate1 and ,warm ,periods in ,arctic1 ,regions4--,state of ,arctic ,regions during ,glacial ,period4--,effects of ,removal of ,ice from ,arctic ,regions4--,ocean-,currents2 ,influence on ,arctic ,climate4--,reason why ,remains of ,inter-glacial ,period are rare in ,arctic ,regions4--,remains of ,ancient ,forests in ,banks's ,land1 ,prince ,patrick's ,island1 c4--,opinions of ,sir ,r4 ,murchison1 ,captain ,osborn1 and ,professor ,haughton4--,tree dug up by ,sir ,e4 ,belcher in lat4 #ge ,n4 ,in the temperate regions the cold periods of the glacial epoch would be far more marked than the warm inter-glacial periods4 ,the condition of things which prevailed during the cold periods would differ far more widely from that which now prevails than would the condition of things during the warm periods4 ,but as regards the polar regions the reverse would be the case2 there the warm inter-glacial periods would be far more marked than the cold periods4 ,the condition of things prevailing in those regions during the warm periods would be in strongest contrast to what now obtains1 but this would not hold true in reference to the cold periods2 for during the latter1 matters there would be pretty much the same as at present1 only a good deal more severe4 ,the reason of this may be seen from what has already been stated in ,chapter ,,iv42 but as it is a point of considerable importance in order to a proper understanding of the physical state of things prevailing in polar regions during the glacial epoch1 ,i shall consider this part of the subject more fully4 ,during the cold periods1 our island1 and nearly all places in the northern temperate regions down to about the same latitude1 would be covered with snow and ice1 and all animal and vegetable life within the glaciated area would to a great extent be destroyed4 ,the presence of the ice would of itself1 for reasons already explained1 lower the mean annual temperature to near the freezing-point4 ,the summers1 notwithstanding the proximity of the sun1 would not be warm1 on the contrary their temperature would rise little above the freezing-point4 ,an excess of evaporation would no doubt take place1 owing to the increase in the intensity of the sun's rays1 but this result would only tend to increase the snowfall4#aca ,during the warm periods our country and the regions under consideration would experience conditions not differing much from those of the present1 but the climate would probably be somewhat warmer and more equable4 ,the proximity of the sun during winter would prevent snow from falling4 ,the summers1 owing to the greater distance of the sun1 would probably be somewhat colder than they are now4 ,but the loss of heat during summer would be to a large extent compensated for by two causes to which we must here refer4 7#a47 ,the much greater amount of heat conveyed by ocean-currents than at present4 7#b47 ,our summers are now cooled to a considerable extent by cold arial currents from the ice-covered regions of the north4 ,but during the period in question there would be little or no ice in arctic regions1 consequently the winds would be comparatively warm1 whatever direction they came from4 ,let us next direct our attention to the state of things in the arctic regions during the glacial epoch4 ,at present ,greenland and other parts of the arctic regions occupied by land are almost wholly covered with ice1 and as a consequence nearly destitute of vegetable life4 ,during the cold periods of the glacial epoch the quantity of snow falling would doubtless be greater and the ice thicker1 but as regards organic life1 matters would not probably be much worse than they are at present4 ,in fact1 so far as ,greenland and the antarctic continent are concerned1 they are about as destitute of plant life as they can be4 ,although an increase in the thickness of the arctic ice would not greatly alter the present state of matters in those regions1 yet what a transformation would ensue upon the disappearance of the ice6 ,this would not only raise the summer temperature some twenty degrees or so1 but would afford the necessary conditions for the existence of abundant animal and plant life4 ,the severity of the climate of ,greenland is due to a very considerable extent1 as we have already seen1 to the presence of ice4 ,get rid of the permanent ice1 and the temperature of the country1 cteris paribus1 would instantly rise4 ,that ,greenland should ever have enjoyed a temperate climate1 capable of supporting abundant vegetation1 has often been matter of astonishment1 but this wonder diminishes when we reflect that during the warm periods it would be in the arctic regions that the greatest heating effect would take place1 this being due mainly to the transference of nearly all the warm inter-tropical waters to one hemisphere4 ,it has been shown in ,chapter ,,ii4 that the heating effects at present resulting from the transference of heat by ocean-currents increase as we approach the poles4 ,as a consequence of this it follows that during the warm periods1 when the quantity of warm water transferred would be nearly doubled1 the increase of heat resulting from this cause would itself increase as the warm pole was approached4 ,this effect1 combined with the shortness of the winter in perihelion and the nearness of the sun during that season1 would prevent the accumulation of snow4 ,during summer1 the sun1 it is true1 would be at a much greater distance from the earth than at present1 but it must be borne in mind that for a period of three months the quantity of heat received from the sun at the north pole would be greater than that received at the equator4 ,consequently1 after the winter's snow was melted1 this great amount of heat would go to raise the temperature1 and the arctic summer could not be otherwise than hot4 ,it is not hot at present1 but this1 be it observed1 is because of the presence of the ice4 ,when we take all these facts into consideration we need not be surprised that ,greenland once enjoyed a condition of climate totally different from that which now obtains in that region4 ,it is1 therefore1 in the arctic and antarctic regions where we ought to find the most marked and decided evidence of warm inter-glacial periods4 ,and doubtless such evidence would be abundantly forthcoming had these regions not been subjected to such intense denudation since the glacial epoch1 and were so large a portion of the land not still buried beneath an icy covering1 and therefore beyond the geologist's reach4 ,only on islands and such outlying places as are not shrouded in snow and ice can we hope to meet with any trace of the warm periods of the glacial epoch3 and we may now proceed to consider what relics of these warm periods have actually been discovered in arctic regions4 ,evidence of ,warm ,periods in ,arctic ,regions4--,the fact that stumps1 c41 of full-grown trees have been found in places where at present nothing is to be met with but fields of snow and ice1 and where the mean annual temperature scarcely rises above the zero of the ,fahrenheit thermometer1 is good evidence to show that the climate of the arctic regions was once much warmer than now4 ,the remains of an ancient forest were discovered by ,captain ,mc,clure1 in ,banks's ,land1 in latitude #gd #dh4 ,he found a great accumulation of trees1 from the sea-level to an elevation of upwards of #cjj feet4 8,i entered a ravine10 says ,captain ,mc,clure1 8some miles inland1 and found the north side of it1 for a depth of #dj feet from the surface1 composed of one mass of wood similar to what ,i had before seen40#acb ,in the ravine he observed a tree protruding about #h feet1 and #c feet in circumference4 ,and he further states that1 8,from the perfect state of the bark1 and the position of the trees so far from the sea1 there can be but little doubt that they grew originally in the country40 ,a cone of one of these fir-trees was brought home1 and was found to belong apparently to the genus ,abies1 resembling ,a4 7,pinus7 alba4 ,in ,prince ,patrick's ,island1 in latitude #gf #ab ,n41 longitude #abb ,w41 near the head of ,walker ,inlet1 and a considerable distance in the interior in one of the ravines1 a tree protruding about #aj feet from a bank was discovered by ,lieutenant ,mecham4 ,it proved to be #d feet in circumference4 ,in its neighbourhood several others were seen1 all of them similar to some he had found at ,cape ,manning2 each of them measured #d feet round and #cj feet in length4 ,the carpenter stated that the trees resembled larch4 ,lieutenant ,mecham1 from their appearance and position1 concluded that they must have grown in the country4#acc ,trees under similar conditions were also found by ,lieutenant ,pim on ,prince ,patrick's ,island1 and by ,captain ,parry on ,melville ,island1 all considerably above the present sea-level and at a distance from the shore4 ,on the coast of ,new ,siberia1 ,lieutenant ,anjou found a cliff of clay containing stems of trees still capable of being used for fuel4 8,this remarkable phenomenon10 says ,captain ,osborn1 8opens a vast field for conjecture1 and the imagination becomes bewildered in trying to realise that period of the world's history when the absence of ice and a milder climate allowed forest trees to grow in a region where now the ground-willow and dwarf-birch have to struggle for existence40 ,sir ,roderick ,murchison came to the conclusion that all those trees were drifted to their present position when the islands of the arctic archipelago were submerged4 ,but it was the difficulty of accounting for the growth of trees in such a region which led him to adopt this hypothesis4 ,his argument is this3 8,if we imagine10 he says1 8that the timber found in those latitudes grew on the spot we should be driven to adopt the anomalous hypothesis that1 notwithstanding physical relations of land and water similar to those which now prevail1 trees of large size grew on such terra firma within a few degrees of the north pole6--a supposition which ,i consider to be wholly incompatible with the data in our possession1 and at variance with the laws of the isothermal lines40#acd ,this reasoning of ,sir ,roderick's may be quite correct1 on the supposition that changes of climate are due to changes in the distribution of sea and land1 as advocated by ,sir ,charles ,lyell4 ,but these difficulties disappear if we adopt the views advocated in the foregoing chapters4 ,as ,captain ,osborn has pointed out1 however1 ,sir ,roderick's hypothesis leaves the real difficulty untouched4 8,a very different climate10 he says1 8must then have existed in those regions to allow driftwood so perfect as to retain its bark to reach such great distances2 and perhaps it may be argued that if that sea was sufficiently clear of ice to allow such timber to drift unscathed to ,prince ,patrick's ,land1 that that very absence of a frozen sea would allow fir-trees to grow in a soil naturally fertile40#ace ,as has been already stated1 all who have seen those trees in arctic regions agree in thinking that they grew in situ4 ,and ,professor ,haughton1 in his excellent account of the arctic archipelago appended to ,mc,clintock's 8,narrative of ,arctic ,discoveries10 after a careful examination of the entire evidence on the subject1 is distinctly of the same opinion2 while the recent researches of ,professor ,heer put it beyond doubt that the drift theory must be abandoned4 ,undoubtedly the arctic archipelago was submerged to an extent that could have admitted of those trees being floated to their present positions4 ,this1 as we shall see1 follows from theory2 but submergence1 without a warmer condition of climate1 would not enable trees to reach those regions with their bark entire4 ,but in reality we are not left to theorise on the subject1 for we have a well-authenticated case of one of those trees being got by ,captain ,belcher standing erect in the position in which it grew4 ,it was found immediately to the northward of the narrow strait opening into ,wellington ,sound1 in lat4 #ge #cb ,n4 long4 #ib ,w41 and about a mile and a half inland4 ,the tree was dug up out of the frozen ground1 and along with it a portion of the soil which was immediately in contact with the roots4 ,the whole was packed in canvas and brought to ,england4 ,near to the spot several knolls of peat mosses about nine inches in depth were found1 containing the bones of the lemming in great numbers4 ,the tree in question was examined by ,sir ,william ,hooker1 who gave the following report concerning it1 which bears out strongly the fact of its having grown in situ4 8,the piece of wood brought by ,sir ,edward ,belcher from the shores of ,wellington ,channel belongs to a species of pine1 probably to the ,pinus 7,abies7 alba1 the most northern conifer4 ,the structure of the wood of the specimen brought home differs remarkably in its anatomical character from that of any other conifer with which ,i am acquainted4 ,each concentric ring 7or annual growth7 consists of two zones of tissue2 one1 the outer1 that towards the circumference1 is broader1 of a pale colour1 and consists of ordinary tubes of fibres of wood1 marked with discs common to all conifer4 ,these discs are usually opposite one another when more than one row of them occur in the direction of the length of the fibre2 and1 what is very unusual1 present radiating lines from the central depression to the circumference4 ,secondly1 the inner zone of each annual ring of wood is narrower1 of a dark colour1 and formed of more slender woody fibres1 with thicker walls in proportion to their diameter4 ,these tubes have few or no discs upon them1 but are covered with spiral stri1 giving the appearance of each tube being formed of a twisted band4 ,the above characters prevail in all parts of the wood1 but are slightly modified in different rings4 ,thus the outer zone is broader in some than in others1 the disc-bearing fibres of the outer zone are sometimes faintly marked with spiral stri1 and the spirally marked fibres of the inner zone sometimes bear discs4 ,these appearances suggest the annual recurrence of some special cause that shall thus modify the first and last formed fibres of each year's deposit1 so that that first formed may differ in amount as well as in kind from that last formed2 and the peculiar conditions of an arctic climate appear to afford an adequate solution4 ,the inner1 or first-formed zone1 must be regarded as imperfectly developed1 being deposited at a season when the functions of the plant are very intermittently exercised1 and when a few short hours of sunshine are daily succeeded by many of extreme cold4 ,as the season advances the sun's heat and light are continuous during the greater part of the twenty-four hours1 and the newly formed wood fibres are hence more perfectly developed1 they are much longer1 present no signs of stri1 but are studded with discs of a more highly organized structure than are usual in the natural order to which this tree belongs40#acf ,another circumstance which shows that the tree had grown where it was found is the fact that in digging up the roots portions of the leaves were obtained4 ,it may also be mentioned that near this place was found an old river channel cut deeply into the rock1 which1 at some remote period1 when the climate must have been less rigorous than at present1 had been occupied by a river of considerable size4 ,now1 it is evident that if a tree could have grown at ,wellington ,sound1 there is no reason why one might not have grown at ,banks's ,land1 or at ,prince ,patrick's ,island4 ,and1 if the climatic condition of the country would allow one tree to grow1 it would equally as well allow a hundred1 a thousand1 or a whole forest4 ,if this1 then1 be the case1 ,sir ,roderick's objection to the theory of growth in situ falls to the ground4 ,another circumstance which favours the idea that those trees grew during the glacial epoch is the fact that although they are recent1 geologically speaking1 and belong to the drift series1 yet they are1 historically speaking1 very old4 ,the wood1 though not fossilized1 is so hardened and changed by age that it will scarcely burn4 ,,chapter ,,xvii4 ,,former ,,glacial ,,epochs4--,,reason ,,of ,,the ,,imperfection ,,of ,,geological ,,records ,,in ,,reference ,,to ,,them4 ,two ,reasons why so little is known of ,glacial ,epochs4--,evidence of ,glaciation to be found on ,land-surfaces4--,where are all our ancient ,land-surfaces8--,the stratified ,rocks consist of a ,series of old ,sea-bottoms4--,transformation of a ,land-surface into a ,sea-bottom obliterates all ,traces of ,glaciation4--,why so little remains of the ,boulder ,clays of former ,glacial ,epochs4--,records of the ,glacial ,epoch are fast disappearing4--,icebergs do not striate the ,sea-bottom4--,mr4 ,campbell's ,observations on the ,coast of ,labrador4--,amount of ,material transported by ,icebergs much exaggerated4--,mr4 ,packard on the ,glacial ,phenomena of ,labrador4--,boulder ,clay the ,product of ,land-ice4--,palontological ,evidence4--,paucity of ,life characteristic of a ,glacial ,period4--,warm ,periods better represented by ,organic ,remains than cold4--,why the ,climate of the ,tertiary ,period was supposed to be warmer than the present4--,mr4 ,james ,geikie on the ,defects of ,palontological ,evidence4--,conclusion4 ,two ,reasons why so little is known of former ,glacial ,epochs4--,if the glacial epoch resulted from the causes discussed in the foregoing chapters1 then such epochs must have frequently supervened4 ,we may1 therefore1 now proceed to consider what evidence there is for the former occurrence of excessive conditions of climate during previous geological ages4 ,when we begin our inquiry1 however1 we soon find that the facts which have been recorded as evidence in favour of the action of ice in former geological epochs are very scanty indeed4 ,two obvious reasons for this may be given1 namely1 7#a7 ,the imperfection of the geological records themselves1 and 7#b7 the little attention hitherto paid toward researches of this kind4 ,the notion1 once so prevalent1 that the climate of our earth was much warmer in the earlier geological ages than it is now1 and that it has ever since been gradually becoming cooler1 was wholly at variance with the idea of former ice-periods4 ,and this conviction of the priori improbability of cold periods having obtained during ,palozoic and ,mesozoic ages tended to prevent due attention being paid to such facts as seemed to bear upon the subject4 ,but our limited knowledge of former glacial epochs must no doubt be attributed chiefly to the actual imperfection of the geological records4 ,so great is this imperfection that the mere absence of direct geological evidence cannot reasonably be regarded as sufficient proof that the conclusions derived from astronomical and physical considerations regarding former ice-periods are improbable4 ,nor is this all4 ,the geological records of ancient glacial conditions are not only imperfect1 but1 as ,i shall endeavour to show1 this imperfection follows as a natural consequence from the principles of geology itself4 ,there are not merely so many blanks or gaps in the records1 but a reason exists in the very nature of geological evidence why such breaks in the record might reasonably be expected to occur4 ,evidence of ,glaciation to be found chiefly on ,land-surfaces4--,it is on a land-surface that the principal traces of the action of ice during a glacial epoch are left1 for it is there that the stones are chiefly striated1 the rocks ground down1 and the boulder clay formed4 ,but where are all our ancient land-surfaces8 ,they are not to be found4 ,the total thickness of the stratified rocks of ,great ,britain is1 according to ,professor ,ramsay1 nearly fourteen miles4 ,but from the top to the bottom of this enormous pile of deposits there is hardly a single land-surface to be detected4 ,true patches of old land-surfaces of a local character exist1 such1 for example1 as the dirt-beds of ,portland2 but1 with the exception of coal-seams1 every general formation from top to bottom has been accumulated under water1 and none but the under-clays ever existed as a land-surface4 ,and it is here1 in such a formation1 that the geologist has to collect all his information regarding the existence of former glacial epochs4 ,the entire stratified rocks of the globe1 with the exception of the coal-beds and under-clays 7in neither of which would one expect to find traces of ice-action71 consist almost entirely of a series of old sea-bottoms1 with here and there an occasional freshwater deposit4 ,bearing this in mind1 what is the sort of evidence which we can now hope to find in these old sea-bottoms of the existence of former ice-periods8 ,every geologist of course admits that the stratified rocks are not old land-surfaces1 but a series of old sea-bottoms formed out of the accumulated material derived from the degradation of primeval land-surfaces4 ,and it is true that all land-surfaces once existed as sea-bottoms2 but the stratified rocks consist of a series of old sea-bottoms which never were land-surfaces4 ,many of them no doubt have been repeatedly above the sea-level1 and may once have possessed land-surfaces2 but these1 with the exception of the under-clays of the various coal measures1 the dirt-beds of ,portland1 and one or two more patches1 have all been denuded away4 ,the important bearing which this consideration has on the nature of the evidence which we can now expect to find of the existence of former glacial epochs has certainly been very much overlooked4 ,if we examine the matter fully we shall be led to conclude that the transformation of a land-surface into a sea-bottom will probably completely obliterate every trace of glaciation which that land-surface may once have presented4 ,we cannot1 for example1 expect to meet with polished and striated stones belonging to a former land glaciation2 for such stones are not carried down bodily and unchanged by our rivers and deposited in the sea4 ,they become broken up by subarial agencies into gravel1 sand1 and clay1 and in this condition are transported seawards4 ,nor even if we supposed it possible that the stones and boulders derived from a mass of till could be carried down to sea by river-action1 could we at the same time fail to admit that such stones would be deprived of all their ice-markings1 and become water-worn and rounded on the way4#acg ,nor can we expect to find boulder clay among the stratified rocks1 for boulder clay is not carried down as such and deposited in the sea1 but under the influence of the denuding agents becomes broken up into soft mud1 clay1 sand1 and gravel1 as it is gradually peeled off the land and swept seawards4 ,patches of boulder clay may have been now and again forced into the sea by ice and eventually become covered up2 but such cases are wholly exceptional1 and their absence in any formation cannot fairly be adduced as a proof that that formation does not belong to a glacial period4 ,the only evidence of the existence of land-ice during former periods which we can reasonably expect to meet with in the stratified rocks1 consists of erratic blocks which may have been transported by icebergs and dropped into the sea4 ,but unless the glaciers of such epochs reached the sea1 we could not possibly possess even this evidence4 ,traces in the stratified rocks of the effects of land-ice during former epochs must1 in the very nature of things1 be rare indeed4 ,the only sort of evidence which1 as a general rule1 we may expect to detect1 is the presence of large erratic blocks imbedded in strata which from their constitution have evidently been formed in still water4 ,but this is quite enough2 for it proves the existence of ice at the time the strata were being deposited as conclusively as though we saw the ice floating with the blocks upon it4 ,this sort of evidence1 when found in low latitudes1 ought to be received as conclusive of the existence of former glacial epochs2 and1 no doubt1 would have been so received had it not been for the idea that1 if these blocks had been transported by ice1 there ought in addition to have been found striated stones1 boulder clay1 and other indications of the agency of land-ice4 ,of course all erratics are not necessarily transported by masses of ice broken from the terminal front of glaciers4 ,the 8ice foot10 formed by the freezing of the sea along the coasts of the higher latitudes of ,greenland1 carries seawards immense quantities of blocks and dbris4 ,and again stones and boulders are frequently frozen into river-ice1 and when the ice breaks up in spring are swept out to sea1 and may be carried some little distance before they are dropped4 ,but both these cases can occur only in regions where the winters are excessive2 nor is it at all likely that such ice-rafts will succeed in making a long voyage4 ,if1 therefore1 we could assure ourselves that the erratics occasionally met with in certain old geological formations in low latitudes were really transported from the land by an ice-foot or a raft of river-ice1 we should be forced to conclude that very severe climatic conditions must have obtained in such latitudes at the time the erratics were dispersed4 ,the reason why we now have1 comparatively speaking1 so little direct evidence of the existence of former glacial periods will be more forcibly impressed upon the mind1 if we reflect on how difficult it would be in a million or so of years hence to find any trace of what we now call the glacial epoch4 ,the striated stones would by that time be all1 or nearly all1 disintegrated1 and the till washed away and deposited in the bottom of the sea as stratified sands and clays4 ,and when these became consolidated into rock and were raised into dry land1 the only evidence that we should probably then have that there ever had been a glacial epoch would be the presence of large blocks of the older rocks1 which would be found imbedded in the upraised formation4 ,we could only infer that there had been ice at work from the fact that by no other known agency could we conceive such blocks to have been transported and dropped in a still sea4 ,probably few geologists believe that during the ,middle ,eocene and the ,upper ,miocene periods our country passed through a condition of glaciation as severe as it has done during the ,post-pliocene period2 yet when we examine the subject carefully1 we find that there is actually no just ground to conclude that it has not4 ,for1 in all probability1 throughout the strata to be eventually formed out of the destruction of the now existing land-surfaces1 evidence of ice-action will be as scarce as in ,eocene or ,miocene strata4 ,if the stratified rocks forming the earth's crust consisted of a series of old land-surfaces instead 7as they actually do7 of a series of old sea-bottoms1 then probably traces of many glacial periods might be detected4 ,nearly all the evidence which we have regarding the glacial epoch has been derived from what we find on the now existing land-surfaces of the globe4 ,but probably not a vestige of this will exist in the stratified beds of future ages1 formed out of the destruction of the present land-surfaces4 ,even the very arctic shell-beds themselves1 which have afforded to the geologist such clear proofs of a frozen sea during the glacial epoch1 will not be found in those stratified rocks2 for they must suffer destruction along with everything else which now exists above the sea-level4 ,there is probably not a single relic of the glacial epoch which has ever been seen by the eye of man that will be treasured up in the stratified rocks of future ages4 ,nothing that does not lie buried in the deeper recesses of the ocean will escape complete disintegration and appear imbedded in those formations4 ,it is only those objects which lie in our existing sea-bottoms that will remain as monuments of the glacial epoch of the ,post-tertiary period4 ,and1 moreover1 it will only be those portions of the sea-bottoms that may happen to be upraised into dry land that will be available to the geologist of future ages4 ,the point to be determined now is this3--,is it probable that the geologist of the future will find in the rocks formed out of the now existing sea-bottoms more evidence of a glacial epoch during ,post-tertiary times than we now do of one during1 say1 the ,miocene1 the ,eocene1 or the ,permian period8 ,unless this can be proved to be the case1 we have no ground whatever to conclude that the cold periods of the ,miocene1 ,eocene1 and ,permian periods were not as severe as that of the glacial epoch4 ,this is evident1 for the only relics which now remain of the glacial epochs of those periods are simply what happened to be protected in the then existing sea-bottoms4 ,every vestige that lay on the land would in all probability be destroyed by subarial agency and carried into the sea in a sedimentary form4 ,but before we can determine whether or not there is more evidence of the glacial epoch in our now existing sea-bottoms than there is of former glacial epochs in the stratified rocks 7which are in reality the sea-bottoms belonging to ancient epochs71 we must first ascertain what is the nature of those marks of glaciation which are to be found in a sea-bottom4 ,icebergs do not striate the ,sea-bottom4--,we know that the rocky face of the country was ground down and striated during the glacial epoch2 and this is now generally believed to have been done by land-ice4 ,but we have no direct evidence that the floor of the ocean1 beyond where it may have been covered with land-ice1 was striated4 ,beyond the limits of the land-ice it could be striated only by means of icebergs4 ,but do icebergs striate the rocky bed of the ocean8 ,are they adapted for such work8 ,it seems to be often assumed that they are4 ,but ,i have been totally unable to find any rational grounds for such a belief4 ,clean ice can have but little or no erosive power1 and never could scratch a rock4 ,to do this it must have grinding materials in the form of sand1 mud1 or stones4 ,but the bottoms of icebergs are devoid of all such materials4 ,icebergs carry the grinding materials on their backs1 not on their bottoms4 ,no doubt1 when the iceberg is launched into the deep1 great masses of sand1 mud1 and stones will be adhering to its bottom4 ,but no sooner is the berg immersed1 than a melting process commences at its sides and lower surface in contact with the water2 and the consequence is1 the materials adhering to the lower surface soon drop off and sink to the bottom of the sea4 ,the iceberg1 divested of these materials1 can now do very little harm to the rocky sea-bottom over which it floats4 ,it is true that an iceberg moving with a velocity of a few miles an hour1 if it came in contact with the sea-bottom1 would1 by the mere force of concussion1 tear up loose and disjointed rocks1 and hurl some of the loose materials to a distance2 but it would do but little in the way of grinding down the rock against which it struck4 ,but even supposing the bottom of the iceberg were properly shod with the necessary grinding materials1 still it would be but a very inefficient grinding agent2 for a floating iceberg would not be in contact with the sea-bottom4 ,and if it were in contact with the sea-bottom1 it would soon become stranded and1 of course1 motionless1 and under such conditions could produce no effect4 ,it is perfectly true that although the bottom of the berg may be devoid of grinding materials1 yet these may be found lying on the surface of the submarine rock over which the ice moves4 ,but it must be borne in mind that the same current which will move the icebergs over the surface of the rock will move the sand1 mud1 and other materials over it also2 so that the markings effected by the ice would in all probability be erased by the current4 ,in the deep recesses of the ocean the water has been found to have but little or no motion4 ,but icebergs always follow the path of currents2 and it is very evident that at the comparatively small depth of a thousand feet or so reached by icebergs the motion of the water will be considerable2 and the continual shifting of the small particles of the mud and sand will in all probability efface the markings which may be made now and again by a passing berg4 ,much has been said regarding the superiority of icebergs as grinding and striating agents in consequence of the great velocity of their motion in comparison with that of land-ice4 ,but it must be remembered that it is while the iceberg is floating1 and before it touches the rock1 that it possesses high velocity4 ,when the iceberg runs aground1 its motion is suddenly arrested or greatly reduced4 ,but if the iceberg advancing upon a sloping sea-bottom is raised up so as to exert great pressure1 it will on this account be the more suddenly arrested1 the motion will be slow1 and the distance passed over short1 before the berg becomes stranded4 ,if it exerts but little pressure on the sea-bottom1 it may retain a considerable amount of motion and advance to a considerable distance before it is brought to a stand2 but1 exerting little pressure1 it can perform but little work4 ,land-ice moves slowly1 but then it exerts enormous pressure4 ,a glacier #a1jjj feet in thickness has a pressure on its rocky bed equal to about #be tons on the square foot2 but an iceberg a mile in thickness1 forced up on a sloping sea-bottom to an elevation of #bj feet 7and this is perhaps more than any ocean-current could effect71 would only exert a pressure of about half a ton on the square foot1 or about #a_/ejth part of the pressure of the glacier #a1jjj feet in thickness4 ,a great deal has been said about the erosive and crushing power of icebergs of enormous thickness1 as if their thickness gave them any additional pressure4 ,an iceberg #ajj feet in thickness will exert just as much pressure as one a mile in thickness4 ,the pressure of an iceberg is not like that of a glacier1 in proportion to its thickness1 but to the height to which it is raised out of the water4 ,an iceberg #ajj feet in thickness raised #aj feet will exert exactly the same pressure as one a mile in thickness raised to an equal height4 ,to be an efficient grinding agent1 steadiness of motion1 as well as pressure1 is essential4 ,a rolling or rocking motion is ill-adapted for grinding down and striating a rock4 ,a steady rubbing motion under pressure is the thing required4 ,but an iceberg is not only deficient in pressure1 but also deficient in steadiness of motion4 ,when an iceberg moving with considerable velocity comes on an elevated portion of the sea-bottom1 it does not move steadily onwards over the rock1 unless the pressure of the berg on the rock be trifling4 ,the resistance being entirely at the bottom of the iceberg1 its momentum1 combined with the pressure of the current1 applied wholly above the point of resistance1 tends to make the berg bend forward1 and in some cases upset 7when it is of a cubical form74 ,the momentum of the moving berg1 instead of being applied in forcing it over the rock against which it comes in contact1 is probably all consumed in work against gravitation in raising the berg upon its front edge4 ,after the momentum is consumed1 unless the berg be completely upset1 it will fall back under the force of gravitation to its original position4 ,but the momentum which it acquires from gravitation in falling backwards carries it beyond its position of repose in an opposite direction4 ,it will thus continue to rock backwards and forwards until the friction of the water brings it to rest4 ,the momentum of the berg1 instead of being applied to the work of grinding and striating the sea-bottom1 will chiefly be consumed in heat in the agitation of the water4 ,but if the berg does advance1 it will do so with a rocking unsteady motion1 which1 as ,mr4 ,couthouy#ach and ,professor ,dana#aci observe1 will tend rather to obliterate striations than produce them4 ,a floating berg moves with great steadiness2 but a berg that has run aground cannot advance with a steady motion4 ,if the rock over which the berg moves offers little resistance1 it may do so2 but in such a case the berg could produce but little effect on the rock4 ,dr4 ,sutherland1 who has had good opportunities to witness the effects of icebergs1 makes some most judicious remarks on the subject4 8,it will be well0 he says1 8to bear in mind that when an iceberg touches the ground1 if that ground be hard and resisting1 it must come to a stand1 and the propelling power continuing1 a slight leaning over in the water1 or yielding motion of the whole mass1 may compensate readily for being so suddenly arrested4 ,if1 however1 the ground be soft1 so as not to arrest the motion of the iceberg at once1 a moraine will be the result2 but the moraine thus raised will tend to bring it to a stand40#adj ,there is another cause referred to by ,professor ,dana1 which1 to a great extent1 must prevent the iceberg from having an opportunity of striating the sea-bottom1 even though it were otherwise well adapted for so doing4 ,it is this3 the bed of the ocean in the track of icebergs must be pretty much covered with stones and rubbish dropped from the melting bergs4 ,and this mass of rubbish will tend to protect the rock4#ada ,if icebergs cannot be shown priori1 from mechanical considerations1 to be well adapted for striating the sea-bottom1 one would naturally expect1 from the confident way in which it is asserted that they are so adapted1 that the fact has been at least established by actual observation4 ,but1 strange as it may appear1 we seem to have little or no proof that icebergs actually striate the bed of the ocean4 ,this can be proved from the direct testimony of the advocates of the iceberg theory themselves4 ,we shall take the testimony of ,mr4 ,campbell1 the author of two well-known works in defence of the iceberg theory1 viz41 8,frost and ,fire10 and 8,a ,short ,american ,tramp40 ,mr4 ,campbell went in the fall of the year #ahfd to the coast of ,labrador1 the ,straits of ,belle ,isle1 and the ,gulf of ,st4 ,lawrence1 for the express purpose of witnessing the effects of icebergs1 and testing the theory which he had formed1 that the ice-markings of the glacial epoch were caused by floating ice and not by land-ice1 as is now generally believed4 ,the following is the result of his observations on the coast of ,labrador4 ,hanly ,harbour1 ,strait of ,belle ,isle3--8,the water is #cg ,f4 in ,july4444 ,as fast as one island of ice grounds and bursts1 another takes its place2 and in winter the whole strait is blocked up by a mass which swings bodily up and down1 grating along the bottom at all depths4444 ,examined the beaches and rocks at the water-line1 especially in sounds4 ,found the rocks ground smooth1 but not striated1 in the sounds0 7,short ,american ,tramp1 pp4 #fh1 #ajg74 ,cape ,charles and ,battle ,harbour3--8,but though these harbours are all frozen every winter1 the rocks at the water-line are not striated0 7p4 #fh74 ,at ,st4 ,francis ,harbour3--8,the water-line is much rubbed1 smooth1 but not striated0 7p4 #gb74 ,cape ,bluff3--8,watched the rocks with a telescope1 and failed to make out stri anywhere2 but the water-line is everywhere rubbed smooth0 7p4 #ge74 ,seal ,islands3--8,no stri are to be seen at the land-wash in these sounds or on open sea-coasts near the present water-line0 7p4 #gf74 ,he only mentions having here found striations in the three following places along the entire coast of ,labrador visited by him2 and in regard to two of these1 it seems very doubtful that the markings were made by modern icebergs4 ,murray's ,harbour3--8,this harbour was blocked up with ice on the #bjth of ,july4 ,the water-line is rubbed1 and in some places striated0 7p4 #fi74 ,pack ,island3--8,the water-line in a narrow sound was polished and striated in the direction of the sound1 about ,n4,n4,w4 ,this seems to be fresh work done by heavy ice drifting from ,sandwich ,bay2 but1 on the other hand1 stages with their legs in the sea1 and resting on these very rocks1 are not swept away by the ice0 7p4 #if74 ,if these markings were modern1 why did not the 8heavy ice0 remove the small fir poles supporting the fishing-stages8 ,red ,bay3--8,landed half-dressed1 and found some stri perfectly fresh at the water-level1 but weathered out a short distance inland0 7p4 #ajg74 ,the striations 8inland0 could not have been made by modern icebergs2 and it does not follow that because the markings at the water-level were not weathered they were produced by modern ice4 ,these are the evidences which he found that icebergs striate rocks1 on a coast of which he says that1 during the year he visited it1 8the winter-drift was one vast solid raft of floes and bergs more than #aej miles wide1 and perhaps #c1jjj feet thick at spots1 driven by a whole current bodily over one definite course1 year after year1 since this land was found0 7p4 #he74 ,but ,mr4 ,campbell himself freely admits that the floating ice which comes aground along the shores does not produce stri4 8,it is sufficiently evident10 he says1 8that glacial stri are not produced by thin bay-ice0 7p4 #gf74 ,and in 8,frost and ,fire10 vol4 ii41 p4 #bcg1 he states that1 8from a careful examination of the water-line at many spots1 it appears that bay-ice grinds rocks1 but does not produce striation40 8,it is impossible10 he continues1 8to get at rocks over which heavy icebergs now move2 but a mass #aej miles wide1 perhaps #c1jjj feet thick in some parts1 and moving at the rate of a mile an hour1 or more1 appears to be an engine amply sufficient to account for stri on rising rocks40 ,and in 8,american ,tramp10 p4 #gf1 he says1 8stri must be made in deep water by the large masses which seem to pursue the even tenor of their way in the steady current which flows down the coast40 ,mr4 ,campbell1 from a careful examination of the sea-bottom along the coast1 finds that the small icebergs do not produce stri1 but the large ones1 which move over rocks impossible to be got at1 8must0 produce them4 ,they 8appear0 to be amply sufficient to do so4 ,if the smaller bergs cannot striate the sea-bottom1 why must the larger ones do so8 ,there is no reason why the smaller bergs should not move as swiftly and exert as much pressure on the sea-bottom as the larger ones4 ,and even supposing that they did not1 one would expect that the light bergs would effect on a smaller scale what the heavy ones would do on a larger4 ,i have no doubt that when ,mr4 ,campbell visited ,labrador he expected to find the sea-coast under the water-line striated by means of icebergs1 and was probably not a little surprised to find that it actually was not4 ,and ,i have no doubt that were the sea-bottom in the tracks of the large icebergs elevated into view1 he would find to his surprise that it was free from striations also4 ,so far as observation is concerned1 we have no grounds from what ,mr4 ,campbell witnessed to conclude that icebergs striate the sea-bottom4 ,the testimony of ,dr4 ,sutherland1 who has had opportunities of seeing the effects of icebergs in arctic regions1 leads us to the same conclusion4 8,except10 he says1 8from the evidence afforded by plants and animals at the bottom1 we have no means whatever to ascertain the effect produced by icebergs upon the rocks4#adb ,in the ,malegat and ,waigat ,i have seen whole clusters of these floating islands1 drawing from #ajj to #bej fathoms1 moving to and fro with every return and recession of the tides4 ,i looked very earnestly for grooves and scratches left by icebergs and glaciers in the rocks1 but always failed to discover any40#adc ,we shall now see whether river-ice actually produces striations or not4 ,if floating ice under any form can striate rocks1 one would expect that it ought to be done by river-ice1 seeing that such ice is obliged to follow one narrow definite track4 ,st4 ,john's ,river1 ,new ,brunswick3--8,this river10 says ,mr4 ,campbell1 8is obstructed by ice during five months of the year4 ,when the ice goes1 there is wild work on the bank4 ,arrived at ,st4 ,john1 drove to the suspension-bridge4444 ,at this spot1 if anywhere in the world1 river-ice ought to produce striation4 ,the whole drainage of a wide basin and one of the strongest tides in the world1 here work continually in one rock-groove2 and in winter this water-power is armed with heavy ice4 ,there are no stri about the water-line40#add ,river ,st4 ,lawrence3--8,in winter the power of ice-floats driven by water-power is tremendous4 ,the river freezes and packs ice till the flow of water is obstructed4 ,the rock-pass at ,quebec is like the ,narrows at ,st4 ,john's1 ,newfoundland4 ,the whole pass1 about a mile wide1 was paved with great broken slabs and round boulders of worn ice as big as small shacks1 piled and tossed1 and heaped and scattered upon the level water below and frozen solid4444 ,this kind of ice does ,,not produce striation at the water-margin at ,quebec4 ,at ,montreal1 when the river #8goes1' the ice goes with it with a vengeance4444 ,the piers are not yet striated by river-ice at ,montreal4444 ,the rocks at the high-water level have no trace of glacial stri4444 ,the rock at ,ottawa is rubbed by river-ice every spring1 and always in one direction1 but it is not striated4444 ,the surfaces are all rubbed smooth1 and the edges of broken beds are rounded where exposed to the ice2 but there are no stri40#ade ,when ,sir ,charles ,lyell visited the ,st4 ,lawrence in #ahdb1 at ,quebec he went along with ,colonel ,codrington 8and searched carefully below the city in the channel of the ,st4 ,lawrence1 at low water1 near the shore1 for the signs of glacial action at the precise point where the chief pressure and friction of packed ice are exerted every year10 but found none4 8,at the bridge above the ,falls of ,montmorenci1 over which a large quantity of ice passes every year1 the gneiss is polished1 and kept perfectly free from lichens1 but not more so than rocks similarly situated at waterfalls in ,scotland4 ,in none of these places were any long straight grooves observable40#adf ,the only thing in the shape of modern ice-markings which he seems to have met with in ,north ,america was a few straight furrows half an inch broad in soft sandstone1 at the base of a cliff at ,cape ,blomidon in the ,bay of ,fundy1 at a place where during the preceding winter 8packed0 ice #ae feet thick had been pushed along when the tide rose over the sandstone ledges4#adg ,the very fact that a geologist so eminent as ,sir ,charles ,lyell1 after having twice visited ,north ,america1 and searched specially for modern ice-markings1 was able to find only two or three scratches1 upon a soft sandstone rock1 which he could reasonably attribute to floating ice1 ought to have aroused the suspicion of the advocates of the iceberg theory that they had really formed too extravagant notions regarding the potency of floating ice as a striating agent4 ,there is no reason to believe that the grooves and markings noticed by ,m4 ,weibye and others on the ,scandinavian coast and other parts of northern ,europe were made by icebergs4 ,professor ,geikie has clearly shown1 from the character and direction of the markings1 that they are the production of land-ice4#adh ,if the floating ice of the ,st4 ,lawrence and the icebergs of ,labrador are unable to striate and groove the rocks1 it is not likely that those of northern ,europe will be able to do so4 ,it will not do for the advocates of the iceberg theory to assume1 as they have hitherto done1 that1 as a matter of course1 the sea-bottom is being striated and grooved by means of icebergs4 ,they must prove that4 ,they must either show that1 as a matter of fact1 icebergs are actually efficient agents in striating the sea-bottom1 or prove from mechanical principles that they must be so4 ,the question must be settled either by observation or by reason2 mere opinion will not do4 ,the ,amount of ,material transported by ,icebergs much exaggerated4--,the transporting of boulders and rubbish1 and not the grinding and striating of rocks1 is evidently the proper function of the iceberg4 ,but even in this respect ,i fear too much has been attributed to it4 ,in reading the details of voyages in the arctic regions one cannot help feeling surprised how seldom reference is made to stones and rubbish being seen on icebergs4 ,arctic voyagers1 like other people1 when they are alluding to the geological effects of icebergs1 speak of enormous quantities of stones being transported by them2 but in reading the details of their voyages1 the impression conveyed is that icebergs with stones and blocks of rock upon them are the exceptions4 ,the greater portion of the narratives of voyages in arctic regions consists of interesting and detailed accounts of the voyager's adventures among the ice4 ,the general appearance of the icebergs1 their shape1 their size1 their height1 their colour1 are all noticed2 but rarely is mention made of stones being seen4 ,that the greater number of icebergs have no stones or rubbish on them is borne out by the positive evidence of geologists who have had opportunities of seeing icebergs4 ,mr4 ,campbell says3--8,it is remarkable that up to this time we have only seen a few doubtful stones on bergs which we have passed4444 ,though no bergs with stones on them or in them have been approached during this voyage1 many on board the ,ariel have been close to bergs heavily laden4444 ,a man who has had some experience of ice has never seen a stone on a berg in these latitudes4 ,captain ,anderson1 of the ,europa1 who is a geologist1 has never seen a stone on a berg in crossing the ,atlantic4 ,no stones were clearly seen on this trip40#adi ,captain ,sir ,james ,anderson 7who has long been familiar with geology1 has spent a considerable part of his life on the ,atlantic1 and has been accustomed to view the iceberg as a geologist as well as a seaman7 has never seen a stone on an iceberg in the ,atlantic4 ,this is rather a significant fact4 ,sir ,charles ,lyell states that1 when passing icebergs on the ,atlantic1 he 8was most anxious to ascertain whether there was any mud1 stones1 or fragments of rocks on any one of these floating masses2 but after examining about forty of them without perceiving any signs of frozen matter1 ,i left the deck when it was growing dusk40#aej ,after he had gone below1 one was said to be seen with something like stones upon it4 ,the captain and officers of the ship assured him that they had never seen a stone upon a berg4 ,the following extract from ,mr4 ,packard's 8,memoir on the ,glacial ,phenomena of ,labrador and ,maine10 will show how little is effected by the great masses of floating ice on the ,labrador coast either in the way of grinding and striating the rocks1 or of transporting stones1 clay1 and other materials4 8,upon this coast1 which during the summer of #ahfd was lined with a belt of floe-ice and bergs probably two hundred miles broad1 and which extended from the ,gulf of ,st4 ,lawrence at ,belles ,amours to the arctic seas1 this immense body of floating ice seemed directly to produce but little alteration in its physical features4 ,if we were to ascribe the grooving and polishing of rocks to the action of floating ice-floes and bergs1 how is it that the present shores far above 7#ejj71 and at least #bej feet below1 the water-line are often jagged and angular1 though constantly stopping the course of masses of ice impelled four to six miles an hour by the joint action of tides1 currents1 and winds8 ,no boulders1 or gravel1 or mud were seen upon any of the bergs or masses of shore-ice4 ,they had dropped all burdens of this nature nearer their points of detachment in the high arctic regions40 444 8,this huge area of floating ice1 embracing so many thousands of square miles1 was of greater extent1 and remained longer upon the coast1 in #ahfd1 than for forty years previous4 ,it was not only pressed upon the coast by the normal action of the ,labrador and ,greenland currents1 which1 in consequence of the rotatory motion of the earth1 tended to force the ice in a south-westerly direction1 but the presence of the ice caused the constant passage of cooler currents of air from the sea over the ice upon the heated land1 giving rise during the present season to a constant succession of north-easterly winds from ,march until early in ,august1 which further served to crowd the ice into every harbour and recess upon the coast4 ,it was the universal complaint of the inhabitants that the easterly winds were more prevalent1 and the ice #8held' later in the harbours this year than for many seasons previous4 ,thus the fisheries were nearly a failure1 and vegetation greatly retarded in its development4 ,but so far as polishing and striating the rocks1 depositing drift material1 and thus modifying the contour of the surface of the present coast1 this modern mass of bergs and floating ice effected comparatively little4 ,single icebergs1 when small enough1 entered the harbours1 and there stranding1 soon pounded to pieces upon the rocks1 melted1 and disappeared4 ,from ,cape ,harrison1 in lat4 #ee1 to ,caribo ,island1 was an interrupted line of bergs stranded in #hj to #ajj or more fathoms1 often miles apart1 while others passed to the seaward down by the eastern coast of ,newfoundland1 or through the ,straits of ,belle ,isle40#aea ,boulder ,clay the ,product of ,land-ice4--,there is still another point connected with icebergs to which we must allude1 viz41 the opinion that great masses of the boulder clay of the glacial epoch were formed from the droppings of icebergs4 ,if boulder clay is at present being accumulated in this manner1 then traces of the boulder clay deposits of former epochs might be expected to occur4 ,it is perfectly obvious that unstratified boulder clay could not have been formed in this way4 ,stones1 gravel1 sand1 clay1 and mud1 the ingredients of boulder clay1 tumbled all together from the back of an iceberg1 could not sink to the bottom of the sea without separating4 ,the stones would reach the bottom first1 then the gravel1 then the sand1 then the clay1 and last of all the mud1 and the whole would settle down in a stratified form4 ,but1 besides1 how could the clay be derived from icebergs8 ,icebergs derive their materials from the land before they are launched into the deep1 and while they are in the form of land-ice4 ,the materials which are found on the backs of icebergs are what fell upon the ice from mountain tops and crags projecting above the ice4 ,icebergs are chiefly derived from continental ice1 such as that of ,greenland1 where the whole country is buried under one continuous mass1 with only a lofty mountain peak here and there rising above the surface4 ,and this is no doubt the chief reason why so few icebergs have stones upon their backs4 ,the continental ice of ,greenland is not1 like the glaciers of the ,alps1 covered with loose stones4 ,dr4 ,robert ,brown informs me that no moraine matter has ever been seen on the inland ice of ,greenland4 ,it is perfectly plain that clay does not fall upon the ice4 ,what falls upon the ice is stones1 blocks of rocks1 and the loose dbris4 ,clay and mud we know1 from the accounts given by arctic voyagers1 are sometimes washed down upon the coast-ice2 but certainly very little of either can possibly get upon an iceberg4 ,arctic voyagers sometimes speak of seeing clay and mud upon bergs2 but it is probable that if they had been near enough they would have found that what they took for clay and mud were merely dust and rubbish4 ,undoubtedly the boulder clay of many places bears unmistakable evidence of having been formed under water2 but it does not on that account follow that it was formed from the droppings of icebergs4 ,the fact that the boulder clay in every case is chiefly composed of materials derived from the country on which the clay lies1 proves that it was not formed from matter transported by icebergs4 ,the clay1 no doubt1 contains stones and boulders belonging to other countries1 which in some cases may have been transported by icebergs2 but the clay itself has not come from another country4 ,but if the clay itself has been derived from the country on which it lies1 then it is absurd to suppose that it was deposited from icebergs4 ,the clay and materials which are found on icebergs are derived from the land on which the iceberg is formed2 but to suppose that icebergs1 after floating about upon the ocean1 should always return to the country which gave them birth1 and there deposit their loads1 is rather an extravagant supposition4 ,from the facts and considerations adduced we are1 ,i would venture to presume1 warranted to conclude that1 with the exception of what may have been produced by land-ice1 very little in the shape of boulder clay or striated rocks belonging to the glacial epoch lies buried under the ocean--and that when the now existing land-surfaces are all denuded1 probably scarcely a trace of the glacial epoch will then be found1 except the huge blocks that were transported by icebergs and dropped into the sea4 ,it is therefore probable that we have as much evidence of the existence of a glacial epoch during former periods as the geologists of future ages will have of the existence of a glacial epoch during the ,post-tertiary period1 and that consequently we are not warranted in concluding that the glacial epoch was something unique in the geological history of our globe4 ,palontological ,evidence4--,it might be thought that if glacial epochs have been numerous1 we ought to have abundance of palontological evidence of their existence4 ,i do not know if this necessarily follows4 ,let us take the glacial epoch itself for example1 which is quite a modern affair4 ,here we do not require to go and search in the bottom of the sea for the evidence of its existence2 for we have the surface of the land in almost identically the same state in which it was when the ice left it1 with the boulder clay and all the wreck of the ice lying upon it4 ,but what geologist1 with all these materials before him1 would be able to find out from palontological evidence alone that there had been such an epoch8 ,he might search the whole1 but would not be able to find fossil evidence from which he could warrantably infer that the country had ever been covered with ice4 ,we have evidence in the fossils of the ,crag and other deposits of the existence of a colder condition of climate prior to the true glacial period1 and in the shell-beds of the ,clyde and other places of a similar state of matters after the great ice-sheets had vanished away4 ,but in regard to the period of the true boulder clay or till1 when the country was enveloped in ice1 palontology has almost nothing whatever to tell us4 8,whatever may be the cause10 says ,sir ,charles ,lyell1 8the fact is certain that over large areas in ,scotland1 ,ireland1 and ,wales1 ,i might add throughout the northern hemisphere on both sides of the ,atlantic1 the stratified drift of the glacial period is very commonly devoid of fossils40#aeb ,in the 8flysch0 of the ,eocene of the ,alps1 to which we shall have occasion to refer in the next chapter1 in which the huge blocks are found which prove the existence of ice-action during that period1 few or no fossils have been found4 ,so devoid of organic remains is that formation1 that it is only from its position1 says ,sir ,charles1 that it is known to belong to the middle or 8nummulitic0 portion of the great ,eocene series4 ,again1 in the conglomerates at ,turin1 belonging to the ,upper ,miocene period1 in which the angular blocks of limestone are found which prove that during that period ,alpine glaciers reached the sea-level in the latitude of ,italy1 not a single organic remain has been found4 ,it would seem that an extreme paucity of organic life is a characteristic of a glacial period1 which warrants us in concluding that the absence of organic remains in any formation otherwise indicative of a cold climate cannot be regarded as sufficient evidence that that formation does not belong to a cold period4 ,in the last chapter it was shown why so little evidence of the warm periods of the glacial epoch is now forthcoming4 ,the remains of the faunas and floras of those periods were nearly wholly destroyed and swept into the adjoining seas by the ice-sheet that covered the land4 ,it is upon the present land-surface that we find the chief evidence of the last glacial epoch1 but the traces of the warm periods of that epoch are hardly now to be met with in that position since they have nearly all been obliterated or carried into the sea4 ,in regard to former glacial epochs1 however1 ice-marked rocks1 scratched stones1 moraines1 till1 c41 no longer exist2 the land-surfaces of those old times have been utterly swept away4 ,the only evidence1 therefore1 of such ancient glacial epochs1 that we can hope to detect1 must be sought for in the deposits that were laid down upon the sea-bottom2 where also we may expect to find traces of the warm periods that alternated during such epochs with glacial conditions4 ,it is plain1 moreover1 that the palontological evidence in favour of warm periods will always be the most abundant and satisfactory4 ,judging from geological evidence alone1 we naturally conclude that1 as a general rule1 the climate of former periods was somewhat warmer than it is at the present day4 ,it is from fossil remains that the geologist principally forms his estimate of the character of the climate during any period4 ,now1 in regard to fossil remains1 the warm periods will always be far better represented than the cold2 for we find that1 as a general rule1 those formations which geologists are inclined to believe indicate a cold condition of climate are remarkably devoid of fossil remains4 ,if a geologist does not keep this principle in view1 he will be very apt to form a wrong estimate of the general character of the climate of a period of such enormous length as say the ,tertiary4 ,suppose that the presently existing sea-bottoms1 which have been forming since the commencement of the glacial epoch1 were to become consolidated into rock and thereafter to be elevated into dry land1 we should then have a formation which might be properly designated the ,post-pliocene4 ,it would represent the time which has elapsed from the beginning of the glacial epoch to the present day4 ,suppose one to be called upon as a geologist to determine from that formation what was the general character of the climate during the period in question1 what would probably be the conclusion at which he would arrive8 ,he would probably find here and there patches of boulder clay containing striated and ice-worn stones4 ,now and again he would meet with bones of the mammoth and the reindeer1 and shells of an arctic type4 ,he would likewise stumble upon huge blocks of the older rocks imbedded in the formation1 from which he would infer the existence of icebergs and glaciers reaching the sea-level4 ,but1 on the whole1 he would perceive that the greater portion of the fossil remains met with in this formation implied a warm and temperate condition of climate4 ,at the lower part of the formation1 corresponding to the time of the true boulder clay1 there would be such a scarcity of organic remains that he would probably feel at a loss to say whether the climate at that time was cold or hot4 ,but if the intense cold of the glacial epoch was not continuous1 but broken up by intervening warm periods during which the ice1 to a considerable extent at least1 disappeared for a long period of time 7and there are few geologists who have properly studied the subject who will positively deny that such was the case71 then the country would no doubt during those warm periods possess an abundance of plant and animal life4 ,it is quite true that we may almost search in vain on the present land-surface for the organic remains which belonged to those inter-glacial periods2 for they were nearly all swept away by the ice which followed4 ,but no doubt in the deep recesses of the ocean1 buried under hundreds of feet of sand1 mud1 clay1 and gravel1 lie multitudes of the plants and animals which then flourished on the land1 and were carried down by rivers into the sea4 ,and along with these lie the skeletons1 shells1 and other exuvi of the creatures which flourished in the warm seas of those periods4 ,now looking at the great abundance of fossils indicative of warm and genial conditions which the lower portions of this formation would contain1 the geologist might be in danger of inferring that the earlier part of the ,post-pliocene period was a warmer period1 whereas we1 at the present day1 looking at the matter from a different standpoint1 declare that part to have been characterized by cold or glacial conditions4 ,no doubt1 if the beds formed during the cold periods of the glacial epoch could be distinguished from those formed during the warm periods1 the fossil remains of the one would indicate a cold condition of climate1 and those of the other a warm condition2 but still1 taking the entire epoch as a whole1 the percentage of fossil remains indicative of a warm condition would probably so much exceed that indicative of a cold condition1 that we should come to the conclusion that the character of the climate1 as a whole1 during the epoch in question was warm and equable4 ,as geologists we have1 as a rule1 no means of arriving at a knowledge of the character of the climate of any given period but through an examination of the sea-bottoms belonging to that period2 for these contain all the evidence upon the subject4 ,but unless we exercise caution1 we shall be very apt1 in judging of the climate of such a period1 to fall into the same error that we have just now seen one might naturally fall into were he called upon to determine the character of the climate during the glacial epoch from the nature of the organic remains which lie buried in our adjoining seas4 ,on this point ,mr4 ,j4 ,geikie's observations are so appropriate1 that ,i cannot do better than introduce them here4 8,when we are dealing10 says this writer1 8with formations so far removed from us in time1 and in which the animal and plant remains depart so widely from existing forms of life1 we can hardly expect to derive much aid from the fossils in our attempts to detect traces of cold climatic conditions4 ,the arctic shells in our ,post-tertiary clays are convincing proofs of the former existence in our latitude of a severe climate2 but when we go so far back as ,palozoic ages1 we have no such clear evidence to guide us4 ,all that palontologists can say regarding the fossils belonging to these old times is simply this1 that they seem to indicate1 generally speaking1 mild1 temperate1 or genial1 and even sometimes tropical1 conditions of climate4 ,many of the fossils1 indeed1 if we are to reason from analogy at all1 could not possibly have lived in cold seas4 ,but1 for aught that we know1 there may have been alternations of climate during the deposition of each particular formation2 and these changes may be marked by the presence or absence1 or by the greater or less abundant development1 of certain organisms at various horizons in the strata4 ,notwithstanding all that has been done1 our knowledge of the natural history of these ancient seas is still very imperfect2 and therefore1 in the present state of our information1 we are not entitled to argue1 from the general aspect of the fossils in our older formations1 that the temperature of the ancient seas was never other than mild and genial40#aec ,conclusion4--,from what has already been stated it will1 ,i trust1 be apparent that1 assuming glacial epochs during past geological ages to have been as numerous and as severe as the ,secular theory demands1 still it would be unreasonable to expect to meet with abundant traces of them4 ,the imperfection of the geological record is such that we ought not to be astonished that so few relics of former ice ages have come down to us4 ,it will also be apparent that the palontological evidence of a warm condition of climate having obtained during any particular age1 is no proof that a glacial epoch did not also supervene during the same cycle of time4 ,indeed it is quite the reverse2 for the warm conditions of which we have proof may indicate merely the existence of an inter-glacial period4 ,furthermore1 if the ,secular theory of changes of climate be admitted1 then evidence of a warm condition of climate having prevailed in arctic regions during any past geological age may be regarded as presumptive proof of the existence of a glacial epoch2 that is to say1 of an epoch during which cold and warm conditions of climate alternated4 ,keeping these considerations in view1 we shall now proceed to examine briefly what evidence we at present have of the former existence of glacial epochs4 ,,chapter ,,xviii4 ,,former ,,glacial ,,epochs2 ,,geological ,,evidence ,,of4 ,cambrian ,conglomerate of ,islay and ,north-west of ,scotland4--,ice-action in ,ayrshire and ,wigtownshire during ,silurian ,period4--,silurian ,limestones in ,arctic ,regions4--,professor ,ramsay on ,ice-action during ,old ,red ,sandstone ,period4--,warm ,climate in ,arctic ,regions during ,old ,red ,sandstone ,period4--,professor ,geikie and ,mr4 ,james ,geikie on a ,glacial ,conglomerate of ,lower ,carboniferous ,age4--,professor ,haughton and ,professor ,dawson on ,evidence of ,ice-action during ,coal ,period4--,mr4 ,w4 ,t4 ,blanford on ,glaciation in ,india during ,carboniferous ,period4--,carboniferous ,formations of ,arctic ,regions4--,professor ,ramsay on ,permian ,glaciers4--,permian ,conglomerate in ,arran4--,professor ,hull on ,boulder ,clay of ,permian ,age4--,permian ,boulder ,clay of ,natal4--,oolitic ,boulder ,conglomerate in ,sutherlandshire4--,warm ,climate in ,north ,greenland during ,oolitic ,period4--,mr4 ,godwin-,austen on ,ice-action during ,cretaceous ,period4--,glacial ,conglomerates of ,eocene ,age in the ,alps4--,m4 ,gastaldi on the ,ice-transported ,limestone ,blocks of the ,superga4--,professor ,heer on the ,climate of ,north ,greenland during ,miocene ,period4 ,,cambrian ,,period4 ,island of ,islay4--,good evidence of ice-action has been observed by ,mr4 ,james ,thomson1 ,f4,g4,s41#aed in strata which he believes to be of ,cambrian age4 ,at ,port ,askaig1 ,island of ,islay1 below a precipitous cliff of quartzite #gj feet in height1 there is a mass of arenaceous talcose schist containing fragments of granite1 some angular1 but most of them rounded1 and of all sizes1 from mere particles to large boulders4 ,as there is no granite in the island from which these boulders could have been derived1 he justly infers that they must have been transported by the agency of ice4 ,the probability of his conclusion is strengthened by the almost total absence of stratification in the deposit in question4 ,north-west of ,scotland4--,mr4 ,j4 ,geikie tells me that much of the ,cambrian conglomerate in the north-west of ,scotland strongly reminds him of the coarse shingle beds 7,alpine diluvium7 which so often crowd the old glacial valleys of ,switzerland and ,northern ,italy4 ,in many places the stones of the ,cambrian conglomerate have a subangular1 blunted shape1 like those of the re-arranged moraine dbris of ,alpine countries4 ,,silurian ,,period4 ,wigtownshire4--,the possibility of glacial action so far back as the ,silurian age has been suggested4 ,in beds of slate and shales in ,wigtownshire of ,lower ,silurian age ,mr4 ,j4 ,carrick ,moore found beds of conglomerate of a remarkable character4 ,the fragments generally vary from the size of one inch to a foot in diameter1 but in some of the beds1 boulders of #c1 #d1 and even #e feet in diameter occur4 ,there are no rocks in the neighbourhood from which any of these fragments could have been derived4 ,the matrix of this conglomerate is sometimes a green trappean-looking sandstone of exceeding toughness1 and sometimes an indurated sandstone indistinguishable from many common varieties of greywacke4#aee ,ayrshire4--,mr4 ,james ,geikie states that in ,glenapp1 and near ,dalmellington1 he found embedded in ,lower ,silurian strata blocks and boulders from one foot to #e feet in diameter of gneiss1 syenite1 granite1 c41 none of which belong to rocks of those neighbourhoods4#aef ,similar cases have been found in ,galway1 ,ireland1 and at ,lisbellaw1 south of ,enniskillen4#aeg ,in ,america1 ,professor ,dawson describes ,silurian conglomerates with boulders #b feet in diameter4 ,arctic ,regions4--,the existence of warm inter-glacial periods during that age may be inferred from the fact that in the arctic regions we find widespread masses of ,silurian limestones containing encrinites1 corals1 and mollusca1 and other fossil remains1 for an account of which see ,professor ,haughton's geological account of the ,arctic ,archipelago appended to ,mc,clintock's 8,narrative of ,arctic ,discoveries40#aeh ,,old ,,red ,,sandstone4 ,north of ,england4--,according to ,professor ,ramsay and some other geologists the brecciated1 subangular conglomerates and boulder beds of the ,old ,red ,sandstone of ,scotland and the ,north of ,england are of glacial origin4 ,when these conglomerates and the recent boulder clay come together it is difficult to draw the line of demarcation between them4 ,professor ,ramsay observed some very remarkable facts in connection with the ,old ,red ,sandstone conglomerates of ,kirkby ,lonsdale1 and ,sedburgh1 in ,westmoreland and ,yorkshire4 ,i shall give the results of his observations in his own words4 8,the result is1 that we have found many stones and blocks distinctly scratched1 and on others the ghosts of scratches nearly obliterated by age and chemical action1 probably aided by pressure at a time when these rocks were buried under thousands of feet of carboniferous strata4 ,in some cases1 however1 the markings were probably produced within the body of the rock itself by pressure1 accompanied by disturbance of the strata2 but in others the longitudinal and cross striations convey the idea of glacial action4 ,the shapes of the stones of these conglomerates1 many of which are from #b to #c feet long1 their flattened sides and subangular edges1 together with the confused manner in which they are often arranged 7like stones in the drift71 have long been enough to convince me of their ice-borne character2 and the scratched specimens1 when properly investigated1 may possibly convince others40#aei ,isle of ,man4--,the conglomerate of the ,old ,red ,sandstone in the ,isle of ,man has been compared by ,mr4 ,cumming to 8a consolidated ancient boulder clay40 ,and he remarks1 8,was it so that those strange trilobitic-looking fishes of that era had to endure the buffeting of ice-waves1 and to struggle amidst the wreck of ice-floes and the crush of bergs80#afj ,australia4--,a conglomerate similar to that of ,scotland has been found in ,victoria1 ,australia1 by ,mr4 ,selwyn1 at several localities4 ,along the ,wild ,duck ,creek1 near ,heathcote1 and also near the ,mia-,mia1 ,spring ,plains1 ,redesdale1 localities in the ,colony of ,victoria1 where it was examined by ,messrs4 ,taylor and ,etheridge1 ,junior1 this conglomerate consists of a mixture of granite pebbles and boulders of various colours and textures1 porphyries1 indurated sandstone1 quartz1 and a peculiar flint-coloured rock in a matrix of bluish-grey very hard mud-cement4#afa ,rocks similar to the pebbles and blocks composing the conglomerate do not occur in the immediate neighbourhood2 and from the curious mixture of large and small angular and water-worn fragments it was conjectured that it might possibly be of glacial origin4 ,scratched stones were not observed1 although a careful examination was made4 ,from similar mud-pebble beds on the ,lerderderg ,river1 ,victoria1 ,mr4 ,p4 ,daintree obtained a few pebbles grooved after the manner of ice-scratched blocks4#afb ,and the existence of a warm condition of climate during the ,old ,red ,sandstone period is evidenced by the fossiliferous limestones of ,england1 ,russia1 and ,america4 ,on the banks of the ,athabasca ,river1 ,rupert-,land1 ,sir ,john ,richardson found beds of limestone containing ,producti1 ,spiriferi1 an ,orthis resembling ,o4 resupinata1 ,terebratula reticularis1#afc and a ,pleurotomaria1 which1 in the opinion of the late ,dr4 ,woodward1 who examined the specimens1 are characteristic of ,devonian rocks of ,devonshire4 ,,carboniferous ,,period4 ,france4--,it is now a good many years since ,mr4 ,godwin-,austen directed attention to what he considered evidence of ice-action during the coal period4 ,this geologist found in the carboniferous strata of ,france large angular blocks which he could not account for without inferring the former action of ice4 8,whether from local elevation10 he says1 8or from climatic conditions1 there are certain appearances over the whole which imply that at one time the temperature must have been very low1 as glacier-action can alone account for the presence of the large angular blocks which occur in the lowest detrital beds of many of the southern coal-basins40#afd ,scotland4--,in ,scotland great beds of conglomerate are met with in various parts1 which are now considered by ,professor ,geikie1 ,mr4 ,james ,geikie1 and other officers of the ,geological ,survey who have had opportunities of examining them1 to be of glacial origin4 8,they are10 says ,mr4 ,james ,geikie1 8quite unstratified1 and the stones often show that peculiar blunted form which is so characteristic of glacial work40#afe ,many of the stones found by ,professor ,geikie1 several of which ,i have had an opportunity of seeing1 are well striated4 ,in #ahea ,professor ,haughton brought forward at the ,geological ,society of ,dublin1 a case of angular fragments of granite occurring in the carboniferous limestone of the county of ,dublin2 and he explained the phenomena by the supposition of the transporting power of ice4 ,north ,america4--,in one of the ,north ,american coal-fields ,professor ,newberry found a boulder of quartzite #ag inches by #ab inches1 imbedded in a seam of coal4 ,similar facts have also been recorded both in the ,united ,states1 and in ,nova ,scotia4 ,professor ,dawson describes what he calls a gigantic esker of ,carboniferous age1 on the outside of which large travelled boulders were deposited1 probably by drift-ice2 while in the swamps within1 the coal flora flourished4#aff ,india4--,mr4 ,w4 ,t4 ,blanford1 of the ,geological ,survey of ,india1 states that in beds considered to be of ,carboniferous age are found large boulders1 some of them as much as #ae feet in diameter4 ,the bed in which these occur is a fine silt1 and he refers the deposition of the boulders to ice-action4 ,within the last three years his views have received singular confirmation in another part of ,india1 where beds of limestone were found striated below certain overlying strata4 ,the probability that these appearances are due1 as ,mr4 ,blanford says1 to the action of ice1 is strengthened by the consideration that about five degrees farther to the north of the district in question rises the cold and high table-land of ,thibet1 which during a glacial epoch would undoubtedly be covered with ice that might well descend over the plains of ,india4#afg ,arctic ,regions4--,a glacial epoch during the ,carboniferous age may be indirectly inferred from the probable existence of warm inter-glacial periods1 as indicated by the limestones with fossil remains found in arctic regions4 ,that an equable condition of climate extended to near the north pole is proved by the fact that in the arctic regions vast masses of carboniferous limestone1 having all the characters of the mountain limestone of ,england1 have been found4 8,these limestones10 says ,mr4 ,isbister1 8are most extensively developed in the north-east extremity of the continent1 where they occupy the greater part of the coast-line1 from the north side of the ,kotzebue ,sound to within a few miles of ,point ,barrow1 and form the chief constituent of the lofty and conspicuous headlands of ,cape ,thomson1 ,cape ,lisburn1 and ,cape ,sabine40#afh ,limestone of the same age occurs extensively along the ,mackenzie ,river4 ,the following fossils have been found in these limestones3--,terebratula resupinata1#afi ,lithostrotion basaltiforme1 ,cyathophyllum dianthum1 ,c4 flexuosum1 ,turbinolia mitrata1 ,productus ,martini1#agj ,dentalium ,sarcinula1 ,spiriferi1 ,orthid1 and encrinital fragments in the greatest abundance4 ,among the fossils brought home from ,dept ,point1 ,albert ,land1 by ,sir ,e4 ,belcher1 ,mr4 ,salter found the following1 belonging to the ,carboniferous period3--,fusulina hyperborea1 ,stylastrea inconferta1 ,zaphrentis ovibos1 ,clisiophyllum tumulus1 ,syringopora 7,aulopora71 ,fenestella ,arctica1 ,spirifera ,keilhavii1 ,productus cora1 ,p4 semireticulatus4#aga ,coal-beds of ,carboniferous age are extensively developed in arctic regions4 ,the fuel is of a highly bituminous character1 resembling1 says ,professor ,haughton1 the gas coals of ,scotland4 ,the occurrence of coal in such high latitudes indicates beyond doubt that a mild and temperate condition of climate must1 during some part of the ,carboniferous age1 have prevailed up to the very pole4 8,in the coal of ,jameson's ,land1 on the east side of ,greenland1 lying in latitude #ga1 and in that of ,melville ,island1 in latitude #ge ,n41 ,professor ,jameson found plants resembling fossils of the coal-fields of ,britain40#agb ,,permian ,,period4 ,england4--,from the researches of ,professor ,ramsay in the ,permian breccias1 we have every reason to believe that during a part of the ,permian age our country was probably covered with glaciers reaching to the sea4 ,these brecciated stones1 he states1 are mostly angular or subangular1 with flattened sides and but very slightly rounded at the edges1 and are imbedded in a deep red marly paste4 ,at ,abberley ,hill some of the masses are from #b to #c feet in diameter1 and in one of the quarries1 near the base of ,woodbury ,hill1 ,professor ,ramsay saw one #b feet in diameter4 ,another was observed at ,woodbury ,rock1 #d feet long1 #c feet broad1 and #a feet thick4 ,the boulders were found in ,south ,staffordshire1 ,enville1 in ,abberley and ,malvern ,hills1 and other places4 8,they seem10 he says1 8to have been derived from the conglomerate and green1 grey1 and purple ,cambrian grits of the ,longmynd1 and from the ,silurian quartz-rocks1 slates1 felstones1 felspathic ashes1 greenstones1 and ,upper ,caradoc rocks of the country between the ,longmynd and ,chirbury4 ,but then10 he continues1 8the south end of the ,malvern ,hills is from forty to fifty miles1 the ,abberleys from twenty-five to thirty-five miles1 ,enville from twenty to thirty miles1 and ,south ,staffordshire from thirty-five to forty miles distant from that country40#agc ,it is physically impossible1 ,professor ,ramsay remarks1 that these blocks could have been transported to such distances by any other agency than that of ice4 ,had they been transported by water1 supposing such a thing possible1 they would have been rounded and water-worn1 whereas many of these stones are flat slabs1 and most of them have their edges but little rounded4 ,and besides many of them are highly polished1 and others grooved and finely striated1 exactly like those of the ancient glaciers of ,scotland and ,wales4 ,some of these specimens are to be seen in the ,museum of ,practical ,geology1 ,jermyn ,street4 ,scotland4--,in the ,island of ,arran1 ,mr4 ,e4 ,a4 ,wunsch and ,mr4 ,james ,thomson found a bed of conglomerate which they considered of ,permian age1 and probably of glacial origin4 ,this conglomerate enclosed angular fragments of various schistose1 volcanic1 and limestone rocks1 and contained carboniferous fossils4 ,ireland4--,at ,armagh1 ,ireland1 ,professor ,hull found boulder beds of ,permian age1 containing pebbles and boulders1 sometimes #b feet in diameter4 ,some of the boulders must have been transported from a region lying about #cj miles to the north-west of the locality in which they now occur4 ,it is difficult to conceive1 says ,professor ,hull1 how rock fragments of such a size could have been carried to their present position by any other agency than that of floating ice4 ,this boulder-bed is overlaid by a recent bed of boulder clay4 ,professor ,ramsay1 who also examined the section1 agrees with ,professor ,hull that the bed is of ,permian age1 and unquestionably of ice-formation4#agd ,professor ,ramsay feels convinced that the same conclusions which he has drawn in regard to the ,permian breccia of ,england will probably yet be found to hold good in regard to much of that of ,north ,germany4#age ,and there appears to be some ground for concluding that the cold of that period even reached to ,india4#agf ,south ,africa4--,an ancient boulder clay1 supposed to be either of ,permian or ,jurassic age1 has been extensively found in ,natal1 ,south ,africa4 ,this deposit1 discovered by ,dr4 ,sutherland1 the ,surveyor-,general of the colony1 is thus described by ,dr4 ,mann3-- 8,the deposit itself consists of a greyish-blue argillaceous matrix1 containing fragments of granite1 gneiss1 graphite1 quartzite1 greenstone1 and clay-slate4 ,these imbedded fragments are of various size1 from the minute dimensions of sand-grains up to vast blocks measuring #f feet across1 and weighing from #e to #aj tons4 ,they are smoothed1 as if they had been subject to a certain amount of attrition in a muddy sediment2 but they are not rounded like boulders that have been subjected to sea-breakers4 ,the fracture of the rock is not conchoidal1 and there is manifest1 in its substance1 a rude disposition towards wavy stratification40 8,dr4 ,sutherland inclines to think that the transport of vast massive blocks of several tons' weight1 the scoring of the subjacent surfaces of sandstone1 and the simultaneous deposition of minute sand-grains and large boulders in the same matrix1 all point to one agency as the only one which can be rationally admitted to account satisfactorily for the presence of this remarkable formation in the situations in which it is found4 ,he believes that the boulder-bearing clay of ,natal is of analogous nature to the great ,scandinavian drift1 to which it is certainly intimately allied in intrinsic mineralogical character2 that it is virtually a vast moraine of olden time2 and that ice1 in some form or other1 has had to do with its formation1 at least so far as the deposition of the imbedded fragments in the amorphous matrix are concerned40#agg ,in the discussion which followed the reading of ,dr4 ,sutherland's paper1 ,professor ,ramsay pointed out that in the ,natal beds enormous blocks of rock occurred1 which were #fj or #hj miles from their original home1 and still remained angular2 and there was a difficulty in accounting for the phenomena on any other hypothesis than that suggested4 ,mr4 ,stow1 in his paper on the ,karoo beds1 has expressed a similar opinion regarding the glacial character of the formation4#agh ,but we have in the ,karoo beds evidence not only of glaciation1 but of a much warmer condition of things than presently exists in that latitude4 ,this is shown from the fact that the shells of the ,trigona-beds indicate a tropical or subtropical condition of climate4 ,arctic ,regions4--,the evidence which we have of the existence of a warm climate during the ,permian period is equally conclusive4 ,the close resemblance of the flora of the ,permian period to that of ,carboniferous times evidently points to the former prevalence of a warm and equable climate4 ,and the existence of the magnesian limestone in high latitudes seems to indicate that during at least a part of the ,permian period1 just as during the accumulation of the carboniferous limestone1 a warm sea must have obtained in those latitudes4 ,,oolitic ,,period4 ,north of ,scotland4--,there is not wanting evidence of something like the action of ice during the ,oolitic period4#agi ,in the ,north of ,scotland ,mr4 ,james ,geikie says there is a coarse boulder conglomerate associated with the ,jurassic strata in the east of ,sutherland1 the possibly glacial origin of which long ago suggested itself to ,professor ,ramsay and other observers4 ,mr4 ,judd believes the boulders to have been floated down by ice from the ,highland mountains at the time the ,jurassic strata were being accumulated4 ,north ,greenland4--,during the ,oolitic period a warm condition of climate extended to ,north ,greenland4 ,for example1 in ,prince ,patrick's ,island1 at ,wilkie ,point1 in lat4 #gf #bj ,n41 and long4 #aag #bj ,w41 ,oolitic rocks containing an ammonite 7,ammonites ,mc,clintocki1 ,haughton71 like ,a4 concavus and other shells of ,oolitic species1 were found by ,captain ,mc,clintock4#ahj ,in ,katmai ,bay1 near ,behring's ,straits1 the following ,oolitic fossils were discovered--,ammonites ,wasnessenskii1 ,a4 biplex1 ,belemnites paxillosus1 and ,unio liassinus4#aha ,captain ,mc,clintock found at ,point ,wilkie1 in ,prince ,patrick's ,island1 lat4 #gf #bj1 a bone of ,ichthyosaurus1 and ,sir ,e4 ,belcher found in ,exmouth ,island1 lat4 #gf #af ,n41 and long4 #if ,w41 at an elevation of #egj feet above the level of the sea1 bones which were examined by ,professor ,owen1 and pronounced to be those of the same animal4#ahb ,mr4 ,salter remarks that at the time that these fossils were deposited1 8a condition of climate something like that of our own shores was prevailing in latitudes not far short of #hj ,n40#ahc ,and ,mr4 ,jukes says that during the ,oolitic period1 8in latitudes where now sea and land are bound in ice and snow throughout the year1 there formerly flourished animals and plants similar to those living in our own province at that time4 ,the questions thus raised10 continues ,mr4 ,jukes1 8as to the climate of the globe when cephalopods and reptiles such as we should expect to find only in warm or temperate seas1 could live in such high latitudes1 are not easy to answer40#ahd ,and ,professor ,haughton remarks1 that he thinks it highly improbable that any change in the position of land and water could ever have produced a temperature in the sea at #gf north latitude which would allow of the existence of ammonites1 especially species so like those that lived at the same time in the tropical warm seas of the ,south of ,england and ,france at the close of the ,liassic1 and commencement of the ,lower ,oolitic period4#ahe ,the great abundance of the limestone and coal of the ,oolitic system shows also the warm and equable condition of the climate which must have then prevailed4 ,,cretaceous ,,period4 ,croydon4--,a large block of crystalline rock resembling granite was found imbedded in a pit1 on the side of the old ,london and ,brighton road near ,purley1 about two miles south of ,croydon4 ,mr4 ,godwin-,austen has shown conclusively that it must have been transported there by means of floating ice4 ,this boulder was associated with loose sea-sand1 coarse shingle1 and a smaller boulder weighing twenty or twenty-five pounds1 and all water-worn4 ,these had all sunk together without separating4 ,hence they must have been firmly held together1 both during the time that they were being floated away1 and also whilst sinking to the bottom of the cretaceous sea4 ,mr4 ,godwin-,austen supposes the whole to have been carried away frozen to the bottom of a mass of ground-ice4 ,when the ice from melting became unable to float the mass attached to it1 the whole would then sink to the bottom together4#ahf ,dover4--,while the workmen were employed in cutting the tunnel on the ,london1 ,chatham1 and ,dover ,railway1 between ,lydden ,hill and ,shepherdswell1 a few miles from ,dover1 they came upon a mass of coal imbedded in chalk1 at a depth of #ahj feet4 ,it was about #d feet square1 and from #d to #aj inches thick4 ,the coal was friable and highly bituminous4 ,it resembled some of the ,wealden or ,jurassic coal1 and was unlike the true coal of the coal-measures4 ,the specific gravity of the coal precluded the supposition that it could have floated away of itself into the cretaceous sea4 8,considering its friability10 says ,mr4 ,godwin-,austen1 8,i do not think that the agency of a floating tree could have been engaged in its transport2 but1 looking at its flat1 angular form1 it seems to me that its history may agree with what ,i have already suggested with reference to the boulder in the chalk at ,croydon4 ,we may suppose that during the ,cretaceous period some bituminous beds of the preceding ,oolitic period lay so as to be covered with water near the sea-margin1 or along some river-bank1 and from which portions could be carried off by ice1 and so drifted away1 until the ice was no longer able to support its load40#ahg ,mr4 ,godwin-,austen then mentions a number of other cases of blocks being found in the chalk4 ,in regard to those cases he appropriately remarks that1 as the cases where the occurrence of such blocks has been observed are likely to be far less numerous than those which have escaped observation1 or failed to have been recorded1 and as the chalk exposed in pits and quarries bears only a most trifling proportion to the whole horizontal extent of the formation1 we have no grounds to conclude that the above are exceptional cases4 ,boulders have also been found in the cretaceous strata of the ,alps by ,escher von der ,linth4#ahh ,the existence of warm periods during the ,cretaceous age is plainly shown by the character of the flora and fauna of that age4 ,the fact that chalk is of organic origin implies that the climate must have been warm and genial1 and otherwise favourable to animal life4 ,this is further manifested by such plants as ,cycas and ,zamia1 which betoken a warm climate1 and by the corals and huge sauroid reptiles which then inhabited our waters4 ,it is1 in fact1 the tropical character of the fauna of that period which induced ,sir ,charles ,lyell to reject ,mr4 ,godwin-,austen's idea that the boulders found in the chalk had been transported by floating ice4 ,such a supposition1 implying a cold climate1 8is10 ,sir ,charles says1 8inconsistent with the luxuriant growth of large chambered univalves1 numerous corals1 and many fish1 and other fossils of tropical forms40 ,the recent discovery of the ,cretaceous formation in ,greenland shows that during that period a mild and temperate condition of climate must have prevailed in that continent up to high latitudes4 8,this formation in ,greenland10 says ,dr4 ,robert ,brown1 8has only been recently separated from the ,miocene formation1 with which it is associated and was supposed to be a part of4 ,it is1 as far as we yet know1 only found in the vicinity of ,kome or ,koke1 near the shores of ,omenak ,fjord1 in about #gj north latitude1 though traces have been found elsewhere on ,disco1 c4 ,the fossils hitherto brought to ,europe have been very few1 and consist of plants which are now preserved in the ,stockholm and ,copenhagen ,museums4 ,from these there seems little doubt that the age assigned to this limited deposit 7so far as we yet know7 by the celebrated palontologist1 ,professor ,oswald ,heer1 of ,zurich1 is the correct one40#ahi ,dr4 ,brown gives a list of the ,cretaceous flora found in ,greenland4 ,,eocene ,,period4 ,switzerland4--,in a coarse conglomerate belonging to the 8flysch0 of ,switzerland1 an ,eocene formation1 there are found certain immense blocks1 some of which consist of a variety of granite which is not known to occur in situ in any part of the ,alps4 ,some of the blocks are #aj feet and upwards in length1 and one at ,halekeren1 at the ,lake of ,thun1 is #aje feet in length1 #ij feet in breadth1 and #de feet in height4 ,similar blocks are found in the ,apennines4 ,these unmistakably indicate the presence of glaciers or floating ice4 ,this conclusion is further borne out by the fact that the 8flysch0 is destitute of organic remains4 ,but the hypothesis that these huge masses were transported to their present sites by glaciers or floating ice has been always objected to1 says ,sir ,charles ,lyell1 8on the ground that the ,eocene strata of ,nummulitic age in ,switzerland1 as well as in other parts of ,europe1 contain genera of fossil plants and animals characteristic of a warm climate4 ,and it has been particularly remarked10 he continues1 8by ,m4 ,desor that the strata most nearly associated with the #8flysch' in the ,alps are rich in echinoderms of the ,spatangus family which have a decided tropical aspect40#aij ,but according to the theory of ,secular ,changes of ,climate1 the very fact that the 8flysch0 is immediately associated with beds indicating a warm or even tropical condition of climate1 is one of the strongest proofs which could be adduced in favour of its glacial character1 for the more severe a cold period of a glacial epoch is1 the warmer will be the periods which immediately precede and succeed4 ,these crocodiles1 tortoises1 and tropical flora probably belong to a warm ,eocene inter-glacial period4 ,,miocene ,,period4 ,italy4--,we have strong evidence in favour of the opinion that a glacial epoch existed during the ,miocene period4 ,it has been shown by ,m4 ,gastaldi1 that during that age ,alpine glaciers extended to the sea-level4 ,near ,turin there is a series of hills1 rising about #ejj or #fjj feet above the valleys1 composed of beds of ,miocene sandstone1 marl1 and gravel1 and loose conglomerate4 ,these beds have been carefully examined and described by ,m4 ,gastaldi4#aia ,the hill of the ,luperga has been particularly noticed by him4 ,many of the stones in these beds are striated in a manner similar to those found in the true till or boulder clay of this country4 ,but what is most remarkable is the fact that large erratic blocks of limestone1 many of them from #aj to #ae feet in diameter1 are found in abundance in these beds4 ,it has been shown by ,gastaldi that these blocks have all been derived from the outer ridge of the ,alps on the ,italian side1 namely1 from the range extending from ,ivrea to the ,lago ,maggiore1 and consequently they must have travelled from twenty to eighty miles4 ,so abundant are these large blocks1 that extensive quarries have been opened in the hills for the sake of procuring them4 ,these facts prove not only the existence of glaciers on the ,alps during the ,miocene period1 but of glaciers extending to the sea and breaking up into icebergs2 the stratification of the beds amongst which the blocks occur sufficiently indicating aqueous action and the former presence of the sea4 ,that the glaciers of the ,southern ,alps actually reached to the sea1 and sent their icebergs adrift over what are now the sunny plains of ,northern ,italy1 is sufficient proof that during the cold period of ,miocene times the climate must have been very severe4 ,indeed1 it may well have been as severe as1 if not even more excessive than1 the intensest severity of climate experienced during the last great glacial epoch4 ,greenland4--,of the existence of warm conditions during ,miocene times1 geology affords us abundant evidence4 ,i shall quote the opinion of ,sir ,charles ,lyell on this point3-- 8,we know10 says ,sir ,charles1 8that ,greenland was not always covered with snow and ice2 for when we examine the tertiary strata of ,disco ,island 7of the ,upper ,miocene period71 we discover there a multitude of fossil plants which demonstrate that1 like many other parts of the arctic regions1 it formerly enjoyed a mild and genial climate4 ,among the fossils brought from that island1 lat4 #gj ,n41 ,professor ,heer has recognised ,sequoia ,landsdorfii1 a coniferous species which flourished throughout a great part of ,europe in the ,miocene period4 ,the same plant has been found fossil by ,sir ,john ,richardson within the ,arctic ,circle1 far to the west on the ,mackenzie ,river1 near the entrance of ,bear ,river2 also by some ,danish naturalists in ,iceland1 to the east4 ,the ,icelandic surturband or lignite1 of this age1 has also yielded a rich harvest of plants1 more than thirty-one of them1 according to ,steenstrup and ,heer1 in a good state of preservation1 and no less than fifteen specifically identical with ,miocene plants of ,europe4 ,thirteen of the number are arborescent2 and amongst others is a tulip-tree 7,liriodendron71 with its fruit and characteristic leaves1 a plane 7,platanus71 a walnut1 and a vine1 affording unmistakable evidence of a climate in the parallel of the ,arctic ,circle which precludes the supposition of glaciers then existing in the neighbourhood1 still less any general crust of continental ice like that of ,greenland40#aib ,at a meeting of the ,british ,association1 held at ,nottingham in ,august #ahff1 ,professor ,heer read a valuable paper on the 8,miocene ,flora of ,north ,greenland40 ,in this paper some remarkable conclusions as to the probable temperature of ,greenland during the ,miocene period were given4 ,upwards of sixty different species brought from ,atanekerdluk1 a place on the ,waigat opposite ,disco1 in lat4 #gj ,n41 have been examined by him4 ,a steep hill rises on the coast to a height of #a1jhj feet1 and at this level the fossil plants are found4 ,large quantities of wood in a fossilized or carbonized condition lie about4 ,captain ,inglefield observed one trunk thicker than a man's body standing upright4 ,the leaves1 however1 are the most important portion of the deposit4 ,the rock in which they are found is a sparry iron ore1 which turns reddish brown on exposure to the weather4 ,in this rock the leaves are found1 in places packed closely together1 and many of them are in a very perfect condition4 ,they give us a most valuable insight into the nature of the vegetation which formed this primeval forest4 ,he arrives at the following conclusions3-- #a4 ,the fossilized plants of ,atanekerdluk cannot have been drifted from any great distance4 ,they must have grown on the spot where they were found4 ,this is shown-- 7a7 ,by the fact that ,captain ,inglefield and ,dr4 ,ruik observed trunks of trees standing upright4 7b7 ,by the great abundance of the leaves1 and the perfect state of preservation in which they are found4 7c7 ,by the fact that we find in the stone both fruits and seeds of the trees whose leaves are also found there4 7d7 ,by the occurrence of insect remains along with the leaves4 #b4 ,the flora of ,atanekerdluk is ,miocene4 #c4 ,the flora is rich in species4 #d4 ,the flora proves without a doubt that ,north ,greenland1 in the ,miocene epoch1 had a climate much warmer than its present one4 ,the difference must be at least #bi ,f4 ,professor ,heer discusses at considerable length this proposition4 ,he says that the evidence from ,greenland gives a final answer to those who objected to the conclusions as to the ,miocene climate of ,europe drawn by him on a former occasion4 ,it is quite impossible that the trees found at ,atanekerdluk could ever have flourished there if the temperature were not far higher than it is at present4 ,this is clear from many of the species1 of which we find the nearest living representative #aj or even #bj of latitude to the south of the locality in question4 ,the trees of ,atanekerdluk were not1 he says1 all at the extreme northern limit of their range1 for in the ,miocene flora of ,spitzbergen1 lat4 #gh ,n41 we find the beech1 plane1 hazelnut1 and some other species identical with those from ,greenland1 and we may conclude1 he thinks1 that the firs and poplars which we meet at ,atanekerdluk and ,bell ,sound1 ,spitzbergen1 must have reached up to the ,north ,pole if land existed there in the tertiary period4 8,the hills of fossilized wood10 he adds1 8found by ,mc,clure and his companions in ,banks's ,land 7lat4 #gd #bg ,n471 are therefore discoveries which should not astonish us1 they only confirm the evidence as to the original vegetation of the polar regions which we have derived from other sources40 ,the ,sequoia landsdorfii is the most abundant of the trees of ,atanekerdluk4 ,the ,sequoia sempervirens is its present representative4 ,this tree has its extreme northern limit about lat4 #ec ,n4 ,for its existence it requires a summer temperature of #ei or #fa ,f4 ,its fruit requires a temperature of #fd for ripening4 ,the winter temperature must not fall below #cd1 and that of the whole year must be at least #di4 ,the temperature of ,atanekerdluk during the time that the ,miocene flora grew could not have been under the above4#aic ,professor ,heer concludes his paper as follows3-- 8,i think these facts are convincing1 and the more so that they are not insulated1 but confirmed by the evidence derivable from the ,miocene flora of ,iceland1 ,spitzbergen1 and ,northern ,canada4 ,these conclusions1 too1 are only links in the grand chain of evidence obtained from the examination of the ,miocene flora of the whole of ,europe4 ,they prove to us that we could not by any re-arrangement of the relative positions of land and water produce for the northern hemisphere a climate which would explain the phenomena in a satisfactory manner4 ,we must only admit that we are face to face with a problem1 whose solution in all probability must be attempted1 and1 we doubt not1 completed by the astronomer40 ,,chapter ,,xix4 ,,geological ,,time4--,,probable ,,date ,,of ,,the ,,glacial ,,epoch4 ,geological ,time measurable from ,astronomical ,data4--,m4 ,leverrier's ,formul4--,tables of ,eccentricity for #c1jjj1jjj ,years in the ,past and #a1jjj1jjj ,years in the ,future4--,how the ,tables have been computed4--,why the ,glacial ,epoch is more recent than had been supposed4--,figures convey a very inadequate ,conception of immense ,duration4--,mode of representing a ,million of ,years4--,probable ,date of the ,glacial ,epoch4 ,if those great ,secular variations of climate which we have been considering be indirectly the result of changes in the eccentricity of the earth's orbit1 then we have a means of determining1 at least so far as regards recent epochs1 when these variations took place4 ,if the glacial epoch be due to the causes assigned1 we have a means of ascertaining1 with tolerable accuracy1 not merely the date of its commencement1 but the length of its duration4 ,m4 ,leverrier has not only determined the superior limit of the eccentricity of the earth's orbit1 but has also given formul by means of which the extent of the eccentricity for any period1 past or future1 may be computed4 ,a well-known astronomer and mathematician1 who has specially investigated the subject1 is of opinion that these formul give results which may be depended upon as approximately correct for four millions of years past and future4 ,an eminent physicist has1 however1 expressed to me his doubts as to whether the results can be depended on for a period so enormous4 ,m4 ,leverrier in his ,memoir has given a table of the eccentricity for #ajj1jjj years before and after #ahjj ,a4,d41 computed for intervals of #aj1jjj years4 ,this table1 no doubt1 embraces a period sufficiently great for ordinary astronomical purposes1 but it is by far too limited to afford information in regard to geological epochs4 ,with the view of ascertaining the probable date of the glacial epoch1 as well as the character of the climate for a long course of ages1 ,table ,i4 was computed from ,m4 ,leverrier's formul4#aid ,it shows the eccentricity of the earth's orbit and longitude of the perihelion for #c1jjj1jjj of years back1 and #a1jjj1jjj of years to come1 at periods #ej1jjj years apart4 ,on looking over the table it will be seen that there are three principal periods when the eccentricity rose to a very high value1 with a few subordinate maxima between4 ,it will be perceived also that during each of those periods the eccentricity does not remain at the same uniform value1 but rises and falls1 in one case twice1 and in the other two cases three times4 ,about #b1fej1jjj years back we have the eccentricity almost at its inferior limit4 ,it then begins to increase1 and fifty thousand years afterwards1 namely at #b1fjj1jjj years ago1 it reaches #jffj2 fifty thousand years after this period it has diminished to #jafg1 which is about its present value4 ,it then begins to increase1 and in another fifty thousand years1 namely at #b1ejj1jjj years ago1 it approaches to almost the superior limit1 its value being then #jgba4 ,it then begins to diminish1 and at #b1dej1jjj years ago it has diminished to #jbeb4 ,these two maxima1 separated by a minimum and extending over a period of #bjj1jjj years1 constitute the first great period of high eccentricity4 ,we then pass onwards for upwards of a million and a half years1 and we come to the second great period4 ,it consists of three maxima separated by two minima4 ,the first maximum occurred at #iej1jjj years ago1 the second or middle one at #hej1jjj years ago1 and the third and last at #gej1jjj years ago--the whole extending over a period of nearly #cjj1jjj years4 ,passing onwards for another million and half years1 or to about #hjj1jjj years in the future1 we come to the third great period4 ,it also consists of three maxima one hundred thousand years apart4 ,those occur at the periods #hjj1jjj1 #ijj1jjj1 and #a1jjj1jjj years to come1 respectively1 separated also by two minima4 ,those three great periods1 two of them in the past and one of them in the future1 included in the ,table1 are therefore separated from each other by an interval of upwards of #a1gjj1jjj years4 ,illustration3 ,,plate ,,iv ,w4 ,a4 ,k4 ,johnston1 ,edinbr4 and ,london4 ,,diagram ,,representing ,,the ,,variations ,,in ,,the ,,eccentricity ,,of ,,the ,,earth',s ,,orbit ,,for ,,three ,,million ,,of ,,years ,,before #ahjj ,a4,d4 ,,one ,,million ,,of ,,years ,,after ,,it4 ,the ,ordinates are joined by straight lines where the values1 at intervals of #aj1jjj years1 between them have not been determined4 ,in this ,table there are seven periods when the earth's orbit becomes nearly circular1 four in the past and three in the future4 ,the ,table shows also four or five subordinate periods of high eccentricity1 the principal one occurring #bjj1jjj years ago4 ,the variations of eccentricity during the four millions of years1 are represented to the eye diagrammatically in ,plate ,,iv4 ,in order to determine with more accuracy the condition of the earth's orbit during the three periods of great eccentricity included in ,table ,i41 ,i computed the values for periods of ten thousand years apart1 and the results are embodied in ,tables ,,ii41 ,,iii41 and ,,iv4 ,there are still eminent astronomers and physicists who are of opinion that the climate of the globe never could have been seriously affected by changes in the eccentricity of its orbit4 ,this opinion results1 no doubt1 from viewing the question as a purely astronomical one4 ,viewed from an astronomical standpoint1 as has been already remarked1 there is actually nothing from which any one could reasonably conclude with certainty whether a change of eccentricity would seriously affect climate or not4 ,by means of astronomy we ascertain the extent of the eccentricity at any given period1 how much the winter may exceed the summer in length 7or the reverse71 how much the sun's heat is increased or decreased by a decrease or an increase of distance1 and so forth2 but we obtain no information whatever regarding how these will actually affect climate4 ,this1 as we have already seen1 must be determined wholly from physical considerations1 and it is an exceedingly complicated problem4 ,an astronomer1 unless he has given special attention to the physics of the question1 is just as apt to come to a wrong conclusion as any one else4 ,the question involves certain astronomical elements2 but when these are determined everything then connected with the matter is purely physical4 ,nearly all the astronomical elements of the question are comprehended in the accompanying ,tables4 ,,table ,i4 ,,the ,,eccentricity ,,and ,,longitude ,,of ,,the ,,perihelion ,,of ,,the ,,earth',s ,,orbit ,,for #c1jjj1jjj ,,years ,,in ,,the ,,past ,,and #a1jjj1jjj ,,years ,,in ,,the ,,future1 ,,computed ,,for ,,intervals ,,of #ej1jjj ,,years4 ---------------------------------------- ----- ,,past ,,time4 ---------------------------------------- --- ,number of years ,eccentricity4,longitude of before epoch #ahjj4 perihelion4 ---------------------------------------- --- #c1jjj1jjj #jjcfe #ci #cj #b1iej1jjj #jjagj #baj #ci #b1ijj1jjj #jjddb #bjj #eb #b1hej1jjj #jjdaf #j #ah #b1hjj1jjj #jjceb #cci #ad #b1gej1jjj #jjcbf #afa #bb #b1gjj1jjj #jjccj #fe #cg #b1fej1jjj #jjjec #cah #dj #b1fjj1jjj #jjffj #aij #d #b1eej1jjj #jjafg #bih #cd #b1ejj1jjj #jjgba #cch #cf #b1dej1jjj #jjbeb #aji #cc #b1djj1jjj #jjdae #aaf #dj #b1cej1jjj #jjbha #cjh #bc #b1cjj1jjj #jjbch #aie #be #b1bej1jjj #jjcbh #ada #ah #b1bjj1jjj #jjceb #cjg #f #b1aej1jjj #jjahc #cjg #e #b1ajj1jjj #jjcjd #ih #dj #b1jej1jjj #jjagj #ccd #df #b1jjj1jjj #jjach #cbd #d #a1iej1jjj #jjdbg #abj #cb #a1ijj1jjj #jjccf #ahh #ca #a1hej1jjj #jjejc #bgb #ad #a1hjj1jjj #jjccd #ced #eb #a1gej1jjj #jjcej #fe #be #a1gjj1jjj #jjjhe #ie #ac #a1fej1jjj #jjjce #afh #bc #a1fjj1jjj #jjcje #aeh #db #a1eej1jjj #jjbci #bbe #eg #a1ejj1jjj #jjdcj #cjc #bi #a1dej1jjj #jjaie #eg #aa #a1djj1jjj #jjcae #ig #ce #a1cej1jjj #jjcbb #bic #ch #a1cjj1jjj #jjjbb #j #dh #a1bej1jjj #jjdge #aje #ej #a1bjj1jjj #jjbhi #bci #cd #a1aej1jjj #jjdgc #bej #bg #a1ajj1jjj #jjcaa #ee #bd #a1jej1jjj #jjcbf #d #h #a1jjj1jjj #jjaea #bdh #bb #iej1jjj #jjeag #ig #ea #ijj1jjj #jjajb #ace #b #hej1jjj #jjgdg #bci #bh #hjj1jjj #jjacb #cdc #di #gej1jjj #jjege #bg #ah #gjj1jjj #jjbbj #bjh #ac #fej1jjj #jjbbf #ada #bi #fjj1jjj #jjdag #cb #cd #eej1jjj #jjaff #bea #ej #ejj1jjj #jjchh #aic #ef #dej1jjj #jjcjh #cef #eb #djj1jjj #jjagj #bij #g #cej1jjj #jjaie #ahb #ej #cjj1jjj #jjdbd #bc #bi #bej1jjj #jjbeh #ei #ci #bjj1jjj #jjefi #afh #ah #aej1jjj #jjccb #bdb #ef #ajj1jjj #jjdgc #caf #ah #ej1jjj #jjaca #ej #ad ---------------------------------------- --- ---------------------------------------- ----- ,,future ,,time4 ---------------------------------------- --- ,number of years ,eccentricity4,longitude of before epoch #ahjj4 perihelion4 ---------------------------------------- --- ,a4,d4 #ahjj #jjafh #ii #cj #ej1jjj #jjagc #ch #ab #ajj1jjj #jjaia #aad #ej #aej1jjj #jjcec #bja #eg #bjj1jjj #jjbdf #bgi #da #bej1jjj #jjbhf #cej #ed #cjj1jjj #jjaeh #agb #bi #cej1jjj #jjjih #bja #dj #djj1jjj #jjdbi #f #i #dej1jjj #jjbca #ih #cg #ejj1jjj #jjecd #aeg #bf #eej1jjj #jjbei #bhg #ca #fjj1jjj #jjcie #bhe #dc #fej1jjj #jjafi #add #c #gjj1jjj #jjceg #ag #ab #gej1jjj #jjaie #j #ec #hjj1jjj #jjfci #adj #ch #hej1jjj #jjadd #agf #da #ijj1jjj #jjfei #bia #af #iej1jjj #jjjhf #aae #ac #a1jjj1jjj #jjebh #eg #ca ---------------------------------------- --- ,,table ,,ii4 ,,eccentricity1 ,,longitude ,,of ,,the ,,perihelion1 ,c41 ,c41 ,,for ,,intervals ,,of #aj1jjj ,,years1 ,,from #b1fej1jjj ,,to #b1dej1jjj ,,years ,,ago4 ,,the ,,glacial ,,epoch ,,of ,,the ,eocene period ,,is ,,probably ,,comprehended ,,within ,,this ,,table4 ---------------------------------------- ---------------------------------------- ------ ,i4 ,,ii4 ,,iii4 ,,iv4 ,winter occurring in aphelion4 ---------------------------------------- ,v4 ,,vi4 ,,vii4 ,,viii4 ,number of,eccentricity,longitude ,number of ,excess of,midwinter,number of ,midwinter years of orbit4 of degrees winter intensitydegrees by temperature before perihelion4 passed over of the which the of ,great ,a4,d4 over by the summer1 sun's midwinter ,britain4 #ahjj4 perihelion4in days4 heat4 temperature ,motion ,present is lowered retrograde intensity at periods #ajjj4 marked ,r4 ---------------------------------------- ---------------------------------------- --- #b1fej1jjj #jjjec #cah #dj ,f4 ,f4 #b1fdj1jjj #jjagc #ed #be #ie #de #b1fcj1jjj #jjcca #ic #cg #ci #ab #aed #ijf #bfb #abh #b1fbj1jjj #jjdgi #abg #ab #cc #ce #bbb #hhd #ccc #eg #b1faj1jjj #jjeia #aeh #cf #ca #bd #bgd #hfb #chc #jg #b1fjj1jjj #jjffj #aij #d #ca #bh #cjf #hea #dae #be #b1eij1jjj #jjfff #bbj #bh #cj #bd #cji #hej #dah #bh #b1ehj1jjj #jjfji #bdi #ef #bi #bh #bhc #hei #cib #jb ---------------------------------------- ---------------------------------------- --- #b1egj1jjj #jjdib #bgg #bd #bg #bh #bbi #hgh #cci #ea #b1efj1jjj #jjcej #cje #b #bg #ch #afb #ijb #bga #aai #b1eej1jjj #jjafg #bih #cd ,r #f #bh #b1edj1jjj #jjaib #bec #eh ,r #dd #cf #b1ecj1jjj #jjcfi #bei #ai #e #ba #aga #hii #bhj #aaj #b1ebj1jjj #jjecg #bhc #g #bc #dh #bej #hga #cei #ca #b1eaj1jjj #jjffj #caj #d #bf #eg #cjf #hea #dae #be #b1ejj1jjj #jjgba #cch #cf #bh #cb #cce #hda #ddb #eb #b1dij1jjj #jjgbb #g #cf #bi #j #ccf #hda #ddc #ec #b1dhj1jjj #jjffb #ce #df #bh #aj #cjh #hej #dag #bg #b1dgj1jjj #jjeec #fc #bf #bg #dj #beg #hfh #cff #bd #b1dfj1jjj #jjdaj #hi #ac #be #dg #aia #hib #cjj #ij #b1dej1jjj #jjbeb #aji #cc #bj #bj #aag ---------------------------------------- ---------------------------------------- --- ,,table ,,iii4 ,,eccentricity1 ,,longitude ,,of ,,the ,,perihelion1 ,c41 ,c41 ,,for ,,intervals ,,of #aj1jjj ,,years1 ,,from #a1jjj1jjj ,,to #gej1jjj ,,years ,,ago4 ,,the ,,glacial ,,epoch ,,of ,,the ,miocene period ,,is ,,probably ,,comprehended ,,within ,,this ,,table4 ---------------------------------------- ---------------------------------------- ------ ,i4 ,,ii4 ,,iii4 ,,iv4 ,winter occurring in aphelion4 ---------------------------------------- ,v4 ,,vi4 ,,vii4 ,,viii4 ,number of,eccentricity,longitude ,number of ,excess of,midwinter,number of ,midwinter years of orbit4 of degrees winter intensitydegrees by temperature before perihelion4 passed over of the which the of ,great ,a4,d4 over by the summer1 sun's midwinter ,britain4 #ahjj4 perihelion4in days4 heat4 temperature ,motion ,present is lowered retrograde intensity at periods #ajjj4 marked ,r4 ---------------------------------------- ---------------------------------------- --- #a1jjj1jjj #jjaea #bdh #bb ,f4 ,f4 #iij1jjj #jjbbd #cac #ej #fe #bh #ihj1jjj #jjcbi #ceh #b #dd #ab #aec #ijf #bfa #abi #igj1jjj #jjdda #cb #dj #cd #ch #bje #hhg #cae #ge #ifj1jjj #jjdia #ff #di #cd #i #bbh #hgh #cch #eb #iej1jjj #jjeag #ig #ea #ca #b #bdj #hgd #cej #dj #idj1jjj #jjdie #abg #db #bi #ea #bcj #hgh #cdj #ej #icj1jjj #jjdbc #aef #aa #bh #bi #aig #hij #cjf #hd #ibj1jjj #jjcje #aha #dj #be #bi #adb #iaj #bej #adj #iaj1jjj #jjaef #aid #ae #ab #ce #ijj1jjj #jjajb #ace #b ,r #ei #ac #hij1jjj #jjbhe #abg #a ,r #h #a #hhj1jjj #jjdef #aeb #cc #be #cb #bab #hhd #cbb #fh #hgj1jjj #jjfjg #ahj #bc #bg #ej #bhb #hei #cij #jj #hfj1jjj #jjgjh #bji #da #bi #ah #cbi #hdc #dcf #df #hej1jjj #jjgdg #bci #bh #bi #dg #cdg #hcg #dec #fc #hdj1jjj #jjfih #bfi #ad #bi #df #cbd #hde #dcb #db #hcj1jjj #jjfbc #bih #bh #bi #ad #bij #heg #djj #aj #hbj1jjj #jjdgf #cbf #d #bg #cf #bba #hha #cca #ei #haj1jjj #jjbif #cdh #cj #bb #bf #hjj1jjj #jjacb #cdc #di ,r #d #da #gij1jjj #jjaga #bic #ai ,r #ej #cj #ghj1jjj #jjcbe #cjc #cg #aj #ah #aeb #ijg #bfj #acj #ggj1jjj #jjdee #cbh #ch #be #a #bab #hhd #cbb #fh #gfj1jjj #jjedj #ceg #ab #bh #cd #bea #hgj #cfj #cj #gej1jjj #jjege #bg #ah #cj #f #bfg #hfd #cgg #ac #gdj1jjj #jjefa #eh #cj #ca #ab #bfa #hfg #cgj #bj #gcj1jjj #jjejg #ij #ee #cb #be #bcf #hgf #cdf #dd #gbj1jjj #jjdbb #abe #ad #cd #ai #aif #hij #cjf #hd #gaj1jjj #jjcjg #agg #bf #eb #ab #adc #iaj #bej #adj #gjj1jjj #jjbbj #bjh #ac #cj #dg ---------------------------------------- ---------------------------------------- --- ,,table ,,iv4 ,,eccentricity1 ,,longitude ,,of ,,the ,,perihelion1 ,c41 ,c41 ,,for ,,intervals ,,of #aj1jjj ,,years1 ,,from #bej1jjj ,,years ,,ago ,,to ,,the ,,present ,,date4 ,,the ,glacial epoch ,,is ,,probably ,,comprehended ,,within ,,this ,,table4 ---------------------------------------- ---------------------------------------- ------ ,i4 ,,ii4 ,,iii4 ,,iv4 ,winter occurring in aphelion4 ---------------------------------------- ,v4 ,,vi4 ,,vii4 ,,viii4 ,number of,eccentricity,longitude ,number of ,excess of,midwinter,number of ,midwinter years of orbit4 of degrees winter intensitydegrees by temperature before perihelion4 passed over of the which the of ,great ,a4,d4 over by the summer1 sun's midwinter ,britain4 #ahjj4 perihelion4in days4 heat4 temperature ,motion ,present is lowered retrograde intensity at periods #ajjj4 marked ,r4 ---------------------------------------- ---------------------------------------- --- ,f4 ,f4 #bej1jjj #jjbeh #ei #ci #bdj1jjj #jjcgd #gd #eh #ae #ai #agd #hih #bhc #ajg ,s #bcj1jjj #jjdgg #ajb #di #bg #ea #bbb #hhe #ccb #eh ,s #bbj1jjj #jjdig #abd #cc #ba #dd #bcb #hgg #cda #di ,s #baj1jjj #jjege #add #ee #bj #bb #bfg #hfd #cgg #ac #bjj1jjj #jjefi #afh #ah #bc #bc #bfe #hfe #cgd #af ,s #aij1jjj #jjecb #aij #d #ba #df #bdg #hga #ceg #cc ,s #ahj1jjj #jjdgf #bji #bb #ai #ah #bba #hha #cca #ei ,s #agj1jjj #jjdcg #bbh #g #ah #de #bjc #hhg #cac #gg #afj1jjj #jjcfd #bcf #ch #h #ca #afi #ijj #bgh #aab #aej1jjj #jjccb #bdb #ef #f #ah #aed #ije #bfb #abh #adj1jjj #jjcdf #bdf #bi #c #cc #afa #ijc #bfi #aba #acj1jjj #jjchd #bei #cd #ac #e #agh #hif #bhh #ajb #abj1jjj #jjdca #bgd #dg #ae #ac #bja #hhh #caj #hj #aaj1jjj #jjdfj #bic #dh #ai #a #bad #hhc #cbd #ff #ajj1jjj #jjdgc #caf #ah #bb #cj #bbj #hha #ccj #fj ,l #ij1jjj #jjdeb #cdj #b #bc #dd #baj #hhe #cbj #gj ,l #hj1jjj #jjcih #d #ac #bd #aa #ahe #hid #bid #if ,l #gj1jjj #jjcaf #bg #bb #bc #i #adg #ijh #bee #ace ,l #fj1jjj #jjbah #df #h #ah #df #ej1jjj #jjaca #ej #ad #d #f ,l #dj1jjj #jjaji #bh #cf ,r #ba #ch ,l #cj1jjj #jjaea #e #ej ,r #bb #df ,l #bj1jjj #jjahh #dd #j #ch #aj ,l #aj1jjj #jjahg #gh #bh #cd #bh ,a4,d4 #ahjj #jjafh #ii #cj #ba #b ---------------------------------------- ---------------------------------------- --- ,in ,tables ,,ii41 ,,iii41 and ,,iv41 column ,i4 represents the dates of the periods1 column ,,ii4 the eccentricity1 column ,,iii4 the longitude of the perihelion4 ,in ,table ,,iv4 the eccentricity and the longitude of the perihelion of the six periods marked with an ,s are copied from a letter of ,mr4 ,stone to ,sir ,charles ,lyell1 published in the ,supplement of the ,phil4 ,mag4 for ,june1 #ahfe2 the eight periods marked ,l are copied from ,m4 ,leverrier's ,table1 to which reference has been made4 ,for the correctness of everything else1 both in this ,table and in the other three1 ,i alone am responsible4 ,column ,,iv4 gives the number of degrees passed over by the perihelion during each #aj1jjj years4 ,from this column it will be seen how irregular is the motion of the perihelion4 ,at four different periods it had a retrograde motion for #bj1jjj years4 ,column ,v4 shows the number of days by which the winter exceeds the summer when the winter occurs in aphelion4 ,column ,,vi4 shows the intensity of the sun's heat during midwinter1 when the winter occurs in aphelion1 the present midwinter intensity being taken at #a1jjj4 ,these six columns comprehend all the astronomical part of the ,tables4 ,regarding the correctness of the principles upon which these columns are constructed1 there is no diversity of opinion4 ,but these columns afford no direct information as to the character of the climate1 or how much the temperature is increased or diminished4 ,to find this we pass on to columns ,,vii4 and ,,viii41 calculated on physical principles4 ,now1 unless the physical principles upon which these three columns are calculated be wholly erroneous1 change of eccentricity must undoubtedly very seriously affect climate4 ,column ,,vii4 shows how many degrees ,fahrenheit the temperature is lowered by a decrease in the intensity of the sun's heat corresponding to column ,,vi4 ,for example1 #hej1jjj years ago1 if the winters occurred then in aphelion1 the direct heat of the sun during midwinter would be only #hcg_/ajjj of what it is at present at the same season of the year1 and column ,,vii4 shows that this decrease in the intensity of the sun's heat would lower the temperature #dec ,f4 ,the principle upon which this result is arrived at is this3--,the temperature of space1 as determined by ,sir ,john ,herschel1 is #bci ,f4 ,m4 ,pouillet1 by a different method1 arrived at almost the same result4 ,if we take the midwinter temperature of ,great ,britain at #ci1 then #bci #ci #bgh will represent the number of degrees of rise due to the sun's heat at midwinter2 in other words1 it takes a quantity of sun-heat which we have represented by #ajjj to maintain the temperature of the earth's surface in ,great ,britain #bgh above the temperature of space4 ,were the sun extinguished1 the temperature of our island would sink #bgh below its present midwinter temperature1 or to the temperature of space4 ,but #hej1jjj years ago1 as will be seen from ,table ,,iii41 if the winters occurred in aphelion1 the heat of the sun at midwinter would only equal #hcg instead of #ajjj as at present4 ,consequently1 if it takes #a1jjj parts of heat to maintain the temperature #bgh above the temperature of space1 #hcg parts of heat will only be able to maintain the temperature #bcbg above the temperature of space2 for #bcbg is to #bgh as #hcg is to #a1jjj4 ,therefore1 if the temperature was then only #bcbg above that of space1 it would be #dec below what it is at present4 ,this is what the temperature would be on the supposition1 of course1 that it depended wholly on the sun's intensity and was not modified by other causes4 ,this method has already been discussed at some length in ,chapter ,,ii4 ,but whether these values be too high or too low1 one thing is certain1 that a very slight increase or a very slight decrease in the quantity of heat received from the sun must affect temperature to a considerable extent4 ,the direct heat of the moon1 for example1 cannot be detected by the finest instruments which we possess2 yet from #bch1jjj observations made at ,prague during #ahdjff1 it would seem that the temperature is sensibly affected by the mere change in the lunar perigee and inclination of the moon's orbit4#aie ,column ,,viii4 gives the midwinter temperature4 ,it is found by subtracting the numbers in column ,,vii4 from #ci1 the present midwinter temperature4 ,i have not given a ,table showing the temperature of the summers at the corresponding periods4 ,this could not well be done2 for there is no relation at the periods in question between the intensity of the sun's heat and the temperature of the summers4 ,one is apt to suppose1 without due consideration1 that the summers ought to be then as much warmer than they are at present1 as the winters were then colder than now4 ,sir ,charles ,lyell1 in his 8,principles10 has given a column of summer temperatures calculated from my table upon this principle4 ,astronomically the principle is correct1 but physically1 as was shown in ,chapter ,,iv41 it is totally erroneous1 and calculated to convey a wrong impression regarding the whole subject of geological climate4 ,the summers at those periods1 instead of being much warmer than they are at present1 would in reality be much colder1 notwithstanding the great increase in the intensity of the sun's heat resulting from the diminished distance of the sun4 ,what1 then1 is the date of the glacial epoch8 ,it is perfectly obvious that if the glacial epoch resulted from a high state of eccentricity1 it must be referred either to the period included in ,table ,,iii4 or to the one in ,table ,,iv4 ,in ,table ,,iii4 we have a period extending from about #ihj1jjj to about #gbj1jjj years ago1 and in ,table ,,iv4 we have a period beginning about #bdj1jjj years ago1 and extending down to about #hj1jjj years ago4 ,as the former period was of greater duration than the latter1 and the eccentricity also attained to a higher value1 ,i at first felt disposed to refer the glacial epoch proper 7the time of the till and boulder clay7 to the former period2 and the latter period1 ,i was inclined to believe1 must have corresponded to the time of local glaciers towards the close of the glacial epoch1 the evidence for which 7moraines7 is to be found in almost every one of our ,highland glens4 ,on this point ,i consulted several eminent geologists1 and they all agreed in referring the glacial epoch to the former period2 the reason assigned being that they considered the latter period to be much too recent and of too short duration to represent that epoch4 ,pondering over the subject during the early part of #ahff1 reasons soon suggested themselves which convinced me that the glacial epoch must be referred to the latter and not to the former period4 ,those reasons ,i shall now proceed to state at some length1 since they have a direct bearing1 as will be seen1 on the whole question of geological time4 ,it is the modern and philosophic doctrine of uniformity that has chiefly led geologists to over-estimate the length of geological periods4 ,this philosophic school teaches1 and that truly1 that the great changes undergone by the earth's crust must have been produced1 not by convulsions and cataclysms of nature1 but by those ordinary agencies that we see at work every day around us1 such as rain1 snow1 frost1 ice1 and chemical action1 c4 ,it teaches that the valleys were not produced by violent dislocations1 nor the hills by sudden upheavals1 but that they were actually carved out of the solid rock by the silent and gentle agency of chemical action1 frost1 rain1 ice1 and running water4 ,it teaches1 in short1 that the rocky face of our globe has been carved into hill and dale1 and ultimately worn down to the sea-level1 by means of these apparently trifling agents1 not only once or twice1 but probably dozens of times over during past ages4 ,now1 when we reflect that with such extreme slowness do these agents perform their work1 that we might watch their operations from year to year1 and from century to century1 if we could1 without being able to perceive that they make any very sensible advance1 we are necessitated to conclude that geological periods must be enormous4 ,and the conclusion at which we thus arrive is undoubtedly correct4 ,it is1 in fact1 impossible to form an adequate conception of the length of geological time4 ,it is something too vast to be fully grasped by our minds4 ,but here we come to the point where the fundamental mistake arises2 ,geologists do not err in forming too great a conception of the extent of geological periods1 but in the mode in which they represent the length of these periods in numbers4 ,when we speak of units1 tens1 hundreds1 thousands1 we can form some notion of what these quantities represent2 but when we come to millions1 tens of millions1 hundreds of millions1 thousands of millions1 the mind is then totally unable to follow1 and we can only use these numbers as representations of quantities that turn up in calculation4 ,we know1 from the way in which they do turn up in our process of calculation1 whether they are correct representations of things in actual nature or not2 but we could not1 from a mere comparison of these quantities with the thing represented by them1 say whether they were actually too small or too great4 ,at present1 geological estimates of time are little else than mere conjectures4 ,geological science has hitherto afforded no trustworthy means of estimating the positive length of geological epochs4 ,geological phenomena tell us most emphatically that these periods must be long2 but how long they have hitherto failed to inform us4 ,geological phenomena represent time to the mind under a most striking and imposing form4 ,they present to the eye1 as it were1 a sensuous representation of time2 the mind thus becomes deeply impressed with a sense of immense duration2 and when one under these feelings is called upon to put down in figures what he believes will represent that duration1 he is very apt to be deceived4 ,if1 for example1 a million of years as represented by geological phenomena and a million of years as represented by figures were placed before our eyes1 we should certainly feel startled4 ,we should probably feel that a unit with six ciphers after it was really something far more formidable than we had hitherto supposed it to be4 ,could we stand upon the edge of a gorge a mile and a half in depth that had been cut out of the solid rock by a tiny stream1 scarcely visible at the bottom of this fearful abyss1 and were we informed that this little streamlet was able to wear off annually only #a_/aj of an inch from its rocky bed1 what would our conceptions be of the prodigious length of time that this stream must have taken to excavate the gorge8 ,we should certainly feel startled when1 on making the necessary calculations1 we found that the stream had performed this enormous amount of work in something less than a million of years4 ,if1 for example1 we could possibly form some adequate conception of a period so prodigious as one hundred millions of years1 we should not then feel so dissatisfied with ,sir ,w4 ,thomson's estimate that the age of the earth's crust is not greater than that4 ,here is one way of conveying to the mind some idea of what a million of years really is4 ,take a narrow strip of paper an inch broad1 or more1 and #hc feet #d inches in length1 and stretch it along the wall of a large hall1 or round the walls of an apartment somewhat over #bj feet square4 ,recall to memory the days of your boyhood1 so as to get some adequate conception of what a period of a hundred years is4 ,then mark off from one of the ends of the strip #a_/aj of an inch4 ,the #a_/aj of the inch will then represent one hundred years1 and the entire length of the strip a million of years4 ,it is well worth making the experiment1 just in order to feel the striking impression that it produces on the mind4 ,the latter period1 which we have concluded to be that of the glacial epoch1 extended1 as we have seen1 over a period of #afj1jjj years4 ,but as the glaciation was only on one hemisphere at a time1 #hj1jjj years or so would represent the united length of the cold periods4 ,in order to satisfy ourselves that this period is sufficiently long to account for all the amount of denudation effected during the glacial epoch1 let us make some rough estimate of the probable rate at which the surface of the country would be ground down by the ice4 ,suppose the ice to grind off only one-tenth of an inch annually this would give upwards of #fej feet as the quantity of rock removed during the time4 ,but it is probable that it did not amount to one-fourth part of that quantity4 ,whether one-tenth of an inch per annum be an over-estimate or an under-estimate of the rate of denudation by the ice1 it is perfectly evident that the period in question is sufficiently long1 so far as denudation is concerned1 to account for the phenomena of the glacial epoch4 ,but admitting that the period under consideration is sufficiently long to account for all the denudation which took place during the glacial epoch1 we have yet to satisfy ourselves that it is also sufficiently remote to account for all the denudation which has taken place since the glacial epoch4 ,are the facts of geology consistent with the idea that the close of the glacial epoch does not date back beyond #hj1jjj years8 ,this question could be answered if we knew the present rate of subarial denudation1 for the present rate evidently does not differ greatly from that which has obtained since the close of the glacial epoch4 ,,chapter ,,xx4 ,,geological ,,time4--,,method ,,of ,,measuring ,,the ,,rate ,,of ,,suba,,rial ,,denudation4 ,rate of ,subarial ,denudation a ,measure of ,time4--,rate determined from ,sediment of the ,mississippi4--,amount of ,sediment carried down by the ,mississippi2 by the ,ganges4--,professor ,geikie on ,modern ,denudation4--,professor ,geikie on the ,amount of ,sediment conveyed by ,european ,rivers4--,rate at which the ,surface of the ,globe is being denuded4--,alfred ,tylor on the ,sediment of the ,mississippi4--,the ,law which determines the ,rate of ,denudation4--,the ,globe becoming less oblate4--,carrying ,power of our ,river ,systems the true ,measure of ,denudation4--,marine ,denudation trifling in comparison to ,subarial4--,previous ,methods of measuring ,geological ,time4--,circumstances which show the recent ,date of the ,glacial ,epoch4--,professor ,ramsay on ,geological ,time4 ,it is almost self-evident that the rate of subarial denudation must be equal to the rate at which the materials are carried off the land into the sea1 but the rate at which the materials are carried off the land is measured by the rate at which sediment is carried down by our river systems4 ,consequently1 in order to determine the present rate of subarial denudation1 we have only to ascertain the quantity of sediment annually carried down by the river systems4 ,knowing the quantity of sediment transported by a river1 say annually1 and the area of its drainage1 we have the means of determining the rate at which the surface of this area is being lowered by subarial denudation4 ,and if we know this in reference to a few of the great continental rivers draining immense areas in various latitudes1 we could then ascertain with tolerable correctness the rate at which the surface of the globe is being lowered by subarial denudation1 and also the length of time which our present continents can remain above the sea-level4 ,explaining this to ,professor ,ramsay during the winter of #ahfe1 ,i learned from him that accurate measurements had been made of the amount of sediment annually carried down by the ,mississippi ,river1 full particulars of which investigations were to be found in the ,proceedings of the ,american ,association for the ,advancement of ,science for #ahdh4 ,these proceedings contain a report by ,messrs4 ,brown and ,dickeson1 which unfortunately over-estimated the amount of sediment transported by the ,mississippi by nearly four times what was afterwards found by ,messrs4 ,humphreys and ,abbot to be the actual amount4 ,from this estimate1 ,i was led to the conclusion that if the ,mississippi is a fair representative of rivers in general1 our existing continents would not remain longer than one million and a half years above the sea-level4#aif ,this was a conclusion so startling as to excite suspicion that there must have been some mistake in reference to ,messrs4 ,brown and ,dickeson's data4 ,it showed beyond doubt1 however1 that the rate of subarial denudation1 when accurately determined by this method1 would be found to be enormously greater than had been supposed4 ,shortly afterwards1 on estimating the rate from the data furnished by ,humphreys and ,abbot1 ,i found the rate of denudation to be about one foot in #f1jjj years4 ,taking the mean elevation of all the land as ascertained by ,humboldt to be #a1jjj feet1 the whole would therefore be carried down into the ocean by our river systems in about #f1jjj1jjj of years if no elevation of the land took place4#aig ,the following are the data and mode of computation by which this conclusion was arrived at4 ,it was found by ,messrs4 ,humphreys and ,abbot that the average amount of sediment held in suspension in the waters of the ,mississippi is about #a_/aejj of the weight of the water1 or #a_/bijj by bulk4 ,the annual discharge of the river is #ai1ejj1jjj1jjj1jjj cubic feet of water4 ,the quantity of sediment carried down into the ,gulf of ,mexico amounts to #f1gbd1jjj1jjj cubic feet4 ,but besides that which is held in suspension1 the river pushes down into the sea about #gej1jjj1jjj cubic feet of earthy matter1 making in all a total of #g1dgd1jjj1jjj cubic feet transferred from the land to the sea annually4 ,where does this enormous mass of material come from8 ,unquestionably it comes from the ground drained by the ,mississippi4 ,the area drained by the river is #a1bdd1jjj square miles4 ,now #g1dgd1jjj1jjj cubic feet removed off #a1bbd1jjj square miles of surface is equal to #a_/deff of a foot off that surface per annum1 or one foot in #d1eff years4 ,the specific gravity of the sediment is taken at #ai1 that of rock is about #be2 consequently the amount removed is equal to one foot of rock in about #f1jjj years4 ,the average height of the ,north ,american continent above the sea-level1 according to ,humboldt1 is #gdh feet2 consequently1 at the present rate of denudation1 the whole area of drainage will be brought down to the sea-level in less than #d1ejj1jjj years1 if no elevation of the land takes place4 ,referring to the above1 ,sir ,charles ,lyell makes the following appropriate remarks3--8,there seems no danger of our overrating the mean rate of waste by selecting the ,mississippi as our example1 for that river drains a country equal to more than half the continent of ,europe1 extends through twenty degrees of latitude1 and therefore through regions enjoying a great variety of climate1 and some of its tributaries descend from mountains of great height4 ,the ,mississippi is also more likely to afford us a fair test of ordinary denudation1 because1 unlike the ,st4 ,lawrence and its tributaries1 there are no great lakes in which the fluviatile sediment is thrown down and arrested on its way to the sea40#aih ,the rate of denudation of the area drained by the river ,ganges is much greater than that of the ,mississippi4 ,the annual discharge of that river is #f1ebc1jjj1jjj1jjj cubic feet of water4 ,the sediment held in suspension is equal to #a_/eaj by weight2 area of drainage #dcb1dhj square miles4 ,this gives one foot of rock in #b1ceh years as the amount removed4 ,rough estimates have been made of the amount of sediment carried down by some eight or ten ,european rivers2 and although those estimates cannot be depended upon as being anything like perfectly accurate1 still they show 7what there is very little reason to doubt7 that it is extremely probable that the ,european continent is being denuded about as rapidly as the ,american4 ,for a full account of all that is known on this subject ,i must refer to ,professor ,geikie's valuable memoir on ,modern ,denudation 7,transactions of ,geological ,society of ,glasgow1 vol4 iii42 also ,jukes and ,geikie's 8,manual of ,geology10 chap4 xxv47 ,it is mainly through the instrumentality of this luminous and exhaustive memoir that the method under consideration has gained such wide acceptance amongst geologists4 ,professor ,geikie finds that at the present rate of erosion the following is the number of years required by the undermentioned rivers to remove one foot of rock from the general surface of their basins4 ,professor ,geikie thus shows that the rate of denudation1 as determined from the amount of sediment carried down the ,mississippi1 is certainly not too high4 ,danube #f1hdf years4 ,mississippi #f1jjj ,nith #d1gbc ,ganges #b1ceh ,rhone #a1ebh ,hoang ,ho #a1dfd ,po #gbi ,by means of subarial agencies continents are being cut up into islands1 the islands into smaller islands1 and so on till the whole ultimately disappears4 ,no proper estimate has been made of the quantity of sediment carried down into the sea by our ,british rivers4 ,but1 from the principles just stated1 we may infer that it must be as great in proportion to the area of drainage as that carried down by the ,mississippi4 ,for example1 the river ,tay1 which drains a great portion of the central ,highlands of ,scotland1 carries to the sea three times as much water in proportion to its area of drainage as is carried by the ,mississippi4 ,and any one who has seen this rapidly running river during a flood1 red and turbid with sediment1 will easily be convinced that the quantity of solid material carried down by it into the ,german ,ocean must be very great4 ,mr4 ,john ,dougall has found that the waters of the ,clyde during a flood hold in suspension #a_/hjj by bulk of sediment4 ,the observations were made about a mile above the city of ,glasgow4 ,but even supposing the amount of sediment held in suspension by the waters of the ,tay to be only one-third 7which is certainly an under-estimate7 of that of the ,mississippi1 viz4 #a_/dejj by weight1 still this would give the rate of denudation of the central ,highlands at one foot in #f1jjj years1 or #a1jjj feet in #f millions of years4 ,it is remarkable that although so many measurements have been made of the amount of fluviatile sediment being transported seawards1 yet that the bearing which this has on the broad questions of geological time and the rate of subarial denudation should have been overlooked4 ,one reason for this1 no doubt1 is that the measurements were made1 not with a view to determine the rate at which the river basins are being lowered1 but mainly to ascertain the age of the river deltas and the rate at which these are being formed4#aii ,the ,law which determines the ,rate at which any ,country is being denuded4--,by means of subarial agencies continents are being cut up into islands1 the islands into smaller islands1 and so on till the whole ultimately disappears4 ,so long as the present order of things remains1 the rate of denudation will continue while land remains above the sea-level2 and we have no warrant for supposing that the rate was during past ages less than it is at the present day4 ,it will not do to object that1 as a considerable amount of the sediment carried down by rivers is boulder clay and other materials belonging to the ,ice age1 the total amount removed by the rivers is on that account greater than it would otherwise be4 ,were this objection true1 it would follow that1 prior to the glacial period1 when it is assumed that there was no boulder clay1 the face of the country must have consisted of bare rock2 for in this case no soil could have accumulated from the disintegration and decomposition of the rocks1 since1 unless the rocks of a country disintegrate more rapidly than the river systems are able to carry the disintegrated materials to the sea1 no surface soil can form on that country4 ,the rate at which rivers carry down sediment is evidently not determined by the rate at which the rocks are disintegrated and decomposed1 but by the quantity of rain falling1 and the velocity with which it moves off the face of the country4 ,every river system possesses a definite amount of carrying-power1 depending upon the slope of the ground1 the quantity of rain falling per annum1 the manner in which the rain falls1 whether it falls gradually or in torrents1 and a few other circumstances4 ,when it so happens1 as it generally does1 that the amount of rock disintegrated on the face of the country is greater than the carrying-power of the river systems can remove1 then a soil necessarily forms4 ,but when the reverse is the case no soil can form on that country1 and it will present nothing but barren rock4 ,this is no doubt the reason why in places like the ,island of ,skye1 for example1 where the rocks are exceedingly hard and difficult to decompose and separate1 the ground steep1 and the quantity of rain falling very great1 there is so much bare rock to be seen4 ,if1 prior to the glacial epoch1 the rocks of the area drained by the ,mississippi did not produce annually more material from their destruction under atmospheric agency than was being carried down by that river1 then it follows that the country must have presented nothing but bare rock1 if the amount of rain falling then was as great as at present4 ,but1 after all1 one foot removed off the general level of the country since the creation of man1 according to ,mosaic chronology1 is certainly not a very great quantity4 ,no person but one who had some preconceived opinions to maintain1 would ever think of concluding that one foot of soil during #f1jjj years was an extravagant quantity to be washed off the face of the country by rain and floods during that long period4 ,those who reside in the country and are eye-witnesses of the actual effects of heavy rains upon the soil1 our soft country roads1 ditches1 brooks1 and rivers1 will have considerable difficulty in actually believing that only one foot has been washed away during the past #f1jjj years4 ,some may probably admit that a foot of soil may be washed off during a period so long as #f1jjj years1 and may tell us that what they deny is not that a foot of loose and soft soil1 but a foot of solid rock can be washed away during that period4 ,but a moment's reflection must convince them that1 unless the rocks of the country were disintegrating and decomposing as rapidly into soil as the rain is carrying the soil away1 the surface of the country would ultimately become bare rock4 ,it is true that the surface of our country in many places is protected by a thick covering of boulder clay2 but when this has once been removed1 the rocks will then disintegrate far more rapidly than they are doing at present4 ,but slow as is the rate at which the country is being denuded1 yet when we take into consideration a period so enormous as #f millions of years1 we find that the results of denudation are really startling4 ,one thousand feet of solid rock during that period would be removed from off the face of the country4 ,but if the mean level of the country would be lowered #a1jjj feet in #f millions of years1 how much would our valleys and glens be deepened during that period8 ,this is a problem well worthy of the consideration of those who treat with ridicule the idea that the general features of our country have been carved out by subarial agency4 ,in consequence of the retardation of the earth's rotation1 occasioned by the friction of the tidal wave1 the sea-level must be slowly sinking at the equator and rising at the poles4 ,but it is probable that the land at the equator is being lowered by denudation as rapidly as the sea-level is sinking4 ,nearly one mile must have been worn off the equator during the past #ab millions of years1 if the rate of denudation all along the equator be equal to that of the basin of the ,ganges4 ,it therefore follows that we cannot infer from the present shape of our globe what was its form1 or the rate at which it was rotating1 at the time when its crust became solidified4 ,although it had been as oblate as the planet ,jupiter1 denudation must in time have given it its present form4 ,there is another effect which would result from the denudation of the equator and the sinking of the ocean at the equator and its rise at the poles4 ,this1 namely1 that it would tend to increase the rate of rotation2 or1 more properly1 it would tend to lessen the rate of tidal retardation4 ,but if the rate of denudation be at present so great1 what must it have been during the glacial epoch8 ,it must have been something enormous4 ,at present1 denudation is greatly retarded by the limited power of our river systems to remove the loose materials resulting from the destruction of the rocks4 ,these materials accumulate and form a thick soil over the surface of the rocks1 which protects them1 to a great extent1 from the weathering effects of atmospheric agents4 ,so long as the amount of rock disintegrated exceeds that which is being removed by the river systems1 the soil will continue to accumulate till the amount of rock destroyed per annum is brought to equal that which is being removed4 ,it therefore follows from this principle that the ,,carrying-,,power ,,of ,,our ,,river ,,systems ,,is ,,the ,,true ,,measure ,,of ,,denudation4 ,but during the glacial epoch the thickness of the soil would have but little effect in diminishing the waste of the rocks2 for at that period the rocks were not decomposed by atmospheric agency1 but were ground down by the mechanical friction of the ice4 ,but the presence of a thick soil at this period1 instead of retarding the rate of denudation1 would tend to increase it tenfold1 for the soil would then be used as grinding-material for the ice-sheet4 ,in places where the ice was1 say1 #b1jjj feet in thickness1 the soil would be forced along over the rocky face of the country1 exerting a pressure on the rocks equal to #ej tons on the square foot4 ,it is true that the rate at which many kinds of rocks decompose and disintegrate is far less than what has been concluded to be the mean rate of denudation of the whole country4 ,this is evident from the fact which has been adduced by some writers1 that inscriptions on stones which have been exposed to atmospheric agency for a period of #b1jjj years or so1 have not been obliterated4 ,but in most cases epitaphs on monuments and tombstones1 and inscriptions on the walls of buildings1 #bjj years old1 can hardly be read4 ,and this is not all3 the stone on which the letters were cut has during that time rotted in probably to the depth of several inches2 and during the course of a few centuries more the whole mass will crumble into dust4 ,the facts which we have been considering show also how trifling is the amount of denudation effected by the sea in comparison with that by subarial agents4 ,the entire sea-coast of the globe1 according to ,dr4 ,a4 ,keith ,johnston1 is #aaf1eca miles4 ,suppose we take the average height of the coast-line at #be feet1 and take also the rate at which the sea is advancing on the land at one foot in #ajj years1 then this gives #ae1chb1ejj1jjj cubic feet of rock as the total amount removed in #ajj years by the action of the sea4 ,the total amount of land is #eg1fjj1jjj square miles1 or #a1fje1gej1jjj1jjj1jjj square feet2 and if one foot is removed off the surface in #f1jjj years1 then #bf1gfc1jjj1jjj1jjj cubic feet is removed by subarial agency in #ajj years1 or about #a1gdj times as much as that removed by the sea4 ,before the sea could denude the globe as rapidly as the subarial agents1 it would have to advance on the land at the rate of upwards of #ag feet annually4 ,it will not do1 however1 to measure marine denudation by the rate at which the sea is advancing on the land4 ,there is no relation whatever between the rate at which the sea is advancing on the land and the rate at which the sea is denuding the land4 ,for it is evident that as the subarial agents bring the coast down to the sea-level1 all that the sea has got to do is simply to advance1 or at most to remove the loose materials which may lie in its path4 ,the amount of denudation which has been effected by the sea during past geological ages1 compared with what has been effected by subarial agency1 is evidently but trifling4 ,denudation is not the proper function of the sea4 ,the great denuding agents are land-ice1 frost1 rain1 running-water1 chemical agency1 c4 ,the proper work which belongs to the sea is the transporting of the loose materials carried down by the rivers1 and the spreading of these out so as to form the stratified beds of future ages4 ,previous ,methods of measuring ,geological ,time unreliable4--,the method which has just been detailed of estimating the rate of subarial denudation seems to afford the only reliable means of a geological character of determining geological time in absolute measure4 ,the methods which have hitherto been adopted not only fail to give the positive length of geological periods1 but some of them are actually calculated to mislead4 ,the common method of calculating the length of a period from the thickness of the stratified rocks belonging to that period is one of that class4 ,nothing whatever can be inferred from the thickness of a deposit as to the length of time which was required to form it4 ,the thickness of a deposit will depend upon a great many circumstances1 such as whether the deposition took place near to land or far away in the deep recesses of the ocean1 whether it occurred at the mouth of a great river or along the sea-shore1 or at a time when the sea-bottom was rising1 subsiding1 or remaining stationary4 ,stratified formations #aj1jjj feet in thickness1 for example1 may1 under some conditions1 have been formed in as many years1 while under other conditions it may have required as many centuries4 ,nothing whatever can be safely inferred as to the absolute length of a period from the thickness of the stratified formations belonging to that period4 ,neither will this method give us a trustworthy estimate of the relative lengths of geological periods4 ,suppose we find the average thickness of the ,cambrian rocks to be1 say1 #bf1jjj feet1 the ,silurian to be #bh1jjj feet1 the ,devonian to be #f1jjj feet1 and the ,tertiary to be #aj1jjj feet1 it would not be safe to assume1 as is sometimes done1 that the relative duration of those periods must have corresponded to these numbers4 ,were we sure that we had got the correct average thickness of all the rocks belonging to each of those formations1 we might probably be able to arrive at the relative lengths of those periods2 but we can never be sure of this4 ,those formations all1 at one time1 formed sea-bottoms2 and we can only measure such deposits as are now raised above the sea-level4 ,but is not it probable that the relative positions of sea and land during the ,cambrian1 ,silurian1 ,old ,red ,sandstone1 ,carboniferous1 and other early periods of the earth's history1 differed more from the present than the distribution of sea and land during the ,tertiary period differed from that which obtains now8 ,may not the greater portion of the ,tertiary deposits be still under the sea-bottom8 ,and if this be the case1 it may yet be found at some day in the distant future1 when these deposits are elevated into dry land1 that they are much thicker than we now conclude them to be4 ,of course1 it is by no means asserted that this is so1 but only that they may be thicker for anything we know to the contrary2 and the possibility that they may1 destroys our confidence in the accuracy of this method of determining the relative lengths of geological periods4 ,neither does palontology afford any better mode of measuring geological time4 ,in fact1 the palontological method of estimating geological time1 either absolute or relative1 from the rate at which species change1 appears to be even still more unsatisfactory4 ,if we could ascertain by some means or other the time that has elapsed from some given epoch 7say1 for example1 the glacial7 till the present day1 and were we sure at the same time that species have changed at a uniform rate during all past ages1 then1 by ascertaining the percentage of change that has taken place since the glacial epoch1 we should have a means of making something like a rough estimate of the length of the various periods4 ,but without some such period to start with1 the palontological method is useless4 ,it will not do to take the historic period as a base-line4 ,it is far too short to be used with safety in determining the distance of periods so remote as those which concern the geologist4 ,but even supposing the palontologist had a period of sufficient length measured off correctly to begin with1 his results would still be unsatisfactory2 for it is perfectly obvious1 that unless the climatic conditions of the globe during the various periods were nearly the same1 the rate at which the species change would certainly not be uniform2 but such has not been the case1 as an examination of the ,tables of eccentricity will show4 ,take1 for example1 that long epoch of #bfj1jjj years1 beginning about #ihj1jjj years ago and terminating about #gbj1jjj years ago4 ,during that long period the changes from cold to warm conditions of climate every #aj1jjj or #ab1jjj years must have been of the most extreme character4 ,compare that period with the period beginning1 say1 #hj1jjj years ago1 and extending to nearly #aej1jjj years into the future1 during which there will be no extreme variations of climate1 and how great is the contrast6 ,how extensive the changes in species must have been during the first period as compared with those which are likely to take place during the latter6 ,besides1 it must also be taken into consideration that organization was of a far more simple type in the earlier ,palozoic ages than during the ,tertiary period1 and would probably on this account change much more slowly in the former than in the latter4 ,the foregoing considerations render it highly probable1 if not certain1 that the rate at which the general surface of the globe is being lowered by subarial denudation cannot be much under one foot in #f1jjj years4 ,how1 if we assign the glacial epoch to that period of high eccentricity beginning #ihj1jjj years ago1 and terminating #gbj1jjj years ago1 then we must conclude that as much as #abj feet must have been denuded off the face of the country since the close of the glacial epoch4 ,but if as much as this had been carried down by our rivers into the sea1 hardly a patch of boulder clay1 or any trace of the glacial epoch1 should be now remaining on the land4 ,it is therefore evident that the glacial epoch cannot be assigned to that remote period1 but ought to be referred to the period terminating about #hj1jjj years ago4 ,we have1 in this latter case1 #ac feet1 equal to about #ah feet of drift1 as the amount removed from the general surface of the country since the glacial epoch4 ,this amount harmonizes very well with the direct evidence of geology on this point4 ,had the amount of denudation since the close of the glacial epoch been much greater than this1 the drift deposits would not only have been far less complete1 but the general appearance and outline of the surface of all glaciated countries would have been very different from what they really are4 ,circumstances which show the ,recent ,date of the ,glacial ,epoch4--,one of the circumstances to which ,i refer is this4 ,when we examine the surface of any glaciated country1 such as ,scotland1 we can easily satisfy ourselves that the upper surface of the ground differs very much from what it would have been had its external features been due to the action of rain and rivers and the ordinary agencies which have been at work since the close of the ,ice period4 ,go where one will in the ,lowlands of ,scotland1 and he shall hardly find a single acre whose upper surface bears the marks of being formed by the denuding agents which are presently in operation4 ,he will observe everywhere mounds and hollows1 the existence of which cannot be accounted for by the present agencies at work4 ,in fact these agencies are slowly denuding pre-existing heights and silting up pre-existing hollows4 ,everywhere one comes upon patches of alluvium which upon examination prove to be simply old glacially formed hollows silted up4 ,true1 the main rivers1 streams1 and even brooks1 occupy channels which have been formed by running water1 either since or prior to the glacial epoch1 but1 in regard to the general surface of the country1 the present agencies may be said to be just beginning to carve a new line of features out of the old glacially formed surface4 ,but so little progress has yet been made1 that the kames1 gravel mounds1 knolls of boulder clay1 c41 still retain in most cases their original form4 ,now1 when we reflect that more than a foot of drift is being removed from the general surface of the country every #e1jjj years or so1 it becomes perfectly obvious that the close of the glacial epoch must be of comparatively recent date4 ,there is another circumstance which shows that the glacial epoch must be referred to the latest period of great eccentricity4 ,if we refer the glacial epoch to the penultimate period of extreme eccentricity1 and place its commencement one million of years back1 then we must also lengthen out to a corresponding extent the entire geological history of the globe4 ,sir ,charles ,lyell1 who is inclined to assign the glacial epoch to this penultimate period1 considers that when we go back as far as the ,lower ,miocene formations1 we arrive at a period when the marine shells differed as a whole from those now existing4 ,but only #e per cent4 of the shells existing at the commencement of the glacial epoch have since died out4 ,hence1 assuming the rate at which the species change to be uniform1 it follows that the ,lower ,miocene period must be twenty times as remote as the commencement of the glacial epoch4 ,consequently1 if it be one million of years since the commencement of the glacial epoch1 #bj millions of years1 ,sir ,charles concludes1 must have elapsed since the time of the ,lower ,miocene period1 and #fj millions of years since the beginning of the ,eocene period1 and about #afj millions of years since the ,carboniferous period1 and about #bdj millions of years must be the time which has elapsed since the beginning of the ,cambrian period4 ,but1 on the other hand1 if we refer the glacial epoch to the latest period of great eccentricity1 and take #bej1jjj years ago as the beginning of that period1 then1 according to the same mode of calculation1 we have #ae millions of years since the beginning of the ,eocene period1 and #dj millions of years since the ,carboniferous period1 and #fj millions of years in all since the beginning of the ,cambrian period4 ,if the beginning of the glacial epoch be carried back a million years1 then it is probable1 as ,sir ,charles ,lyell concludes1 that the beginning of the ,cambrian period will require to be placed #bdj millions of years back4 ,but it is very probable that the length of time embraced by the pre-,cambrian ages of geological history may be as great as that which has elapsed since the close of the ,cambrian period1 and1 if this be so1 then we shall be compelled to admit that nearly #ejj millions of years have passed away since the beginning of the earth's geological history4 ,but we have evidence of a physical nature which proves that it is absolutely impossible that the existing order of things1 as regards our globe1 can date so far back as anything like #ejj millions of years4 ,the arguments to which ,i refer are those which have been advanced by ,professor ,sir ,william ,thomson at various times4 ,these arguments are well known1 and to all who have really given due attention to them must be felt to be conclusive4 ,it would be superfluous to state them here2 ,i shall1 however1 for reasons which will presently appear1 refer briefly to one of them1 and that one which seems to be the most conclusive of all1 viz41 the argument derived from the limit to the age of the sun's heat4 ,professor ,ramsay on ,geological ,time4--,in an interesting suggestive memoir1 8,on ,geological ,ages as items of ,geological ,time10#bjj ,professor ,ramsay discusses the comparative values of certain groups of formations as representative of geological time1 and arrives at the following general conclusion1 viz41 8,that the local continental era which began with the ,old ,red ,sandstone and closed with the ,new ,red ,marl is comparable1 in point of geological time1 to that occupied in the deposition of the whole of the ,mesozoic1 or ,secondary series1 later than the ,new ,red ,marl and all the ,cainozoic or ,tertiary formations1 and indeed of all the time that has elapsed since the beginning of the deposition of the ,lias down to the present day40 ,this conclusion is derived partly from a comparison of the physical character of the formations constituting each group1 but principally from the zoological changes which took place during the time represented by them4 ,the earlier period represented by the ,cambrian and ,silurian rocks he also1 from the same considerations1 considers to have been very long1 but he does not attempt to fix its relative length4 ,of the absolute length of any or all of these great eras of geological time no estimate or guess is given4 ,he believes1 however1 that the whole time represented by all the fossiliferous rocks1 from the earliest ,cambrian to the most recent1 is1 geologically speaking1 short compared with that which went before it4 ,after quoting ,professor ,huxley's enumeration of the many classes and orders of marine life 7identical with those still existing71 whose remains characterize the lowest ,cambrian rocks1 he says1 8,the inference is obvious that in this earliest known varied life we find no evidence of its having lived near the beginning of the zoological series4 ,in a broad sense1 compared with what must have gone before1 both biologically and physically1 all the phenomena connected with this old period seem to my mind to be quite of a recent description1 and the climates of seas and lands were of the very same kind as those that the world enjoys at the present day40444 8,in the words of ,darwin1 when discussing the imperfection of the geological record of this history1 #8we possess the last volume alone relating only to two or three countries1' and the reason why we know so little of pre-,cambrian faunas and the physical characters of the more ancient formations as originally deposited1 is that below the ,cambrian strata we get at once involved in a sort of chaos of metamorphic strata4'0 ,it seems to me that ,professor ,ramsay's results lead to the same conclusion regarding the positive length of geological periods as those derived from physical considerations4 ,it is true that his views lead us back to an immense lapse of unknown time prior to the ,cambrian period1 but this practically tends to shorten geological periods4 ,for it is evident that the geological history of our globe must be limited by the age of the sun's heat1 no matter how long or short its age may be4 ,this being the case1 the greater the length of time which must have elapsed prior to the ,cambrian period1 the less must be the time which has elapsed since that period4 ,whatever is added to the one period must be so much taken from the other4 ,consequently1 the longer we suppose the pre-,cambrian periods to have been1 the shorter must we suppose the post-,cambrian to be4 ,,chapter ,,xxi4 ,,the ,,probable ,,age ,,and ,,origin ,,of ,,the ,,sun4 ,gravitation ,theory4--,amount of ,heat emitted by the ,sun4--,meteoric ,theory4--,helmholtz's ,condensation ,theory4--,confusion of ,ideas4--,gravitation not the chief ,source of the ,sun's ,heat4--,original ,heat4--,source of ,original ,heat4--,original ,heat derived from ,motion in ,space4--,conclusion as to ,date of ,glacial ,epoch4--,false ,analogy4--,probable ,date of ,eocene and ,miocene ,periods4 ,gravitation ,theory of the ,origin and ,source of the ,sun's ,heat4--,there are two forms in which this theory has been presented3 the first1 the meteoric theory1 propounded by ,dr4 ,meyer1 of ,heilbronn2 and the second1 the contraction theory1 advocated by ,helmholtz4 ,it is found that #hcd foot-pounds of heat per second are incident upon a square foot of the earth's surface exposed to the perpendicular rays of the sun4 ,the amount radiated from a square foot of the sun's surface is to that incident on a square foot of the earth's surface as the square of the sun's distance to the square of his radius1 or as #df1djj to #a4 ,consequently #c1hfi1jjj foot-pounds of heat are radiated off every square foot of the sun's surface per second--an amount equal to about #g1jjj horse power4 ,the total amount radiated from the whole surface of the sun per annum is #h1cdj #ajcj foot-pounds4 ,to maintain the present rate of radiation1 it would require the combustion of about #a1ejj lbs4 of coal per hour on every square foot of the sun's surface2 and were the sun composed of that material1 it would be all consumed in less than #e1jjj years4 ,the opinion that the sun's heat is maintained by combustion cannot be entertained for a single moment4 ,a pound of coal falling into the sun from an infinite distance would produce by its concussion more than #f1jjj times the amount of heat that would be generated by its combustion4 ,it is well known that the velocity with which a body falling from an infinite distance would reach the sun would be equal to that which would be generated by a constant force equal to the weight of the body at the sun's surface operating through a space equal to the sun's radius4 ,one pound would at the sun's surface weigh about #bh pounds4 ,taking the sun's radius at #dda1jjj miles1#bja the energy of a pound of matter falling into the sun from infinite space would equal that of a #bh-pound weight descending upon the earth from an elevation of #dda1jjj miles1 supposing the force of gravity to be as great at that elevation as it is at the earth's surface4 ,it would amount to upwards of #fe1jjj1jjj1jjj foot-pounds4 ,a better idea of this enormous amount of energy exerted by a one-pound weight falling into the sun will be conveyed by stating that it would be sufficient to raise #a1jjj tons to a height of #e miles4 ,it would project the ,warrior1 fully equipped with guns1 stores1 and ammunition1 over the top of ,ben ,nevis4 ,gravitation is now generally admitted to be the only conceivable source of the sun's heat4 ,but if we attribute the energy of the sun to gravitation as a source1 we assign it to a cause the value of which can be accurately determined4 ,prodigious as is the energy of a single pound of matter falling into the sun1 nevertheless a range of mountains1 consisting of #agf cubic miles of solid rock1 falling into the sun1 would maintain his heat for only a single second4 ,a mass equal to that of the earth would maintain the heat for only #ic years1 and a mass equal to that of the sun itself falling into the sun would afford but #cc1jjj1jjj years' sun-heat4 ,it is quite possible1 however1 that a meteor may reach the sun with a velocity far greater than that which it could acquire by gravitation2 for it might have been moving in a direct line towards the sun with an original velocity before coming under the sensible influence of the sun's attraction4 ,in this case a greater amount of heat would be generated by the meteor than would have resulted from its merely falling into the sun under the influence of gravitation4 ,but then meteors of this sort must be of rare occurrence4 ,the meteoric theory of the sun's heat has now been pretty generally abandoned for the contraction theory advanced by ,helmholtz4 ,suppose1 with ,helmholtz1 that the sun originally existed as a nebulous mass1 filling the entire space presently occupied by the solar system and extending into space indefinitely beyond the outermost planet4 ,the total amount of work in foot-pounds performed by gravitation in the condensation of this mass to an orb of the sun's present size can be found by means of the following formula given by ,helmholtz1#bjb #c r#b,m#b ,work of condensation -- ------------------------ g #e ,rm ,m is the mass of the sun1 m the mass of the earth1 ,r the sun's radius1 and r the earth's radius4 ,taking ,m #dbcj #ajbg lbs41 m #aa1ibj #ajba lbs41 ,r #b1cbh1ejj1jjj feet1 and r #bj1hhi1bgb feet2 we have then for the total amount of work performed by gravitation in foot-pounds1 #c 7#bj1hhi1bgbe7b 7#dbcj #ajbg7b ,work -- ---------------------------------------- ---------------------------------- #e #b1cbh1ejj1jjj #aa1ibj #ajba #afh1gij #ajcf foot-pounds4 ,the amount of heat thus produced by gravitation would suffice for nearly #bj1bcg1ejj years4 ,these calculations are based upon the assumption that the density of the sun is uniform throughout4 ,but it is highly probable that the sun's density increases towards the centre1 in which case the amount of work performed by gravitation would be somewhat more than the above4 ,some confusion has arisen in reference to this subject by the introduction of the question of the amount of the sun's specific heat4 ,if we simply consider the sun as an incandescent body in the process of cooling1 the question of the amount of the sun's specific heat is of the utmost importance2 because the absolute amount of heat which the sun is capable of giving out depends wholly upon his temperature and specific heat4 ,in this case three things only are required3 7#a71 the sun's mass2 7#b71 temperature of the mass2 7#c71 specific heat of the mass4 ,but if we are considering what is the absolute amount of heat which could have been given out by the sun on the hypothesis that gravitation1 either according to the meteoric theory suggested by ,meyer or according to the contraction theory advocated by ,helmholtz1 is the only source of his heat1 then we have nothing whatever to do with any inquiries regarding the specific heat of the sun4 ,this is evident because the absolute amount of work which gravitation can perform in the pulling of the particles of the sun's mass together1 is wholly independent of the specific heat of those particles4 ,consequently1 the amount of energy in the form of heat thus imparted to the particles by gravity must also be wholly independent of specific heat4 ,that is to say1 the amount of heat imparted to a particle will be the same whatever may be its specific heat4 ,even supposing we limit the geological history of our globe to #ajj millions of years1 it is nevertheless evident that gravitation will not account for the supply of the sun's heat during so long a period4 ,there must be some other source of much more importance than gravitation4 ,what other source of energy greater than that of gravitation can there be8 ,it is singular that the opinion should have become so common even among physicists1 that there is no other conceivable source than gravitation from which a greater amount of heat could have been derived4 ,the ,origin and ,chief ,source of the ,sun's ,heat4--,according to the foregoing theories regarding the source of the sun's heat1 it is assumed that the matter composing the sun1 when it existed in space as a nebulous mass1 was not originally possessed of temperature1 but that the temperature was given to it as the mass became condensed under the force of gravitation4 ,it is supposed that the heat given out was simply the heat of condensation4 ,but it is quite conceivable that the nebulous mass might have been possessed of an original store of heat previous to condensation4 ,it is quite possible that the very reason why it existed in such a rarefied or gaseous condition was its excessive temperature1 and that condensation only began to take place when the mass began to cool down4 ,it seems far more probable that this should have been the case than that the mass existed in so rarefied a condition without temperature4 ,for why should the particles have existed in this separated form when devoid of the repulsive energy of heat1 seeing that in virtue of gravitation they had such a tendency to approach to one another8 ,but if the mass was originally in a heated condition1 then in condensing it would have to part not only with the heat generated in condensing1 but also with the heat which it originally possessed1 a quantity which would no doubt much exceed that produced by condensation4 ,to illustrate this principle1 let us suppose a pound of air1 for example1 to be placed in a cylinder and heat applied to it4 ,if the piston be so fixed that it cannot move1 #bcde foot-pounds of heat will raise the temperature of the air #a ,c4 ,but if the piston be allowed to rise as the heat is applied1 then it will require #ccjb foot-pounds of heat to raise the temperature #a ,c4 ,it requires #ieg foot-pounds more heat in the latter case than in the former4 ,the same amount of energy1 viz41 #bcde foot-pounds1 in both cases goes to produce temperature2 but in the latter case1 where the piston is allowed to move1 #ieg foot-pounds of additional heat are consumed in the mechanical work of raising the piston4 ,suppose1 now1 that the air is allowed to cool under the same conditions3 in the one case #bcde foot-pounds of heat will be given out while the temperature of the air sinks #a ,c42 in the other case1 where the piston is allowed to descend1 #ccjb foot-pounds will be given out while the temperature sinks #a ,c4 ,in the former case1 the air in cooling has simply to part with the energy which it possesses in the form of temperature2 but in the latter case it has1 in addition to this1 to part with the energy bestowed upon its molecules by the descending piston4 ,while the temperature of the gas is sinking #a1 #ieg foot-pounds of energy in the form of heat are being imparted to it by the descending piston2 and these have to be got rid of before the temperature is lowered by #a4 ,consequently #bcde foot-pounds of the heat given out previously existed in the air under the form of temperature1 and the remaining #ieg foot-pounds given out were imparted to the air by the descending piston while the gas was losing its temperature4 #bcde foot-pounds represent the energy or heat which the air previously possessed1 and #ieg the energy or heat of condensation4 ,in the case of the cooling of the sun from a nebulous mass1 there would of course be no external force or pressure exerted on the mass analogous to that of the piston on the air2 but there would be1 what is equivalent to the same1 the gravitation of the particles to each other4 ,there would be the pressure of the whole mass towards the centre of convergence4 ,in the case of air1 and all perfect gases cooling under pressure1 about #bcd foot-pounds of the original heat possessed by the gas are given out while #ie foot-pounds are being generated by condensation4 ,we have1 however1 no reason whatever to believe that in the case of the cooling of the sun the same proportions would hold true4 ,the proportion of original heat possessed by the mass of the sun to that produced by condensation may have been much greater than #bcd to #ie1 or it may have been much less4 ,in the absence of all knowledge on this point1 we may in the meantime assume that to be the proportion4 ,the total quantity of heat given out by the sun resulting from the condensation of his mass1 on the supposition that the density of the sun is uniform throughout1 we have seen to be equal to #bj1bcg1ejj years' sun-heat4 ,then the quantity of heat given out1 which previously existed in the mass as original temperature1 must have been #di1hej1jjj years' heat1 making in all #gj1jhg1ejj years' heat as the total amount4 ,the above quantity represents1 of course1 the total amount of heat given out by the mass since it began to condense4 ,but the geological history of our globe must date its beginning at a period posterior to that4 ,for at that time the mass would probably occupy a much greater amount of space than is presently possessed by the entire solar system2 and consequently1 before it had cooled down to within the limits of the earth's present orbit1 our earth could not have had an existence as a separate planet4 ,previously to that time it must have existed as a portion of the sun's fiery mass4 ,if we assume that it existed as a globe previously to that1 and came in from space after the condensation of the sun1 then it is difficult to conceive how its orbit should be so nearly circular as it is at present4 ,let us assume that by the time that the mass of the sun had condensed to within the space encircled by the orbit of the planet ,mercury 7that is1 to a sphere having1 say1 a radius of #ah1jjj1jjj miles7 the earth's crust began to form2 and let this be the time when the geological history of our globe dates its commencement4 ,the total amount of heat generated by the condensation of the sun's mass from a sphere of this size to its present volume would equal #ai1gdj1jjj years' sun-heat4 ,the amount of original heat given out during that time would equal #dh1fbe1jjj years' sun-heat1--thus giving a total of #fh1cfe1jjj years' sun-heat enjoyed by our globe since that period4 ,the total quantity may possibly1 of course1 be considerably more than that1 owing to the fact that the sun's density may increase greatly towards his centre4 ,but we should require to make extravagant assumptions regarding the interior density of the sun and the proportion of original heat to that produced by condensation before we could manage to account for anything like the period that geological phenomena are supposed by some to demand4 ,the question now arises1 by what conceivable means could the mass of the sun have become possessed of such a prodigious amount of energy in the form of heat previous to condensation8 ,what power could have communicated to the mass #ej1jjj1jjj years' heat before condensation began to take place8 ,the ,sun's ,energy may have originally been derived from ,motion in ,space4--,there is nothing at all absurd or improbable in the supposition that such an amount of energy might have been communicated to the mass4 ,the ,dynamical ,theory of ,heat affords an easy explanation of at least how such an amount of energy may have been communicated4 ,two bodies1 each one-half the mass of the sun1 moving directly towards each other with a velocity of #dgf miles per second1 would by their concussion generate in a single moment the #ej1jjj1jjj years' heat4 ,for two bodies of that mass moving with a velocity of #dgf miles per second would possess #dadi #ajch foot-pounds of energy in the form of vis viva2 and this1 converted into heat by the stoppage of their motion1 would give an amount of heat which would cover the present rate of the sun's radiation1 for a period of #ej1jjj1jjj years4 ,why may not the sun have been composed of two such bodies8 ,and why may not the original store of heat possessed by him have all been derived from the concussion of these two bodies8 ,two such bodies coming into collision with that velocity would be dissipated into vapour by such an inconceivable amount of heat as would thus be generated2 and when they condensed on cooling1 they would form one spherical mass like the sun4 ,it is perfectly true that two such bodies could never attain the required amount of velocity by their mutual gravitation towards each other4 ,but there is no necessity whatever for supposing that their velocities were derived from their mutual attraction alone4 ,they might have been approaching towards each other with the required velocity wholly independent of gravitation4 ,we know nothing whatever regarding the absolute motion of bodies in space4 ,and beyond the limited sphere of our observation1 we know nothing even of their relative motions4 ,there may be bodies moving in relation to our system with inconceivable velocity4 ,for anything that we know to the contrary1 were one of these bodies to strike our earth1 the shock might be sufficient to generate an amount of heat that would dissipate the earth into vapour1 though the striking body might not be heavier than a cannon-ball4 ,there is1 however1 nothing very extraordinary in the velocity which we have found would be required in the two supposed bodies to generate the #ej1jjj1jjj years' heat4 ,a comet1 having an orbit extending to the path of the planet ,neptune1 approaching so near the sun as to almost graze his surface in passing1 would have a velocity of about #cij miles per second1 which is within #hf miles of the required velocity4 ,but in the original heating and expansion of the sun into a gaseous mass1 an amount of work must have been performed against gravitation equal to that which has been performed by gravitation during his cooling and condensation1 a quantity which we have found amounts to about #bj1jjj1jjj years' heat4 ,the total amount of energy originally communicated by the concussion must have been equal to #gj1jjj1jjj years' sun-heat4 ,a velocity of #efc miles per second would give this amount4 ,it must be borne in mind1 however1 that the #efc miles per second is the velocity at the moment of collision2 about one-half of this velocity would be derived from the mutual attraction of the two bodies in their approach to each other4 ,suppose each body to be equal in volume to the sun1 and of course one-half the density1 the amount of velocity which they would acquire by their mutual attraction would be #bgd miles per second1 consequently we have to assume an original or projected velocity of only #bhi miles per second4 ,if we admit that gravitation is not sufficient to account for the amount of heat given out by the sun during the geological history of our globe1 we are compelled to assume that the mass of which the sun is composed existed prior to condensation in a heated condition2 and if so1 we are further obliged to admit that the mass must have received its heat from some source or other4 ,and as the dissipation of heat into space must have been going on1 in all probability1 as rapidly before as after condensation took place1 we are further obliged to conclude that the heat must have been communicated to the mass immediately before condensation began1 for the moment the mass began to lose its heat condensation would ensue4 ,if we confine our speculations to causes and agencies known to exist1 the cause which has been assigned appears to be the only conceivable one that will account for the production of such an enormous amount of heat4 ,the general conclusion to which we are therefore led from physical considerations regarding the age of the sun's heat is1 that the entire geological history of our globe must be comprised within less than #ajj millions of years1 and that consequently the commencement of the glacial epoch cannot date much farther back than #bdj1jjj years4 ,the facts of geology1 more especially those in connection with denudation1 seem to geologists to require a period of much longer duration than #ajj millions of years1 and it is this which has so long prevented them accepting the conclusions of physical science in regard to the age of our globe4 ,but the method of measuring subarial denudation already detailed seems to me to show convincingly that the geological data1 when properly interpreted1 are in perfect accord with the deductions of physical science4 ,perhaps there are now few who have fairly considered the question who will refuse to admit that #ajj millions of years are amply sufficient to comprise the whole geological history of our globe4 ,a false ,analogy supposed to exist between ,astronomy and ,geology4--,perhaps one of the things which has tended to mislead on this point is a false analogy which is supposed to subsist between astronomy and geology1 viz41 that geology deals with unlimited time1 as astronomy deals with unlimited space4 ,a little consideration1 however1 will show that there is not much analogy between the two cases4 ,astronomy deals with the countless worlds which lie spread out in the boundless infinity of space2 but geology deals with only one world4 ,no doubt reason and analogy both favour the idea that the age of the material universe1 like its magnitude1 is immeasurable2 we have no reason1 however1 to conclude that it is eternal1 any more than we have to infer that it is infinite4 ,but when we compare the age of the material universe with its magnitude1 we must not take the age of one of its members 7say1 our globe7 and compare it with the size of the universe4 ,neither must we compare the age of all the presently existing systems of worlds with the magnitude of the universe2 but we must compare the past history of the universe as it stretches back into the immensity of bygone time1 with the presently existing universe as it stretches out on all sides into limitless space4 ,for worlds precede worlds in time as worlds lie beyond worlds in space4 ,each world1 each individual1 each atom is evidently working out a final purpose1 according to a plan prearranged and predetermined by the ,divine ,mind from all eternity4 ,and each world1 like each individual1 when it serves the end for which it was called into existence1 disappears to make room for others4 ,this is the grand conception of the universe which naturally impresses itself on every thoughtful mind that has not got into confusion about those things called in science the ,laws of ,nature4#bjc ,but the geologist does not pass back from world to world as they stand related to each other in the order of succession in time1 as the astronomer passes from world to world as they stand related to each other in the order of coexistence in space4 ,the researches of the geologist1 moreover1 are not only confined to one world1 but it is only a portion of the history of that one world that can come under his observation4 ,the oldest of existing formations1 so far as is yet known1 the ,laurentian ,gneiss1 is made up of the waste of previously existing rocks1 and it1 again1 has probably been derived from the degradation of rocks belonging to some still older period4 ,regarding what succeeds these old ,laurentian rocks geology tells us much2 but of the formations that preceded1 we know nothing whatever4 ,for anything that geology shows to the contrary1 the time which may have elapsed from the solidifying of the earth's crust to the deposition of the ,laurentian strata--an absolute blank--may have been as great as the time that has since intervened4 ,probable ,date of the ,eocene and ,miocene ,periods4--,if we take into consideration the limit which physical science assigns to the age of our globe1 and the rapid rate at which1 as we have seen1 denudation takes place1 it becomes evident that the enormous period of #c millions of years comprehended in the foregoing tables must stretch far back into the ,tertiary age4 ,supposing that the mean rate of denudation during that period was not greater than the present rate of denudation1 still we should have no less than #ejj feet of rock worn off the face of the country and carried into the sea during these #c millions of years4 ,this fact shows how totally different the appearance and configuration of the country in all probability was at the commencement of this period from what it is at the present day4 ,if it be correct that the glacial epoch resulted from the causes which we have already discussed1 those tables ought to aid us in our endeavour to ascertain how much of the ,tertiary period may be comprehended within these #c millions of years4 ,we have already seen 7,chapter ,,xviii47 that there is evidence of a glacial condition of climate at two different periods during the ,tertiary age1 namely1 about the middle of the ,miocene and ,eocene periods respectively4 ,as has already been shown1 the more severe a glacial epoch is1 the more marked ought to be the character of its warm inter-glacial periods2 the greater the extension of the ice during the cold periods of a glacial epoch the further should that ice disappear in arctic regions during the corresponding warm periods4 ,thus the severity of a glacial epoch may in this case be indirectly inferred from the character of the warm periods and the extent to which the ice may have disappeared from arctic regions4 ,judged by this test1 we have every reason to believe that the ,miocene glacial epoch was one of extreme severity4 ,the ,eocene conglomerate1 devoid of all organic remains1 and containing numerous enormous ice-transported blocks1 is1 as we have seen1 immediately associated with nummulitic strata charged with fossils characteristic of a warm climate4 ,referring to this ,sir ,charles ,lyell says1 8,to imagine icebergs carrying such huge fragments of stone in so southern a latitude1 and at a period immediately preceded and followed by the signs of a warm climate1 is one of the most perplexing enigmas which the geologist has yet been called upon to solve40#bjd ,it is perfectly true that1 according to the generally received theories of the cause of a glacial climate the whole is a perplexing enigma1 but if we adopt the ,secular theory of change of climate1 every difficulty disappears4 ,according to this theory the very fact of the conglomerate being formed at a period immediately preceded and succeeded by warm conditions of climate1 is of itself strong presumptive evidence of the conglomerate being a glacial formation4 ,but this is not all1 the very highness of the temperature of the preceding and succeeding periods bears testimony to the severity of the intervening glacial period4 ,despite the deficiency of direct evidence regarding the character of the ,miocene and ,eocene glacial periods1 we are not warranted1 for reasons which have been stated in ,chapter ,,xvii41 to conclude that these periods were less severe than the one which happened in ,quaternary times4 ,judging from indirect evidence1 we have some grounds for concluding that the ,miocene glacial epoch at least was even more severe and protracted than our recent glacial epoch4 ,by referring to ,table ,i41 or the accompanying diagram1 it will be seen that prior to the period which ,i have assigned as that of the glacial epoch1 there are two periods when the eccentricity almost attained its superior limit4 ,the first period occurred #b1ejj1jjj years ago1 when it reached #jjgba1 and the second period #hej1jjj years ago1 when it attained a still higher value1 viz41 #jjgdg1 being within #jjjbh of the superior limit4 ,to the first of these periods ,i am disposed to assign the glacial epoch of ,eocene times1 and to the second that of the ,miocene age4 ,with the view of determining the character of these periods ,tables ,,ii4 and ,,iii4 have been computed4 ,they give the eccentricity and longitude of perihelion at intervals of #aj1jjj years4 ,it will be seen from ,table ,,ii4 that the ,eocene period extends from about #b1fbj1jjj to about #b1dfj1jjj years ago2 and from ,table ,,iii4 it will be gathered that the ,miocene period lasted from about #ihj1jjj to about #gbj1jjj years ago4 ,in order to find whether the eccentricity attained a higher value about #hej1jjj years ago than #jjgdg1 ,i computed the values for one or two periods immediately before and after that period1 and satisfied myself that the value stated was indeed the highest1 as will be seen from the subjoined table3-- #hea1jjj #jjgded #hej1jjj #jjgdffd #hdi1ejj #jjgdff #hdi1jjj #jjgdff ,how totally different must have been the condition of the earth's climate at that period from what it is at present6 ,taking the mean distance of the sun to be #ia1djj1jjj miles1 his present distance at midwinter is #hi1hfd1dhj miles2 but at the period in question1 when the winter solstice was in perihelion1 his distance at midwinter would be no less than #ih1bbd1bhi miles4 ,but this is not all2 our winters are at present shorter than our summers by #gh days1 but at that period they would be longer than the summers by #cdg days4 ,at present the difference between the perihelion and aphelion distance of the sun amounts to only #c1jfi1ehj miles1 but at the period under consideration it would amount to no less than #ac1fdh1egi miles6 ,,chapter ,,xxii4 ,a ,,method ,,of ,,determining ,,the ,,mean ,,thickness ,,of ,,the ,,sedimentary ,,rocks ,,of ,,the ,,globe4 ,prevailing ,methods defective4--,maximum ,thickness of ,british ,rocks4--,three ,elements in the ,question4--,professor ,huxley on the ,rate of ,deposition4--,thickness of ,sedimentary ,rocks enormously over-estimated4--,observed ,thickness no ,measure of mean ,thickness4--,deposition of ,sediment principally along ,sea-margin4--,mistaken ,inference regarding the ,absence of a ,formation4--,immense ,antiquity of existing ,oceans4 ,various attempts have been made to measure the positive length of geological periods4 ,some geologists have sought to determine1 roughly1 the age of the stratified rocks by calculations based upon their probable thickness and the rate at which they may have been deposited4 ,this method1 however1 is worthless1 because the rates which have been adopted are purely arbitrary4 ,one geologist will take the rate of deposit at a foot in a hundred years1 while another will assume it to be a foot in a thousand or perhaps ten thousand years2 and1 for any reasons that have been assigned1 the one rate is just as likely to be correct as the other3 for if we examine what is taking place in the ocean-bed at the present day1 we shall find in some places a foot of sediment laid down in a year1 while in other places a foot may not be deposited in a thousand years4 ,the stratified rocks were evidently formed at all possible rates4 ,when we speak of the rate of their formation1 we must of course refer to the mean rate2 and it is perfectly true that if we knew the thickness of these rocks and the mean rate at which they were deposited1 we should have a ready means of determining their positive age4 ,but there appears to be nearly as great uncertainty regarding the thickness of the sedimentary rocks as regarding the rate at which they were formed4 ,no doubt we can roughly estimate their probable maximum thickness2 for instance1 ,professor ,ramsay has found from actual measurement1 that the sedimentary formations of ,great ,britain have a maximum thickness of upwards of #gb1jjj feet2 but all such measurements give us no idea of their mean thickness4 ,what is the mean thickness of the sedimentary rocks of the globe8 ,on this point geology does not afford a definite answer4 ,whatever the present mean thickness of the sedimentary rocks of our globe may be1 it must be small in comparison to the mean thickness of all the sedimentary rocks which have been formed4 ,this is obvious from the fact that the sedimentary rocks of one age are partly formed from the destruction of the sedimentary rocks of former ages4 ,from the ,laurentian age down to the present day1 the stratified rocks have been undergoing constant denudation4 ,unless we take into consideration the quantity of rock removed during past ages by denudation1 we cannot--even though we knew the actual mean thickness of the existing sedimentary rocks of the globe1 and the rate at which they were formed--arrive at an estimate regarding the length of time represented by these rocks4 ,for if we are to determine the age of the stratified rocks from the rate at which they were formed1 we must have1 not the present quantity of sedimentary rocks1 but the present plus the quantity which has been denuded during past ages4 ,in other words1 we must have the absolute quantity formed4 ,in many places the missing beds must have been of enormous thickness4 ,the time represented by beds which have disappeared is1 doubtless1 as already remarked1 much greater than that represented by the beds which now remain4 ,the greater mass of the sedimentary rocks has been formed out of previously existing sedimentary rocks1 and these again out of sedimentary rocks still older4 ,as the materials composing our stratified beds may have passed through many cycles of destruction and re-formation1 the time required to have deposited at a given rate the present existing mass of sedimentary rocks may be but a fraction of the time required to have deposited at the same rate the total mass that has actually been formed4 ,to measure the age of the sedimentary rocks by the present existing rocks1 assumed to be formed at some given rate1 even supposing the rate to be correct1 is a method wholly fallacious4 8,the aggregate of sedimentary strata in the earth's crust10 says ,sir ,charles ,lyell1 8can never exceed in volume the amount of solid matter which has been ground down and washed away by rivers1 waves1 and currents4 ,how vast1 then1 must be the spaces which this abstraction of matter has left vacant6 ,how far exceeding in dimensions all the valleys1 however numerous1 and the hollows1 however vast1 which we can prove to have been cleared out by aqueous erosion60#bje ,i presume there are few geologists who would not admit that if all the rocks which have in past ages been removed by denudation were restored1 the mean thickness of the sedimentary rocks of the globe would be at least equal to their present maximum thickness1 which we may take at #gb1jjj feet4 ,there are three elements in the question2 of which if two are known1 the third is known in terms of the other two4 ,if we have the mean thickness of all the sedimentary rocks which have been formed and the mean rate of formation1 then we have the time which elapsed during the formation2 or having the thickness and the time1 we have the rate2 or1 having the rate and the time1 we have the thickness4 ,one of these three1 namely1 the rate1 can1 however1 be determined with tolerable accuracy if we are simply allowed to assume--what is very probable1 as has already been shown--that the present rate at which the sedimentary deposits are being formed may be taken as the mean rate for past ages4 ,if we know the rate at which the land is being denuded1 then we know with perfect accuracy the rate at which the sedimentary deposits are being formed in the ocean4 ,this is obvious1 because all the materials denuded from the land are deposited in the sea2 and what is deposited in the sea is just what comes off the land1 with the exception of the small proportion of calcareous matter which may not have been derived from the land1 and which in our rough estimate may be left out of account4 ,now the mean rate of subarial denudation1 we have seen1 is about one foot in #f1jjj years4 ,taking the proportion of land to that of water at #egf to #a1cij1 then one foot taken off the land and spread over the sea-bottom would form a layer #e inches thick4 ,consequently1 if one foot in #f1jjj years represents the mean rate at which the land is being denuded1 one foot in #ad1djj years represents the mean rate at which the sedimentary rocks are being formed4 ,assuming1 as before1 that #gb1jjj feet would represent the mean thickness of all the sedimentary rocks which have ever been formed1 this1 at the rate of one foot in #ad1djj years1 gives #a1jcf1hjj1jjj years as the age of the stratified rocks4 ,professor ,huxley1 in his endeavour to show that #ajj1jjj1jjj years is a period sufficiently long for all the demands of geologists1 takes the thickness of the stratified rocks at #ajj1jjj feet1 and the rate of deposit at a foot in #a1jjj years4 ,one foot of rock per #a1jjj years gives1 it is true1 #ajj1jjj feet in #ajj1jjj1jjj years4 ,but what about the rocks which have disappeared8 ,if it takes a hundred millions of years to produce a mass of rock equal to that which now exists1 how many hundreds of millions of years will it require to produce a mass equal to what has actually been produced8 ,professor ,huxley adds1 8,i do not know that any one is prepared to maintain that the stratified rocks may not have been formed on the average at the rate of #a_/hcrd of an inch per annum40 ,when the rate1 however1 is accurately determined1 it is found to be1 not #a_/hcrd of an inch per annum1 but only #a_/abjjth of an inch1 so that the #ajj1jjj feet of rock must have taken #a1ddj1jjj1jjj years in its formation1--a conclusion which1 according to the results of modern physics1 is wholly inadmissible4 ,either the thickness of the sedimentary rocks has been over-estimated1 or the rate of their formation has been under-estimated1 or both4 ,if it be maintained that a foot in #ad1djj years is too slow a rate of deposit1 then it must be maintained that the land must have been denuded at a greater rate than one foot in #f1jjj years4 ,but most geologists probably felt surprised when the announcement was first made1 that at this rate of denudation the whole existing land of the globe would be brought under the ocean in #f1jjj1jjj of years4 ,the error1 no doubt1 consists in over-estimating the thickness of the sedimentary rocks4 ,assuming1 for physical reasons already stated1 that #ajj1jjj1jjj years limits the age of the stratified rocks1 and that the proportion of land to water and the rate of denudation have been on the average the same as at present1 the mean thickness of sedimentary rocks formed in the #ajj1jjj1jjj years amounts to only #g1jjj feet4 ,but be it observed that this is the mean thickness on an area equal to that of the ocean4 ,over the area of the globe it amounts to only #e1jjj feet2 and this1 let it be observed also1 is the total mean thickness formed1 without taking into account what has been removed by denudation4 ,if we wish to ascertain what is actually the present mean thickness1 we must deduct from this #e1jjj feet an amount of rock equal to all the sedimentary rocks which have been denuded during the #ajj1jjj1jjj years2 for the #e1jjj feet is not the present mean thickness1 but the total mean thickness formed during the whole of the #ajj1jjj1jjj years4 ,if we assume1 what no doubt most geologists would be willing to grant1 that the quantity of sedimentary rocks now remaining is not over one-half of what has been actually deposited during the history of the globe1 then the actual mean thickness of the stratified rocks of the globe is not over #b1ejj feet4 ,this startling result would almost necessitate us to suspect that the rate of subarial denudation is probably greater than one foot in #f1jjj years4 ,but1 be this as it may1 we are apt1 in estimating the mean thickness of the stratified rocks of the globe from their ascertained maximum thickness1 to arrive at erroneous conclusions4 ,there are considerations which show that the mean thickness of these rocks must be small in proportion to their maximum thickness4 ,the stratified rocks are formed from the sediment carried down by rivers and streamlets and deposited in the sea4 ,it is obvious that the greater quantity of this sediment is deposited near the mouths of rivers1 and along a narrow margin extending to no great distance from the land4 ,did the land consist of numerous small islands equally distributed over the globe1 the sediment carried off from these islands would be spread pretty equally over the sea-bottom4 ,but the greater part of the land-surface consists of two immense continents4 ,consequently1 the materials removed by denudation are not spread over the ocean-bottom1 but on a narrow fringe surrounding those two continents4 ,were the materials spread over the entire ocean-bed1 a foot removed off the general surface of the land would form a layer of rock only five inches thick4 ,but in the way in which the materials are at present deposited1 the foot removed from the land would form a layer of rock many feet in thickness4 ,the greater part of the sediment is deposited within a few miles of the shore4 ,the entire coast-line of the globe is about #aaf1ejj miles4 ,i should think that the quantity of sediment deposited beyond1 say1 #ajj miles from this coast-line is not very great4 ,no doubt several of the large rivers carry sediment to a much greater distance from their mouths than #ajj miles1 and ocean currents may in some cases carry mud and other materials also to great distances4 ,but it must be borne in mind that at many places within the #ajj miles of this immense coast-line little or no sediment is deposited1 so that the actual area over which the sediment carried off the land is deposited is probably not greater than the area of this belt--#aaf1ejj miles long and #ajj miles broad4 ,this area on which the sediment is deposited1 on the above supposition1 is therefore equal to about #aa1fej1jjj square miles4 ,the amount of land on the globe is about #eg1fjj1jjj square miles4 ,consequently1 one foot of rock1 denuded from the surface of the land and deposited on this belt1 would make a stratum of rock #e feet in thickness2 but were the sediment spread over the entire bed of the ocean1 it would form1 as has already been stated1 a stratum of rock of only #e inches in thickness4 ,suppose that no subsidence of the land should take place for a period of1 say1 #c1jjj1jjj of years4 ,during that period #ejj feet would be removed by denudation1 on an average1 off the land4 ,this would make a formation #b1ejj feet thick1 which some future geologist might call the ,post-tertiary formation4 ,but this1 be it observed1 would be only the mean thickness of the formation on this area2 its maximum thickness would evidently be much greater1 perhaps twice1 thrice1 or even four times that thickness4 ,a geologist in the future1 measuring the actual thickness of the formation1 might find it in some places #aj1jjj feet in thickness1 or perhaps far more4 ,but had the materials been spread over the entire ocean-bed1 the formation would have a mean thickness of little more than #bjj feet2 and spread over the entire surface of the globe1 would form a stratum of scarcely #aej feet in thickness4 ,therefore1 in estimating the mean thickness of the stratified rocks of the globe1 a formation with a maximum thickness of #aj1jjj feet may not represent more than #aej feet4 ,a formation with a mean thickness of #aj1jjj feet represents only #fjj feet4 ,it may be objected that in taking the present rate at which the sedimentary deposits are being formed as the mean rate for all ages1 we probably under-estimate the total amount of rock formed1 because during the many glacial periods which must have occurred in past ages the amount of materials ground off the rocky surface of the land in a given period would be far greater than at present4 ,but1 in reply1 it must be remembered that although the destruction in ice-covered regions would be greater during these periods than at present1 yet the quantity of materials carried down by rivers into the sea would be less4 ,at the present day the greater part of the materials carried down by our rivers is not what is being removed off the rocky face of the country1 but the boulder clay1 sand1 and other materials which were ground off during the glacial epoch4 ,it is therefore possible1 on this account1 that the rate of deposit may have been less during the glacial epoch than at present4 ,when any particular formation is wanting in a given area1 the inference generally drawn is1 that either the formation has been denuded off the area1 or the area was a land-surface during the period when that formation was being deposited4 ,from the foregoing it will be seen that this inference is not legitimate2 for1 supposing that the area had been under water1 the chances that materials should have been deposited on that area are far less than are the chances that there should not4 ,there are sixteen chances against one that no formation ever existed in the area4 ,if the great depressions of the ,atlantic1 ,pacific1 and ,indian ,oceans be1 for example1 as old as the beginning of the ,laurentian period--and they may be so for anything which geology can show to the contrary--then under these oceans little or no stratified rocks may exist4 ,the supposition that the great ocean basins are of immense antiquity1 and that consequently only a small proportion of the sedimentary strata can possibly occupy the deeper bed of the sea1 acquires still more probability when we consider the great extent and thickness of the ,old ,red ,sandstone1 the ,permian1 and other deposits1 which1 according to ,professor ,ramsay and others1 have been accumulated in vast inland lakes4 ,,chapter ,,xxiii4 ,,the ,,physical ,,cause ,,of ,,the ,,submergence ,,and ,,emergence ,,of ,,the ,,land ,,during ,,the ,,glacial ,,epoch4 ,displacement of the ,earth's ,centre of ,gravity by ,polar ,ice-cap4--,simple ,method of estimating ,amount of ,displacement4--,note by ,sir ,w4 ,thomson on foregoing ,method4--,difference between ,continental ,ice and a ,glacier4--,probable ,thickness of the ,antarctic ,ice-cap4--,probable ,thickness of ,greenland ,ice-sheet4--,the ,icebergs of the ,southern ,ocean4--,inadequate ,conceptions regarding the ,magnitude of ,continental ,ice4 ,displacement of the ,earth's ,centre of ,gravity by ,polar ,ice-cap4#bjf--;,in order to represent the question in its most simple elementary form1 ,i shall assume an ice-cap of a given thickness at the pole and gradually diminishing in thickness towards the equator in the simple proportion of the sines of the latitudes1 where at the equator its thickness of course is zero4 ,let us assume1 what is actually the case1 that the equatorial diameter of the globe is somewhat greater than the polar1 but that when the ice-cap is placed on one hemisphere the whole forms a perfect sphere4 ,i shall begin with a period of glaciation on the southern hemisphere4 ,let ,w ,n ,e ,s 7,fig4 #e7 be the solid part of the earth1 and c its centre of gravity4 ,and let ,e ,s ,w be an ice-cap covering the southern hemisphere4 ,let us in the first case assume the earth to be of the same density as the cap4 ,the earth with its cap forms now a perfect sphere with its centre of gravity at o2 for ,w ,n ,e ,s is a circle1 and o is its centre4 ,suppose now the whole to be covered with an ocean a few miles deep1 the ocean will assume the spherical form1 and will be of uniform depth4 ,let the southern winter solstice begin now to move round from the aphelion4 ,the ice-cap will also commence gradually to diminish in thickness1 and another cap will begin to make its appearance on the northern hemisphere4 ,as the northern cap may be supposed1 for simplicity of calculation1 to increase at the same rate that the southern will diminish1 the spherical form of the earth will always be maintained4 ,by the time that the northern cap has reached a maximum1 the southern cap will have completely disappeared4 ,the circle ,w ,n ,e ,s will now represent the earth with its cap on the northern hemisphere1 and o will be its centre of gravity2 for o is the centre of the circle ,w ,n ,e ,s4 ,and as the distance between the centres o and o is equal to ,n ,n1 the thickness of the cap at the pole ,n ,n will therefore represent the extent to which the centre of gravity has been displaced4 ,it will also represent the extent to which the ocean has risen at the north pole and sunk at the south4 ,this is evident2 for as the sphere ,w ,n ,e ,s is the same in all respects as the sphere ,w ,n ,e ,s1 with the exception only that the cap is on the opposite side1 the surface of the ocean at the poles will now be at the same distance from the centre o as it was from the centre o when the cap covered the southern hemisphere4 ,hence the distance between o and o must be equal to the extent of the submergence at the north pole and the emergence at the south4 ,neglect the attraction of the altering water on the water itself1 which later on will come under our consideration4 ,illustration3 ,fig4 #e4 ,we shall now consider the result when the earth is taken at its actual density1 which is generally believed to be about #ee4 ,the density of ice being #ib1 the density of the cap to that of the earth will therefore be as #a to #f4 ,illustration3 ,fig4 #f4 ,let ,fig4 #f represent the earth with an ice-cap on the northern hemisphere1 whose thickness is1 say1 #f1jjj feet at the pole4 ,the centre of gravity of the earth without the cap is at c4 ,when the cap is on1 the centre of gravity is shifted to o1 a point a little more than #ejj feet to the north of c4 ,had the cap and the earth been of equal density1 the centre of gravity would have been shifted to o the centre of the figure1 a point situated1 of course1 #c1jjj feet to the north of c4 ,now it is very approximately true that the ocean will tend to adjust itself as a sphere around the centre of gravity1 o4 ,thus it would of course sink at the south pole and rise to the same extent at the north1 in any opening or channel in the ice allowing the water to enter4 ,let the ice-cap be now transferred over to the southern hemisphere1 and the condition of things on the two hemispheres will in every particular be reversed4 ,the centre of gravity will then lie to the south of c1 or about #a1jjj feet from its former position4 ,consequently the transference of the cap from the one hemisphere to the other will produce a total submergence of about #a1jjj feet4 ,it is1 of course1 absurd to suppose that an ice-cap could ever actually reach down to the equator4 ,it is probable that the great ice-cap of the glacial epoch nowhere reached even halfway to the equator4 ,our cap must therefore terminate at a moderately high latitude4 ,let it terminate somewhere about the latitude of the north of ,england1 say at latitude #ee4 ,all that we have to do now is simply to imagine our cap1 up to that latitude1 becoming converted into the fluid state4 ,this would reduce the cap to less than one-half its former mass4 ,but it would not diminish the submergence to anything like that extent4 ,for although the cap would be reduced to less than one-half its former mass1 yet its influence in displacing the centre of gravity would not be diminished to that extent4 ,this is evident2 for the cap now extending down to only latitude #ee1 has its centre of gravity much farther removed from the earth's centre of gravity than it had when it extended down to the equator4 ,consequently it now possesses1 in proportion to its mass1 a much greater power in displacing the earth's centre of gravity4 ,there is another fact which must be taken into account4 ,the common centre of gravity of the earth and cap is not exactly the point around which the ocean tends to adjust itself4 ,it adjusts itself not in relation to the centre of gravity of the solid mass alone1 but in relation to the common centre of gravity of the entire mass1 solid and liquid4 ,now the water which is pulled over from the one hemisphere to the other by the attraction of the cap will also aid in displacing the centre of gravity4 ,it will co-operate with the cap and carry the true centre of gravity to a point beyond that of the centre of gravity of the earth and cap1 and thus increase the effect4 ,it is of course perfectly true that when the ice-cap does not extend down to the equator1 as in the latter supposition1 and is of less density than the globe1 the ocean will not adjust itself uniformly around the centre of gravity2 but the deviation from perfect uniformity is so trifling1 as will be seen from the appended note of ,sir ,william ,thomson1 that for all practical purposes it may be entirely left out of account4 ,in the ,reader for ,january #ac1 #ahff1 ,i advanced an objection to the submergence theory on the grounds that the lowering of the ocean-level by the evaporation of the water to form the ice-cap1 would exceed the submergence resulting from the displacement of the earth's centre of gravity4 ,but1 after my letter had gone to press1 ,i found that ,i had overlooked some important considerations which seem to prove that the objection had no real foundation4 ,for during a glacial period1 say on the northern hemisphere1 the entire mass of ice which presently exists on the southern hemisphere would be transferred to the northern1 leaving the quantity of liquid water to a great extent unchanged4 ,note on the preceding by ,sir ,william ,thomson1 ,f4,r4,s4 8,mr4 ,croll's estimate of the influence of a cap of ice on the sea-level is very remarkable in its relation to ,laplace's celebrated analysis1 as being founded on that law of thickness which leads to expressions involving only the first term of the series of #8,laplace's functions1' or #8spherical harmonics4' ,the equation of the level surface1 as altered by any given transference of solid matter1 is expressed by equating the altered potential function to a constant4 ,this function1 when expanded in the series of spherical harmonics1 has for its first term the potential due to the whole mass supposed collected at its altered centre of gravity4 ,hence a spherical surface round the altered centre of gravity is the first approximation in ,laplace's method of solution for the altered level surface4 ,mr4 ,croll has with admirable tact chosen1 of all the arbitrary suppositions that may be made foundations for rough estimates of the change of sea-level due to variations in the polar ice-crusts1 the one which reduces to zero all terms after the first in the harmonic series1 and renders that first approximation 7which always expresses the essence of the result7 the whole solution1 undisturbed by terms irrelevant to the great physical question4 8,mr4 ,croll1 in the preceding paper1 has alluded with remarkable clearness to the effect of the change in the distribution of the water in increasing1 by its own attraction1 the deviation of the level surface above that which is due to the given change in the distribution of solid matter4 ,the remark he makes1 that it is round the centre of gravity of the altered solid and altered liquid that the altering liquid surface adjusts itself1 expresses the essence of ,laplace's celebrated demonstration of the stability of the ocean1 and suggests the proper elementary solution of the problem to find the true alteration of sea-level produced by a given alteration of the solid4 ,as an assumption leading to a simple calculation1 let us suppose the solid earth to rise out of the water in a vast number of small flat-topped islands1 each bounded by a perpendicular cliff1 and let the proportion of water area to the whole be equal in all quarters4 ,let all of these islands in one hemisphere be covered with ice1 of thickness according to the law assumed by ,mr4 ,croll--that is1 varying in simple proportion of the sine of the latitude4 ,let this ice be removed from the first hemisphere and similarly distributed over the islands of the second4 ,by working out according to ,mr4 ,croll's directions1 it is easily found that the change of sea-level which this will produce will consist in a sinking in the first hemisphere and rising in the second1 through heights varying according to the same law 7that is1 simple proportionality to sines of latitudes71 and amounting at each pole to 7#a - 7it ------------------1 #a - w where t denotes the thickness of the ice-crust at the pole2 i the ratio of the density of ice1 and w that of sea-water to the earth's mean density2 and the ratio of the area of ocean to the whole surface4 8,thus1 for instance1 if we suppose 1 and t #f1jjj feet1 and take and #a_/7e7 as the densities of ice and water respectively1 we find for the rise of sea-level at one pole1 and depression at the other1 #fjjj ------------------------1 #b #a #a - -- -- #c #e or approximately #chj feet4 8,i shall now proceed to consider roughly what is the probable extent of submergence which1 during the glacial epoch1 may have resulted from the displacement of the earth's centre of gravity by means of the transferrence of the polar ice from the one hemisphere to the other40 ,difference between ,continental-ice and a ,glacier4--,an ordinary glacier descends in virtue of the slope of its bed1 and1 as a general rule1 it is on this account thin at its commencement1 and thickens as it descends into the lower valleys1 where the slope is less and the resistance to motion greater4 ,but in the case of continental ice matters are entirely different4 ,the slope of the ground exercises little or no influence on the motion of the ice4 ,in a continent of one or two thousand miles across1 the general slope of the ground may be left out of account2 for any slight elevation which the centre of such a continent may have will not compensate for the resistance offered to the flow of the ice by mountain ridges1 hills1 and other irregularities of its surface4 ,the ice can move off such a surface only in consequence of pressure acting from the interior4 ,in order to produce such a pressure1 there must be a piling up of the ice in the interior2 or1 in other words1 the ice-sheet must thicken from the edge inwards to the centre4 ,we are necessarily led to the same conclusion1 though we should not admit that the ice moves in consequence of pressure from behind1 but should hold1 on the contrary1 that each particle of ice moves by gravity in virtue of its own weight2 for in order to have such a motion there must be a slope1 and as the slope is not on the ground1 it must be on the ice itself3 consequently we must conclude that the upper surface of the ice slopes upwards from the edge to the interior4 ,what1 then1 is the least slope at which the ice will descend8 ,mr4 ,hopkins found that ice barely moves on a slope of one degree4 ,we have therefore some data for arriving at least at a rough estimate of the probable thickness of an ice-sheet covering a continent1 such1 for example1 as ,greenland or the ,antarctic ,continent4 ,probable ,thickness of the ,antarctic ,ice-cap4--,the antarctic continent is generally believed to extend1 on an average1 from the ,south ,pole down to about1 at least1 lat4 #gj4 ,in round numbers1 we may take the diameter of this continent at #b1hjj miles4 ,the distance from the edge of this ice-cap to its centre1 the ,south ,pole1 will1 therefore1 be #a1djj miles4 ,the whole of this continent1 like ,greenland1 is undoubtedly covered with one continuous sheet of ice gradually thickening inwards from its edge to its centre4 ,a slope of one degree continued for #a1djj miles will give twenty-four miles as the thickness of the ice at the pole4 ,but suppose the slope of the upper surface of the cap to be only one-half this amount1 viz41 a half degree1--and we have no evidence that a slope so small would be sufficient to discharge the ice1--still we have twelve miles as the thickness of the cap at the pole4 ,to those who have not been accustomed to reflect on the physical conditions of the problem1 this estimate may doubtless be regarded as somewhat extravagant2 but a slight consideration will show that it would be even more extravagant to assume that a slope of less than half a degree would be sufficient to produce the necessary outflow of the ice4 ,in estimating the thickness of a sheet of continental ice of one or two thousand miles across1 our imagination is apt to deceive us4 ,we can easily form a pretty accurate sensuous representation of the thickness of the sheet2 but we can form no adequate representation of its superficial area4 ,we can represent to the mind with tolerable accuracy a thickness of a few miles1 but we cannot do this in reference to the area of a surface #b1hjj miles across4 ,consequently1 in judging what proportion the thickness of the sheet should bear to its superficial area1 we are apt to fall into the error of under-estimating the thickness4 ,we have a striking example of this in regard to the ocean4 ,the thing which impresses us most forcibly in regard to the ocean is its profound depth4 ,a mean depth of1 say1 three miles produces a striking impression2 but if we could represent to the mind the vast area of the ocean as correctly as we can do its depth1 shallowness rather than depth would be the impression produced4 ,a sheet of water #ajj yards in diameter1 and only one inch deep1 would not be called a deep but a very shallow pool or thin layer of water4 ,but such a layer would be a correct representation of the ocean in miniature4 ,were we in like manner to represent to the eye in miniature the antarctic ice-cap1 we would call it a thin crust of ice4 ,taking the mean thickness of the ice at four miles1 the antarctic ice-sheet would be represented by a carpet covering the floor of an ordinary-sized dining-room4 ,were those who consider the above estimate of the thickness of the antarctic ice-cap as extravagantly great called upon to sketch on paper a section of what they should deem a cap of moderate thickness1 ninety-nine out of every hundred would draw one of much greater thickness than twelve miles at the centre4 ,the diagram on following page 7,fig4 #g7 represents a section across the cap drawn to a natural scale2 the upper surface of the sheet having a slope of half a degree4 ,no one on looking at the section would pronounce it to be too thick at the centre1 unless he were previously made aware that it represented a thickness of twelve miles at that place4 ,it may be here mentioned that had the section been drawn upon a much larger scale--had it1 for instance1 been made seven feet long1 instead of seven inches--it would have shown to the eye in a more striking manner the thinness of the cap4 ,but to avoid all objections on the score of over-estimating the thickness of the cap1 ,i shall assume the angle of the upper surface to be only a quarter of a degree1 and the thickness of the sheet one-half what it is represented in the section4 ,the thickness at the pole will then be only six miles instead of twelve1 and the mean thickness of the cap two instead of four miles4 ,illustration3 ,fig4 #g4 ,section across ,antarctic ,ice-cap1 drawn to a natural scale4 ,length represented by section #b1hjj miles4 ,thickness at centre 7,south ,pole7 #ab miles4 ,slope of upper surface half-degree4 ,is there any well-grounded reason for concluding the above to be an over-estimate of the actual thickness of the antarctic ice8 ,it is not so much in consequence of any priori reason that can be urged against the probability of such a thickness of ice1 but rather because it so far transcends our previous experience that we are reluctant to admit such an estimate4 ,if we never had any experience of ice thicker than what is found in ,england1 we should feel startled on learning for the first time that in the valleys of ,switzerland the ice lay from #bjj to #cjj feet in depth4 ,again1 if we had never heard of glaciers thicker than those of ,switzerland1 we could hardly credit the statement that in ,greenland they are actually from #b1jjj to #c1jjj feet thick4 ,we1 in this country1 have long been familiar with ,greenland2 but till very lately no one ever entertained the idea that that continent was buried under one continuous mass of ice1 with scarcely a mountain top rising above the icy mantle4 ,and had it not been that the geological phenomena of the glacial epoch have for so many years accustomed our minds to such an extraordinary condition of things1 ,dr4 ,rink's description of the ,greenland ice would probably have been regarded as the extravagant picture of a wild imagination4 ,let us now consider whether or not the facts of observation and experience1 so far as they go1 bear out the conclusions to which physical considerations lead us in reference to the magnitude of continental ice2 and more especially as regards the ice of the antarctic regions4 ,first4 ,in so far as the antarctic ice-sheet is concerned1 observation and experience to a great extent may be said to be a perfect blank4 ,one or two voyagers have seen the outer edge of the sheet at a few places1 and this is all4 ,in fact1 we judge of the present condition of the interior of the antarctic continent in a great measure from what we know of ,greenland4 ,but again1 our experience of ,greenland ice is almost wholly confined to the outskirts4 ,few have penetrated into the interior1 and1 with the exception of ,dr4 ,hayes and ,professor ,nordenskjld1 none1 as far as ,i know1 have passed to any considerable distance over the inland ice4 ,dr4 ,robert ,brown in his interesting memoir on 8,das ,innere von ,grnland10#bjg gives an account of an excursion made in #agdg by a ,danish officer of the name of ,dalager1 from ,fredrikshaab1 near the southern extremity of the continent1 into the interior4 ,after a journey of a day or two1 he reached an eminence from which he saw the inland ice stretching in an unbroken mass as far as the eye could reach1 but was unable to proceed further4 ,dr4 ,brown gives an account also of an excursion made in the beginning of ,march1 #ahcj1 by ,o4 ,b4 ,kielsen1 a ,danish whale-fisher1 from ,holsteinborg 7lat4 #fg ,n474 ,after a most fatiguing journey of several days1 he reached a high point from which he could see the ice of the interior4 ,next morning he got up early1 and towards midday reached an extensive plain4 ,from this the land sank inwards1 and ,kielsen now saw fully in view before him the enormous ice-sheet of the interior4 ,he drove rapidly over all the little hills1 lakes1 and streams1 till he reached a pretty large lake at the edge of the ice-sheet4 ,this was the end of his journey1 for after vainly attempting to climb up on the ice-sheet1 he was compelled to retrace his steps1 and had a somewhat difficult return4 ,when he arrived at the fiord1 he found the ice broken up1 so that he had to go round by the land way1 by which he reached the dept on the #ith of ,march4 ,the distance which he traversed in a straight line from ,holsteinborg into the interior measured eighty ,english miles4 ,dr4 ,hayes's excursion was made1 however1 not upon the real inland ice1 but upon a smaller ice-field connected with it2 while ,professor ,nordenskjld's excursion was made at a place too far south to afford an accurate idea of the actual condition of the interior of ,north ,greenland1 even though he had penetrated much farther than he actually did4 ,however1 the state of things as recorded by ,hayes and by ,nordenskjld affords us a glimpse into the condition of things in the interior of the continent4 ,they both found by observation1 what follows as a necessary result from physical considerations1 that the upper surface of the ice plain1 under which hills and valleys are buried1 gradually slopes upwards towards the interior of the continent4 ,professor ,nordenskjld states that when at the extreme point at which he reached1 thirty geographical miles from the coast1 he had attained an elevation of #b1bjj feet1 and that the inland ice continued constantly to rise towards the interior1 so that the horizon towards the east1 north1 and south1 was terminated by an ice-border almost as smooth as that of the ocean40#bjh ,dr4 ,hayes and his party penetrated inwards to the distance of about seventy miles4 ,on the first day they reached the foot of the great ,mer de ,glace2 the second day's journey carried them to the upper surface of the ice-sheet4 ,on the third day they travelled #cj miles1 and the ascent1 which had been about #f1 diminished gradually to about #b4 ,they advanced on the fourth day about #be miles2 the temperature being #cj below zero 7,fah474 8,our station at the camp10 he says1 8was sublime as it was dangerous4 ,we had attained an altitude of #e1jjj feet above the sea-level1 and were #gj miles from the coast1 in the midst of a vast frozen ,sahara immeasurable to the human eye4 ,there was neither hill1 mountain1 nor gorge1 anywhere in view4 ,we had completely sunk the strip of land between the ,mer de ,glace and the sea1 and no object met the eye but our feeble tent1 which bent to the storm4 ,fitful clouds swept over the face of the full-orbed moon1 which1 descending towards the horizon1 glimmered through the drifting snow that scudded over the icy plain--to the eye in undulating lines of downy softness1 to the flesh in showers of piercing darts40#bji ,dr4 ,rink1 referring to the inland ice1 says that the elevation or height above the sea of this icy plain at its junction with the outskirts of the country1 and where it begins to lower itself through the valleys to the firths1 is1 in the ramifications of the ,bay of ,omenak1 found to be #b1jjj feet1 from which level it gradually rises towards the interior4#baj ,dr4 ,robert ,brown1 who1 along with ,mr4 ,whymper in #ahfg1 attempted a journey to some distance over the inland ice1 is of opinion that ,greenland is not traversed by any ranges of mountains or high land1 but that the entire continent1 #a1bjj miles in length and #djj miles in breadth1 is covered with one continuous unbroken field of ice1 the upper surface of which1 he says1 rises by a gentle slope towards the interior4#baa ,suppose now the point reached by ,hayes to be within #bjj miles of the centre of dispersion of the ice1 and the mean slope from that point to the centre1 as in the case of the antarctic cap1 to be only half a degree2 this would give #aj1jjj feet as the elevation of the centre above the point reached4 ,but the point reached was #e1jjj feet above sea-level1 consequently the surface of the ice at the centre of dispersion would be #ae1jjj feet above sea-level1 which is about one-fourth what ,i have concluded to be the elevation of the surface of the antarctic ice-cap at its centre4 ,and supposing we assume the general surface of the ground to have in the central region an elevation as great as #e1jjj feet1 which is not at all probable1 still this would give #aj1jjj feet for the thickness of the ice at the centre of the ,greenland continent4 ,but if we admit this conclusion in reference to the thickness of the ,greenland ice1 we must admit that the antarctic ice is far thicker1 because the thickness1 other things being equal1 will depend upon the size1 or1 more properly1 upon the diameter of the continent2 for the larger the surface the greater is the thickness of ice required to produce the pressure requisite to make the rate of discharge of the ice equal to the rate of increase4 ,now the area of the antarctic continent must be at least a dozen of times greater than that of ,greenland4 ,second4 ,that the antarctic ice must be far thicker than the arctic is further evident from the dimensions of the icebergs which have been met with in the ,southern ,ocean4 ,no icebergs over three hundred feet in height have been found in the arctic regions1 whereas in the antarctic regions1 as we shall see1 icebergs of twice and even thrice that height have been reported4 ,third4 ,we have no reason to believe that the thickness of the ice at present covering the antarctic continent is less than that which covered a continent of a similar area in temperate regions during the glacial epoch4 ,take1 for example1 the ,north ,american continent1 or1 more properly1 that portion of it covered by ice during the glacial epoch4 ,professor ,dana has proved that during that period the thickness of the ice on the ,american continent must in many places have been considerably over a mile4 ,he has shown that over the northern border of ,new ,england the ice had a mean thickness of #f1ejj feet1 while its mean thickness over the ,canada watershed1 between ,st4 ,lawrence and ,hudson's ,bay1 was not less than #ab1jjj feet1 or upwards of two miles and a quarter 7see ,american ,journal of ,science and ,art for ,march1 #ahgc74 ,fourth4 ,some may object to the foregoing estimate of the amount of ice on the antarctic continent1 on the grounds that the quantity of snowfall in that region cannot be much4 ,but it must be borne in mind that1 no matter however small the annual amount of snowfall may be1 if more falls than is melted1 the ice must continue to accumulate year by year till its thickness in the centre of the continent be sufficiently great to produce motion4 ,the opinion that the snowfall of the antarctic regions is not great does not1 however1 appear to be borne out by the observation and experience of those who have visited those regions4 ,captain ,wilkes1 of the ,american ,exploring ,expedition1 estimated it at #cj feet per annum2 and ,sir ,james ,ross says1 that during a whole month they had only three days free from snow4 ,the fact that perpetual snow is found at the sea-level at lat4 #fd ,s4 proves that the snowfall must be great4 ,but there is another circumstance which must be taken into account1 viz41 that the currents carrying moisture move in from all directions towards the pole1 consequently the area on which they deposit their snow becomes less and less as the pole is reached1 and this must1 to a corresponding extent1 increase the quantity of snow falling on a given area4 ,let us assume1 for example1 that the clouds in passing from lat4 #fj to lat4 #hj deposit moisture sufficient to produce1 say1 #cj feet of snow per annum1 and that by the time they reach lat4 #hj they are in possession of only one-tenth part of their original store of moisture4 ,as the area between lat4 #hj and the pole is but one-eighth of that between lat4 #fj and #hj1 this would1 notwithstanding1 give #bd feet as the annual amount of snowfall between lat4 #hj and the pole4#bab ,fifth4 ,the enormous size and thickness of the icebergs which have been met with in the ,southern ,ocean testify to the thickness of the antarctic ice-cap4 ,we know from the size of some of the icebergs which have been met with in the southern hemisphere that the ice at the edge of the cap where the bergs break off must in some cases be considerably over a mile in thickness1 for icebergs of more than a mile in thickness have been found in the southern hemisphere4 ,the following are the dimensions of a few of these enormous bergs taken from the ,twelfth ,number of the ,meteorological ,papers published by the ,board of ,trade1 and from the excellent paper of ,mr4 ,towson on the ,icebergs of the ,southern ,ocean1 published also by the ,board of ,trade4#bac ,with one or two exceptions1 the heights of the bergs were accurately determined by angular measurement3-- ,sept4 #ajth1 #ahef4--,the ,lightning1 when in lat4 #ee #cc ,s41 long4 #adj ,w41 met with an iceberg #dbj feet high4 ,nov41 #ahci4--;,in lat4 #da ,s41 long4 #hg #cj ,e41 numerous icebergs #djj feet high were met with4 ,sept41 #ahdj4--;,in lat4 #cg ,s41 long4 #ae ,e41 an iceberg #a1jjj feet long and #djj feet high was met with4 ,feb41 #ahfj4--;,captain ,clark1 of the ,lightning1 when in lat4 #ee #bj ,s41 long4 #abb #de ,w41 found an iceberg #ejj feet high and #c miles long4 ,dec4 #ast1 #ahei4--;,an iceberg1 #ehj feet high1 and from two and a half to three miles long1 was seen by ,captain ,smithers1 of the ,edmond1 in lat4 #ej #eb ,s41 long4 #dc #eh ,w4 ,so strongly did this iceberg resemble land1 that ,captain ,smithers believed it to be an island1 and reported it as such1 but there is little or no doubt that it was in reality an iceberg4 ,there were pieces of drift-ice under its lee4 ,nov41 #ahef4--,three large icebergs1 #ejj feet high1 were found in lat4 #da #j ,s41 long4 #db #j ,e4 ,jan41 #ahfa4--;,five icebergs1 one #ejj feet high1 were met with in lat4 #ee #df ,s41 long4 #aee #ef ,w4 ,jan41 #ahfa4--;,in lat4 #ef #aj ,s41 long4 #afj #j ,w41 an iceberg #ejj feet high and half a mile long was found4 ,jan41 #ahfg4--,the barque ,scout1 from the ,west ,coast of ,america1 on her way to ,liverpool1 passed some icebergs #fjj feet in height1 and of great length4 ,april1 #ahfd4--,the ,royal ,standard came in collision with an iceberg #fjj feet in height4 ,dec41 #ahef4--;,four large icebergs1 one of them #gjj feet high1 and another #ejj feet1 were met with in lat4 #ej #ad ,s41 long4 #db #ed ,e4 ,dec4 #beth1 #ahfa4--,the ,queen of ,nations fell in with an iceberg in lat4 #ec #de ,s41 long4 #agj #j ,w41 #gbj feet high4 ,dec41 #ahef4--;,captain ,p4 ,wakem1 ship ,ellen ,radford1 found1 in lat4 #eb #ca ,s41 long4 #dc #dc ,w41 two large icebergs1 one at least #hjj feet high4 ,mr4 ,towson states that one of our most celebrated and talented naval surveyors informed him that he had seen icebergs in the southern regions #hjj feet high4 ,march #bcrd1 #ahee4--,the ,agneta passed an iceberg in lat4 #ec #ad ,s41 long4 #ad #da ,e41 #ifj feet in height4 ,aug4 #afth1 #ahdj4--,the ,dutch ship1 ,general ,baron von ,geen1 passed an iceberg #a1jjj feet high in lat4 #cg #cb ,s41 long4 #ad #aj ,e4 ,may #aeth1 #ahei4--,the ,roseworth found in lat4 #ec #dj ,s41 long4 #abc #ag ,w41 an iceberg as large as 8,tristan d',acunha40 ,in the regions where most of these icebergs were met with1 the mean density of the sea is about #ajbef4 ,the density of ice is #ib4 ,the density of icebergs to that of the sea is therefore as #a to #aaae2 consequently every foot of ice above water indicates #hg feet below water4 ,it therefore follows that those icebergs #djj feet high had #c1dhj feet under water1--#c1hhj feet would consequently be the total thickness of the ice4 ,the icebergs which were #ejj feet high would be #d1hej feet thick1 those #fjj feet high would have a total thickness of #e1hbj feet1 and those #gjj feet high would be no less than #f1gij feet thick1 which is more than a mile and a quarter4 ,the iceberg #ifj feet high1 sighted by the ,agneta1 would be actually #i1cab feet thick1 which is upwards of a mile and three-quarters4 ,although the mass of an iceberg below water compared to that above may be taken to be about #hg to #a1 yet it would not be always safe to conclude that the thickness of the ice below water bears the same proportion to its height above4 ,if the berg1 for example1 be much broader at its base than at its top1 the thickness of the ice below water would bear a less proportion to the height above water than as #hg to #a4 ,but a berg such as that recorded by ,captain ,clark1 #ejj feet high and three miles long1 must have had only #a_/hg of its total thickness above water4 ,the same remark applies also to the one seen by ,captain ,smithers1 which was #ehj feet high1 and so large that it was taken for an island4 ,this berg must have been #e1fbh feet in thickness4 ,the enormous berg which came in collision with the ,royal ,standard must have been #e1hbj feet thick4 ,it is not stated what length the icebergs #gcj1 #ifj1 and #a1jjj feet high respectively were2 but supposing that we make considerable allowance for the possibility that the proportionate thickness of ice below water to that above may have been less than as #hg to #a1 still we can hardly avoid the conclusion that the icebergs were considerably above a mile in thickness4 ,but if there are icebergs above a mile in thickness1 then there must be land-ice somewhere on the southern hemisphere of that thickness4 ,in short1 the great antarctic ice-cap must in some places be over a mile in thickness at its edge4 ,inadequate ,conceptions regarding the ,magnitude of ,continental ,ice4--,few things have tended more to mislead geologists in the interpretation of glacial phenomena than inadequate conceptions regarding the magnitude of continental ice4 ,without the conception of continental ice the known facts connected with glaciation would be perfectly inexplicable4 ,it was only when it was found that the accumulated facts refused to be explained by any other conception1 that belief in the very existence of such a thing as continental ice became common4 ,but although most geologists now admit the existence of continental ice1 yet1 nevertheless1 adequate conceptions of its real magnitude are by no means so common4 ,year by year1 as the outstanding facts connected with glaciation accumulate1 we are compelled to extend our conceptions of the magnitude of land-ice4 ,take the following as an example4 ,it was found that the transport of the ,wastdale ,crag blocks1 the direction of the stri on the islands of the ,baltic1 on ,caithness and on the ,orkney1 ,shetland1 and ,faroe1 islands1 the boulder clay with broken shells in ,caithness1 ,holderness1 and other places1 were inexplicable on the theory of land-ice4 ,but it was so only in consequence of the inadequacy of our conceptions of the magnitude of the ice2 for a slight extension of our ideas of its thickness has explained not only these phenomena1#bad but others of an equally remarkable character1 such as the striation of the ,long ,island and the submerged rock-basins around our coasts described by ,mr4 ,james ,geikie4 ,in like manner1 if we admit the theory of the glacial epoch propounded in former chapters1 all that is really necessary to account for the submergence of the land is a slight extension of our hitherto preconceived estimate of the thickness of the ice on the antarctic continent4 ,if we simply admit a conclusion to which all physical considerations1 as we have seen1 necessarily lead us1 viz41 that the antarctic continent is covered with a mantle of ice at least two miles in thickness1 we have then a complete explanation of the cause of the submergence of the land during the glacial epoch4 ,although of no great importance to the question under consideration1 it may be remarked that1 except during the severest part of the glacial epoch1 we have no reason to believe that the total quantity of ice on the globe was much greater than at present1 only it would then be all on one hemisphere4 ,remove two miles of ice from the antarctic continent1 and place it on the northern hemisphere1 and this1 along with the ice that now exists on this hemisphere1 would equal1 in all probability1 the quantity existing on our hemisphere during the glacial epoch2 at least1 before it reached its maximum severity4 ,,chapter ,,xxiv4 ,,the ,,physical ,,cause ,,of ,,the ,,submergence ,,and ,,emergence ,,of ,,the ,,land ,,during ,,the ,,glacial ,,epoch4--,continued4 ,extent of ,submergence from ,displacement of ,earth's ,centre of ,gravity4--,circumstances which show that the ,glacial ,submergence resulted from ,displacement of the ,earth's ,centre of ,gravity4--,agreement between ,theory and observed ,facts4--,sir ,charles ,lyell on submerged ,areas during ,tertiary ,period4--,oscillations of ,sea-level in ,relation to ,distribution4--,extent of ,submergence on the ,hypothesis that the ,earth is fluid in the ,interior4 ,extent of ,submergence from ,displacement of ,earth's ,centre of ,gravity4--,how much1 then1 would the transference of the two miles of ice from the southern to the northern hemisphere raise the level of the ocean on the latter hemisphere8 ,this mass1 be it observed1 is equal to only one-half that represented in our section4 ,a considerable amount of discussion has arisen in regard to the method of determining this point4 ,according to the method already detailed1 which supposes the rise at the pole to be equal to the extent of the displacement of the earth's centre of gravity1 the rise at the ,north ,pole would be about #chj feet1 taking into account the effect produced by the displaced water2 and the rise in the latitude of ,edinburgh would be #cab feet4 ,the fall of level on the southern hemisphere would1 of course1 be equal to the rise of level on the northern4 ,according to the method advanced by ,mr4 ,d4 ,d4 ,heath1#bae the rise of level at the ,north ,pole would be about #fej feet4 ,archdeacon ,pratt's method#baf makes the rise still greater2 while according to ,rev4 ,o4 ,fisher's method#bag the rise would be no less than #b1jjj feet4 ,there is1 however1 another circumstance which must be taken into account1 which will give an additional rise of upwards of one hundred feet4 ,the greatest extent of the displacement of the earth's centre of gravity1 and consequently the greatest rise of the ocean resulting from that displacement1 would of course occur at the time of maximum glaciation1 when the ice was all on one hemisphere4 ,but owing to the following circumstance1 a still greater rise than that resulting from the displacement of the earth's centre of gravity alone might take place at some considerable time1 either before or after the period of maximum glaciation4 ,it is not at all probable that the ice would melt on the warm hemisphere at exactly the same rate as it would form on the cold hemisphere4 ,it is probable that the ice would melt more rapidly on the warm hemisphere than it would form on the cold4 ,suppose that during the glacial epoch1 at a time when the cold was gradually increasing on the northern and the warmth on the southern hemisphere1 the ice should melt more rapidly off the antarctic continent than it was being formed on the arctic and subarctic regions2 suppose also that1 by the time a quantity of ice1 equal to one-half what exists at present on the antarctic continent1 had accumulated on the northern hemisphere1 the whole of the antarctic ice had been melted away1 the sea would then be fuller than at present by the amount of water resulting from the one mile of melted ice4 ,the height to which this would raise the general level of the sea would be as follows3-- ,the antarctic ice-cap is equal in area to #a_/bcdf of that covered by the ocean4 ,the density of ice to that of water being taken at #ib to #a1 it follows that #be feet #f inches of ice melted off the cap would raise the general level of the ocean one foot1 and the one mile of ice melted off would raise the level #bjj feet4 ,this #bjj feet of rise resulting from the melted ice we must add to the rise resulting from the displacement of the earth's centre of gravity4 ,the removal of the two miles of ice from the antarctic continent would displace the centre of gravity #aij feet1 and the formation of a mass of ice equal to the one-half of this on the arctic regions would carry the centre of gravity #ie feet farther2 giving in all a total displacement of #bhe feet1 thus producing a rise of sea-level at the ,north ,pole of #bhe feet1 and in the latitude of ,edinburgh of #bcd feet4 ,add to this the rise of #bjj feet resulting from the melted ice1 and we have then #dhe feet of submergence at the pole1 and #dcd feet in the latitude of ,edinburgh4 ,a rise to a similar extent might probably take place after the period of maximum glaciation1 when the ice would be melting on the northern hemisphere more rapidly than it would be forming on the southern4 ,if we assume the antarctic ice-cap to be as thick as is represented in the diagram1 the extent of the submergence would of course be double the above1 and we might have in this case a rise of sea-level in the latitude of ,edinburgh to the extent of from #hjj to #a1jjj feet4 ,but be this as it may1 it is evident that the quantity of ice on the antarctic continent is perfectly sufficient to account for the submergence of the glacial epoch1 for we have little evidence to conclude that the general submergence much exceeded #djj or #ejj feet4#bah ,we have evidence in ,england and other places of submergence to the extent of from #a1jjj to #b1jjj feet1 but these may be quite local1 resulting from subsidence of the land in those particular areas4 ,elevations and depressions of the land have taken place in all ages1 and no doubt during the glacial epoch also4 ,circumstances which show that the ,glacial ,submergence resulted from ,displacement of the ,earth's ,centre of ,gravity4--,in favour of this view of the cause of the submergence of the glacial epoch1 it is a circumstance of some significance1 that in every part of the globe where glaciation has been found evidence of the submergence of the land has also been found along with it4 ,the invariable occurrence of submergence along with glaciation points to some physical connection between the two4 ,it would seem to imply1 either that the two were the direct effects of a common cause1 or that the one was the cause of the other2 that is1 the submergence the cause of the glaciation1 or the glaciation the cause of the submergence4 ,there is1 ,i presume1 no known cause to which the two can be directly related as effects4 ,nor do ,i think that there is any one who would suppose that the submergence of the land could have been the cause of its glaciation1 even although he attributed all glacial effects to floating ice4 ,the submergence of our country would1 of course1 have allowed floating ice to pass over it had there been any to pass over2 but submergence would not have produced the ice1 neither would it have brought the ice from the arctic regions where it already existed4 ,but although submergence could not have been the cause of the glacial epoch1 yet we can1 as we have just seen1 easily understand how the ice of the glacial epoch could have been the cause of the submergence4 ,if the glacial epoch was brought about by an increase in the eccentricity of the earth's orbit1 then a submergence of the land as the ice accumulated was a physical necessity4 ,there is another circumstance connected with glacial submergence which it is difficult to reconcile with the idea that it resulted from a subsidence of the land4 ,it is well known that during the glacial epoch the land was not once under water only1 but several times2 and1 besides1 there were not merely several periods when the land stood at a lower level in relation to the sea than at present1 but there were also several periods when it stood at a much higher level than now4 ,and this holds true1 not merely of our own country1 but of every country on the northern hemisphere where glaciation has yet been found4 ,all this follows as a necessary consequence from the theory that the oscillations of sea-level resulted from the transference of the ice from the one hemisphere to the other2 but it is wholly inconsistent with the idea that they resulted from upheavals and subsidence of the land during a very recent period4 ,but this is not all1 there is more still to be accounted for4 ,it has been the prevailing opinion that at the time when the land was covered with ice1 it stood at a much greater elevation than at present4 ,it is1 however1 not maintained that the facts of geology establish such a conclusion4 ,the greater elevation of the land is simply assumed as an hypothesis to account for the cold4#bai ,the facts of geology1 however1 are fast establishing the opposite conclusion1 viz41 that when the country was covered with ice1 the land stood in relation to the sea at a lower level than at present1 and that the continental periods or times when the land stood in relation to the sea at a higher level than now were the warm inter-glacial periods1 when the country was free of snow and ice1 and a mild and equable condition of climate prevailed4 ,this is the conclusion towards which we are being led by the more recent revelations of surface geology1 and also by certain facts connected with the geographical distribution of plants and animals during the glacial epoch4 ,the simple occurrence of a rise and fall of the land in relation to the sea-level in one or in two countries during the glacial epoch1 would not necessarily imply any physical connection4 ,the coincidence of these movements with the glaciation of the land might have been purely accidental2 but when we find that a succession of such movements occurred1 not merely in one or in two countries1 but in every glaciated country where proper observations have been made1 we are forced to the conclusion that the connection between the two is not accidental1 but the result of some fixed cause4 ,if we admit that an increase in the eccentricity of the earth's orbit was the cause of the glacial epoch1 then we must admit that all those results followed as necessary consequences4 ,for if the glacial epoch lasted for upwards of one hundred thousand years or so1 there would be a succession of cold and warm periods1 and consequently a succession of elevations and depressions of sea-level4 ,and the elevations of the sea-level would take place during the cold periods1 and the depressions during the warm periods4 ,but the agreement between theory and observed facts does not terminate here4 ,it follows from theory that the greatest oscillations of sea-level would take place during the severest part of the glacial epoch1 when the eccentricity of the earth's orbit would be at its highest value1 and that the oscillations would gradually diminish in extent as the eccentricity diminished and the climate gradually became less severe4 ,now it is well known that this is actually what took place2 the great submergence1 as well as the great elevation or continental period1 occurred during the earlier or more severe part of the glacial epoch1 and as the climate grew less severe these changes became of less extent1 till we find them terminating in our submerged forests and #be-;foot raised beach4 ,it follows1 therefore1 according to the theory advanced1 that the mere fact of an area having been under sea does not imply that there has been any subsidence or elevation of the land1 and that consequently the inference which has been drawn from these submerged areas as to changes in physical geography may be in many cases not well founded4 ,sir ,charles ,lyell1 in his 8,principles10 publishes a map showing the extent of surface in ,europe which has been covered by the sea since the earlier part of the ,tertiary period4 ,this map is intended to show the extraordinary amount of subsidence and elevation of the land which has taken place during that period4 ,it is necessary for ,sir ,charles's theory of the cause of the glacial epoch that changes in the physical geography of the globe to an enormous extent should have taken place during a very recent period1 in order to account for the great change of climate which occurred at that epoch4 ,but if the foregoing results be anything like correct1 it does not necessarily follow that there must have been great changes in the physical geography of ,europe1 simply because the sea covered those areas marked in the map1 for this may have been produced by oscillations of sea-level1 and not by changes in the land4 ,in fact1 the areas marked in ,sir ,charles's map as having been covered by the sea1 are just those which would be covered were the sea-level raised a few hundred feet4 ,no doubt there were elevations and subsidences in many of the areas marked in the map during the ,tertiary period1 and to this cause a considerable amount of the submergence might be due2 but ,i have little doubt that by far the greater part must be attributed to oscillations of sea-level4 ,it is no objection that the greater part of the shells and other organic remains found in the marine deposits of those areas are not indicative of a cold or glacial condition of climate1 for1 as we have seen1 the greatest submergence would probably have taken place either before the more severe cold had set in or after it had to a great extent passed away4 ,that the submergence of those areas probably resulted from elevations of sea-level rather than depressions of the land1 is further evident from the following considerations4 ,if we suppose that the climate of the glacial epoch was brought about mainly by changes in the physical geography of the globe1 we must assume that these great changes took place1 geologically speaking1 at a very recent date4 ,then when we ask what ground is there for assuming that any such change in the relations of sea and land as is required actually took place1 the submergence of those areas is adduced as the proof4 ,did it follow as a physical necessity that all submergence must be the result of subsidence of the land1 and not of elevations of the sea1 there would be some force in the reasons adduced4 ,but such a conclusion by no means follows1 and1 priori1 it is just as likely that the appearance of the ice was the cause of the submergence as that the submergence was the cause of the appearance of the ice4 ,again1 a subsidence of the land to the extent required would to a great extent have altered the configuration of the country1 and the main river systems of ,europe2 but there is no evidence that any such change has taken place4 ,all the main valleys are well known to have existed prior to the glacial epoch1 and our rivers to have occupied the same channels then as they do now4 ,in the case of some of the smaller streams1 it is true1 a slight deviation has resulted at some points from the filling up of their channels with drift during the glacial epoch2 but as a general rule all the principal valleys and river systems are older than the glacial epoch4 ,this1 of course1 could not be the case if a subsidence of the land sufficiently great to account for the submergence of the areas in question1 or changes in the physical geography of ,europe necessary to produce a glacial epoch1 had actually taken place4 ,the total absence of any geological evidence for the existence of any change which could explain either the submergence of the areas in question or the climate of the glacial epoch1 is strong evidence that the submergence of the glacial epoch1 as well as of the areas in question1 was the result of a simple oscillation of sea-level resulting from the displacement of the earth's centre of gravity by the transferrence of the ice-cap from the southern to the northern hemisphere4 ,oscillations of ,sea-level in relation to ,distribution4--,the oscillations of sea-level resulting from the displacement of the earth's centre of gravity help to throw new light on some obscure points connected with the subject of the geographical distribution of plants and animals4 ,at the time when the ice was on the southern hemisphere during the glacial epoch1 and the northern hemisphere was enjoying a warm and equable climate1 the sea-level would be several hundred feet lower than at present1 the ,north ,sea would probably be dry land1 and ,great ,britain and ,ireland joined to the continent1 thus opening up a pathway from the continent to our island4 ,as has been shown in former chapters1 during the inter-glacial periods the climate would be much warmer and more equable than now1 so that animals from the south1 such as the hippopotamus1 hyna1 lion1 ,elephas antiquus and ,rhinoceros megarhinus1 would migrate into this country1 where at present they could not live in consequence of the cold4 ,we have therefore an explanation1 as was suggested on a former occasion1#bbj of the fact that the bones of these animals are found mingled in the same grave with those of the musk-ox1 mammoth1 reindeer1 and other animals which lived in this country during the cold periods of the glacial epoch2 the animals from the north would cross over into this country upon the frozen sea during the cold periods1 while those from the south would find the ,english ,channel dry land during the warm periods4 ,the same reasoning will hold equally true in reference to the old and new world4 ,the depth of ,behring ,straits is under #cj fathoms2 consequently a lowering of the sea-level of less than #bjj feet would connect ,asia with ,america1 and thus allow plants and animals1 as ,mr4 ,darwin believes1 to pass from the one continent to the other4#bba ,during this period1 when ,behring ,straits would be dry land1 ,greenland would be comparatively free from ice1 and the arctic regions enjoying a comparatively mild climate4 ,in this case plants and animals belonging to temperate regions could avail themselves of this passage1 and thus we can explain how plants belonging to temperate regions may have1 during the ,miocene period1 passed from the old to the new continent1 and vice vers4 ,as has already been noticed1 during the time of the greatest extension of the ice1 the quantity of ice on the southern hemisphere might be considerably greater than what exists on the entire globe at present4 ,in that case there might1 in addition to the lowering of the sea-level resulting from the displacement of the earth's centre of gravity1 be a considerable lowering resulting from the draining of the ocean to form the additional ice4 ,this decrease and increase in the total quantity of ice which we have considered would affect the level of the ocean as much at the equator as at the poles2 consequently during the glacial epoch there might have been at the equator elevations and depressions of sea-level to the extent of a few hundred feet4 ,extent of ,submergence on the ,hypothesis that the ,earth is fluid in the ,interior4--,but we have been proceeding upon the supposition that the earth is solid to its centre4 ,if we assume1 however1 what is the general opinion among geologists1 that it consists of a fluid interior surrounded by a thick and rigid crust or shell1 then the extent of the submergence resulting from the displacement of the centre of gravity for a given thickness of ice must be much greater than ,i have estimated it to be4 ,this is evident1 because1 if the interior of the globe be in a fluid state1 it1 in all probability1 consists of materials differing in density4 ,the densest materials will be at the centre1 and the least dense at the outside or surface4 ,now the transferrence of an ice-cap from the one pole to the other will not merely displace the ocean--the fluid mass on the outside of the shell--but it will also displace the heavier fluid materials in the interior of the shell4 ,in other words1 the heavier materials will be attracted by the ice-cap more forcibly than the lighter1 consequently they will approach towards the cap to a certain extent1 sinking1 as it were1 into the lighter materials1 and displacing them towards the opposite pole4 ,this displacement will of course tend to shift the earth's centre of gravity in the direction of the ice-cap1 because the heavier materials are shifted in this direction1 and the lighter materials in the opposite direction4 ,this process will perhaps be better understood from the following figures4 ,illustration3 ,fig4 #h4 ,fig4 #i4 ,o4 ,the ,ocean4 ,s4 ,solid ,crust or ,shell4 ,f1 ,f#a1 ,f#b1 ,f#c4 ,the various concentric layers of the fluid interior4 ,the layers increase in density towards the centre4 ,i4 ,the ,ice-cap4 ,c4 ,centre of gravity4 ,c#a4 ,the displaced centre of gravity4 ,in ,fig4 #h1 where there is no ice-cap1 the centre of gravity of the earth coincides with the centre of the concentric layers of the fluid interior4 ,in ,fig4 #i1 where there is an ice-cap placed on one pole1 the concentric layer ,f#a being denser than layer ,f1 is attracted towards the cap more forcibly than ,f1 and consequently sinks to a certain depth in ,f4 ,again1 ,f#b being denser than ,f#a1 it also sinks to a certain extent in ,f#a4 ,and again ,f#c1 the mass at the centre1 being denser than ,f#b1 it also sinks in ,f#b4 ,all this being combined with the effects of the ice-cap1 and the displaced ocean outside the shell1 the centre of gravity of the entire globe will no longer be at ,c1 but at ,c#a1 a considerable distance nearer to the side of the shell on which the cap rests than ,c1 and also a considerable distance nearer than it would have been had the interior of the globe been solid4 ,there are here three causes tending to shift the centre of gravity1 7#a7 the ice-cap1 7#b7 the displaced ocean1 and 7#c7 the displaced materials in the interior4 ,two of the three causes mutually react on each other in such a way as to increase each other's effect4 ,thus the more the ocean is drawn in the direction of the ice-cap1 the more effect it has in drawing the heavier materials in the interior in the same direction2 and in turn the more the heavier materials in the interior are drawn towards the cap1 the greater is the displacement of the earth's centre of gravity1 and of course1 as a consequence1 the greater is the displacement of the ocean4 ,it may be observed also that1 other things being equal1 the thinner the solid crust or shell is1 and the greater the difference in the density of the fluid materials in the interior1 the greater will be the extent of the displacement of the ocean1 because the greater will be the displacement of the centre of gravity4 ,it follows that if we knew 7#a7 the extent of the general submergence of the glacial epoch1 and 7#b7 the present amount of ice on the southern hemisphere1 we could determine whether or not the earth is fluid in the interior4 ,,chapter ,,xxv4 ,,the ,,influence ,,of ,,the ,,obliquity ,,of ,,the ,,ecliptic ,,on ,,climate ,,and ,,on ,,the ,,level ,,of ,,the ,,sea4 ,the direct ,effect of ,change of ,obliquity on ,climate4--,mr4 ,stockwell on the maximum ,change of ,obliquity4--,how ,obliquity affects the ,distribution of ,heat over the ,globe4--,increase of ,obliquity diminishes the ,heat at the ,equator and increases that at the ,poles4--,influence of ,change of ,obliquity on the ,level of the ,sea4--,when the ,obliquity was last at its superior ,limit4--,probable ,date of the #be-;foot raised ,beach4--,probable ,extent of ,rise of ,sea-level resulting from ,increase of ,obliquity4--,lieutenant-,colonel ,drayson's and ,mr4 ,belt's ,theories4--,sir ,charles ,lyell on ,influence of ,obliquity4 ,the direct ,effect of ,change in the ,obliquity of the ,ecliptic on ,climate4--,there is still another cause which1 ,i feel convinced1 must to a very considerable extent have affected climate during past geological ages4 ,i refer to the change in the obliquity of the ecliptic4 ,this cause has long engaged the attention of geologists and physicists1 and the conclusion generally come to is that no great effect can be attributed to it4 ,after giving special attention to the matter1 ,i have been led to the very opposite conclusion4 ,it is quite true1 as has been urged1 that the changes in the obliquity of the ecliptic cannot sensibly affect the climate of temperate regions2 but it will produce a slight change on the climate of tropical latitudes1 and a very considerable effect on that of the polar regions1 especially at the poles themselves4 ,we shall now consider the matter briefly4 ,it was found by ,laplace that the obliquity of the ecliptic will oscillate to the extent of #a #bb #cd on each side of #bc #bh1 the obliquity in the year #ahja4bbb ,this point has lately been examined by ,mr4 ,stockwell1 and the results at which he has arrived are almost identical with those of ,laplace4 8,the mean value of the obliquity10 he says1 8of both the apparent and fixed ecliptics to the equator is #bc #ag #ag4 ,the limits of the obliquity of the apparent ecliptic to the equator are #bd #ce #eh and #ba #eh #cf2 whence it follows that the greatest and least declinations of the sun at the solstices can never differ from each other to any greater extent than #b #cg #bb40bbc ,this change will but slightly affect the climate of the temperate regions1 but it will exercise a very considerable influence on the climate of the polar regions4 ,according to ,mr4 ,meech1#bbd if #cfebd thermal days represent the present total annual quantity of heat received at the equator from the sun1 #aeaei thermal days will represent the quantity received at the poles4 ,adopting his method of calculation1 it turns out that when the obliquity of the ecliptic is at the maximum assigned by ,laplace the quantity received at the equator would be #cfcea thermal days1 and at the poles #afjjd thermal days4 ,the equator would therefore receive #agc thermal days less heat1 and the poles #hde thermal days more heat than at present4 ,,annual ,,amount ,,of ,,sun',s ,,heat4 ---------------------------------------- --- ,amount in #ahja4 ,amount at ,obliquity #bc #bh4 maximum1 ,difference4 #bd #ej #cd84 ---------------------------------------- -- ,latitude4 ,thermal ,thermal ,thermal days4 days4 days4 #j #cfebd #cfcea #agc #dj #bhhee #bhhcb #jbc #gj #agcjd #agiad #faj #hj #aeffc #afdfc #hjj #ij #aeaei #afjjd #hde ---------------------------------------- -- ,when the obliquity was at a maximum1 the poles would therefore be receiving #ai rays for every #ah they are receiving at present4 ,the poles would then be receiving nearly as much heat as latitude #gf is receiving at present4 ,the increase of obliquity would not sensibly affect the polar winter4 ,it is true that it would slightly increase the breadth of the frigid zone1 but the length of the winter at the poles would remain unaffected4 ,after the sun disappears below the horizon his rays are completely cut off1 so that a further descent of #a #bb #cd would make no material difference in the climate4 ,in the temperate regions1 the sun's altitude at the winter solstice would be #a #bb #cd less than at present4 ,this would slightly increase the cold of winter in those regions4 ,but the increase in the amount of heat received by the polar regions would materially affect the condition of the polar summer4 ,what1 then1 is the rise of temperature at the poles which would result from the increase of #hde thermal days in the total amount received from the sun8 ,an increase of #hde thermal days1 or #a_/ahth of the total quantity received from the sun1 according to the mode of calculation adopted in ,chap4 ,,ii4 would produce1 all other things being equal1 a rise in the mean annual temperature equal to #ad or #ae4 ,according to ,professor ,dove#bbe there is a difference of #gf between the mean annual temperature of latitude #gf and the pole2 the temperature of the former being #ih1 and that of the latter #bb4 ,since it follows that when the obliquity of the ecliptic is at a maximum the poles would receive about as much heat per annum as latitude #gf receives at present1 it may be supposed that the temperature of the poles at that period ought to be no higher than that of latitude #gf at the present time4 ,a little consideration will1 however1 show that this by no means follows4 ,professor ,dove's ,tables represent correctly the mean annual temperature corresponding to every tenth degree of latitude from the equator to the pole4 ,but it must be observed that the rate at which the temperature diminishes from the equator to the pole is not proportionate to the decrease in the total quantity of heat received from the sun as we pass from the equator to the pole4 ,were the mean annual temperature of the various latitudes proportionate to the amount of direct heat received1 the equator would be much warmer than it actually is at present1 and the poles much colder4 ,the reason of this1 as has been shown in ,chapter ,,ii41 is perfectly obvious4 ,there is a constant transferrence of heat from the equator to the poles1 and of cold from the poles to the equator4 ,the warm water of the equator is constantly flowing towards the poles1 and the cold water at the poles is constantly flowing to the equator4 ,the same is the case in regard to the arial currents4 ,consequently a great portion of the direct heat of the sun goes1 not to raise the temperature of the equator1 but to heat the poles4 ,and1 on the other hand1 the cold materials at the poles are transferred to the equator1 and thus lower the temperature of that part of the globe to a great extent4 ,the present difference of temperature between lat4 #gf and the pole1 determined according to the rate at which the temperature is found to diminish between the equator and the pole1 amounts to only about #g or #h4 ,but were there no mutual transferrence of warm and cold materials between the equatorial and polar regions1 and were the temperature of each latitude to depend solely upon the direct rays of the sun1 the difference would far exceed that amount4 ,now1 when the obliquity of the ecliptic was at its superior limit1 and the poles receiving about #a_/ahth more direct heat from the sun than at present1 the increase of temperature due to this increase of heat would be far more than #g or #h4 ,it would probably be nearly double that amount4 8,we may1 therefore1 conclude that when the obliquity of the ecliptic was at a maximum1 and the poles were receiving #a_/ahth more heat than at present1 the temperature of the poles ought to have been about #ad or #ae warmer than at the present day1 provided1 of course1 that this extra heat was employed wholly in raising the temperature4 ,were the polar regions free from snow and ice1 the greater portion of the extra heat would go to raise the temperature4 ,but as those regions are covered with snow and ice1 the extra heat would have no effect in raising the temperature1 but would simply melt the snow and ice4 ,the ice-covered surface upon which the rays fell could never rise above #cb4 ,at the period under consideration1 the total annual quantity of ice melted at the poles would be #a_/ahth more than at present4 ,the general effect which the change in the obliquity of the ecliptic would have upon the climate of the polar regions when combined with the effects resulting from the eccentricity of the earth's orbit1 would be this3--,when the eccentricity was at a very high value1 the hemisphere whose winter occurred in the aphelion 7for physical reasons1 which have already been discussed7#bbf would be under a condition of glaciation1 while the other hemisphere1 having its winter in perihelion1 would be enjoying a warm and equable climate4 ,when the obliquity of the ecliptic was at a maximum1 and #a_/ahth more heat falling at the poles than at present1 the effect would be to modify to a great extent the rigour of the glaciation in the polar zone of the hemisphere under a glacial condition1 and1 on the other hand1 to produce a more rapid melting of the ice on the other hemisphere enjoying the equable climate4 ,the effects of eccentricity and obliquity thus combined would probably completely remove the polar ice-cap from off the latter hemisphere1 and forest trees might then grow at the pole4 ,again1 when the obliquity was at its minimum condition and less heat reaching the poles than at present1 the glaciation of the former hemisphere would be increased and the warmth of the latter diminished4 ,the ,influence of ,change in the ,obliquity of the ,ecliptic on the ,level of the ,sea4--,one very remarkable effect which seems to result indirectly from a variation of the obliquity under certain conditions1 is an influence on the level of the sea4 ,as this probably may have had something to do with those recent changes of sea-level with which the history of the submarine forests and raised beaches have made us all so familiar1 it may be of interest to enter at some length into this part of this subject4 ,it appears almost certain that at the time when the northern winter solstice was in the aphelion last1 a rise of the sea on the northern hemisphere to a considerable number of feet must have taken place from the combined effect of eccentricity and obliquity4 ,about #aa1gjj years ago1 the northern winter solstice was in the aphelion4 ,the eccentricity at that time was #jahg1 being somewhat greater than it is now2 but the winters occurring in aphelion instead of1 as now1 in perihelion1 they would on that account be probably #aj or #ae colder than they are at the present day4 ,it is probable1 also1 for reasons stated in a previous chapter1 that the ,gulf-stream at that time would be considerably less than now4 ,this would tend to lower the temperature to a still greater extent4 ,as snow instead of rain must have fallen during winter to a greater extent than at present1 this no doubt must have produced a slight increase in the quantity of ice on the northern hemisphere had no other cause come into operation4 ,but the condition of things1 we have every reason to believe1 must have been affected by the greater obliquity of the ecliptic at that period4 ,we have no formula1 except1 perhaps1 that given by ,mr4 ,stockwell1 from which to determine with perfect accuracy the extent of the obliquity at a period so remote as the one under consideration4 ,if we adopt the formula given by ,struve and ,peters1 which agrees pretty nearly with that obtained from ,mr4 ,stockwell's formula1 we have the obliquity at a maximum about the time that the solstice-point was in the aphelion4 ,the formula given by ,leverrier places the maximum somewhat later4 ,at all events1 we cannot be far from the truth in assuming that at the time the northern winter solstice was in the aphelion1 the obliquity of the ecliptic would be about a maximum1 and that since then it has been gradually diminishing4 ,it is evident1 then1 that the annual amount of heat received by the arctic regions1 and especially about the pole1 would be considerably greater than at present4 ,and as the heat received on those regions is chiefly employed in melting the ice1 it is probable that the extra amount of ice which would then be melted in the arctic regions would prevent that slight increase of ice which would otherwise have resulted in consequence of the winter occurring in the aphelion4 ,the winters at that period would be colder than they are at present1 but the total quantity of ice on the northern hemisphere would not probably be greater4 ,let us now turn to the southern hemisphere4 ,as the southern winter would then occur in the perihelion1 this would tend to produce a slight decrease in the quantity of ice on the southern hemisphere4 ,but on this hemisphere the effects of eccentricity would not1 as on the northern hemisphere1 be compensated by those of obliquity2 for both causes would here tend to produce the same effect2 namely1 a melting of the ice in the antarctic regions4 ,it is probable that at this time the quantity of warm water flowing from the equatorial regions into the ,southern ,ocean would be much greater than at present4 ,this would tend to raise the temperature of the air of the antarctic regions1 and thus assist in melting the ice4 ,these causes1 combined with the great increase of heat resulting from the change of obliquity1 would tend to diminish to a considerable extent the quantity of ice on the southern hemisphere4 ,i think we may assume that the slight increase of eccentricity at that period1 the occurrence of the southern winter in perihelion1 and the extra quantity of warm water flowing from the equatorial to the antarctic regions1 would produce an effect on the south polar ice-cap equal to that produced by the increase in the obliquity of the ecliptic4 ,it would1 therefore1 follow that for every eighteen pounds of ice melted annually at present at the south pole twenty pounds would then be melted4 ,let us now consider the effect that this condition of things would have upon the level of the sea4 ,it would evidently tend to produce an elevation of the sea-level on the northern hemisphere in two ways4 #ast4 ,the addition to the sea occasioned by the melting of the ice from off the antarctic land would tend to raise the general level of the sea4 #bndly4 ,the removal of the ice would also tend to shift the earth's centre of gravity to the north of its present position--and as the sea must shift along with the centre1 a rise of the sea on the northern hemisphere would necessarily take place4 ,the question naturally suggests itself1 might not the last rise of the sea1 relative to the land1 have resulted from this cause8 ,we know that during the period of the #be-;foot beach1 the time when the estuarine mud1 which now forms the rich soil of the ,carses of the ,forth and ,tay1 was deposited1 the sea1 in relation to the land1 stood at least #bj or #cj feet higher than at present4 ,but immediately prior to this period1 we have the age of the submarine forests and peat-beds1 when the sea relative to the land stood lower than it does now4 ,we know also that these changes of level were not mere local affairs4 ,there seems every reason to believe that our ,carse clay1 as ,mr4 ,fisher states1 is the equivalent of the marine mud1 with ,scrobicularia1 which covers the submarine forests of ,england4#bbg ,and on the other hand1 those submarine forests are not confined to one locality4 8,they may be traced10 says ,mr4 ,jamieson1 8round the whole of ,britain and ,ireland1 from ,orkney to ,cornwall1 from ,mayo to the shores of ,fife1 and even1 it would seem1 along a great part of the western sea-board of ,europe1 as if they bore witness to a period of widespread elevation1 when ,ireland and ,britain1 with all its numerous islands1 formed one mass of dry land1 united to the continent1 and stretching out into the ,atlantic40#bbh 8,these submarine forests08 remarks ,de la ,beche1 also1 8are to be found under the same general condition from the shores of ,scandinavia to those of ,spain and ,portugal1 and around the ,british islands40#bbi ,those buried forests are not confined to ,europe1 but are found in the valley of the ,mississippi and in ,nova ,scotia1 and other parts of ,north ,america4 ,and again1 the strata which underlie those forests and peat-beds bear witness to the fact of a previous elevation of the sea-level4 ,in short1 we have evidence of a number of oscillations of sea-level during post-tertiary times4#bcj ,had there been only one rise of the land relative to the sea-level1 or one depression1 it might quite reasonably1 as already remarked1 have been attributed to an upheaval or a sinking of the ground1 occasioned by some volcanic1 chemical1 or other agency4 ,but certainly those repeated oscillations of sea-level1 extending as they do over so wide an area1 look more like a rising and sinking of the sea than of the land4 ,but1 be this as it may1 since it is now established1 ,i presume1 beyond controversy1 that the old notion that the general level of the sea remains permanent1 and that the changes must be all attributed to the land is wholly incorrect1 and that the sea1 as well as the land1 is subject to changes of level1 it is certainly quite legitimate to consider whether the last elevation of the sea-level relatively to the land may not have resulted from the rising of the sea rather than from the sinking of the land1 in short1 whether it may not be attributed to the cause we are now considering4 ,the fact that those raised beaches and terraces are found at so many different heights1 and also so discontinuously along our coasts1 might be urged as an objection to the opinion that they were due to changes in the level of the sea itself4 ,space will not permit me to enter upon the discussion of this point at present2 but it may be stated that this objection is more apparent than real4 ,it by no means follows that beaches of the same age must be at the same level4 ,this has been shown very clearly by ,mr4 ,w4 ,pengelly in a paper on 8,raised ,beaches10 read before the ,british ,association at ,nottingham1 #ahff4 ,we have1 as ,i think1 evidence amounting to almost absolute certainty that #aa1gjj years ago the general sea-level on the northern hemisphere must have been higher than at present4 ,and in order to determine the question of the #be-;foot beach1 we have merely to consider whether a rise to something like this extent probably took place at the period in question4 ,we have at present no means of determining the exact extent of the rise which must have taken place at that period1 for we cannot tell what quantity of ice was then melted off the antarctic regions4 ,but we have the means of making a very rough estimate1 which1 at least1 may enable us to determine whether a rise of some #bj or #cj feet may not possibly have taken place4 ,if we assume that the southern ice-cap extends on an average down to lat4 #gj1 we shall have an area equal to #a_/ccafc of the entire surface of the globe4 ,the proportion of land to that of water1 taking into account the antarctic continent1 is as #ebf to #abgb4 ,the southern ice-cap will therefore be equal to #a_/bcdf of the area covered by water4 ,the density of ice to that of water being taken at #ib to #a1 it follows that #be feet #f inches of ice melted from off the face of the antarctic continent would raise the level of the ocean one foot4 ,if #dgj feet were melted off--and this is by no means an extravagant supposition1 when we reflect that for every #ah pounds of ice presently melted an additional pound or two pounds1 or perhaps more1 would then be melted1 and that for many ages in succession--the water thus produced from the melted ice would raise the level of the sea #ah feet #e inches4 ,the removal of the #dgj feet of solid ice-- which must be but a very small fraction of the total quantity of ice lying upon the antarctic continent--would shift the earth's centre of gravity about #g feet to the north of its present position4 ,the shifting of the centre of gravity would cause the sea to sink on the southern hemisphere and rise on the northern4 ,and the quantity of water thus transferred from the southern hemisphere to the northern would carry the centre of gravity about one foot further1 and thus give a total displacement of the centre to the extent of about #h feet4 ,the sea would therefore rise about #h feet at the ,north ,pole1 and in the latitude of ,edinburgh about #f feet #g inches4 ,this1 added to the rise of #ah feet #e inches1 occasioned by the melting of the ice1 would give #be feet as the total rise in the latitude of ,scotland #aa1gjj years ago4 ,each square foot of surface at the poles #aa1gjj years ago would be receiving #ah1bbc1ajj foot-pounds more of heat annually than at present4 ,if we deduct #bb per cent4 as the amount absorbed in passing through the atmosphere1 we have #ad1bad1jjj foot-pounds4 ,this would be sufficient to melt #bbf feet of ice4 ,but if #ej1 instead of #bb1 per cent4 were cut off1 #ade cubic feet would be melted4 ,in this case the #dgj feet of ice would be melted1 independently of the effects of eccentricity1 in about #cbj years4 ,and supposing that only one-fourth part of the extra heat reached the ground1 #dgj feet of ice would be removed in about #fdj years4 ,as to the exact time that the obliquity was at a maximum1 previous to that of #aa1gjj years ago1 our uncertainty is still greater4 ,if we are permitted to assume that the ecliptic passes from its maximum to its minimum state and back to its maximum again with anything like uniformity1 at the rate assigned by ,leverrier and others1 the obliquity would not be far from a maximum about #fj1jjj years ago4 ,taking the rate of precession at #ejbaabi1 and assuming it to be uniform--which it probably is not--the winter solstice would be in the aphelion about #fa1cjj years ago4#bca ,in short1 it seems not at all improbable that at the time the solstice-point was in the aphelion1 the obliquity of the ecliptic would not be far from its maximum state4 ,but at that time the value of the eccentricity was #jjbc1 instead of #jjahg1 its value at the last period4 ,consequently the rise of the sea would probably be somewhat greater than it was #aa1gjj years ago4 ,might not this be the period of the #dj-;foot beach8 ,in this case #aa1jjj or #ab1jjj years would be the age of the #be-;foot beach1 and #fj1jjj years the age of the #dj-;foot beach4 ,about #bb1jjj years ago1 the winter solstice was in the perihelion1 and as the eccentricity was then somewhat greater than it is at present1 the winters would be a little warmer and the climate more equable than it is at the present day4 ,this perhaps might be the period of the submarine forests and lower peat-beds which underlie the ,carse clays1 ,scrobicularia mud1 and other deposits belonging to the age of the #be-;foot beach4 ,at any rate1 it is perfectly certain that a condition of climate at this period prevailed exceedingly favourable to the growth of peat4 ,it follows also that at this time1 owing to a greater accumulation of ice on the southern hemisphere1 the sea-level would be a few feet lower than at present1 and that forests and peat may have then grown on places which are now under the sea-level4 ,for a few thousand years before and after #aa1gjj years ago1 when the winter solstice was evidently not far from the aphelion1 and the sea standing considerably above its present level1 would probably1 as we have already stated1 be the time when the ,carse clays and other recent deposits lying above the present level of the river were formed4 ,and it is also a singular fact that the condition of things at that period must have been exceedingly favourable to the formation of such estuarine deposits2 for at that time the winter temperature of our island1 as has been already shown1 would be considerably lower than at present1 and1 consequently1 during that season1 snow1 to a much larger extent than now1 would fall instead of rain4 ,the melting of the winter's accumulation of snow on the approach of summer would necessarily produce great floods1 similar to what occur in the northern parts of ,asia and ,america at the present day from this very same cause4 ,the loose upper soil would be carried down by those floods and deposited in the estuaries of our rivers4 ,the foregoing is a rough and imperfect sketch of the history of the climate and the physical conditions of our globe for the past #fj1jjj years1 in so far as physical and cosmical considerations seem to afford us information on the subject1 and its striking agreement with that derived from geological sources is an additional evidence in favour of the opinion that geological and cosmical phenomena are physically related by a bond of causation4 ,lieutenant-,colonel ,drayson's ,theory of the ,cause of the ,glacial ,epoch4--,in a paper read before the ,geological ,society by ,lieutenant-,colonel ,drayson1 ,r4,a41 on the #bbnd ,february1 #ahga1bcb that author states1 that after calculating from the recorded positions of the pole of the heavens during the last #b1jjj years1 he finds the pole of the ecliptic is not the centre of the circle traced by the pole of the heavens4 ,the pole of the heavens1 he considers1 describes a circle round a point #f distant from the pole of the ecliptic and #bi #be #dg from the pole of the heavens1 and that about #ac1gjj years b4c4 the angular distance of the two poles was #ce #be #dg4 ,this would bring the ,arctic ,circle down to latitude #ed #cd #ac ,n4 ,i fear that this is a conclusion that will not be generally accepted by those familiar with celestial mechanics4 ,but1 be this as it may1 my present object is not to discuss the astronomical part of ,colonel ,drayson's theory1 but to consider whether the conclusions which he deduces from his theory in regard to the cause of the glacial epoch be legitimate or not4 ,assuming for argument's sake that the obliquity of the ecliptic can possibly reach to #ce or #cf1 so as to bring the ,arctic ,circle down to the centre of ,england1 would this account for the glacial epoch8 ,colonel ,drayson concludes that the shifting of the ,arctic ,circle down to the latitude of ,england would induce here a condition of climate similar to that which obtains in arctic regions4 ,this seems to be the radical error of the theory4 ,it is perfectly true that were the ,arctic ,circle brought down to latitude #ed #ce part of our island would be in the arctic regions1 but it does not on that account follow that our island would be subjected to an arctic climate4 ,the polar regions owe their cold not to the obliquity of the ecliptic1 but to their distance from the equator4 ,indeed were it not for obliquity those regions would be much colder than they really are1 and an increase of obliquity1 instead of increasing their cold1 would really make them warmer4 ,the general effect of obliquity1 as we have seen1 is to diminish the amount of heat received in equatorial and tropical regions1 and to increase it in the polar and temperate regions4 ,the greater the obliquity1 and1 consequently1 the farther the sun recedes from the equator1 the smaller is the quantity of heat received by equatorial regions1 and the greater the amount bestowed on polar and temperate regions4 ,if1 for example1 we represent the present amount of heat received from the sun at the equator on a given surface at #ajj parts1 #dbdg parts will then represent the amount received at the poles on the same given surface4 ,but were the obliquity increased to #ce the amount received at the equator would be reduced to #idic parts1 and that at the poles increased to #eiha2 being an increase at the poles of nearly one half4 ,at latitude #fj the present quantity is equal to #eg parts2 but about #fc parts would be received were the obliquity increased to #ce4 ,it therefore follows that although the ,arctic ,circle were brought down to the latitude of ,london so that the ,british islands would become a part of the arctic regions1 the mean temperature of these islands would not be lowered1 but the reverse4 ,the winters would no doubt be colder than they are at present1 but the cold of winter would be far more than compensated for by the heat of summer4 ,it is not a fair representation of the state of things1 merely to say that an increase of obliquity tends to make the winters colder and the summers hotter1 for it affects the summer heat far more than it does the winter cold4 ,and the greater the obliquity the more does the increase of heat during summer exceed the decrease during winter4 ,this is obvious because the greater the obliquity the greater the total annual amount of heat received4 ,if an increase of obliquity tended to produce an increase of ice in temperate and polar regions1 and thus to lead to a glacial epoch1 then the greater the obliquity the greater would be the tendency to produce such an effect4 ,conceive1 then1 the obliquity to go on increasing until it ultimately reached its absolute limit1 #ij1 and the earth's axis to coincide with the plane of the ecliptic4 ,the ,arctic ,circle would then extend to the equator4 ,would this produce a glacial epoch8 ,certainly not4 ,a square foot of surface at the poles would then be receiving as much heat per annum as a square foot at the equator at present1 supposing the sun remained on the equator during the entire year4 ,less heat1 however1 would be reaching the equatorial regions than now4 ,at present1 as we have just seen1 the annual quantity of heat received at either pole is to that received at the equator as #dbdg to #ajj2 but at the period under consideration the poles would be actually obtaining one-half more heat than the equator4 ,the amount received per square foot at the poles1 to that received per square foot at the equator1 would be in the ratio of half the circumference of a circle to its diameter1 or as #aegjh to #a4 ,but merely to say that the poles would be receiving more heat per annum than the equator is at present1 does not convey a correct idea of the excessive heat which the poles would then have to endure2 for it must be borne in mind that the heat reaching the equator is spread over the whole year1 whereas the poles would get their total amount during the six months of their summer4 ,consequently1 for six months in the year the poles would be obtaining far more than double the quantity of heat received at present by the equator during the same length of time1 and more than three times the quantity then received by the equator4 ,the amount reaching the pole during the six months to that reaching the equator would be as #cadaf to #a4 ,at the equator twelve hours' darkness alternates with twelve hours' sunshine1 and this prevents the temperature from rising excessively high2 but at the poles it would be continuous sunshine for six months without the ground having an opportunity of cooling for a single hour4 ,at the summer solstice1 when the sun would be in the zenith of the pole1 the amount of heat received there every twenty-four hours would actually be nearly three-and-a-quarter times greater than that presently received at the equator4 ,now what holds true with regard to the poles would hold equally true1 though to a lesser extent1 of polar and temperate regions4 ,we can form but a very inadequate idea of the condition of things which would result from such an enormous increase of heat4 ,nothing living on the face of the globe could exist in polar regions under so fearful a temperature as would then prevail during summer months4 ,how absurd would it be to suppose that this condition of things would tend to produce a glacial epoch6 ,not only would every particle of ice in polar regions be dissipated1 but the very seas around the pole would be1 for several months in the year1 at the boiling point4 ,if it could be shown from physical principles--which1 to say the least1 is highly improbable--that the obliquity of the ecliptic could ever have been as great as #ce1 it would to a very considerable extent account for the comparative absence of ice in ,greenland and other regions in high latitudes1 such as we know was the case during the ,carboniferous1 ,miocene1 and other periods4 ,but although a great increase of obliquity might cause a melting of the ice1 yet it could not produce that mild condition of climate which we know prevailed in high latitudes during those periods2 while no increase of obliquity1 however great1 could in any way tend to produce a glacial epoch4 ,colonel ,drayson1 however1 seems to admit that this great increase of obliquity would make our summers much warmer than they are at present4 ,how1 then1 according to his theory1 is the glacial epoch accounted for8 ,the following is the author's explanation as stated in his own words3-- 8,at the date #ac1gjj ,b4,c4 the same conditions appear to have prevailed down to about #ed of latitude during winter as regards the sun being only a few degrees above the horizon4 ,we are1 then1 warranted in concluding that the same climate prevailed down to #ed of latitude as now exists in winter down to #fg of latitude4 8,thus in the greater part of ,england and ,wales1 and in the whole of ,scotland1 icebergs of large size would be formed each winter2 every river and stream would be frozen and blocked with ice1 the whole country would be covered with a mantle of snow and ice1 and those creatures which could neither migrate nor endure the cold of an arctic climate would be exterminated40--8,the ,last ,glacial ,epoch10 p4 #adf4 8,at the summer solstice the midday altitude of the sun for the latitude #ed would be about #ga1 an altitude equal to that which the sun now attains in the south of ,italy1 the south of ,spain1 and in all localities having a latitude of about #dj40 8,there would1 however1 be this singular difference from present conditions1 that in latitude #ed the sun at the period of the summer solstice would remain the whole twenty-four hours above the horizon2 a fact which would give extreme heat to those very regions which1 six months previously1 had been subjected to an arctic cold4 ,not only would this greatly increased heat prevail in the latitude of #ed1 but the sun's altitude would be #ab greater at midday in midsummer1 and also #ab greater at midnight in high northern latitudes1 than it ever attains now2 consequently the heat would be far greater than at present1 and high northern regions1 even around the pole itself1 would be subjected to a heat during summer far greater than any which now ever exists in those localities4 ,the natural consequence would be1 that the icebergs and ice which had during the severe winter accumulated in high latitudes would be rapidly thawed by this heat0 7p4 #adh74 8,each winter the whole northern and southern hemispheres would be one mass of ice2 each summer nearly the whole of the ice of each hemisphere would be melted and dispersed0 7p4 #aej74 ,according to this theory1 not only is the whole country covered each winter with a continuous mass of ice1 but large icebergs are formed during that short season1 and when the summer heat sets in all is melted away4 ,here we have a misapprehension not only as to the actual condition of things during the glacial epoch1 but even as to the way in which icebergs and land-ice are formed4 ,icebergs are formed from land-ice1 but land-ice is not formed during a single winter1 much less a mass of sufficient thickness to produce icebergs4 ,land-ice of this thickness requires the accumulated snows of centuries for its production4 ,all that we could really have1 according to this theory1 would be a thick covering of snow during winter1 which would entirely disappear during summer1 so that there could be no land-ice4 ,mr4 ,thomas ,belt's ,theory4--,the theory that the glacial epoch resulted from a great increase in the obliquity of the ecliptic has recently been advocated by ,mr4 ,thomas ,belt4#bcc ,his conceptions on the subject1 however1 appear to me to be even more irreconcilable with physics than those we have been considering4 ,lieutenant-,colonel ,drayson admits that the increase of heat to polar regions resulting from the great increase of obliquity would dissipate the ice there1 but ,mr4 ,belt does not even admit that an increase of obliquity would bring with it an increase of heat1 far less that it would melt the polar ice4 ,on the contrary1 he maintains that the tendency of obliquity is to increase the rigour of polar climate1 and that this is the reason 8that now around the poles some lands are being glaciated1 for excepting for that obliquity snow and ice would not accumulate1 excepting on mountain chains40 8,thus10 he says1 8there exist glacial conditions at present around the poles1 due primarily to the obliquity of the ecliptic40 ,and he also maintains that if there were no obliquity and the earth's axis were perpendicular to the plane of its orbit1 an eternal 8spring would reign around the arctic circle10 and that 8under such circumstances the piling up of snow1 or even its production at the sea-level1 would be impossible1 excepting perhaps in the immediate neighbourhood of the poles1 where the rays of the sun would have but little heating power from its small altitude40 ,mr4 ,belt has apparently been led to these strange conclusions by the following singular misapprehension of the effects of obliquity on the distribution of the sun's heat over the globe4 8,the obliquity of the ecliptic10 he remarks1 8does not affect the mean amount of heat received at any one point from the sun1 but it causes the heat and the cold to predominate at different seasons of the year40 ,it is not necessary to dwell further on the absurdity of the supposition that an increase of obliquity can possibly account for the glacial epoch1 but we may in a few words consider whether a decrease of obliquity would mitigate the climate and remove the snow from polar regions4 ,supposing obliquity to disappear and the earth's axis to become perpendicular to the plane of its orbit1 it is perfectly true that day and night would be equal all over the globe1 but then the quantity of heat received by the polar regions would be far less than at present4 ,it is well known that at present at the equinoxes1 when day and night are equal1 snow and not rain prevails in the arctic regions1 and can we suppose it could be otherwise in the case under consideration8 ,how1 we may well ask1 could these regions1 deprived of their summer1 get rid of their snow and ice8 ,but even supposing it could be shown that a change in the obliquity of the ecliptic to the extent assumed by ,mr4 ,belt and ,lieutenant-,colonel ,drayson would produce a glacial epoch1 still the assumption of such a change is one which physical astronomy will not permit4 ,mr4 ,belt does not appear to dispute the accuracy of the methods by which it is proved that the variations of obliquity are confined within narrow limits2 but he maintains that physical astronomers1 in making their calculations have left out of account some circumstances which materially affect the problem4 ,these1 according to ,mr4 ,belt1 are the following3--7#a7 ,upheavals and subsidences of the land which may have taken place in past ages4 7#b7 ,the unequal distribution of sea and land on the globe4 7#c7 ,the fact that the equatorial protuberance is not a regular one1 8but approaches in a general outline to an ellipse1 of which the greater diameter is two miles longer than the other40 7#d7 ,the heaping up of ice around the poles during the glacial period4 ,we may briefly consider whether any or all of these can sensibly affect the question at issue4 ,in reference to the last-mentioned element1 it is no doubt true that if an immense quantity of water were removed from the ocean and placed around the poles in the form of ice it would affect the obliquity of the ecliptic2 but this is an element of change which is not available to ,mr4 ,belt1 because according to his theory the piling up of the ice is an effect which results from the change of obliquity4 ,in reference to the difference of two miles in the equatorial diameters of the earth1 the fact must be borne in mind that the longer diameter passes through nearly the centre of the great depression of the ,pacific ,ocean1#bcd whereas the shorter diameter passes through the opposite continents of ,asia and ,america4 ,now1 when we take into consideration the fact that these continents are not only two-and-a-half times denser than the ocean1 but have a mean elevation of about #a1jjj feet above the sea-level1 it becomes perfectly obvious that the earth's mass must be pretty evenly distributed around its axis of rotation1 and that therefore the difference in the equatorial diameters can exercise no appreciable effect on the change of obliquity4 ,it follows also that the present arrangement of sea and land is the best that could be chosen to prevent disturbance of motion4 ,that there ever were upheavals and depressions of the land of so enormous a magnitude as to lead to a change of obliquity to the extent assumed by ,lieutenant-,colonel ,drayson and ,mr4 ,belt is what1 ,i presume1 few geologists would be willing to admit4 ,suppose the great table-land of ,thibet1 with the ,himalaya ,mountains1 were to sink under the sea1 it would hardly produce any sensible effect on the obliquity of the ecliptic4 ,nay more2 supposing that all the land in the globe were sunk under the sea-level1 or the ocean beds converted into dry land1 still this would not materially affect obliquity4 ,the reason is very obvious4 ,the equatorial bulge is so immense that those upheavals and depressions would not to any great extent alter the oblate form of the earth4 ,the only cause which could produce any sensible effect on obliquity1 as has already been noticed1 would be the removal of the water of the ocean and the piling of it up in the form of ice around the poles2 but this is a cause which is not available to ,mr4 ,belt4 ,sir ,charles ,lyell's ,theory4--,i am also unable to agree with ,sir ,charles ,lyell's conclusions in reference to the influence of the obliquity of the ecliptic on climate4 ,sir ,charles says1 8,it may be remarked that if the obliquity of the ecliptic could ever be diminished to the extent of four degrees below its present inclination1 such a deviation would be of geological interest1 in so far as it would cause the sun's light to be disseminated over a broader zone inside of the arctic and antarctic circles4 ,indeed1 if the date of its occurrence in past time could be ascertained1 this greater spread of the solar rays1 implying a shortening of the polar night1 might help in some slight degree to account for a vegetation such as now characterizes lower latitudes1 having had in the ,miocene and ,carboniferous periods a much wider range towards the pole40#bce ,the effects1 as we have seen1 would be directly the reverse of what is here stated1 viz41 the more the obliquity was diminished the less would the sun's rays spread over the arctic and antarctic regions1 and conversely the more the obliquity was increased the greater would be the amount of heat spread over polar latitudes4 ,the farther the sun recedes from the equator1 the greater becomes the amount of heat diffused over the polar regions2 and if the obliquity could possibly attain its absolute limit 7#ij71 it is obvious that the poles would then be receiving more heat than the equator is now4 ,,chapter ,,xxvi4 ,,coal ,,an ,,inter-,,glacial ,,formation4 ,climate of ,coal ,period ,inter-glacial in ,character4--,coal ,plants indicate an ,equable1 not a ,tropical ,climate4--,conditions necessary for ,preservation of ,coal ,plants4--,oscillations of ,sea-level necessarily implied4--,why our ,coal-fields contain more than ,one ,coal-seam4--,time required to form a ,bed of ,coal4--,why ,coal ,strata contain so little evidence of ,ice-action4--,land ,flat during ,coal ,period4--,leading ,idea of the ,theory4--,carboniferous ,limestones4 ,an ,inter-glacial ,climate the one best suited for the ,growth of the ,coal ,plants4--,no assertion1 perhaps1 could appear more improbable1 or is more opposed to all hitherto received theories1 than the one that the plants which form our coal grew during a glacial epoch4 ,but1 nevertheless1 if the theory of secular changes of climate1 discussed in the foregoing chapters1 be correct1 we have in warm inter-glacial periods 7as was pointed out several years ago7#bcf the very condition of climate best suited for the growth of those kinds of trees and vegetation of which our coal is composed4 ,it is the generally received opinion among both geologists and botanists that the flora of the ,coal period does not indicate the existence of a tropical1 but a moist1 equable1 and temperate climate4 8,it seems to have become10 says ,sir ,charles ,lyell1 8a more and more received opinion that the coal plants do not on the whole indicate a climate resembling that now enjoyed in the equatorial zone4 ,tree-ferns range as far south as the southern parts of ,new ,zealand1 and ,araucanian pines occur in ,norfolk ,island4 ,a great preponderance of ferns and lycopodiums indicates moisture1 equability of temperature1 and freedom from frost1 rather than intense heat40#bcg ,mr4 ,robert ,brown1 the eminent botanist1 considers that the rapid and great growth of many of the coal plants showed that they grew in swamps and shallow water of equable and genial temperature4 8,generally speaking10 says ,professor ,page1 8we find them resembling equisetums1 marsh-grasses1 reeds1 club-mosses1 tree-ferns1 and coniferous trees2 and these in existing nature attain their maximum development in warm1 temperate1 and subtropical1 rather than in equatorial regions4 ,the ,wellingtonias of ,california and the pines of ,norfolk ,island are more gigantic than the largest coniferous tree yet discovered in the coal-measures40#bch ,the ,coal period was not only characterized by a great preponderance over the present in the quantity of ferns growing1 but also in the number of different species4 ,our island possesses only about #ej species1 while no fewer than #adj species have been enumerated as having inhabited those few isolated places in ,england over which the coal has been worked4 ,and ,humboldt has shown that it is not in the hot1 but in the mountainous1 humid1 and shady parts of the equatorial regions that the family of ferns produces the greatest number of species4 8,dr4 ,hooker thinks that a climate warmer than ours now is1 would probably be indicated by the presence of an increased number of flowering plants1 which would doubtless have been fossilized with the ferns2 whilst a lower temperature1 equal to the mean of the seasons now prevailing1 would assimilate our climate to that of such cooler countries as are characterized by a disproportionate amount of ferns40#bci 8,the general opinion of the highest authorities10 says ,professor ,hull1 8appears to be that the climate did not resemble that of the equatorial regions1 but was one in which the temperature was free from extremes2 the atmosphere being warm and moist1 somewhat resembling that of ,new ,zealand and the surrounding islands1 which we endeavour to imitate artificially in our hothouses40#bdj ,the enormous quantity of the carboniferous vegetation shows also that the climate under which it grew could not have been of a tropical character1 or it must have been decomposed by the heat4 ,peat1 so abundant in temperate regions1 is not to be found in the tropics4 ,the condition most favourable to the preservation of vegetable remains1 at least under the form of peat1 is a cool1 moist1 and equable climate1 such as prevails in the ,falkland ,islands at the present day4 8,in these islands10 says ,mr4 ,darwin1 8almost every kind of plant1 even the coarse grass which covers the whole surface of the land1 becomes converted into this substance40#bda ,from the evidence of geology we may reasonably infer that were the difference between our summer and winter temperature nearly annihilated1 and were we to enjoy an equable climate equal to1 or perhaps a little above1 the present mean annual temperature of our island1 we should then have a climate similar to what prevailed during the ,carboniferous epoch4 ,but we have already seen that such must have been the character of our climate at the time that the eccentricity of the earth's orbit was at a maximum1 and winter occurred when the earth was in the perihelion of its orbit4 ,for1 as we have already shown1 the earth would in such a case be #ad1bab1gjj miles nearer to the sun in winter than in summer4 ,this enormous difference1 along with other causes which have been discussed1 would almost extinguish the difference between summer and winter temperature4 ,the almost if not entire absence of ice and snow1 resulting from this condition of things1 would1 as has already been shown1 tend to raise the mean annual temperature of the climate higher than it is at present4 ,conditions necessary for the ,preservation of the ,coal ,plants4--,but in order to the formation of coal1 it is not simply necessary to have a condition of climate suitable for the growth1 but also for the preservation1 of a luxuriant vegetation4 ,the very existence of coal is as much due to the latter circumstance as to the former2 nay more1 as we shall yet see1 the fact that a greater amount of coal belongs to the ,carboniferous period than to any other1 was evidently due not so much to a more extensive vegetable growth during that age1 suited to form coal1 as to the fact that that flora has been better preserved4 ,now1 as will be presently shown1 we have not merely in the warm periods of a glacial epoch a condition of climate best suited for the growth of coal plants1 but we have also in the cold periods of such an epoch the condition most favourable for the preservation of those plants4 ,one circumstance necessary for the preservation of plants is that they should have been covered over by a thick deposit of sand1 mud1 or clay1 and for this end it is necessary that the area upon which the plants grew should have become submerged4 ,it is evident that unless the area had become submerged1 the plants could not have been covered over with a thick deposit2 and1 even supposing they had been covered over1 they could not have escaped destruction from subarial denudation unless the whole had been under water4 ,another condition favourable1 if not essential1 to the preservation of the plants1 is that they should have been submerged in a cold and not in a warm sea4 ,assuming that the coal plants grew during a warm period of a glacial epoch1 we have in the cold period which succeeded all the above conditions necessarily secured4 ,it is now generally admitted that the coal trees grew near broad estuaries and on immense flat plains but little elevated above sea-level4 ,but that the ,lepidodendra1 ,sigillari1 and other trees1 of which our coal is almost wholly composed1 grew on dry ground1 elevated above sea-level1 and not in swamps and shallow water1 as was at one time supposed1 has been conclusively established by the researches of ,principal ,dawson and others4 ,after the growth of many generations of trees1 the plain is eventually submerged under the sea1 and the whole1 through course of time1 becomes covered over with thick deposits of sand1 gravel1 and other sediments carried down by streams from the adjoining land4 ,after this the submerged plain becomes again elevated above the sea-level1 and forms the site of a second forest1 which1 after continuing to flourish for long centuries1 is in turn destroyed by submergence1 and1 like the former1 becomes covered over with deposits from the land4 ,this alternate process of submergence and emergence goes on till we have a succession of buried forests one above another1 with immense stratified deposits between4 ,these buried forests ultimately become converted into beds of coal4 ,this1 ,i presume1 is a fair representation of the generally admitted way in which our coal-beds had their origin4 ,it is also worthy of notice that the stratified beds between the coal-seams are of marine and not of lacustrine origin4 ,on this point ,i may quote the opinion of ,professor ,hull1 a well-known authority on the subject3 8,whilst admitting10 he says1 8the occasional presence of lacustrine strata associated with the coal-measures1 ,i think we may conclude that the whole formation has been essentially of marine and estuarine origin40#bdb ,coal-beds necessarily imply ,oscillations of ,sea-level4--,it may also be observed that each coal-seam indicates both an elevation and a depression of the land4 ,if1 for example1 there are six coal-seams1 one above the other1 this proves that the land must have been1 at least1 six times below and six times above sea-level4 ,this repeated oscillation of the land has been regarded as a somewhat puzzling and singular circumstance4 ,but if we assume coal to be an inter-glacial formation1 this difficulty not only disappears1 but all the various circumstances which we have been detailing are readily explained4 ,we have to begin with a warm inter-glacial period1 with a climate specially suited for the growth of the coal trees4 ,during this period1 as has been shown in the chapter on ,submergence1 the sea would be standing at a lower level than at present1 laying bare large tracts of sea-bottom1 on which would flourish the coal vegetation4 ,this condition of things would continue for a period of #h1jjj or #aj1jjj years1 allowing the growth of many generations of trees4 ,when the warm period came to a close1 and the cold and glacial condition set in1 the climate became unsuited for the growth of the coal plants4 ,the sea would begin to rise1 and the old sea-bottoms on which1 during so long a period1 the forests grew1 would be submerged and become covered by sedimentary deposits brought down from the land4 ,these forests becoming submerged in a cold sea1 and buried under an immense mass of sediment1 were then now protected from destruction1 and in a position to become converted into coal4 ,the cold continuing for a period of #aj1jjj years1 or thereby1 would be succeeded by another warm period1 during which the submerged areas became again a land-surface1 on which a second forest flourished for another #aj1jjj years1 which in turn became submerged and buried under drift on the approach of the second cold period4 ,this alternate process of submergence and emergence of the land1 corresponding to the rise and fall of sea-level during the cold and warm periods1 would continue so long as the eccentricity of the earth's orbit remained at a high value1 till we might have1 perhaps1 five or six submerged forests1 one above the other1 and separated by great thicknesses of stratified deposits1 these submerged forests being the coal-beds of the present day4 ,illustration3 ,fig4 #aj4 ,it is probable that the forests of the ,coal period would extend inland over the country1 but only such portions as were slightly elevated above sea-level would be submerged and covered over by sediment and thus be preserved1 and ultimately become coal-seams4 ,the process will be better understood from the following diagram4 ,let ,a ,b represent the surface of the ground prior to a glacial epoch1 and to the formation of the beds of coal and stratified deposits represented in the diagram4 ,let ,s ,s be the normal sea-level4 ,suppose the eccentricity of the earth's orbit begins to increase1 and the winter solstice approaches the perihelion1 we have then a moderately warm period4 ,the sea-level sinks to #a1 and forests of sigillari and other coal trees cover the country from the sea-shore at #a1 stretching away inland in the direction of ,b4 ,in course of time the winter solstice moves round to aphelion and a cold period follows4 ,the sea begins to rise and continues rising till it reaches #a4 ,denudation and the severity of the climate destroy every vestige of the forest from #a backwards into the interior2 but the portion #a #a being submerged and covered over by sediment brought down from the land is preserved4 ,the eccentricity continuing to increase in extent1 the second inter-glacial period is more warm and equable than the first1 and the sea this time sinks to #b4 ,a second forest now covers the country down to the sea-shore at #b4 ,this second warm period is followed by the second cold period1 more severe than the first1 and the sea-level rises to #b4 ,denudation and severity of climate now destroy every remnant of the forest1 from #b inland1 but of course the submerged portion of #b #b1 like the former portion #a #a1 is preserved4 ,during the third warm period 7the eccentricity being still on the increase7 the sea-level sinks to #c1 and the country for the third time is covered by forests1 which extend down to #c4 ,this third warm period is followed by a cold glacial period more severe than the preceding1 and the sea-level rises to #c1 and the submerged portion of the forest from #c to #c becomes covered with drift1--the rest as before being destroyed by denudation and the severity of the climate4 ,we shall assume that the eccentricity has now reached a maximum1 and that during the fourth inter-glacial period the sea-level sinks only to #d1 the level to which it sank during the second inter-glacial period4 ,the country is now covered for the fourth time by forests4 ,the cold period which succeeds not being so severe as the last1 the sea rises only to #d1 which1 of course1 marks the limit of the fourth forest4 ,the eccentricity continuing to diminish1 the fifth forest is only submerged up to #e1 and the sixth and last one up to #f4 ,the epoch of cold and warm periods being now at a close1 the sea-level remains stationary at its old normal position ,s ,s4 ,here we have six buried forests1 the one above the other1 which1 through course of ages1 become transformed into coal-beds4 ,it does not1 however1 necessarily follow that each separate coal-seam represents a warm period4 ,it is quite possible that two or more seams separated from each other by thin partings or a few feet of sedimentary strata might have been formed during one warm period2 for during a warm period minor oscillations of sea-level sufficient to submerge the land to some depth might quite readily have taken place from the melting of polar ice1 as was shown in the chapter on ,submergence4 ,it may be noticed that in order to make the section more distinct1 its thickness has been greatly exaggerated4 ,it will also be observed that beds #d1 #e1 and #f extend considerably to the left of what is represented in the section4 ,but it is not to be supposed that the whole phenomena of the coal-fields can be explained without supposing a subsidence of the land4 ,the great depth to which the coal-beds have been sunk1 in many cases1 must be attributed to a subsidence of the level4 ,a series of beds formed during a glacial epoch1 may1 owing to a subsidence of the land1 be sunk to a great depth1 and become covered over with thousands of feet of sediment2 and then on the occurrence of another glacial epoch1 a new series of coal-beds may be formed on the surface4 ,thus the upper series may be separated from the lower by thousands of feet of sedimentary rock4 ,there is another consequence resulting from the sinking of the land1 which must be taken into account4 ,had there been no sinking of the land during the ,carboniferous age1 the quantity of coal-beds now remaining would be far less than it actually is1 for it is in a great measure owing to their being sunk to a great depth that they have escaped destruction by the enormous amount of denudation which has taken place since that remote age4 ,it therefore follows that only a very small fraction of the submerged forests of the ,coal period do actually now exist in the form of coal4 ,generally it would only be those areas which happened to be sunk to a considerable depth1 by a subsidence of the land1 that would escape destruction from denudation4 ,but no doubt the areas which would thus be preserved bear but a small proportion to those destroyed4 ,length of ,inter-glacial ,period1 as indicated by the ,thickness of a ,bed of ,coal4--,a fact favourable to the idea that the coal-seams were formed during inter-glacial periods is1 that the length of those periods agrees pretty closely with the length of time supposed to be required to form a coal-seam of average thickness4 ,other things being equal1 the thickness of a coal-seam would depend upon the length of the inter-glacial period4 ,if the rate of precession and motion of the perihelion were always uniform the periods would all be of equal length4 ,but although the rate of precession is not subject to much variation1 such is not the case in regard to the motion of the perihelion1 as will be seen from the tables of the longitude of the perihelion given in ,chapter ,,xix4 ,sometimes the motion of the perihelion is rapid1 at other times slow1 while in some cases its motion is retrograde4 ,in consequence of this1 an inter-glacial period may not be more than some six or seven thousand years in length1 while in other cases its length may be as much as fifteen or sixteen thousand years4 ,according to ,boussingault1 luxuriant vegetation at the present day takes from the atmosphere about a half ton of carbon per acre annually1 or fifty tons per acre in a century4 ,fifty tons of carbon of the specific gravity of coal1 about #ae1 spread evenly over the surface of an acre1 would make a layer nearly one-third of an inch4#bdc ,humboldt makes the estimate a little higher1 viz41 one half-inch4 ,taking the latter estimate1 it would require #g1bjj years to form a bed of coal a yard thick4 ,dr4 ,heer1 of ,zurich1 thinks that it would not require more than #a1djj years to form a bed of coal one yard thick2#bdd while ,mr4 ,maclaren thinks that a bed of coal one yard thick would be formed in #a1jjj years4#bde ,professor ,phillip1 calculating from the amount of carbon taken from the atmosphere1 as determined by ,liebig1 considers that if it were converted into ordinary coal with about #ge per cent4 of carbon1 it would yield one inch in #abge years1 or a yard in #d1fjj years4#bdf ,there is here a considerable amount of difference in regard to the time required to form a yard of coal4 ,the truth1 however1 may probably be somewhere between the two extremes1 and we may assume #e1jjj years to be about the time4 ,in a warm period of #ae1jjj years we should then have deposited a seam of coal #i feet thick1 while during a warm period of #g1jjj years we would have a seam of only #d feet4 ,reason why the ,coal ,strata present so little ,evidence of ,ice-action4--,there are two objections which will1 no doubt1 present themselves to the reader's mind4 7#a47 ,if coal be an inter-glacial formation1 why do the coal strata present so little evidence of ice-action8 ,if the coal-seams represent warm inter-glacial periods1 the intervening beds must represent cold or glacial periods1 and if so1 they ought to contain more abundant evidence of ice-action than they really do4 7#b47 ,in the case of the glacial epoch1 almost every vestige of the vegetation of the warm periods was destroyed by the ice of the cold periods2 why then did not the same thing take place during the glacial epoch of the ,carboniferous period8 ,during the glacial epoch the face of the country was in all probability covered for ages with the most luxuriant vegetation2 but scarcely a vestige of that vegetation now remains1 indeed the very soil upon which it grew is not to be found4 ,all that now remains is the wreck and desolation produced by the ice-sheet that covered the country during the cold periods of that epoch1 consisting of transported blocks of stones1 polished and grooved rocks1 and a confused mass of boulder clay4 ,here we have in this epoch nothing tangible presenting itself but the destructive effects of the ice which swept over the land4 ,why1 then1 in reference to the glacial epochs of the ,carboniferous age should we have such abundant evidence of the vegetation of the warm periods1 and yet so little evidence of the effect of the ice of the cold periods8 ,the answer to these two objections will go a great way to explain why we have so much coal belonging to the ,carboniferous age1 and so little belonging to any other age2 and it will1 ,i think1 be found in the peculiar physical character of the country during the ,carboniferous age4 ,the areas on which the forests of the ,coal period grew escaped the destructive power of glaciers and land-ice on account of the flat nature of the ground4 ,there are few points on which geologists are more unanimous than in regard to the flat character of the country during the ,coal period4 ,there does not seem to be any very satisfactory evidence that the interior of the country rose to any very great elevation4 ,mr4 ,godwin-,austen thinks that during the ,coal period there must have been 8a vast expanse of continuous horizontal surface at very slight elevations above the sea-level40#bdg ,of the widely spread terrestrial surface of the ,coal-measure period1 portions1 he believes1 attained a considerable elevation4 ,but in contrast to this he states1 8,there is a feature which seems to distinguish this period physically from all subsequent periods1 and which consists in the vast expanse of continuous horizontal surface which the land area presented1 bordering on1 and at very slight elevations above1 the sea-level40#bdh ,hugh ,miller1 describing in his usual graphic way the appearance of the country during the ,coal period1 says3--8,it seems to have been a land consisting of immense flats1 unvaried1 mayhap1 by a single hill1 in which dreary swamps1 inhabited by doleful creatures1 spread out on every hand for hundreds and thousands of miles2 and a gigantic and monstrous vegetation formed1 as ,i have shown1 the only prominent features of the scenery40#bdi ,now1 if this is in any way like a just representation of the general features of the country during the ,coal period1 it was physically impossible1 no matter however severe the climate may have been1 that there could have been in this country at that period anything approaching to continental ice1 or perhaps even to glaciers of such dimensions as would reach down to near the sea-level1 where the coal vegetation now preserved is supposed chiefly to have grown4 ,the condition of things which would prevail would more probably resemble that of ,siberia than that of ,greenland4 ,the absence of all traces of ice-action in the strata of the coal-measures can in this case be easily explained4 ,for as by supposition there were no glaciers1 there could have been no scratching1 grooving1 or polishing of the rocks2 neither could there have been any icebergs1 for the large masses known as icebergs are the terminal portions of glaciers which have reached down to the sea4 ,again1 there being no icebergs1 there of course could have been no grinding or scratching of the rocks forming the floor of the ocean4 ,true1 during summer1 when the frozen sea broke up1 we should then have immense masses of floating ice1 but these masses would not be of sufficient thickness to rub against the sea-bottom4 ,but even supposing that they did occasionally touch the bottom here and there1 we could not possibly find the evidence of this in any of the strata of the coal-measures4 ,we could not expect to find any scratchings or markings on the sandstone or shale of those strata indicating the action of ice1 for at that period there were no beds of sandstone or shale1 but simply beds of sand and mud1 which in future ages became consolidated into sandstone and shale4 ,a mass of ice might occasionally rub along the sea-bottom1 and leave its markings on the loose sand or soft mud forming that bottom1 but the next wave that passed over it would obliterate every mark1 and leave the surface as smooth as before4 ,neither could we expect to find any large erratics or boulders in the coal strata1 for these must come from the land1 and as by supposition there were no glaciers or land-ice at that period1 there was therefore no means of transporting them4 ,in ,greenland the icebergs sometimes carry large boulders1 which are dropped into the sea as the icebergs melt away2 but these blocks have all either been transported on the backs of glaciers from inland tracts1 or have fallen on the field-ice along the shore from the face of crags and overhanging precipices4 ,but as there were probably neither glaciers reaching to the sea1 nor perhaps precipitous cliffs along the sea-shore1 there could have been few or no blocks transported by ice and dropped into the sea of the ,carboniferous period1 and of course we need not expect to find them in the sandstone and shale which during that epoch formed the bed of the ocean4 ,there would no doubt be coast-line ice and ground-ice in rivers1 carrying away large quantities of gravel and stones2 but these gravels and stones would of course be all water-worn1 and although found in the strata of the coal-measures1 as no doubt they actually are1 they would not be regarded as indicating the action of ice4 ,the simple absence of relics of ice-action in the coal-measures proves nothing whatever in regard to whether there were cold periods during their formation or not4 ,this comparative absence of continental ice might be one reason why the forests of the ,carboniferous period have been preserved to a much greater extent than those of any other age4 ,it must be observed1 however1 that the conclusions at which we have arrived in reference to the comparative absence of continental ice applies only to the areas which now constitute our coal-fields4 ,the accumulation of ice on the antarctic regions1 and on some parts of the arctic regions1 might have been as great during that age as it is at present4 ,had there been no continental ice there could have been no such oscillations of sea-level as is assumed in the foregoing theory4 ,the leading idea of the theory1 expressed in a few words1 is1 that the glacial epochs of the ,carboniferous age were as severe1 and the accumulation of ice as great1 as during any other age1 only there were large tracts of flat country1 but little elevated above the sea-level1 which were not covered by ice4 ,these plains1 during the warm inter-glacial periods1 were covered with forests of sigillari and other coal trees4 ,portions of those forests were protected by the submergence which resulted from the rise of the sea-level during the cold or glacial periods and the subsequent subsidence of the land4 ,those portions now constitute our coal-beds4 ,but that coal may be an inter-glacial formation is no mere hypothesis1 for we have in the well-known ,drnten beds--described in ,chapter ,,xv4--an actual example of such a formation4 ,carboniferous ,limestones4--,as a general rule the limestones of the ,carboniferous period1 like the coal1 are found in beds separated by masses of sandstone and other stratified deposits1 which proves that the corals1 crinoids1 and other creatures1 of the remains of which it is composed1 did not live continuously on during the entire ,limestone period4 ,these limestones are a marine formation4 ,if the land was repeatedly submerged the coal must of necessity have been produced in seams with stratified deposits between1 but there is no reason why the same should have been the case with the limestones4 ,if the climatic condition of the sea continued the same we should not have expected this alternate succession of life and death2 but1 according to the theory of alternate cold and warm periods1 such a condition follows as a necessary consequence1 for during the warm periods1 when the land was covered with a luxuriant vegetation1 the sea-bottom would be covered with mollusca1 crinoids1 corals1 c41 fitted to live only in a moderately warm sea2 but when the cold came on those creatures would die1 and their remains1 during the continuance of the cold period1 would become slowly covered over with deposits of sand and clay4 ,on the return of the warm period those deposits would soon become covered with life as before1 forming another bed of limestone1 and this alternation of life and death would go on as long as the glacial epoch continued4 ,it is true that in ,derbyshire1 and in the south of ,ireland and some other places1 the limestone is found in one mass of several hundred feet in thickness without any beds of sandstone or shale1 but then it is nowhere found in one continuous mass from top to bottom without any lines of division4 ,these breaks or divisions may as distinctly mark a cold period as though they had been occupied by beds of sandstone4 ,the marine creatures ceased to exist1 and when the rough surface left by their remains became smoothed down by the action of the waves into a flat plain1 another bed would begin to form upon this floor so soon as life again appeared4 ,two agencies working together probably conspired to produce these enormous masses of limestone divided only by breaks marking different periods of elaboration4 ,corals grow in warm seas1 and there only in water of a depth ranging from #bj to #cj fathoms4 ,the cold of a period of glaciation would not only serve to destroy them1 but they would be submerged so much beyond the depth proper for their existence that even were it possible that with the submergence a sufficient temperature was left1 they would inevitably perish from the superincumbent mass of water4 ,we are therefore1 as it seems to me1 warranted in concluding that the separate masses of ,derbyshire limestone were formed during warm inter-glacial periods1 and that the lines of division represent cold periods of glaciation during which the animals perished by the combined influence of cold and pressure of water4 ,the submergence of the coral banks in deep water on a sea-bottom1 which1 like the land1 was characteristically flat and even1 implies its carrying away far into the bosom of the ocean1 and consequently remote from any continent and the river-borne detritus thereof4 ,,chapter ,,xxvii4 ,,path ,,of ,,the ,,ice-,,sheet ,,in ,,north-,,western ,,europe ,,and ,,its ,,relations ,,to ,,the ,,boulder ,,clay ,,of ,,caithness4#bej ,character of ,caithness ,boulder ,clay4--,theories of the ,origin of the ,caithness ,clay4--,mr4 ,jamieson's ,theory4--,mr4 ,c4 ,w4 ,peach's ,theory4--,the proposed ,theory4--,thickness of ,scottish ,ice-sheet4--,pentlands striated on their ,summits4--,scandinavian ,ice-sheet4--,north ,sea filled with ,land-ice4--,great ,baltic ,glacier4--,jutland and ,denmark crossed by ,ice4--,sir ,r4 ,murchison's ,observations4--,orkney1 ,shetland1 and ,faroe ,islands striated across4--,loess accounted for4--,professor ,geikie's ,suggestion4--,professor ,geikie and ,b4 ,n4 ,peach's ,observations on ,east ,coast of ,caithness4--,evidence from ,chalk ,flints and ,oolitic ,fossils in ,boulder ,clay4 ,the ,nature of the ,caithness ,boulder ,clay4--,a considerable amount of difficulty has been felt by geologists in accounting for the origin of the boulder clay of ,caithness4 ,it is an unstratified clay1 of a deep grey or slaty colour1 resembling much that of the ,caithness flags on which it rests4 ,it is thus described by ,mr4 ,jamieson 7,quart4 ,jour4 ,geol4 ,soc41 vol4 xxii41 p4 #bfa73-- 8,the glacial drift of ,caithness is particularly interesting as an example of a boulder clay which in its mode of accumulation and ice-scratched dbris very much resembles that unstratified stony mud which occurs underneath glaciers--the #8moraine profonde1' as some call it4 8,the appearance of the drift along the ,haster ,burn1 and in many other places in ,caithness1 is in fact precisely the same as that of the old boulder clay of the rest of ,scotland1 except that it is charged with remains of sea-shells and other marine organisms4 8,if want of stratification1 hardness of texture1 and abundance of well-glaciated stones and boulders are to be the tests for what we call genuine boulder clay1 then much of the ,caithness drift will stand the ordeal40 ,so far1 therefore1 as the mere appearance of the drift is concerned1 it would at once be pronounced to be true ,lower ,till1 the product of land-ice4 ,but there are two circumstances connected with it which have been generally regarded as fatal to this conclusion4 7#a7 ,the stri on the rocks show that the ice which formed the clay must have come from the sea1 and not from the interior of the country2 for their direction is almost at right angles to what it would have been had the ice come from the interior4 ,over the whole district1 the direction of the grooves and scratches1 not only of the rocks but even of the stones in the clay1 is pretty nearly ,n4,w4 and ,s4,e4 8,when examining the sections along the ,haster ,burn10 says ,mr4 ,jamieson1 8in company with ,mr4 ,joseph ,anderson1 ,i remarked that the stri on the imbedded fragments generally agreed in direction with those of the rocks beneath4 ,the scratches on the boulders1 as usual1 run lengthways along the stones when they are of an elongated form2 and the position of these stones1 as they lie imbedded in the drift1 is1 as a rule1 such that their longer axes point in the same direction as do the scratches on the solid rock beneath2 showing that the same agency that scored the rocks also ground and pushed along the drift40 ,mr4 ,c4 ,w4 ,peach informs me that he seldom or never found a stone with two sets of stri on it1 a fact indicating1 as ,mr4 ,jamieson remarks1 that the drift was produced by one great movement invariably in the same direction4 ,let it be borne in mind that the ice1 which thus moved over ,caithness in this invariable track1 must either have come from the ,atlantic to the ,n4,w41 or from the ,moray ,firth to the ,s4,e4 7#b7 ,the boulder clay of ,caithness is full of sea-shells and other marine remains4 ,the shells are in a broken condition1 and are interspersed like the stones through the entire mass of the clay4 ,mr4 ,jamieson states that he nowhere observed any instance of shells being found in an undisturbed condition1 8nor could ,i hear10 he says1 8of any such having been found2 there seems to be no such thing as a bed of laminated silt with shells in situ40 ,the shell-fragments are scratched and ice-worn1 the same as the stones found in the clay4 ,not only are the shells glaciated1 but even the foraminifera1 when seen through the microscope1 have a rubbed and worn appearance4 ,the shells have evidently been broken1 striated1 and pushed along by the ice at the time the boulder clay was being formed4 ,theories regarding the ,origin of the ,caithness ,clay4--,mr4 ,jamieson1 as we have seen1 freely admits that the boulder clay of ,caithness has the appearance of true land-ice till1 but from the ,n4,w4 and ,s4,e4 direction of the stri on the rocks1 and the presence of sea-shells in the clay1 he has come to the conclusion that the glaciation of ,caithness has been effected by floating ice at a time when the district was submerged4 ,i have always felt convinced that ,mr4 ,jamieson had not hit upon the true explanation of the phenomena4 7#a7 ,it is physically impossible that any deposit formed by icebergs could be wholly unstratified4 ,suppose a mass of the materials which would form boulder clay is dropped into the sea from1 say an iceberg1 the heavier parts1 such as stones1 will reach the bottom first4 ,then will follow lighter materials1 such as sand1 then clay1 and last of all the mud will settle down over the whole in fine layers4 ,the different masses dropped from the various icebergs1 will1 no doubt1 lie in confusion one over the other1 but each separate mass will show signs of stratification4 ,a good deal of boulder clay evidently has been formed in the sea1 but if the clay be unstratified1 it must have been formed under glaciers moving along the sea-bottom as on dry ground4 ,whether unstratified boulder clay may happen to be formed under water or on dry land1 it must in either case be the product of land-ice4#bea ,those who imagine that materials1 differing in specific gravity like those which compose boulder clay1 dropped into water1 can settle down without assuming the stratified form1 should make the experiment1 and they would soon satisfy themselves that the thing is physically impossible4 ,the notion that unstratified boulder clay could be formed by deposits from floating ice1 is not only erroneous1 but positively pernicious1 for it tends to lead those who entertain it astray in regard to the whole question of the origin of drift4 7#b7 ,it is also physically impossible that ice-markings1 such as those everywhere found on the rocky face of the district1 and on the pebbles and shells imbedded in the clay1 could have been effected by any other agency than that of land-ice4 ,i need not here enter into any discussion on this point1 as this has been done at considerable length in another place4#beb ,in the present case1 however1 it is unnecessary1 because if it can be shown that all the facts are accounted for in the most natural manner by the theory of land-ice1 no one will contend for the floating-ice theory2 for it is admitted that1 with the exception of the direction of the stri and the presence of the shells1 all the facts agree better with the land-ice than with the floating-ice theory4 ,my first impression on the subject was that the glaciation of ,caithness had been effected by the polar ice-cap1 which1 during the severer part of the glacial epoch1 must have extended down to at least the latitude of the north of ,scotland4 ,on a former occasion 7see the ,reader for #adth ,october1 #ahfe7 it was shown that all the northern seas1 owing to their shallowness1 must1 at that period1 have been blocked up with solid ice1 which displaced the water and moved along the sea-bottoms the same as on dry land4 ,in fact1 the northern seas1 including the ,german ,ocean1 being filled at the time with glacier-ice1 might be regarded as dry land4 ,ice of this sort1 moving along the bed of the ,german ,ocean or ,north ,sea1 and over ,caithness1 could not fail to push before it the shells and other animal remains lying on the sea-bottom1 and to mix them up with the clay which now remains upon the land as evidence of its progress4 ,about two years ago ,i had a conversation with ,mr4 ,c4 ,w4 ,peach on the subject4 ,this gentleman1 as is well known1 has long been familiar with the boulder clay of ,caithness4 ,he felt convinced that the clay of that country is the true ,lower ,till1 and not a more recent deposit1 as ,mr4 ,jamieson supposes4 ,he expressed to me his opinion that the glaciation of ,caithness had been effected by masses of land-ice crossing the ,moray ,firth from the mountain ranges to the south-east1 and passing over ,caithness in its course4 ,the difficulty which seems to beset this theory is1 that a glacier entering the ,firth would not leave it and ascend over the ,caithness coast4 ,it would take the path of least resistance and move into the ,north ,sea1 where it would find a free passage into deeper water4 ,mr4 ,peach's theory is1 however1 an important step in the right direction4 ,it is a part of the truth1 but ,i believe not the whole truth4 ,the following is submitted as a solution of the question4 ,the ,proposed ,theory4--,it may now be regarded as an established fact that1 during the severer part of the glacial period1 ,scotland was covered with one continuous mantle of ice1 so thick as to bury under it the ,ochil1 ,sidlaw1 ,pentland1 ,campsie1 and other moderately high mountain ranges4 ,for example1 ,mr4 ,j4 ,geikie and ,mr4 ,b4 ,n4 ,peach found that the great masses of the ice from the ,north-west ,highlands1 came straight over the ,ochils of ,perthshire and the ,lomonds of ,fife4 ,in fact1 these mountain ridges were not sufficiently high to deflect the icy stream either to the right hand or to the left2 and the flattened and rounded tops of the ,campsie1 ,pentland1 and ,lammermoor ranges bear ample testimony to the denuding power of ice4 ,further1 to quote from ,mr4 ,jamieson1 8the detached mountain of ,schehallion in ,perthshire1 #c1ejj feet high1 is marked near the top as well as on its flanks1 and this not by ice flowing down the sides of the hill itself1 but by ice pressing over it from the north4 ,on the top of another isolated hill1 called ,morven1 about #c1jjj feet high1 and situated a few miles to the north of the village of ,ballater1 in the county of ,aberdeen1 ,i found granite boulders unlike the rock of the hill1 and apparently derived from the mountains to the west4 ,again1 on the highest watersheds of the ,ochils1 at altitudes of about #b1jjj feet1 ,i found this summer 7#ahfd7 pieces of mica schist full of garnets1 which seem to have come from the ,grampian ,hills to the north-west1 showing that the transporting agent had overflowed even the highest parts of the ,ochil ridge4 ,and on the ,west ,lomonds1 in ,fifeshire1 at ,clattering-well ,quarry1 #a1dej feet high1 ,i found ice-worn pebbles of ,red ,sandstone and porphyry in the dbris covering the ,carboniferous ,limestone of the top of the ,bishop ,hill4 ,facts like these meet us everywhere4 ,thus on the ,perthshire ,hills1 between ,blair ,athol and ,dunkeld1 ,i found ice-worn surfaces of rocks on the tops of hills1 at elevations of #b1bjj feet1 as if caused by ice pressing over them from the north-west1 and transporting boulders at even greater heights40#bec ,facts still more important1 however1 in their bearing on the question before us were observed on the ,pentland range by ,mr4 ,bennie and myself during the summer of #ahgj4 ,on ascending ,allermuir1 one of the hills forming the northern termination of the ,pentland range1 we were not a little surprised to find its summit ice-worn and striated4 ,the top of the hill is composed of a compact porphyritic felstone1 which is very much broken up2 but wherever any remains of the original surface could be seen1 it was found to be polished and striated in a most decided manner4 ,these stri are all in one uniform direction1 nearly east and west2 and on minutely examining them with a lens we had no difficulty whatever in determining that the ice which effected them came from the west and not from the east1 a fact which clearly shows that they must have been made at the time when1 as is well known1 the entire ,midland valley was filled with ice1 coming from the ,north-west ,highlands4 ,on the summit of the hill we also found patches of boulder clay in hollow basins of the rock4 ,at one spot it was upwards of a foot in depth1 and rested on the ice-polished surface4 ,the clay was somewhat loose and sandy1 as might be expected of a layer so thin1 exposed to rain1 frost1 and snow1 during the long course of ages which must have elapsed since it was deposited there4 ,of #ajj pebbles collected from the clay1 just as they turned up1 every one1 with the exception of three or four composed of hard quartz1 presented a flattened and ice-worn surface2 and forty-four were distinctly striated3 in short1 every stone which was capable of receiving and retaining scratches was striated4 ,a number of these stones must have come from the ,highlands to the north-west4#bed ,the height of ,allermuir is #a1fag feet1 and1 from its position1 it is impossible that the ice could have gone over its summit1 unless the entire ,midland valley1 at this place1 had been filled with ice to the depth of more than #a1fjj feet4 ,the hill is situated about four or five miles to the south of ,edinburgh1 and forms1 as has already been stated1 the northern termination of the ,pentland range4 ,immediately to the north lies the broad valley of the ,firth of ,forth1 more than twelve miles across1 offering a most free and unobstructed outlet for the great mass of ice coming along the ,midland valley from the west4 ,now1 when we reflect how easily ice can accommodate itself to the inequalities of the channel along which it moves1 how it can turn to the right hand or to the left1 so as to find for itself the path of least resistance1 it becomes obvious that the ice never would have gone over ,allermuir1 unless not only the ,midland valley at this point1 but also the whole surrounding country had been covered with one continuous mass of ice to a depth of more than #a1fjj feet4 ,but it must not be supposed that the height of ,allermuir represents the thickness of the ice2 for on ascending ,scald ,law1 a hill four miles to the south-west of ,allermuir1 and the highest of the ,pentland range1 we found1 in the dbris covering its summit1 hundreds of transported stones of all sizes1 from one to eighteen inches in diameter4 ,we also dug up a ,greenstone boulder about eighteen inches in diameter1 which was finely polished and striated4 ,as the height of this hill is #a1hih feet1 the mass of ice covering the surrounding country must have been at least #a1ijj feet deep4 ,but this is not all4 ,directly to the north of the ,pentlands1 in a line nearly parallel with the east coast1 and at right angles to the path of ice from the interior1 there is not1 with the exception of the solitary peak of ,east ,lomond1 and a low hill or two of the ,sidlaw range1 an eminence worthy of the name of a hill nearer than the ,grampians in the north of ,forfarshire1 distant upwards of sixty miles4 ,this broad plain1 extending from almost the ,southern to the ,northern ,highlands1 was the great channel through which the ice of the interior of ,scotland found an outlet into the ,north ,sea4 ,if the depth of the ice in the ,firth of ,forth1 which forms the southern side of this broad hollow1 was at least #a1ijj feet1 it is not at all probable that its depth in the northern side1 formed by the ,valley of ,strathmore and the ,firth of ,tay1 which lay more directly in the path of the ice from the ,north ,highlands1 could have been less4 ,here we have one vast glacier1 more than sixty miles broad and #a1ijj feet thick1 coming from the interior of the country4 ,it is1 therefore1 evident that the great mass of ice entering the ,north ,sea to the east of ,scotland1 especially about the ,firths of ,forth and ,tay1 could not have been less1 and was probably much more1 than from #a1jjj to #b1jjj feet in thickness4 ,the grand question now to be considered is1 ,what became of the huge sheet of ice after it entered the ,north ,sea8 ,did it break up and float away as icebergs8 ,this appears to have been hitherto taken for granted2 but the shallowness of the ,north ,sea shows such a process to have been utterly impossible4 ,the depth of the sea in the ,english ,channel is only about twenty fathoms1 and although it gradually increases to about forty fathoms at the ,moray ,firth1 yet we must go to the north and west of the ,orkney and ,shetland ,islands ere we reach the #ajj fathom line4 ,thus the average depth of the entire ,north ,sea is not over forty fathoms1 which is even insufficient to float an iceberg #cjj feet thick4 ,no doubt the ,north ,sea1 for two reasons1 is now much shallower than it was during the period in question4 7#a47 ,there would1 at the time of the great extension of the ice on the northern hemisphere1 be a considerable submergence1 resulting from the displacement of the earth's centre of gravity4#bee 7#b47 ,the sea-bed is now probably filled up to a larger extent with drift deposits than it was at the ice period4 ,but1 after making the most extravagant allowance for the additional depth gained on this account1 still there could not possibly have been water sufficiently deep to float a glacier of #a1jjj or #b1jjj feet in thickness4 ,indeed1 the ,north ,sea would have required to be nearly ten times deeper than it is at present to have floated the ice of the glacial period4 ,we may1 therefore1 conclude with the most perfect certainty that the ice-sheet of ,scotland could not possibly have broken up into icebergs in such a channel1 but must have moved along on the bed of the sea in one unbroken mass1 and must have found its way to the deep trough of the ,atlantic1 west of the ,orkney and ,shetland ,islands1 ere it broke up and floated away in the iceberg form4 ,it is hardly necessary to remark that the waters of the ,north ,sea would have but little effect in melting the ice4 ,a shallow sea like this1 into which large masses of ice were entering1 would be kept constantly about the freezing-point1 and water of this temperature has but little melting power1 for it takes #adb lbs4 of water1 at #cc1 to melt one pound of ice4 ,in fact1 an icy sea tends rather to protect the ice entering it from being melted than otherwise4 ,and besides1 owing to fresh acquisitions of snow1 the ice-sheet would be accumulating more rapidly upon its upper surface than it would be melting at its lower surface1 supposing there were sea-water under that surface4 ,the ice of ,scotland during the glacial period must1 of necessity1 have found its way into warmer water than that of the ,north ,sea before it could have been melted4 ,but this it could not do without reaching the ,atlantic1 and in getting there it would have to pass round by the ,orkney ,islands1 along the bed of the ,north ,sea1 as land-ice4 ,this will explain how the ,orkney ,islands may have been glaciated by land-ice2 but it does not1 however1 explain how ,caithness should have been glaciated by that means4 ,these islands lay in the very track of the ice on its way to the ,atlantic1 and could hardly escape being overridden2 but ,caithness lay considerably to the left of the path which we should expect the ice to have taken4 ,the ice would not leave its channel1 turn to the left1 and ascend upon ,caithness1 unless it were forced to do so4 ,what1 then1 compelled the ice to pass over ,caithness8 ,path of the ,scandinavian ,ice4--,we must consider that the ice from ,scotland and ,england was but a fraction of that which entered the ,north ,sea4 ,the greater part of the ice of ,scandinavia must have gone into this sea1 and if the ice of our island could not find water sufficiently deep in which to float1 far less would the much thicker ice of ,scandinavia do so4 ,the ,scandinavian ice1 before it could break up1 would thus1 like the ,scottish ice1 have to cross the bed of the ,north ,sea and pass into the ,atlantic4 ,it could not pass to the north1 or to the north-west1 for the ocean in these directions would be blocked up by the polar ice4 ,it is true that along the southern shore of ,norway there extends a comparatively deep trough of from one to two hundred fathoms4 ,but this is evidently not deep enough to have floated the ,scandinavian ice-sheet2 and even supposing it had been sufficiently deep1 the floating ice must have found its way to the ,atlantic1 and this it could not have done without passing along the coast4 ,now1 its passage would not only be obstructed by the mass of ice continually protruding into the sea directly at right angles to its course1 but it would be met by the still more enormous masses of ice coming off the entire ,norwegian coast-line4 ,and1 besides this1 the ice entering the ,arctic ,ocean from ,lapland and the northern parts of ,siberia1 except the very small portion which might find an outlet into the ,pacific through ,behring's ,straits1 would have to pass along the ,scandinavian coast in its way to the ,atlantic4 ,no matter1 then1 what the depth of this trough may have been1 if the ice from the land1 after entering it1 could not make its escape1 it would continue to accumulate till the trough became blocked up2 and after this1 the great mass from the land would move forward as though the trough had no existence4 ,thus1 the only path for the ice would be by the ,orkney and ,shetland ,islands4 ,its more direct and natural path would1 no doubt1 be to the south-west1 in the direction of our shores2 and in all probability1 had ,scotland been a low flat island1 instead of being a high and mountainous one1 the ice would have passed completely over it4 ,but its mountainous character1 and the enormous masses of ice at the time proceeding from its interior1 would effectually prevent this1 so that the ice of ,scandinavia would be compelled to move round by the ,orkney ,islands4 ,consequently1 these two huge masses of moving ice--the one from ,scotland and the much greater one from ,scandinavia--would meet in the ,north ,sea1 probably not far from our shores1 and would move1 as represented in the diagram1 side by side northwards into the ,atlantic as one gigantic glacier4 ,nor can this be regarded as an anomalous state of things2 for in ,greenland and the antarctic continent the ice does not break up into icebergs on reaching the sea1 but moves along the sea-bottom in a continuous mass until it reaches water sufficiently deep to float it4 ,it is quite possible that the ice at the present day may nowhere traverse a distance of three or four hundred miles of sea-bottom1 but this is wholly owing to the fact that it finds water sufficiently deep to float it before having travelled so far4 ,were ,baffin's ,bay and ,davis's ,straits1 for example1 as shallow as the ,north ,sea1 the ice of ,greenland would not break up into icebergs in these seas1 but cross in one continuous mass to and over the ,american continent4 ,the median line of the ,scandinavian and ,scottish ice-sheets would be situated not far from the east coast of ,scotland4 ,the ,scandinavian ice would press up as near to our coast as the resistance of the ice from this side permitted4 ,the enormous mass of ice from ,scotland1 pressing out into the ,north ,sea1 would compel the ,scandinavian ice to move round by the ,orkneys1 and would also keep it at some little distance from ,scotland4 ,where1 on the other hand1 there was but little resistance offered by ice from the interior of this country 7and this might be the case along many parts of the ,english coast71 the ,scandinavian ice might reach the shores1 and even overrun the country for some distance inland4 ,we have hitherto confined our attention to the action of ice proceeding from ,norway2 but if we now consider what took place in ,sweden and the ,baltic1 we shall find more conclusive proof of the downward pressure of ,scandinavian ice on our own shores4 ,the western half of ,gothland is striated in the direction of ,n4,e4 and ,s4,w41 and that this has been effected by a huge mass of ice covering the country1 and not by local glaciers1 is apparent from the fact observed by ,robert ,chambers1#bef and officers of the ,swedish ,geological ,survey1 that the general direction of the groovings and stri on the rocks bears little or no relation to the conformation of the surface1 showing that the ice was of sufficient thickness to move straight forward1 regardless of the inequalities of the ground4 ,at ,gottenburg1 on the shores of the ,cattegat1 and all around ,lake ,wener and ,lake ,wetter1 the ice-markings are of the most remarkable character1 indicating1 in the most decided manner1 that the ice came from the interior of the country to the north-east in one vast mass4 ,all this mass of ice must have gone into the shallow ,cattegat1 a sea not sufficiently deep to float even an ordinary glacier4 ,the ice coming off ,gothland would therefore cross the ,cattegat1 and thence pass over ,jutland into the ,north ,sea4 ,after entering the ,north ,sea1 it would be obliged to keep between our shores and the ice coming direct from the western side of ,scandinavia4 ,but this is not all4 ,a very large proportion of the ,scandinavian ice would pass into the ,gulf of ,bothnia1 where it could not possibly float4 ,it would then move south into the ,baltic as land-ice4 ,after passing down the ,baltic1 a portion of the ice would probably move south into the flat plains in the north of ,germany1 but the greater portion would keep in the bed of the ,baltic1 and of course turn to the right round the south end of ,gothland1 and thence cross over ,denmark into the ,north ,sea4 ,that this must have been the path of the ice is1 ,i think1 obvious from the observations of ,murchison1 ,chambers1 ,hrbye1 and other geologists4 ,sir ,roderick ,murchison found--though he does not attribute it to land-ice--that the ,aland ,islands1 which lie between the ,gulf of ,bothnia and the ,baltic1 are all striated in a north and south direction4#beg ,upsala and ,stockholm1 a tract of flat country projecting for some distance into the ,baltic1 is also grooved and striated1 not in the direction that would be effected by ice coming from the interior of ,scandinavia1 but north and south1 in a direction parallel to what must have been the course of the ice moving down the ,baltic4#beh ,this part of the country must have been striated by a mass of ice coming from the direction of the ,gulf of ,bothnia4 ,and that this mass must have been great is apparent from the fact that ,lake ,malar1 which crosses the country from east to west1 at right angles to the path of the ice1 does not seem to have had any influence in deflecting the icy stream4 ,that the ice came from the north and not from the south is also evident from the fact that the northern sides of rocky eminences are polished1 rounded1 and ice-worn1 while the southern sides are comparatively rough4 ,the northern banks of ,lake ,malar1 for example1 which1 of course1 face the south1 are rough1 while the southern banks1 which must have offered opposition to the advance of the ice1 are smoothed and rounded in a most singular manner4 ,again1 that the ice1 after passing down the ,baltic1 turned to the right along the southern end of ,gothland1 is shown by the direction of the stri and ice-groovings observed on such islands as ,gothland1 land1 and ,bornholm4 ,sir ,r4 ,murchison found that the island of ,gothland is grooved and striated in one uniform direction from ,n4,e4 to ,s4,w4 8,these groovings10 says ,sir ,roderick1 8so perfectly resemble the flutings and stri produced in the ,alps by the actual movement of glaciers1 that neither ,m4 ,agassiz nor any one of his supporters could detect a difference40 ,he concludes1 however1 that the markings could not have been made by land-ice1 because ,gothland is not only a low1 flat island in the middle of the ,baltic1 but is 8at least #djj miles distant from any elevation to which the term of mountain can be applied40 ,this1 of course1 is conclusive against the hypothesis that ,gothland and the other islands of the ,baltic could have been glaciated by ordinary glaciers2 but it is quite in harmony with the theory that the ,gulf of ,bothnia and the entire ,baltic were filled with one continuous mass of land-ice1 derived from the drainage of the greater part of ,sweden1 ,lapland1 and ,finland4 ,in fact1 the whole glacial phenomena of ,scandinavia are inexplicable on the hypothesis of local glaciers4 ,that the ,baltic was completely filled by a mass of ice moving from the north is further evidenced by the fact that the mainland1 not only at ,upsala1 but at several places along the coast of ,gothland1 is grooved and striated parallel to the shore1 and often at right angles to the markings of the ice from the interior1 showing that the present bed of the ,baltic was not large enough to contain the icy stream4 ,for example1 along the shores between ,kalmar and ,karlskrona1 as described by ,sir ,roderick ,murchison and by ,m4 ,hrbye1 the striations are parallel to the shore4 ,perhaps the slight obstruction offered by the island of land1 situated so close to the shore1 would deflect the edge of the stream at this point over on the land4 ,the icy stream1 after passing ,karlskrona1 bent round to the west along the present entrance to the ,baltic1 and again invaded the mainland1 and crossed over the low headland of ,christianstadt1 and thence passed westward in the direction of ,zealand4 ,illustration3 ,,plate ,v4 ,w4 ,a4 ,k4 ,johnston1 ,edinbr4 and ,london4 ,,chart ,,showing ,,the ,,probable ,,path ,,of ,,the ,,ice ,,in ,,north-,,western ,,europe ,,during ,,the ,,period ,,of ,,maximum ,,glaciation4 ,the lines also represent the actual direction of the striae on the rocks4 ,this immense ,baltic glacier would in all probability pass over ,denmark1 and enter the ,north ,sea somewhere to the north of the ,river ,elbe1 and would then have to find an outlet to the ,atlantic through the ,english ,channel1 or pass in between our eastern shores and the mass from ,gothland and the north-western shores of ,europe4 ,the entire probable path of the ice may be seen by a reference to the accompanying chart 7,plate ,v47 ,that the ice crossed over ,denmark is evident from the fact that the surface of that country is strewn with dbris derived from the ,scandinavian peninsula4 ,taking all these various considerations into account1 the conclusion is inevitable that the great masses of ice from ,scotland would be obliged to turn abruptly to the north1 as represented in the diagram1 and pass round into the ,atlantic in the direction of ,caithness and the ,orkney ,islands4 ,if the foregoing be a fair representation of the state of matters1 it is physically impossible that ,caithness could have escaped being overridden by the land-ice of the ,north ,sea4 ,caithness1 as is well known1 is not only a low1 flat tract of land1 little elevated above the sea-level1 and consequently incapable of supporting large glaciers2 but1 in addition1 it projects in the form of a headland across the very path of the ice4 ,unless ,caithness could have protected itself by pushing into the sea glaciers of one or two thousand feet in thickness1 it could not possibly have escaped the inroads of the ice of the ,north ,sea4 ,but ,caithness itself could not have supported glaciers of this magnitude1 neither could it have derived them from the adjoining mountainous regions of ,sutherland1 for the ice of this county found a more direct outlet than along the flat plains of ,caithness4 ,the shells which the boulder clay of ,caithness contains have thus evidently been pushed out of the bed of the ,north ,sea by the land-ice1 which formed the clay itself4 ,the fact that these shells are not so intensely arctic as those found in some other quarters of ,scotland1 is no evidence that the clay was not formed during the most severe part of the glacial epoch1 for the shells did not live in the ,north ,sea at the time that it was filled with land-ice4 ,the shells must have belonged to a period prior to the invasion of the ice1 and consequently before the cold had reached its greatest intensity4 ,neither is there any necessity for supposing the shells to be pre-glacial1 for these shells may have belonged to an inter-glacial period4 ,in so far as ,scotland is concerned1 it would be hazardous to conclude that a plant or an animal is either pre-glacial or post-glacial simply because it may happen not to be of an arctic or of a boreal type4 ,the same remarks which apply to ,caithness apply to a certain extent to the headland at ,fraserburgh4 ,it1 too1 lay in the path of the ice1 and from the direction of the stri on the rocks1 and the presence of shells in the clay1 as described by ,mr4 ,jamieson1 it bears evidence also of having been overridden by the land-ice of the ,north ,sea4 ,in fact1 we have1 in the invasion of ,caithness and the headland at ,fraserburgh by the land-ice of the ,north ,sea1 a repetition of what we have seen took place at ,upsala1 ,kalmar1 ,christianstadt1 and other flat tracts along the sides of the ,baltic4 ,the scarcity1 or perhaps entire absence of ,scandinavian boulders in the ,caithness clay is not in any way unfavourable to the theory1 for it would only be the left edge of the ,north ,sea glacier that could possibly pass over ,caithness2 and this edge1 as we have seen1 was composed of the land-ice from ,scotland4 ,we might expect1 however1 to find ,scandinavian blocks on the ,shetland and ,faroe ,islands1 for1 as we shall presently see1 there is pretty good evidence to prove that the ,scandinavian ice passed over these islands4 ,the ,shetland and ,faroe ,islands glaciated by ,land-ice4--,it is also worthy of notice that the stri on the rocks in the ,orkney1 ,shetland1 and ,faroe ,islands1 all point in the direction of ,scandinavia1 and are what would be effected by land-ice moving in the paths indicated in the diagram4 ,and it is a fact of some significance1 that when we proceed north to ,iceland1 the stri1 according to the observations of ,robert ,chambers1 seem to point towards ,north ,greenland4 ,is it possible that the entire ,atlantic1 from ,scandinavia to ,greenland1 was filled with land-ice8 ,astounding as this may at first appear1 there are several considerations which render such a conclusion probable4 ,the observations of ,chambers1 ,peach1 ,hibbert1 ,allan1 and others1 show that the rocky face of the ,shetland and ,faroe ,islands has been ground1 polished1 and striated in a most remarkable manner4 ,that this could not have been done by ice belonging to the islands themselves is obvious1 for these islands are much too small to have supported glaciers of any size1 and the smallest of them is striated as well as the largest4 ,besides1 the uniform direction of the stri on the rocks shows that it must have been effected by ice passing over the islands4 ,that the striations could not have been effected by floating icebergs at a time when the islands were submerged is1 ,i think1 equally obvious1 from the fact that not only are the tops of the highest eminences ice-worn1 but the entire surface down to the present sea-level is smoothed and striated2 and these striations conform to all the irregularities of the surface4 ,this last fact ,professor ,geikie has clearly shown is wholly irreconcilable with the floating-ice theory4#bei ,mr4 ,peach#bfj found vertical precipices in the ,shetlands grooved and striated1 and the same thing was observed by ,mr4 ,thomas ,allan on the ,faroe ,islands4#bfa ,that the whole of these islands have been glaciated by a continuous sheet of ice passing over them was the impression left on the mind of ,robert ,chambers after visiting them4#bfb ,this is the theory which alone explains all the facts4 ,the only difficulty which besets it is the enormous thickness of the ice demanded by the theory4 ,but this difficulty is very much diminished when we reflect that we have good evidence1 from the thickness of icebergs which have been met with in the ,southern ,ocean1#bfc that the ice moving off the antarctic continent must be in some places considerably over a mile in thickness4 ,it is then not so surprising that the ice of the glacial epoch1 coming off ,greenland and ,northern ,europe1 should not have been able to float in the ,north ,atlantic4 ,why the ,ice of ,scotland was of such enormous ,thickness4--,the enormous thickness of the ice in ,scotland1 during the glacial epoch1 has been a matter of no little surprise4 ,it is remarkable how an island1 not more than #ajj miles across1 should have been covered with a sheet of ice so thick as to bury mountain ranges more than #a1jjj feet in height1 situated almost at the sea-shore4 ,but all our difficulties disappear when we reflect that the seas around ,scotland1 owing to their shallowness1 were1 during the glacial period1 blocked up with solid ice4 ,scotland1 ,scandinavia1 and the ,north ,sea1 would form one immense table-land of ice1 from #a1jjj to #b1jjj feet above the sea-level4 ,this table-land would terminate in the deep waters of the ,atlantic by a perpendicular wall of ice1 extending probably from the west of ,ireland away in the direction of ,iceland4 ,from this barrier icebergs would be continually breaking off1 rivalling in magnitude those which are now to be met with in the antarctic seas4 ,the great ,extension of the ,loess accounted for4--,an effect which would result from the blocking up of the ,north ,sea with land-ice1 would be that the waters of the ,rhine1 ,elbe1 and ,thames would have to find an outlet into the ,atlantic through the ,english ,channel4 ,professor ,geikie has suggested to me that if the ,straits of ,dover were not then open--quite a possible thing--or were they blocked up with land-ice1 say by the great ,baltic glacier crossing over from ,denmark1 the consequence would be that the waters of the ,rhine and ,elbe would be dammed back1 and would inundate all the low-lying tracts of country to the south2 and this might account for the extraordinary extension of the ,loess in the basin of the ,rhine1 and in ,belgium and the north of ,france4#bfd ,illustration3 ,,plate ,,vi4 ,,chart ,,showing ,,path ,,of ,,the ,,ice ,w4 ,a4 ,k4 ,johnston1 ,edinbr and ,london4 ,note4 ,curved lines shew path of ,ice4 ,arrows shew direction of striae as observed by ,prof4 ,geikie ,b4 ,n4 ,peach4 ,short thick lines shew direction of striae by other observers4 ,note on the ,glaciation of ,caithness4 ,i have very lately received a remarkable confirmation of the path of the ,caithness ice in observations communicated to me by ,professor ,geikie and ,mr4 ,b4 ,n4 ,peach4 ,the latter geologist says1 8,near the ,ord of ,caithness and on to ,berriedale the stri pass off the land and out to sea2 but near ,dunbeath1 #f miles north-east of ,berriedale1 they begin to creep up out of the sea on to the land and range from about #ae to #aj east of north4 ,where the stri pass out to the sea the boulder clay is made up of the materials from inland and contains no shells1 but immediately the stri begin to creep up on to the land then shells begin to make their appearance2 and there is a difference1 moreover1 in the colour of the clay1 for in the former case it is red and incoherent1 and in the latter hard and dark-coloured40 ,the accompanying chart 7,plate ,,vi47 shows the outline of the ,caithness coast and the direction of the stri as observed by ,professor ,geikie and ,mr4 ,peach1 and no demonstration could be more conclusive as to the path of the ice and the obstacles it met than these observations1 supplemented and confirmed as they are by other recorded facts to which ,i shall presently allude4 ,had the ice-current as it entered the ,north ,sea off the ,sutherland coast met with no obstacle it would have ploughed its way outwards till it broke off in glaciers and floated away4 ,but it is clear that the great press of ,scandinavian ice and the smaller mass of land-ice from the ,morayshire coast converging in the ,north ,sea filled up its entire bed1 and these1 meeting the opposing current from the ,sutherland coast1 turned it back upon itself1 and forced it over the north-east part of ,caithness4 ,the farther south on the ,sutherland coast that the ice entered the sea the deeper would it be able to penetrate into the ocean-bed before it met an opposition sufficiently strong to turn its course1 and the wider would be its sweep2 but when we come to the ,sutherland coast we reach a point where the land-ice--as1 for example1 near ,dunbeath--is forced to bend round before it even reaches the sea-shore1 as will be seen from the accompanying diagram4 ,we are led to the same conclusions regarding the path of the ice in the ,north ,sea from the presence of oolitic fossils and chalk flints found likewise in the boulder clay of ,caithness1 for these1 as we shall see1 evidently must have come from the sea4 ,at the meeting of the ,british ,association1 ,edinburgh1 #ahej1 ,hugh ,miller exhibited a collection of boreal shells with fragments of oolitic fossils1 chalk1 and chalk flints from the boulder clay of ,caithness collected by ,mr4 ,dick1 of ,thurso4 ,my friend1 ,mr4 ,c4 ,w4 ,peach1 found that the chalk flints in the boulder clay of ,caithness become more abundant as we proceed northward1 while the island of ,stroma in the ,pentland ,firth he found to be completely strewn with them4 ,this same observer found1 also1 in the ,caithness clay stones belonging to the ,oolitic and ,lias formations1 with their characteristic fossils1 while ammonites1 belemnites1 fossil wood1 c41 c41 were also found loose in the clay4#bfe ,the explanation evidently is1 that these remains were derived from an outcrop of oolitic and cretaceous beds in the ,north ,sea4 ,it is well known that the eastern coast of ,sutherlandshire is fringed with a narrow strip of oolite1 which passes under the sea1 but to what distance is not yet ascertained4 ,outside the ,oolitic formation the chalk beds in all probability crop out4 ,it will be seen from a glance at the accompanying chart 7,plate ,,vi47 that the ice which passed over the north-eastern part of ,caithness must have crossed the out-cropping chalk beds4 ,as has already been stated in the foregoing chapter1 the headland of ,fraserburgh1 north-eastern corner of ,aberdeenshire1 bears evidence1 both from the direction of the stri and broken shells in the boulder clay1 of having been overridden also by land-ice from the ,north ,sea4 ,this conclusion is strengthened by the fact that chalk flints and oolitic fossils have also been abundantly met with in the clay by ,dr4 ,knight1 ,mr4 ,james ,christie1 ,mr4 ,w4 ,ferguson1 ,mr4 ,t4 ,f4 ,jamieson1 and others4 ,,chapter ,,xxviii4 ,,north ,,of ,,england ,,ice-,,sheet1 ,,and ,,transport ,,of ,,wastdale ,,crag ,,blocks4#bff ,transport of ,blocks2 ,theories of4--,evidence of ,continental ,ice4--,pennine ,range probably striated on ,summit4--,glacial ,drift in ,centre of ,england4--,mr4 ,lacy on ,drift of ,cotteswold ,hills4--,england probably crossed by ,land-ice4--,mr4 ,jack's ,suggestion4--,shedding of ,ice ,north and ,south4--,south of ,england ,ice-sheet4--,glaciation of ,west ,somerset4--,why ,ice-markings are so rare in ,south of ,england4--,form of ,contortion produced by ,land-ice4 ,considerable difficulty has been felt in accounting for the transport of the ,wastdale granite boulders across the ,pennine chain to the east4 ,professors ,harkness1#bfg and ,phillips1#bfh ,messrs4 ,searles ,wood1 jun41#bfi ,mackintosh1#bgj and ,i presume all who have written on the subject1 agree that these blocks could not have been transported by land-ice4 ,the agency of floating ice under some form or other is assumed by all4 ,we have in ,scotland phenomena of an exactly similar nature4 ,the summits of the ,ochils1 the ,pentlands1 and other mountain ranges in the east of ,scotland1 at elevations of from #a1ejj to #b1jjj feet1 are not only ice-marked1 but strewn over with boulders derived from rocks to the west and north-west4 ,many of them must have come from the ,highlands distant some #ej or #fj miles4 ,it is impossible that these stones could have been transported1 or the summits of the hills striated1 by means of ordinary glaciers4 ,neither can the phenomena be attributed to the agency of icebergs carried along by currents4 ,for we should require to assume not merely a submergence of the land to the extent of #b1jjj feet or so1--an assumption which might be permitted1--but also that the currents bearing the icebergs took their rise in the elevated mountains of the ,highlands 7a most unlikely place71 and that these currents radiated in all directions from that place as a centre4 ,in short1 the glacial phenomena of ,scotland are wholly inexplicable upon any other theory than that1 during at least a part of the glacial epoch1 the entire island from sea to sea was covered with one continuous mass of ice of not less than #b1jjj feet in thickness4 ,in my paper on the ,boulder ,clay of ,caithness 7see preceding chapter71 ,i have shown that if the ice was #b1jjj feet or so in thickness1 it must1 in its motion seawards1 have followed the paths indicated by the curved lines in the chart accompanying that paper 7,see ,plate ,v474 ,in so far as ,scotland is concerned and ,scandinavia also1 these lines represent pretty accurately not only the paths actually taken by the boulders1 but also the general direction of the ice-markings on all the elevated mountain ridges4 ,but if ,scotland was covered to such an extent with ice1 it is not at all probable that ,westmoreland and the other mountainous districts of the ,north of ,england could have escaped being enveloped in a somewhat similar manner4 ,now if we admit the supposition of a continuous mass of ice covering the ,north of ,england1 all our difficulties regarding the transport of the ,wastdale blocks across the ,pennine chain disappear4 ,an inspection of the chart above referred to will show that these blocks followed the paths which they ought to have done upon the supposition that they were conveyed by continental ice4 ,that ,wastdale ,crag itself suffered abrasion by ice moving over it1 in the direction indicated by the lines in the diagram1 is obvious from what has been recorded by ,dr4 ,nicholson and ,mr4 ,mackintosh4 ,they both found the ,crag itself beautifully moutonne up to its summit1 and striated in a ,w4,s4,w4 and ,e4,n4,e4 direction4 ,mr4 ,mackintosh states that these scorings run obliquely up the sloping face of the crag4 ,ice scratches crossing valleys and running up the sloping faces of hills and over their summits are the sure marks of continental ice1 which meet the eye everywhere in ,scotland4 ,dr4 ,nicholson found in the drift covering the lower part of the crag1 pebbles of the ,coniston flags and grits from the west4#bga ,the fact that in ,westmoreland the direction of the ice-markings1 as a general rule1 corresponds with the direction of the main valleys1 is no evidence whatever that the country was not at one period covered with a continuous sheet of ice2 because1 for long ages after the period of continental ice1 the valleys would be occupied by glaciers1 and these1 of course1 would necessarily leave the marks of their presence behind4 ,this is just what we have everywhere in ,scotland4 ,it is on the summits of the hills and elevated ridges1 where no glacier could possibly reach1 that we find the sure evidence of continental ice4 ,but that land-ice should have passed over the tops of hills #a1jjj or #b1jjj feet in height is a thing hitherto regarded by geologists as so unlikely that few of them ever think of searching in such places for ice-markings1 or for transported stones4 ,although little has been recorded on this point1 ,i hardly think it likely that there is in ,scotland a hill under #b1jjj feet wholly destitute of evidence that ice has gone over it4 ,if there were hills in ,scotland that should have escaped being overridden by ice1 they were surely the ,pentland ,hills2 but these1 as was shown on a former occasion1#bgb were completely buried under the mass of ice covering the flat surrounding country4 ,i have no doubt whatever that if the summits of the ,pennine range were carefully examined1 say under the turf1 evidence of ice-action1 in the form of transported stones or scratches on the rock1 would be found4#bgc ,nor is the fact that the ,wastdale boulders are not rounded and ice-marked1 or found in the boulder clay1 but lie on the surface1 any evidence that they were not transported by land-ice4 ,for it would not be the stones under the ice1 but those falling on the upper surface of the sheet1 that would stand the best chance of being carried over mountain ridges4 ,but such blocks would not be crushed and ice-worn2 and it is on the surface of the clay1 and not imbedded in it1 that we should expect to find them4 ,it is quite possible that the dispersion of the ,wastdale boulders took place at various periods4 ,during the period of local glaciers the blocks would be carried along the line of the valleys4 ,all ,i wish to maintain is that the transport of the blocks across the ,pennine chain is easily accounted for if we admit1 what is very probable1 that the great ice-covering of ,scotland overlapped the high grounds of the ,north of ,england4 ,the phenomenon is the same in both places1 and why not attribute it to the same cause8 ,there is another curious circumstance connected with the drift of ,england which seems to indicate the agency of an ice-covering4 ,as far back as #ahai1 ,dr4 ,buckland1 in his ,memoir on the ,quartz ,rock of ,lickey ,hill1#bgd directed attention to the fact1 that on the ,cotteswold ,hills there are found pebbles of hard red chalk which must have come from the ,wolds of ,yorkshire and ,lincolnshire4 ,he pointed out also that the slaty and porphyritic pebbles probably came from ,charnwood ,forest1 near ,leicester4 ,professor ,hull1 of the ,geological ,survey1 considers that 8almost all the ,northern ,drift of this part of the country had been derived from the dbris of the rocks of the ,midland ,counties40#bge ,he came also to the conclusion that the slate fragments may have been derived from ,charnwood ,forest4 ,in the ,vale of ,moreton he found erratic boulders from two feet to three feet in diameter4 ,the same northern character of the drift of this district is remarked by ,professor ,ramsay and ,mr4 ,aveline1 in their ,memoir of the ,geology of parts of ,gloucestershire4 ,in ,leicestershire and ,northamptonshire the officers of the ,geological ,survey found in abundance drift which must have come from ,lincolnshire and ,yorkshire to the north-east4 ,mr4 ,lucy1 who has also lately directed attention to the fact that the ,cotteswold ,hills are sprinkled over with boulders from ,charnwood ,forest1 states also that1 on visiting the latter place1 he found that many of the stones contained in it had come from ,yorkshire1 still further to the north-east4#bgf ,mr4 ,searles ,wood1 jun41 in his interesting paper on the ,boulder ,clay of the ,north of ,england1#bgg states that enormous quantities of the chalk dbris from the ,yorkshire ,wold are found in ,leicester1 ,rutland1 ,warwick1 ,northampton1 and other places to the south and south-west4 ,mr4 ,wood justly concludes that this chalk dbris could not have been transported by water4 8,if we consider10 he says1 8the soluble nature of chalk1 it must be evident that none of this dbris can have been detached from the parent mass1 either by water-action1 or by any other atmospheric agency than moving ice4 ,the action of the sea1 of rivers1 or of the atmosphere1 upon chalk1 would take the form of dissolution1 the degraded chalk being taken up in minute quantities by the water1 and held in suspension by it1 and in that form carried away2 so that it seems obvious that this great volume of rolled chalk can have been produced in no other way than by the agency of moving ice2 and for that agency to have operated to an extent adequate to produce a quantity that ,i estimate as exceeding a layer #bjj feet thick over the entire ,wold1 nothing less than the complete envelopment of a large part of the ,wold by ice for a long period would suffice40 ,i have already assigned my reasons for disbelieving the opinion that such masses of drift could have been transported by floating ice2 but if we refer it to land-ice1 it is obvious that the ice could not have been in the form of local glaciers1 but must have existed as a sheet moving in a south and south-west direction1 from ,yorkshire1 across the central part of ,england4 ,but how is this to harmonize with the theory of glaciation1 which is advanced to explain the transport of the ,shap boulders8 ,the explanation has1 ,i think1 been pointed out by a writer in the ,glasgow ,herald1#bgh of the #bfth ,november1 #ahgj1 in a review of ,mr4 ,lucy's paper4 ,in my paper on the ,boulder ,clay of ,caithness1 ,i had represented the ice entering the ,north ,sea from the east coast of ,scotland and ,england1 as all passing round the north of ,scotland4 ,but the reviewer suggests that the ice entering at places to the south of1 say1 ,flamborough ,head1 would be deflected southwards instead of northwards1 and thus pass over ,england4 8,it is improbable1 however10 says the writer1 8that this joint ice-sheet would1 as ,mr4 ,croll supposes1 all find its way round the north of ,scotland into the deep sea4 ,the southern uplands of ,scotland1 and probably also the mountains of ,northumberland1 propelled1 during the coldest part of the glacial period1 a land ice-sheet in an eastward direction4 ,this sheet would be met by another streaming outward from the south-western part of ,norway--in a diametrically opposite direction4 ,in other words1 an imaginary line might be drawn representing the course of some particular boulder in the moraine profonde from ,england met by a boulder from ,norway1 in the same straight line4 ,with a dense ice-sheet to the north of this line1 and an open plain to the south1 it is clear that all the ice travelling east or west from points to the south of the starting-points of our two boulders would be #8shed' off to the south4 ,there would be a point somewhere along the line1 at which the ice would turn as on a pivot--this point being nearer ,england or ,scandinavia1 as the degree of pressure exercised by the respective ice-sheets should determine4 ,there is very little doubt that the point in question would be nearer ,england4 ,further1 the direction of the joint ice-sheet could not be due south unless the pressure of the component ice-sheets should be exactly equal4 ,in the event of that from ,scandinavia pressing with greater force1 the direction would be to the south-west4 ,this is the direction in which the drifts described by ,mr4 ,lucy have travelled40 ,i can perceive no physical objection to this modification of the theory4 ,what the ice seeks is the path of least resistance1 and along this path it will move1 whether it may lie to the south or to the north4 ,and it is not at all improbable that an outlet to the ice would be found along the natural hollow formed by the valleys of the ,trent1 ,avon1 and ,severn4 ,ice moving in this direction would no doubt pass down the ,bristol ,channel and thence into the ,atlantic4 ,might not the shedding of the north of ,england ice-sheet to the north and south1 somewhere not far from ,stainmoor1 account for the remarkable fact pointed out by ,mr4 ,searles ,wood1 that the boulder clay1 with ,shap boulders1 to the north of the ,wold is destitute of chalk2 while1 on the other hand1 the chalky boulder clay to the south of the ,wold is destitute of ,shap boulders8 ,the ice which passed over ,wastdale ,crag moved to the ,e4,n4,e41 and did not cross the chalk of the ,wold2 while the ice which bent round to the south by the ,wold came from the district lying to the south of ,wastdale ,crag1 and consequently did not carry with it any of the granite from that ,crag4 ,in fact1 ,mr4 ,searles ,wood has himself represented on the map accompanying his ,memoir this shedding of the ice north and south4 ,these theoretical considerations are1 of course1 advanced for what they are worth4 ,hitherto geologists have been proceeding upon the supposition of an ice-sheet and an open ,north ,sea2 but the latter is an impossibility4 ,but if we suppose the seas around our island to have been filled with land-ice during the glacial epoch1 the entire glacial problem is changed1 and it does not then appear so surprising that ice should have passed over ,england4 ,note on the ,south of ,england ,ice-sheet4 ,if what has already been stated regarding the north of ,england be anything like correct1 it is evident that the south of ,england could not possibly have escaped glaciation4 ,if the ,north ,sea was so completely blocked up by ,scandinavian ice1 that the great mass of ice from the ,cumberland mountains entering the sea on the east coast was compelled to bend round and find a way of escape across the centre of ,england in the direction of the ,bristol ,channel1 it is scarcely possible that the immense mass of ice filling the ,baltic ,sea and crossing over ,denmark could help passing across at least a portion of the south of ,england4 ,the ,north ,sea being blocked up1 its natural outlet into the ,atlantic would be through the ,english ,channel2 and it is not likely that it could pass through without impinging to some extent upon the land4 ,already geologists are beginning to recognise the evidence of ice in this region4 ,mr4 ,w4 ,c4 ,lucy1 in the ,geological ,magazine for ,june1 #ahgd1 records the finding by himself of evidences of glaciation in ,west ,somerset1 in the form of 8rounded rocky knolls10 near ,minehead1 like those of glaciated districts2 of a bed of gravel and clay #gj feet deep1 which he considered to be boulder clay4 ,he also mentions the occurrence near ,portlock of a large mass of sandstone well striated1 only partially detached from the parent rock4 ,in the same magazine for the following month ,mr4 ,h4 ,b4 ,woodward records the discovery by ,mr4 ,usher of some 8rum stuff0 near ,yarcombe1 in the ,black ,down ,hills of ,devonshire1 which1 on investigation1 proved to be boulder clay2 and further1 that it was not a mere isolated patch1 but occurred in several other places in the same district4 ,mr4 ,c4 ,w4 ,peach informs me that on the ,cornwall coast1 near ,dodman ,point1 at an elevation of about #fj feet above sea-level1 he found the rock surface well striated and ice-polished4 ,in a paper on the ,drift ,deposits of the ,bath district1 read before the ,bath ,natural ,history and ,antiquarian ,field ,club1 ,march #ajth1 #ahgd1 ,mr4 ,c4 ,moore describes the rock surfaces as grooved1 with deep and long-continued furrows similar to those usually found on glaciated rocks1 and concludes that during the glacial period they were subjected to ice-action4 ,this conclusion is confirmed by the fact of there being found1 immediately overlying these glaciated rocks1 beds of gravel with intercalated clay-beds1 having a thickness of #cj feet1 in which mammalian remains of arctic types are abundant4 ,the most characteristic of which are ,elephas primigenius1 ,e4 antiquus1 ,rhinoceros tichorhinus1 ,bubalus moschatus1 and ,cervus tarandus4 ,there is little doubt that when the ground is better examined many other examples will be found4 ,one reason1 probably1 why so little evidence of glaciation in the south of ,england has been recorded1 is the comparative absence of rock surfaces suitable for retaining ice-markings4 ,there is1 however1 one class of evidence which might determine the question of the glaciation of the south of ,england as satisfactorily as markings on the rock4 ,the evidence to which ,i refer is that of contorted beds of sand or clay4 ,in ,england contortions from the sinking of the beds are1 of course1 quite common1 but a thoughtful observer1 who has had a little experience of ice-formed contortions1 can easily1 without much trouble1 distinguish the latter from the former4 ,contortions resulting from the lateral pressure of the ice assume a different form from those produced by the sinking of the beds4 ,in ,scotland1 for example1 there is one well-marked form of contortion1 which not only proves the existence of land-ice1 but also the direction in which it moved4 ,the form of contortion to which ,i refer is the bending back of the stratified beds upon themselves1 somewhat in the form of a fishing-hook4 ,this form of contortion will be better understood from the accompanying figure4 ,illustration3 ,fig4 #aa4 ,,section ,,of ,,contorted ,,drift ,,near ,,musselburgh4 a ,boulder ,clay2 b ,laminated ,clay2 c ,sand1 ,gravel1 and ,clay1 contorted4 ,depth of ,section1 twenty-two feet4--,h4 ,,skae4 ,,chapter ,,xxix4 ,,evidence ,,from ,,buried ,,river ,,channels ,,of ,a ,,continental ,,period ,,in ,,britain4#bgi ,remarks on the ,drift ,deposits4--,examination of ,drift by ,borings4--,buried ,river ,channel from ,kilsyth to ,grangemouth4--,channels not excavated by ,sea nor by ,ice4--,section of buried ,channel at ,grangemouth4--,mr4 ,milne ,home's ,theory4--,german ,ocean dry ,land4--,buried ,river ,channel from ,kilsyth to the ,clyde4--,journal of ,borings4--,marine ,origin of the ,drift ,deposits4--,evidence of ,inter-glacial ,periods4--,oscillations of ,sea-level4--,other buried ,river ,channels4 ,remarks on the ,drift ,deposits4--,the drift and other surface deposits of the country have chiefly been studied from sections observed on the banks of streams1 railway cuttings1 ditches1 foundations of buildings1 and other excavations4 ,the great defect of such sections is that they do not lay open a sufficient depth of surface4 ,they may1 no doubt1 represent pretty accurately the character and order of the more recent deposits which overlie the boulder clay1 but we are hardly warranted in concluding that the succession of deposits belonging to the earlier part of the glacial epoch1 the period of the true till1 is fully exhibited in such limited sections4 ,suppose1 for example1 the glacial epoch proper--the time of the lower boulder clay--to have consisted of a succession of alternate cold and warm periods1 there would1 in such a case1 be a series of separate formations of boulder clay2 but we could hardly expect to find on the flat and open face of the country1 where the surface deposits are generally not of great depth1 those various formations of till lying the one superimposed upon the other4 ,for it is obvious that the till formed during one ice-period would1 as a general rule1 be either swept away or re-ground and laid down by the ice of the succeeding period4 ,if the very hardest rocks could not withstand the abrading power of the enormous masses of ice which passed over the surface of the country during the glacial epoch1 it is hardly to be expected that the comparatively soft boulder clay would be able to do so4 ,it is probable that the boulder clay of one period would be used as grinding materials by the ice of the succeeding periods4 ,the boulder clay which we find in one continuous mass may1 therefore1 in many cases1 have been ground off the rocks underneath at widely different periods4 ,if we wish to find the boulder clays belonging to each of the successive cold periods lying1 the one superimposed on the other in the order of time in which they were formed1 we must go and search in some deep gorge or valley1 where the clay has not only accumulated in enormous masses1 but has been partially protected from the destructive power of the ice4 ,but it is seldom that the geologist has an opportunity of seeing a complete section down to the rock-head in such a place4 ,in fact1 excepting by bores for minerals1 or by shafts of pits1 the surface1 to a depth of one or two hundred feet1 is never passed through or laid open4 ,examination of ,drift by ,borings4--,with the view of ascertaining if additional light would be cast on the sequence of events1 during the formation of the boulder clay1 by an examination of the journals of bores made through a great depth of surface deposits1 a collection of about #bej bores1 put down in all parts of the mining districts of ,scotland1 was made4 ,an examination of these bores shows most conclusively that the opinion that the boulder clay1 or lower till1 is one great undivided formation1 is wholly erroneous4 ,these #bej bores1 as already stated1#bhj represent a total thickness of #ba1cdh feet1 giving #hf feet as the mean thickness of the deposits passed through4 ,twenty of these bores have one boulder clay1 with beds of stratified sand or gravel beneath the clay2 #be have #b boulder clays1 with stratified beds of sand and gravel between2 #aj have #c boulder clays2 one has #d boulder clays2 #b have #e boulder clays2 and one has no fewer than #f separate masses of boulder clay1 with stratified beds of sand and gravel between2 #af have two or three separate boulder clays1 differing altogether in colour and hardness1 without any stratified beds between4 ,we have1 therefore1 out of #bej bores1 #ge of them representing a condition of things wholly different from that exhibited to the geologist in ordinary sections4 ,these bores bear testimony to the conclusion that the glacial epoch consisted of a succession of cold and warm periods1 and not of one continuous and unbroken period of ice1 as was at one time generally supposed4 ,the full details of the character of the deposits passed through by these bores1 and their bearing on the history of the glacial epoch1 have been given by ,mr4 ,james ,bennie1 in an interesting paper read before the ,glasgow ,geological ,society1#bha to which ,i would refer all those interested in the subject of surface geology4 ,but it is not to the mere contents of the bores that ,i wish at present to direct attention1 but to a new and important result1 to which they have unexpectedly led4 ,buried ,river ,channel1 ,kilsyth to ,grangemouth1 ,firth of ,forth4--,these borings reveal the existence of a deep pre-glacial1 or perhaps inter-glacial1 trough or hollow1 extending from the ,clyde above ,bowling across the country by ,kilsyth1 along the valley of the ,forth and ,clyde ,canal1 to the ,firth of ,forth at ,grangemouth4 ,this trough is filled up with immense deposits of mud1 sand1 gravel1 and boulder clay4 ,these deposits not only fill it up1 but they cover it over to such an extent that it is absolutely impossible to find on the surface a single trace of it2 and had it not been for borings1 and other mining operations1 its existence would probably never have been known4 ,in places where the bottom of the trough is perhaps #bjj feet below the sea-level1 we find on the surface not a hollow1 but often an immense ridge or elliptical knoll of sand1 gravel1 or boulder clay1 rising sometimes to #aej or #bjj feet above the present sea-level4 ,i need not here enter into any minute details regarding the form1 depth1 and general outline of this trough1 or of the character of the deposits covering it1 these having already been described by ,mr4 ,bennie1 but shall proceed to the consideration of circumstances which seem to throw light on the physical origin of this curious hollow1 and to the proof which it unexpectedly affords that ,scotland1 during probably an early part of the glacial epoch1 stood higher in relation to the sea-level than it does at present2 or rather1 as ,i would be disposed to express it1 the sea stood much lower than at present4 ,from the fact that all along the line of this trough the surface of the country is covered with enormous beds of stratified sands and gravels of marine origin1 which proves that the sea must have at a recent period occupied the valley1 my first impression was that this hollow had been scooped out by the sea4 ,this conclusion appeared at first sight quite natural1 for at the time that the sea filled the valley1 owing to the ,gulf-stream impinging on our western shores1 a strong current would probably then pass through from the ,atlantic on the west to the ,german ,ocean on the east4 ,however1 considerations soon began to suggest themselves wholly irreconcilable with this hypothesis4 ,the question immediately arose1 if the tendency of the sea occupying the valley is to deepen it1 by wearing down its rocky bottom1 and removing the abraded materials1 then why is the valley filled up to such a prodigious extent with marine deposits8 ,does not the fact of the whole valley being filled up from sea to sea with marine deposits to a depth of from #ajj to #bjj feet1 and in some places1 to even #djj feet1 show that the tendency of the sea filling this valley is to silt it up rather than to deepen it8 ,what conceivable change of conditions could account for operations so diverse8 ,that the sea could not have cut out this trough1 is1 however1 susceptible of direct proof4 ,the height of the surface of the valley at the watershed or highest part1 about a mile to the east of ,kilsyth1 where the ,kelvin and the ,bonny ,water1 running in opposite directions1--the one west into the ,clyde1 and the other east into the ,carron1--take their rise1 is #afj feet above the sea-level4 ,consequently1 before the sea could pass through the valley at present1 the sea-level would require to be raised #afj feet4 ,but in discussing the question as to the origin of this pre-glacial hollow1 we must suppose the surface deposits of the valley all removed1 for this hollow was formed before these deposits were laid down4 ,let us take the average depth of these deposits at the watershed to be #ej feet4 ,it follows that1 assuming the hollow in question to have been formed by the sea1 the sea-level at the time must have been at least #aaj feet higher than at present4 ,were the surface deposits of the country entirely removed1 the district to the west and north-west of ,glasgow would be occupied by a sea which would stretch from the ,kilpatrick ,hills1 north of ,duntocher1 to ,paisley1 a distance of about five miles1 and from near ,houston to within a short way of ,kirkintilloch1 a distance of more than twelve miles4 ,this basin would contain a few small islands and sunken rocks1 but its mean depth1 as determined from a great number of surface bores obtained over its whole area1 would be not much under #gj or #hj feet4 ,but we shall1 however1 take the depth at only #ej feet4 ,now1 if we raise the sea-level so as to allow the water just barely to flow over the watershed of the valley1 the sea in this basin would therefore be #afj feet deep4 ,let us now see what would be the condition of things on the east end of the valley4 ,the valley1 for several miles to the east of ,kilsyth1 continues very narrow1 but on reaching ,larbert it suddenly opens into the broad and flat carse lands through which the ,forth and ,carron wind4 ,the average depth at which the sea would stand at present in this tract of country1 were the surface removed1 as ascertained from bores1 would be at least #ajj feet1 or about double that in the western basin4 ,consequently1 when the sea was sufficiently high to pass over the watershed1 the water would be here #baj feet in depth1 and several miles in breadth4 ,illustration3 ,,plate ,,vii4 ,w4 ,a4 ,k4 ,johnston ,edinbr4 and ,london4 ,,chart ,,of ,,the ,,midland ,,valley1 ,,showing ,,buried ,,river ,,channels4 ,the blue parts represent the area which would be covered by sea were the land submerged to the extent of #bjj feet4 ,the heavy black lines ,a and ,b represent the buried ,river ,channels4 ,but in order to have a current of some strength passing through the valley1 let us suppose the sea at the time to have stood #aej feet higher in relation to the land than at present4 ,this would give #dj feet as the depth of the sea on the watershed1 and #bjj feet as the depth in the western basin1 and #bej feet as the depth in the eastern4 ,an examination of the ,ordnance ,survey map of the district will show that the #bjj feet contour lines which run along each side of the valley from ,kilsyth to ,castlecary come1 in several places1 to within one-third of a mile of each other4 ,from an inspection of the ground1 ,i found that1 even though the surface deposits were removed off the valley1 it would not sensibly affect the contours at those places4 ,it is therefore evident that though the sea may have stood even #bjj feet higher than at present1 the breadth of the strait at the watershed and several other points could not have exceeded one-third of a mile4 ,it is also evident that at those places the current would be flowing with the greatest velocity1 for here it was not only narrowest1 but also shallowest4 ,a reference to ,plate ,,vii4 will show the form of the basins4 ,the stippled portion1 coloured blue1 represents the area which would be covered by the sea were the land submerged to the extent of #bjj feet4 ,let us take the breadth of the current in the western basin at1 say1 three miles4 ,this is two miles less than the breadth of the basin itself4 ,suppose the current at the narrow parts between ,kilsyth and ,castlecary to have had a velocity of1 say1 five miles an hour4 ,now1 as the mean velocity of the current at the various parts of its course would be inversely proportionate to the sectional areas of those parts1 it therefore follows that the mean velocity of the current in the western basin would be only #a_/deth of what it was in the narrow pass between ,kilsyth and ,castlecary4 ,this would give a mile in nine hours as the velocity of the water in the western basin4 ,in the eastern basin the mean velocity of the current1 assuming its breadth to be the same as in the western1 would be only a mile in eleven hours4 ,in the central part of the current the velocity at the surface would probably be considerably above the mean1 but at the sides and bottom it would1 no doubt1 be under the mean4 ,in fact1 in these two basins the current would be almost insensible4 ,the effect of such a current would simply be to widen and deepen the valley all along that part between ,kilsyth and ,castlecary where the current would be flowing with considerable rapidity4 ,but it would have little or no effect in deepening the basins at each end1 but the reverse4 ,it would tend rather to silt them up4 ,if the current flowed from west to east1 the materials removed from the narrow part between ,kilsyth and ,castlecary1 where the velocity of the water was great1 would be deposited when the current almost disappeared in the eastern part of the valley4 ,sediment carried by a current flowing at the rate of five miles an hour1 would not remain in suspension when the velocity became reduced to less than five miles a day4 ,but even supposing it were shown that the sea under such conditions could have deepened the valley along the whole distance from the ,clyde to the ,forth1 still this would not explain the origin of the trough in question4 ,what we are in search of is not the origin of the valley itself1 but the origin of a deep and narrow hollow running along the bottom of it4 ,a sea filling the whole valley1 and flowing with considerable velocity1 would1 under certain conditions1 no doubt deepen and widen it1 but it would not cut out along its bottom a deep1 narrow trough1 with sides often steep1 and in some places perpendicular and even overhanging4 ,this hollow is evidently an old river-bed scooped out of the rocky valley by a stream1 flowing probably during an early part of the glacial period4 ,during the latter part of the summer of #ahfh1 ,i spent two or three weeks of my holidays in tracing the course of this buried trough from ,kilsyth to the river ,forth at ,grangemouth1 and ,i found unmistakable evidence that the eastern portion of it1 stretching from the watershed to the ,forth1 had been cut out1 not by the sea1 but by a stream which must have followed almost the present course of the ,bonny ,water4 ,i found that this deep hollow enters the ,forth a few hundred yards to the north of ,grangemouth ,harbour1 at the extraordinary depth of #bfj feet below the present sea-level4 ,at the period when the sea occupied the valley of the ,forth and ,clyde ,canal1 the bottom of the trough at this spot would therefore be upwards of #djj feet below the level of the sea4 ,a short distance to the west of ,grangemouth1 and also at ,carron1 several bores were put down in lines almost at right angles across the trough1 and by this means we have been enabled to form a pretty accurate estimate of its depth1 breadth1 and shape at those places4 ,i shall give the details of one of those sections4 ,between ,towncroft ,farm and the river ,carron1 a bore was put down to the depth of #bgc feet before the rock was reached4 ,about #aej yards to the north of this there is another bore1 giving #bcd feet as the depth to the rock2 #aej yards still further north the depth of the surface deposits1 as determined by a third bore1 is #aee feet4 ,this last bore is evidently outside of the hollow1 for one about #aej yards north of it gives the same depth of surface1 which seems to be about its average depth for a mile or two around4 ,about half a mile to the south of the hollow at this place the surface deposits are #aej feet deep4 ,from a number of bores obtained at various points within a circuit of #a miles1 the surface appears to have a pretty uniform depth of #aej feet or thereby4 ,for the particulars of these 8bores0 ,i am indebted to the kindness of ,mr4 ,mackay1 of ,grangemouth4 ,to the south of the trough 7see ,fig4 #ab7 there is a fault running nearly parallel to it1 having a down-throw to the north1 and cutting off the coal and accompanying strata to the south4 ,but an inspection of the section will show that the hollow in question is no way due to the fault1 but has been scooped out of the solid strata4 ,illustration3 ,fig4 #ab4 ,,section ,,of ,,buried ,,river-,,bed ,,near ,,towncroft ,,farm1 ,,grangemouth4 ,the main coal wrought extensively here is cut off by the trough1 as will be seen from the section4 ,mr4 ,dawson1 of ,carron ,iron ,works1 informs me that at ,carronshore pit1 about a mile and a quarter above where this section is taken1 the coal was found to be completely cut off by this trough4 ,in one of the workings of this pit1 about forty years ago1 the miners cut into the trough at #dj fathoms below the surface1 when the sand rushed in with irresistible pressure1 and filled the working4 ,again1 about a mile below where the section is taken1 or about two miles below ,carronshore1 and just at the spot where the trough enters the ,firth1 it was also cut into in one of the workings of the ,heuck pit at a depth of #dj fathoms from the surface4 ,fortunately1 however1 at this point the trough is filled with boulder clay instead of sand1 and no damage was sustained4 ,here1 for a distance of two miles1 the ,main coal and 8,upper ,coxroad0 are cut off by this hollow2 or rather1 ,i should say this hollow has been cut through the coal-seams4 ,the 8,under ,coxroad10 lying about #ad fathoms below the position of the 8,main0 coal1 as will be seen in the descriptive section 7,fig4 #ab71 is not reached by the trough1 and passes undisturbed under it4 ,this hollow would seem to narrow considerably as it recedes westwards1 for at ,carronshore pit-shaft the surface is #ach feet deep2 but not much over #aej yards to the south of this is the spot where the coal was cut off by the trough at a depth of #dj fathoms or #bdj feet4 ,here it deepens upwards of #ajj feet in little more than #aej yards4 ,that it is narrow at this place is proved by the fact1 that a bore put down near ,carronbank1 a little to the south1 shows the surface to be only #aef feet deep4 ,in the section 7,fig4 #ab7 the line described as 8#aej feet above sea-level0 registers the height of the sea-level at the time when the central valley was occupied by sea #dj feet deep at the watershed4 ,now1 if this hollow1 which extends right along the whole length of the valley1 had been cut out by the sea1 the surface of the rock #aej feet below the present surface of the ground would be the sea-bottom at the time1 and the line marked 8#aej feet above sea-level0 would be the surface of the sea4 ,the sea would therefore be here #cjj feet deep for several miles around4 ,it cannot be supposed that the sea acting on a broad flat plain of several miles in extent should cut out a deep1 narrow hollow1 like the one exhibited in the section1 and leave the rest of the plain a flat sea-bottom4 ,and it must be observed1 that this is not a hollow cut merely in a sea-beach1 but one extending westward to ,kilsyth4 ,now1 if this hollow was cut out by the sea1 it must have been done1 not by the waves beating on the beach1 but by a current flowing through the valley4 ,the strongest current that could possibly pass through the narrow part between ,kilsyth and ,castlecary would be wholly insensible when it reached ,grangemouth1 where the water was #cjj feet deep1 and several miles broad4 ,consequently1 it is impossible that the current could have scooped out the hollow represented in the section4 ,again1 if this hollow had been scooped out by the sea1 it ought to be deepest between ,kilsyth and ,castlecary1 where the current was narrowest2 but the reverse is actually the case4 ,it is shallowest at the place where the current was narrowest1 and deepest at the two ends where the current was broadest4 ,in the case of a trough cut by a sea current1 we must estimate its depth from the level of the sea4 ,its depth is the depth of the water in it while it was being scooped out4 ,the bottom of the trough in the highest and narrowest part of the valley east of ,kilsyth is #dj feet above the present sea-level4 ,consequently1 its depth at this point at the period in question1 when the sea-level was #aej feet higher than at present1 would be #aaj feet4 ,the bottom of the trough at ,grangemouth is #bfj feet below the present sea-level2 add to this #aej feet1 and we have #daj feet as its depth here at the time in question4 ,if this hollow was scooped out by the sea1 how then does it thus happen that at the place where the current was strongest and confined to a narrow channel by hills on each side1 it cut its channel to a depth of only #aaj feet1 whereas at the place where it had scarcely any motion it has cut1 on a flat and open plain several miles broad1 a channel to a depth of #daj feet8 ,but1 suppose we estimate the relative amount of work performed by the sea at ,kilsyth and ,grangemouth1 not by the actual depth of the bottom of the trough at these two places below the sea-level at the time that the work was performed1 but by the present actual depth of the bottom of the trough below the rocky surface of the valley1 this will still not help us out of the difficulty4 ,taking1 as before1 the height of the rocky bed of the valley at the watershed at #aaj feet above the present sea-level1 and the bottom of the trough at #dj feet1 this gives #gj feet as the depth scooped out of the rock at that place4 ,the depth of the trough at ,grangemouth below the rocky surface is #aah feet4 ,here we have only #gj feet cut out at the only place where there was any resistance to the current1 as well as the place where it possessed any strength2 whereas at ,grangemouth1 where there was no resistance1 and no strength of current1 #aah feet has been scooped out4 ,such a result as this is diametrically opposed to all that we know of the dynamics of running water4 ,we may1 therefore1 conclude that it is physically impossible that this hollow could have been cut out by the sea4 ,owing to the present tendency among geologists to attribute effects of this kind to ocean-currents1 ,i have been induced to enter thus at much greater length than would otherwise have been necessary into the facts and arguments against the possibility of the hollow having been excavated by the sea4 ,in the present case the discussion is specially necessary1 for here we have positive evidence of the sea having occupied the valley for ages1 along which this channel has been cut4 ,consequently1 unless it is proved that the sea could not possibly have scooped out the channel1 most geologists would be inclined to attribute it to the sea-current which is known to have passed through the valley rather than to any other cause4 ,but that it is a hollow of denudation1 and has been scooped out by some agent1 is perfectly certain4 ,by what agent1 then1 has the erosion been made8 ,the only other cause to which it can possibly be attributed is either land-ice or river-action4 ,the supposition that this hollow was scooped out by ice is not more tenable than the supposition that the work has been done by the sea4 ,a glacier filling up the entire valley and descending into the ,german ,ocean would unquestionably not only deepen the valley1 but would grind down the surface over which it passed all along its course4 ,but such a glacier would not cut a deep and narrow channel along the bottom of the valley4 ,a glacier that could do this would be a small and narrow one1 just sufficiently large to fill this narrow trough2 for if it were much broader than the trough1 it would grind away its edges1 and make a broad trough instead of a narrow one4 ,but a glacier so small and narrow as only to fill the trough1 descending from the hills at ,kilsyth to the sea at ,grangemouth1 a distance of fifteen miles1 is very improbable indeed4 ,the resistance to the advance of the ice along such a slope would cause the ice to accumulate till probably the whole valley would be filled4#bhb ,there is no other way of explaining the origin of this hollow1 but upon the supposition of its being an old river-bed4 ,but there is certainly nothing surprising in the fact of finding an old watercourse under the boulder clay and other deposits4 ,unless the present contour of the country be very different from what it was at the earlier part of the glacial epoch1 there must have then been watercourses corresponding to the ,bonny ,water and the river ,carron of the present day2 and that the remains of these should be found under the present surface deposits is not surprising1 seeing that these deposits are of such enormous thickness4 ,when water began to flow down our valleys1 on the disappearance of the ice at the close of the glacial epoch1 the ,carron and the ,bonny ,water would not be able to regain their old rocky channels1 but would be obliged to cut1 as they have done1 new courses for themselves on the surface of the deposits under which their old ones lay buried4 ,although an old pre-glacial or inter-glacial river-bed is in itself an object of much interest and curiosity1 still1 it is not on that account that ,i have been induced to enter so minutely into the details of this buried hollow4 ,there is something of far more importance attached to this hollow than the mere fact of its being an old watercourse4 ,for the fact that it enters the ,firth of ,forth at a depth of #bfj feet below the present sea-level1 proves incontestably that at the time this hollow was occupied by a stream1 the land must have stood at least between #bjj and #cjj feet higher in relation to the sea-level than at present4 ,we have seen that the old surface of the country in the neighbourhood of ,grangemouth1 out of which this ancient stream cut its channel1 is at least #aej feet below the present sea-level4 ,now1 unless this surface had been above the sea-level at that time1 the stream would not have cut a channel in it4 ,but it has not merely cut a channel1 but cut one to a depth of #abj feet4 ,it is impossible that this channel could have been occupied by a river of sufficient volume to fill it4 ,it is not at all likely that the river which scooped it out could have been much larger than the ,carron of the present day1 for the area of drainage1 from the very formation of the country1 could not have been much greater above ,grangemouth than at present4 ,an elevation of the land would1 no doubt1 increase the area of the drainage of the stream measured from its source to where it might then enter the sea1 because it would increase the length of the stream2 but it would neither increase the area of drainage1 nor the length of the stream above ,grangemouth4 ,kilsyth would be the watershed then as it is now4 ,what we have here is not the mere channel which had been occupied by the ancient ,carron1 but the valley in which the channel lay4 ,it may1 perhaps1 be more properly termed a buried river valley2 formed1 no doubt1 like other river valleys by the denuding action of rain and river4 ,the river ,carron at present is only a few feet deep4 ,suppose the ancient ,carron1 which flowed in this old channel1 to have been say #aj feet deep4 ,this would show that the land in relation to the sea at that time must have stood at least #bej feet higher than at present4 ,if #aj feet was the depth of this old river1 and ,grangemouth the place where it entered the sea1 then #bej feet would be the extent of the elevation4 ,but it is probable that ,grangemouth was not the mouth of the river2 it would likely be merely the place where it joined the river ,forth of that period4 ,we have every reason to believe that the bed of the ,german ,ocean was then dry land1 and that the ,forth1 ,tay1 ,tyne1 and other ,british rivers flowing eastward1 as ,mr4 ,godwin-,austin supposes1 were tributaries to the ,rhine1 which at that time was a huge river passing down the bed of the ,german ,ocean1 and entering the ,atlantic to the west of the ,orkney ,islands4 ,that the ,german ,ocean1 as well as the sea-bed of the ,western ,hebrides1 was dry land at a very recent geological period1 is so well known1 that1 on this point1 ,i need not enter into details4 ,we may1 therefore1 conclude that the river ,forth1 after passing ,grangemouth1 would continue to descend until it reached the ,rhine4 ,if1 by means of borings1 we could trace the old bed of the ,forth and the ,rhine up to the point where the latter entered the ,atlantic1 in the same way as we have done the ,bonny ,water and the ,carron1 we should no doubt obtain a pretty accurate estimate as to the height at which the land stood at that remote period4 ,nothing whatever1 ,i presume1 is known as to the depth of the deposits covering the bed of the ,german ,ocean along what was then the course of the ,rhine4 ,it must1 no doubt1 be something enormous4 ,we are also in ignorance as to the thickness of the deposits covering the ancient bed of the ,forth4 ,a considerable number of bores have been put down at various parts of the ,firth of ,forth in connection with the contemplated railway bridge across the ,firth1 but in none of those bores has the rock been reached4 ,bores to a depth of #age feet have been made without even passing through the deposits of silt which probably overlie an enormous thickness of sand and boulder clay4 ,even in places where the water is #dj fathoms deep and quite narrow1 the bottom is not rock but silt4 ,it is1 however1 satisfactory to find on the land a confirmation of what has long been believed from evidence found in the seas around our island1 that at a very recent period the sea-level in relation to the land must have been some hundreds of feet lower than at the present day1 and that our island must have at that time formed a part of the great eastern continent4 ,a curious fact was related to me by ,mr4 ,stirling1 the manager of the ,grangemouth collieries1 which seems to imply a great elevation of the land at a period long posterior to the time when this channel was scooped out4 ,in sinking a pit at ,orchardhead1 about a mile to the north of ,grangemouth1 the workmen came upon the boulder clay after passing through about #aaj feet of sand1 clay1 and gravel4 ,on the upper surface of the boulder clay they found cut out what ,mr4 ,stirling believes to have been an old watercourse4 ,it was #ag feet deep1 and not much broader4 ,the sides of the channel appear to have been smooth and water-worn1 and the whole was filled with a fine sharp sand beautifully stratified4 ,as this channel lay about #ajj feet below the present sea-level1 it shows that if it actually be an old watercourse1 it must have been scooped out at a time when the land in relation to the sea stood at least #ajj feet higher than at present4 ,buried ,river ,channel from ,kilsyth to the ,clyde4--,in all probability the western half of this great hollow1 extending from the watershed at ,kilsyth to the ,clyde1 is also an old river channel1 probably the ancient bed of the ,kelvin4 ,this point cannot1 however1 be satisfactorily settled until a sufficient number of bores have been made along the direct line of the hollow1 so as to determine with certainty its width and general form and extent4 ,that the western channel is as narrow as the eastern is very probable4 ,it has been found that its sides at some places1 as1 for example1 at ,garscadden1 are very steep4 ,at one place the north side is actually an overhanging buried precipice1 the bottom of which is about #bjj feet below the sea-level4 ,we know also that the coal and ironstone in that quarter are cut through by the trough1 and the miners there have to exercise great caution in driving their workings1 in case they might cut into it4 ,the trough along this district is filled with sand1 and is known to the miners of the locality as the 8sand-dyke40 ,to cut into running sand at a depth of #dj or #ej fathoms is a very dangerous proceeding1 as will be seen from the details given in ,mr4 ,bennie's paper#bhc of a disaster which occurred about twenty years ago to a pit near ,duntocher1 where this trough was cut into at a depth of #ea fathoms from the surface4 ,the depth of this hollow1 below the present sea-level at ,drumry1 as ascertained by a bore put down1 is #bcj feet4 ,for several miles to the east the depth is nearly as great4 ,consequently1 if this hollow be an old river-bed1 the ancient river that flowed in it must have entered the ,clyde at a depth of more than #bjj feet below the present sea-level2 and if so1 then it follows that the rocky bed of the ancient ,clyde must lie buried under more than #bjj feet of surface deposits from ,bowling downwards to the sea4 ,whether this is the case or not we have no means at present of determining4 ,the manager to the ,clyde ,trustees informs me1 however1 that in none of the borings or excavations which have been made has the rock ever been reached from ,bowling downwards4 ,the probability is1 that this deep hollow passes downwards continuously to the sea on the western side of the island as on the eastern4#bhd ,the following journals of a few of the borings will give the reader an idea of the character of the deposits filling the channels4 ,the beds which are believed to be boulder clay are printed in italics3-- ,,borings ,,made ,,through ,,the ,,deposits ,,filling ,,the ,,western ,,channel4 ,bore1 ,drumry ,farm1 on ,lands of ,garscadden4 ft4 ins4 ,surface soil #b #f ,sand and gravel #c #f ,dry sand #aa #j ,blue mud #h #f ,light mud and sand beds #ac #j ,sand #ca #f ,sand and mud #h #j ,sand and gravel #ai #f ,sand #h #f ,gravel #bd #d ,sand #e #j ,gravel #i #f ,sand #ga #f ,sand 7coaly7 #a #j ,sand #i #j ,sand 7coaly7 #a #j ,sand #aj #c ,red clay and gravel #d #h ,sand #a #e ,gravel #b #j ,sand #b #h ,gravel #aj #f ,sand #a #f ,gravel #h #aj ,clay stones and gravel #cc #c ---------------- #big #aj ,bore on ,mains of ,garscadden1 one mile north-east of ,drumry4 ft4 ins4 ,surface soil #a #j ,blue clay and stones #fj #j ,red clay and stones #ah #j ,soft clay and sand beds #g #j ,gravel #f #j ,large gravel #i #j ,sand and gravel #g #j ,hard gravel #a #f ,sand and gravel #af #f ,dry sand #cj #j ,black sand #b #j ,dry sand #cc #j ,wet sand #h #j ,light mud #e #j ,sand #c #j ,gravel #e #f ,sandstone1 black #j #f ,blue clay and stones #a #d ,whin block #j #aj ,sandy clay #d #f ---------------- #bai #h ,bore nearly half a mile south-west of ,millichen4 ft4 ins4 ,sandy clay #e #j ,brown clay and stones #ag #j ,mud #ae #j ,sandy mud #ca #j ,sand and gravel with water #bh #j ,sandy clay and gravel #ag #j ,sand #e #j ,mud #f #j ,sand #ad #j ,gravel #cj #j ,brown sandy clay and stones #cj #j ,hard red gravel #d #f ,light mud and sand #a #h ,light clay and stones #f #f ,light clay and whin block #bf #j ,fine sandy mud #cf #j ,brown clay and gravel and stones #ad #d ,bark clay and stones #fh #j ---------------- #cee #j ,bore at ,west ,millichen1 about #ajj yards east of farm-house4 ft4 ins4 ,soil #a #f ,muddy sand and stones #d #f ,soft mud #d #j ,sand and gravel #de #j ,sandy mud and stones #bj #f ,coarse gravel #aa #f ,clay and gravel #a #d ,fine mud #g #j ,sand and gravel #b #j ,sandy mud #cj #f ,brown sandy clay and stones #be #j ,sand and gravel #f #j ,brown sandy clay and stones #ab #j ,sand #b #j ,brown sandy clay and stones #d #j ,mud #e #j ,mud and sand #aj #i ,sand and stones #b #i ,blue clay and stones #e #j ---------------- #bjj #d ,,borings ,,made ,,through ,,the ,,deposits ,,filling ,,the ,,eastern ,,channel4 ,no4 #a4 ,between ,towncroft ,farm and ,carron ,river--#bjj yards from river4 ,height of surface1 #ab feet above sea-level4 ,feet4 ,surface sand #f ,blue mud #d ,sand #d ,gravel #c ,sand #cc ,red clay #df ,soft blue till #ag ,hard blue till #adj ,sand #bj ------ #bgc ,no4 #b4 ,about #aej yards north of ,no4 #a4 ,height of surface1 #ab feet above sea-level4 ,feet4 ,surface sand #f ,blue mud #c ,shell bed #a ,gravel #b ,blue mud #h ,gravel #c ,blue muddy sand #ae ,red clay #di ,blue till and stones #bj ,sand #bj ,hard blue till and stones #bd ,sand #b ,hard blue till and stones #dj ,sand #g ,hard blue till #bd ------ #bcd ,no4 #c4 ,about #aej yards north of ,no4 #b4 ,height of surface1 #ab feet above sea-level4 ,feet4 ,surface sand #f ,soft mud with shells #aa ,blue mud and sand 7hard7 #c ,channel 7rough gravel7 #c ,fine sand #h ,running sand 7red and fine7 #ag ,red clay #cj ,soft till #cf ,sand 7pure7 #b ,soft till and sand #ag ,gravel #h ,hard blue till #ad ------ #aee ,no4 #d4 ,about #ajj yards from ,no4 #a4 ,feet4 ,surface #e ,blue mud #e ,black sand #c ,gravel #c ,red clay and stones #cd ,red clay #dd ,soft blue till #cb ,hard blue till and stones #ajd ,grey sand not passed through #bb ------ #beb ,rock-head not reached4 ,no4 #e4 ,about #ej yards north of ,no4 #d4 ,feet4 ,surface #f ,blue mud #c ,shell bed #a ,channel #b ,blue mud #h ,channel #c ,blue mud and sand #ae ,red clay and sand #aj ,red clay #di ,blue till and stones #bj ,sand #bj ,hard blue till and stones #bd ,sand #b ,hard blue till and stones #dj ,sand #g ,hard blue till #bd ------ #baa ,no4 #f4 ,between ,heuck and ,carron ,river4 ,feet4 ,sandy clay #g ,mud #af ,brown sandy clay and stones #c ,mud #cf ,brown clay #ci ,blue till and stones #ed ------ #aee ,the question arises as to what is the origin of the stratified sands and gravels filling up the buried river channels4 ,are they of marine or of freshwater origin8 ,mr4 ,dugald ,bell#bhe and ,mr4 ,james ,geikie#bhf are inclined to believe that as far as regards those filling the western channel they are of lacustrine origin2 that they were formed in lakes1 produced by the damming back of the water resulting from the melting of the ice4 ,i am1 however1 for the following reasons1 inclined to agree with ,mr4 ,bennie's opinion that they are of marine origin4 ,it will be seen1 by a comparison of the journals of the borings made through the deposits in the eastern channel with those in the western1 that they are of a similar character2 so that1 if we suppose those in the western channel to be of freshwater origin1 we may from analogy infer the same in reference to the origin of those in the eastern channel4 ,but1 as we have already seen1 the deposits extend to the ,firth of ,forth at ,grangemouth1 where they are met with at a depth of #bfj feet below sea-level4 ,consequently1 if we conclude them to be of freshwater origin1 we are forced to the assumption1 not that the water formed by the melted ice was dammed back1 but that the sea itself was dammed back1 and that by a wall extending to a depth of not less than two or three hundred feet1 so as to allow of a lake being formed in which the deposits might accumulate2 assuming1 of course1 that the absolute level of the land was the same then as it is now4 ,but as regards the stratified deposits of ,grangemouth1 we have direct evidence of their marine origin down to the bottom of the ,red ,clay that immediately overlies the till and its intercalated beds1 which on an average is no less than #he feet1 and in some cases #ajj feet1 below the present surface4 ,from this deposit1 ,foraminifera1 indicating an arctic condition of sea1 were determined by ,mr4 ,david ,robertson4 ,marine shells were also found in this bed1 and along with them the remains of a seal1 which was determined by ,professor ,turner to be of an exceedingly arctic type1 thus proving that these deposits were not only marine but glacial4 ,direct fossil evidence as to the character of the deposits occupying the western basin1 is1 however1 not so abundant1 but this may be owing to the fact that during the sinking of pits1 no special attention has been paid to the matter4 ,at ,blairdardie1 in sinking a pit-shaft through these deposits1 shells were found in a bed of sand between two immense masses of boulder clay4 ,the position of this bed will be better understood from the following section of the pit-shaft3-- ,feet4 ,surface soil #d ,blue clay #i ,hard stony clay #fi ,sand with1 a few shells #c ,stony clay and boulders #df ,mud and running sand #aa ,hard clay1 boulders1 and broken rock #bg ------ #agj ,but as the shells were not preserved1 we have1 of course1 no means of determining whether they were of marine or of freshwater origin4 ,in another pit1 at a short distance from the above1 ,cyprina ,islandica was found in a bed at the depth of #ed feet below the surface4#bhg ,in a paper read by ,mr4 ,james ,smith1 of ,jordanhill1 to the ,geological ,society1 ,april #bdth1 #ahej1bhh the discovery is recorded of a stratified bed containing ,tellina proxima intercalated between two distinct boulder clays4 ,the bed was discovered by ,mr4 ,james ,russell in sinking a well at ,chapelhall1 near ,airdrie4 ,its height above sea-level was #eaj feet4 ,the character of the shell not only proves the marine origin of the bed1 but also the existence of a submergence to that extent during an inter-glacial period4 ,on the other hand1 the difficulty besetting the theory of the marine origin of the deposits is this4 ,the intercalated boulder clays bear no marks of stratification1 and are evidently the true unstratified till formed when the country was covered by ice4 ,but the fact that these beds are both underlaid and overlaid by stratified deposits would1 on the marine theory1 imply not merely the repeated appearance and disappearance of the ice1 but also the repeated submergence and emergence of the land4 ,if the opinion be correct that the submergences and emergences of the glacial epoch were due to depressions and elevations of the land1 and not to oscillations of sea-level1 then the difficulty in question is1 indeed1 a formidable one4 ,but1 on the other hand1 if the theory of submergences propounded in ,chapters ,,xxiii4 and ,,xxiv4 be the true one1 the difficulty entirely disappears4 ,the explanation is as follows1 viz41 during a cold period of the glacial epoch1 when the winter solstice was in aphelion1 the low grounds would be covered with ice1 under which a mass of till would be formed4 ,after the cold began to decrease1 and the ice to disappear from the plains1 the greatest rise of the ocean1 for reasons already stated1 would take place4 ,the till covering the low grounds would be submerged to a considerable depth and would soon be covered over by mud1 sand1 and gravel1 carried down by streams from the high ground1 which1 at the time1 would still be covered with snow and ice4 ,in course of time the sea would begin to sink and a warm and continental period of1 perhaps1 from #f1jjj to #aj1jjj years1 would follow1 when the sea would be standing at a much lower level than at present4 ,the warm period would be succeeded by a second cold period1 and the ice would again cover the land and form a second mass of till1 which1 in some places1 would rest directly on the former till1 while in other places it would be laid down upon the surface of the sands and gravels overlying the first mass4 ,again1 on the disappearance of the ice the second mass of till would be covered over in like manner by mud1 sand1 and gravel1 and so on1 while the eccentricity of the earth's orbit continued at a high value4 ,in this way we might have three1 four1 five1 or more masses of till separated by beds of sand and gravel4 ,it will be seen from ,table ,,iv4 of the eccentricity of the earth's orbit1 given in ,chapter ,,xix41 that the former half of that long succession of cold and warm periods1 known as the glacial epoch1 was much more severe than the latter half4 ,that is to say1 in the former half the accumulation of ice during the cold periods1 and its disappearance in polar regions during the warm periods1 would be greater than in the latter half4 ,it was probable that it was during the warm periods of the earlier part of the glacial epoch that the two buried channels of the ,midland valley were occupied by rivers1 and that it was during the latter and less severe part of the glacial epoch that these channels became filled up with that remarkable series of deposits which we have been considering4 ,other buried ,river ,channels4--,a good many examples of buried river channels have been found both in ,scotland and in ,england1 though none of them of so remarkable a character as the two occupying the valley of the ,forth and ,clyde ,canal which have been just described4 ,i may1 however1 briefly refer to one or two localities where some of these occur4 7#a47 ,an ancient buried river channel1 similar to the one extending from ,kilsyth to ,grangemouth1 exists in the coal-fields of ,durham1 and is known to miners in the district as the 8,wash40 ,its course was traced by ,mr4 ,nicholas ,wood1 ,f4,g4,s41 and ,mr4 ,e4 ,f4 ,boyd1 from ,durham to ,newcastle1 a distance of fourteen miles4#bhi ,it traverses1 after passing the city of ,durham1 a portion of the valley of the ,wear1 passes ,chester-le-,street1 and then follows the valley of the river ,team1 and terminates at the river ,tyne4 ,and what is remarkable1 it enters the ,tyne at a depth of #adj feet below the present level of the sea4 ,this curious hollow lies buried1 like the ,scottish one just alluded to1 under an enormous mass of drift1 and it is only through means of boring and other mining operations that its character has been revealed4 ,the bottom and sides of this channel everywhere bear evidence of long exposure to the abrading influence of water in motion2 the rocky bottom being smoothed1 furrowed1 and water-worn4 ,the river ,wear of the present day flows to the sea over the surface of the drift at an elevation of more than #ajj feet above this buried river-bed4 ,at the time that this channel was occupied by running water the sea-level must have been at least #adj feet lower than at present4 ,this old river evidently belongs to the same continental period as those of ,scotland4 7#b47 ,from extensive borings and excavations1 made at the docks of ,hull and ,grimsby1 it is found that the ancient bed of the ,humber is buried under more than #ajj feet of silt1 clay1 and gravel4 ,at ,hull the bottom of this buried trough was found to be #aaj feet below the sea-level4 ,and what is most interesting at both these places1 the remains of a submerged forest was found at a depth of from thirty to fifty feet below the sea-level4 ,in some places two forests were found divided by a bed of leafy clay from five to fifteen feet thick4 7#c47 ,in the valleys of ,norfolk we also find the same conditions exhibited4 ,the ancient bed of the ,yare and other rivers of this district enter the sea at a depth of more than #ajj feet below the present sea-level4 ,at ,yarmouth the surface was found #agj feet thick1 and the deep surface extends along the ,yare to beyond ,norwich4 ,buried forests are also found here similar to those on the ,humber4 ,it is probable that all our ,british rivers flow into the sea over their old buried channels1 except in cases where they may have changed their courses since the beginning of the glacial epoch4 7#d47 ,in the ,sanquhar ,coal ,basin1 at the foot of the ,kello ,water1 an old buried river course was found by ,mr4 ,b4 ,n4 ,peach4 ,it ran at right angles to the ,kello1 and was filled with boulder clay which cut off the coal2 but1 on driving the mine through the clay1 the coal was found in position on the other side4 7#e47 ,an old river course1 under the boulder clay1 is described by ,mr4 ,milne ,home in his memoir on the ,mid-,lothian coal-fields4 ,it has been traced out from ,niddry away in a ,n4,e4 direction by ,new ,craighall4 ,at ,niddry1 the hollow is about #ajj yards wide and between #fj and #gj feet deep4 ,it seems to deepen and widen as it approaches towards the sea1 for at ,new ,craighall it is about #bjj yards wide and #ig feet deep4 ,this old channel will probably enter the sea about ,musselburgh4 ,like the channels in the ,midland ,valley of ,scotland already described1 it is so completely filled up by drift that not a trace of it is to be seen on the surface4 ,and like these1 also1 it must have belonged to a period when the sea-level stood much lower than at present4 7#f47 ,at ,hailes' ,quarry1 near ,edinburgh1 there is to be seen a portion of an ancient watercourse under the boulder drift4 ,a short account of it was given by ,dr4 ,page in a paper read before the ,edinburgh ,geological ,society4#bij ,the superincumbent sandstone1 he says1 has been cut to a depth of #fj feet4 ,the width of the channel at the surface varies from #ab to #ad feet1 but gradually narrows to #b or #c feet at the bottom4 ,the sides and bottom are smoothed and polished1 and the whole is now filled with till and boulders4 7#g47 ,one of the most remarkable buried channels is that along the ,valley of ,strathmore1 supposed to be the ancient bed of the ,tay4 ,it extends from ,dunkeld1 the south of ,blairgowrie1 ,ruthven1 and ,forfar1 and enters the ,german ,ocean at ,lunan ,bay4 ,its length is about #cd miles4 8,no great river10 says ,sir ,charles ,lyell1 8follows this course1 but it is marked everywhere by lakes or ponds1 which afford shell-marl1 swamps1 and peat moss1 commonly surrounded by ridges of detritus from #ej to #gj feet high1 consisting in the lower part of till and boulders1 and in the upper of stratified gravels1 sand1 loam1 and clay1 in some instances curved or contorted40#bia 8,it evidently marks an ancient line1 by which1 first1 a great glacier descended from the mountains to the sea1 and by which1 secondly1 at a later period1 the principal water drainage of this country was effected40#bib 7#h47 ,a number of examples of ancient river courses1 underneath the boulder clay1 are detailed by ,professor ,geikie in his glacial drift of ,scotland4 ,some of the cases described by him have acquired additional interest from the fact of their bearing decided testimony to the existence of inter-glacial warm periods4 ,i shall briefly refer to a few of the cases described by him4 ,in driving a trial mine in a pit at ,chapelhall1 near ,airdrie1 the workmen came upon what they believed to be an old river course4 ,at the end of the trial mine the ironstone1 with its accompanying coal and fire-clay1 were cut off at an angle of about #bj by a stiff1 dark-coloured earth1 stuck full of angular pieces of white sandstone1 coal1 and shale1 with rounded pebbles of greenstone1 basalt1 quartz1 c4 ,above this lay a fine series of sand and clay beds4 ,above these stratified beds lay a depth of #ej or #fj feet of true boulder clay4 ,the channel ran in the direction of north-east and south-west4 ,mr4 ,russell1 of ,chapelhall1 informs ,professor ,geikie that another of the same kind1 a mile farther to the north-west1 had been traced in some of the pit workings4 8,it is clear10 says ,professor ,geikie1 8that whatever may be the true explanation of these channels and basins1 they unquestionably belong to the period of the boulder clay4 ,the ,chapelhall basin lies1 indeed1 in a hollow of the carboniferous rocks1 but its stratified sands and clays rest on an irregular floor of true till4 ,the old channel near the banks of the ,calder is likewise scooped out of sandstones and shales2 but it has a coating of boulder clay1 on which its finely-laminated sands and clays repose1 as if the channel itself had once been filled with boulder clay1 which was re-excavated to allow of the deposition of the stratified deposits4 ,in all cases1 a thick mantle of coarse1 tumultuous boulder clay buries the whole40#bic ,professor ,geikie found between the mouth of the ,pease ,burn and ,st4 ,abb's ,head1 ,berwickshire1 several ancient buried channels4 ,one at the ,menzie ,cleuch1 near ,redheugh ,shore1 was filled to the brim with boulder clay4 ,another1 the ,lumsden ,dean1 half a mile to the east of ,fast ,castle1 on the bank of the ,carmichael ,burn1 near the parish church of ,carmichael1--an old watercourse of the boulder clay period--is to be seen4 ,the valley of the ,mouse ,water he instances as a remarkable example4 ,one or two he found in ,ayrshire1 and also one on the banks of the ,lyne ,water1 a tributary of the ,tweed4 7#i47 ,in the valley of the ,clyde1 above ,hamilton1 several buried river channels have been observed4 ,they are thus described by ,mr4 ,james ,geikie3--#bid 8,in the ,wishaw district1 two deep1 winding troughs1 filled with sand and fine gravel1 have been traced over a considerable area in the coal workings4#bie ,these troughs form no feature at the surface1 but are entirely concealed below a thick covering of boulder clay4 ,they appear to be old stream courses1 and are in all probability the pre-glacial ravines of the ,calder ,water and the ,tillon ,burn4 ,the #8sand-dyke' that represents the pre-glacial course of the ,calder ,water runs for some distance parallel to the present course of the stream down to ,wishaw ,house1 where it is intersected by the ,calder1 and the deposits which choke it up are well seen in the steep wooded banks below the house and in the cliff on the opposite side4 ,it next strikes to south-east1 and is again well exposed on the road-side leading down from ,wishaw to the ,calder ,water4 ,from this point it has been traced underground1 more or less continuously1 as far as ,wishaw ,ironworks4 ,beyond this place the coal-seams sink to a greater depth1 and therefore cease to be intersected by the ancient ravine1 the course of which1 however1 may still be inferred from the evidence obtained during the sinking of shafts and trial borings4 ,in all probability it runs south1 and enters the old course of the ,clyde a little below ,cambusnethan ,house4 ,only a portion of the old ravine of the ,tillon ,burn is shown upon the ,map4 ,it is first met with in the coal-workings of ,cleland ,townhead 7,sheet #ca74 ,from this place it winds underground in a southerly direction until it is intersected by the present ,tillon ,burn1 a little north of ,glencleland 7,sheet #ca74 ,it now runs to south-west1 keeping parallel to the burn1 and crosses the valley of the ,calder just immediately above the mouth of the ,tillon4 ,from this point it can be traced in pit-shafts1 open-air sections1 borings1 and coal-workings1 by ,ravenscraig1 ,nether ,johnstone1 and ,robberhall ,belting1 on to the ,calder ,water below ,coursington ,bridge 7,sheet #ca74 ,it would thus appear that in pre-glacial times the ,calder and the ,tillon were independent streams1 and that since glacial times the ,calder ,water1 forsaking its pre-glacial course1 has cut its way across the intervening ground1 ploughing out deep ravines in the solid rocks1 until eventually it united with the ,tillon4 ,similar buried stream courses occur at other places4 ,thus1 at ,fairholme1 near ,larkhall1 as already mentioned 7par4 #id71 the pre-glacial course of the ,avon has been traced in pit-shafts and borings for some distance to the north4 ,another old course1 filled up with boulder clay1 is exposed in a burn near ,plotcock1 a mile south-west from ,millheugh2 and a similar pre-glacial ravine was met with in the cement-stone workings at ,calderwood4#bif ,indeed1 it might be said with truth that nearly all the rocky ravines through which the waters flow1 especially in the carboniferous areas1 are of post-glacial age--the pre-glacial courses lying concealed under masses of drift4 ,most frequently1 however1 the present courses of the streams are partly pre-glacial and partly post-glacial4 ,in the pre-glacial portions the streams flow through boulder clay1 in the post-glacial reaches their course1 as just mentioned1 is usually in rocky ravines4 ,the ,avon and the ,calder1 with their tributaries1 afford numerous illustrations of these phenomena40 ,the question naturally arises1 ,when were those channels scooped out8 ,to what geological period must those ancient rivers be referred8 ,it will not do to conclude that those channels must be pre-glacial simply because they contain boulder clay4 ,had the glacial epoch been one unbroken period of cold1 and the boulder clay one continuous formation1 then the fact of finding boulder clay in those channels would show that they were pre-glacial4 ,but when we find undoubted geological evidence of a warm condition of climate of long continuance1 during the severest part of the glacial epoch1 when the ice1 to a great extent1 must have disappeared1 and water began to flow as usual down our valleys1 all that can reasonably be inferred from the fact of finding till in those channels1 is that they must be older than the till they contain4 ,we cannot infer that they are older than all the till lying on the face of the country4 ,the probability1 however1 is1 that some of them are of pre-glacial and others of inter-glacial origin4 ,that many of these channels have been used as watercourses during the glacial epoch1 or rather during warm periods of that epoch1 is certain1 from the fact that they have been filled with boulder clay1 then re-excavated1 and finally filled up again with the clay4 ,,chapter ,,xxx4 ,,the ,,physical ,,cause ,,of ,,the ,,motion ,,of ,,glaciers4--,,theories ,,of ,,glacier-,,motion4 ,why the ,question of ,glacier-motion has been found to be so difficult4--,the ,regelation ,theory4--,it accounts for the ,continuity of a ,glacier1 but not for its ,motion4--,gravitation proved by ,canon ,moseley insufficient to shear the ,ice of a ,glacier4--,mr4 ,mathew's ,experiment4--,no ,parallel between the bending of an ,ice ,plank and the shearing of a ,glacier4--,mr4 ,ball's ,objection to ,canon ,moseley's ,experiment4--,canon ,moseley's ,method of determining the ,unit of ,shear4--,defect of ,method4--,motion of a ,glacier in some ,way dependent on ,heat4--,canon ,moseley's ,theory4--,objections to his ,theory4--,professor ,james ,thomson's ,theory4--,this ,theory fails to explain ,glacier-motion4--,de ,saussure and ,hopkins's 8,sliding0 ,theories4--,m4 ,charpentier's 8,dilatation0 ,theory4--,important ,element in the ,theory4 ,the cause of the motion of glaciers has proved to be one of the most difficult and perplexing questions within the whole domain of physics4 ,the main difficulty lies in reconciling the motion of the glacier with the physical properties of the ice4 ,a glacier moves down a valley very much in the same way as a river1 the motion being least at the sides and greatest at the centre1 and greater at the surface than at the bottom4 ,in a cross section scarcely two particles will be moving with the same velocity4 ,again1 a glacier accommodates itself to the inequalities of the channel in which it moves exactly as a semifluid or plastic substance would do4 ,so thoroughly does a glacier behave in the manner of a viscous or plastic body that ,professor ,forbes was induced to believe that viscosity was a property of the ice1 and that in virtue of this property it was enabled to move with a differential motion and accommodate itself to all the inequalities of its channel without losing its continuity just as a mass of mud or putty would do4 ,but experience proves that ice is a hard and brittle substance far more resembling glass than putty4 ,in fact it is one of the most brittle and unyielding substances in nature4 ,so unyielding is a glacier that it will snap in two before it will stretch to any perceptible extent4 ,this is proved by the fact that crevasses resulting from a strain on the glacier consist at first of a simple crack scarcely wide enough to admit the blade of a penknife4 ,all the effects which were considered to be due to the viscosity of the ice have been fully explained and accounted for on the principle of fracture and regelation discovered by ,faraday4 ,the principle of regelation explains why the ice moving with a differential motion and accommodating itself to the inequalities of its channel is yet enabled to retain its continuity1 but it does not account for the cause of glacier motion4 ,in fact it rather involves the question in deeper mystery than before4 ,for it is far more difficult to conceive how the particles of a hard and brittle solid like that of ice can move with a differential motion1 than it is to conceive how this may take place in the case of a soft and yielding substance4 ,the particles of ice have all to be displaced one over another and alongside each other1 and as those particles are rigidly fixed together this connection must be broken before the one can slide over the other4 ,shearing-force1 as ,canon ,moseley shows1 comes into play4 ,were ice a plastic substance there would not be much difficulty in understanding how the particles should move the one over the other1 but it is totally different when we conceive ice to be a solid and unyielding substance4 ,the difficulty in connection with glacier-motion is not to account for the continuity of the ice1 for the principle of regelation fully explains this1 but to show how it is that one particle succeeds in sliding over the over4 ,the principle of regelation1 instead of assisting to remove this difficulty1 increases it tenfold4 ,regelation does not explain the cause of glacier-motion1 but the reverse4 ,it rather tends to show that a glacier should not move4 ,what1 then1 is the cause of glacier-motion8 ,according to the regelation theory1 gravitation is the impelling cause4 ,but is gravitation sufficient to shear the ice in the manner in which it is actually done in a glacier8 ,i presume that few who have given much thought to the subject of glacier-motion have not had some slight misgivings in regard to the commonly received theory4 ,there are some facts which ,i never could harmonize with this theory4 ,for example1 boulder clay is a far looser substance than ice2 its shearing-force must be very much less than that of ice2 yet immense masses of boulder clay will lie immovable for ages on the slope of a hill so steep that one can hardly venture to climb it1 while a glacier will come crawling down a valley which by the eye we could hardly detect to be actually off the level4 ,again1 a glacier moves faster during the day than during the night1 and about twice as fast during summer as during winter4 ,professor ,forbes1 for example1 found that the ,glacier des ,bois near its lower extremity moved sometimes in ,december only #aae inches daily1 while during the month of ,july its rate of motion sometimes reached #eba inches per day4 ,why such a difference in the rate of motion between day and night1 summer and winter8 ,the glacier is not heavier during the day than it is during the night1 or during the summer than it is during the winter2 neither is the shearing-force of the great mass of the ice of a glacier sensibly less during day than night1 or during summer than winter2 for the temperature of the great mass of the ice does not sensibly vary with the seasons4 ,if this be the case1 then gravitation ought to be as able to shear the ice during the night as during the day1 or during the winter as during the summer4 ,at any rate1 if there should be any difference it ought to be but trifling4 ,it is true that1 owing to the melting of the ice1 the crevices of the glacier are more gorged with water during summer than winter2 and this1 as ,professor ,forbes maintains1#big may tend to make the glacier move faster during the former than the latter season4 ,but the advocates of the regelation theory cannot conclude1 with ,professor ,forbes1 that the water favours the motion of the glacier by making the ice more soft and plastic4 ,the melting of the ice1 according to the regelation theory1 cannot very materially aid the motion of the glacier4 ,the theory which has led to the general belief that the ice of a glacier is sheared by the force of gravity appears to be the following4 ,it is supposed that the only forces to which the motion of a glacier can be referred are gravitation and heat2 but as the great mass of a glacier remains constantly at the same uniform temperature it is concluded to be impossible that the motion of the glacier can be due to this cause1 and therefore of course it must be attributed to gravitation1 there being no other cause4 ,that gravitation is insufficient to shear the ice of a glacier has been clearly demonstrated by ,canon ,moseley4#bih ,he determined by experiment the amount of force required to shear one square inch of ice1 and found it to be about #ge lbs4 ,by a process of calculation which will be found detailed in the ,memoir referred to1 he demonstrated that to descend by its own weight at the rate at which ,professor ,tyndall observed the ice of the ,mer de ,glace to be descending at the ,tacul1 the unit of shearing force of the ice could not have been more than #acaica lbs4 ,consequently it will require a force more than #cd times the weight of the glacier to shear the ice and cause it to descend in the manner in which it is found to descend4 ,it is now six years since ,canon ,moseley's results were laid before the public1 and no one1 as far as ,i am aware1 has yet attempted to point out any serious defect in his mathematical treatment of the question4 ,seeing the great amount of interest manifested in the question of glacier-motion1 ,i think we are warranted to conclude that had the mathematical part of the memoir been inconclusive its defects would have been pointed out ere this time4 ,the question1 then1 hinges on whether the experimental data on which his calculations are based be correct4 ,or1 in other words1 is the unit of shear of ice as much as #ge lbs48 ,this part of ,mr4 ,moseley's researches has not passed unquestioned4 ,mr4 ,ball and ,mr4 ,mathews1 both of whom have had much experience among glaciers1 and have bestowed considerable attention on the subject of glacier-motion1 have objected to the accuracy of ,mr4 ,moseley's unit of shear4 ,i have carefully read the interesting memoirs of ,mr4 ,mathews and ,mr4 ,ball in reply to ,canon ,moseley1 but ,i am unable to perceive that anything which they have advanced materially affects his general conclusions as regards the commonly received theory4 ,mr4 ,mathews objects to ,canon ,moseley's experiments on the grounds that extraneous forces are brought to bear upon the substance submitted to operation1 and that conditions are thus introduced which do not obtain in the case of an actual glacier4 8,it would throw10 he says1 8great light upon our inquiry if we were to change this method of procedure and simply to observe the deportment of masses of ice under the influence of no external forces but the gravitation of their own particles40#bii ,a plank of ice six inches wide and #b inches in thickness was supported at each end by bearers six feet apart4 ,from the moment the plank was placed in position it began to sink1 and continued to do so until it touched the surface over which it was supported4 ,mr4 ,mathews remarks that with this property of ice1 viz41 its power to change its form under strains produced by its own gravitation1 combined with the sliding movement demonstrated by ,hopkins1 we have an adequate cause for glacier-motion4 ,mr4 ,mathews concludes from this experiment that the unit of shear in ice1 instead of being #ge lbs41 is less than #a lbs4 ,there is1 however1 no parallel between the bending of the ice-plank and the shearing of a glacier4 ,mr4 ,mathews' experiment appears to prove too much1 as will be seen from the following reply of ,canon ,moseley3-- 8,now ,i will10 he says1 8suggest to ,mr4 ,mathews a parallel experiment and a parallel explanation4 ,if a bar of wrought iron #a inch square and #bj feet long were supported at its extremities1 it would bend by its weight alone1 and would therefore shear4 ,now the weight of such a rod would be about #fg lbs4 ,according to ,mr4 ,mathews's explanation in the case of the ice-plank1 the unit of shear in wrought-iron should therefore be #fg lbs4 per square inch4 ,it is actually #ej1jjj lbs40#cjj ,whatever theory we may adopt as to the cause of the motion of glaciers1 the deflection of the plank in the way described by ,mr4 ,mathews follows as a necessary consequence4 ,although no weight was placed upon the plank1 it does not necessarily follow that the deflection was caused by the weight of the ice alone2 for1 according to ,canon ,moseley's own theory of the motion of glaciers by heat1 the plank ought to be deflected in the middle1 just as it was in ,mr4 ,mathews's experiment4 ,a solid body1 when exposed to variations of temperature1 will expand and contract transversely as well as longitudinally4 ,ice1 according to ,canon ,moseley's theory1 expands and contracts by heat4 ,then if the plank expands transversely1 the upper half of the plank must rise and the lower half descend4 ,but the side which rises has to perform work against gravity1 whereas the side which descends has work performed upon it by gravity2 consequently more of the plank will descend than rise1 and this will1 of course1 tend to lower or deflect the plank in the middle4 ,again1 when the plank contracts1 the lower half will rise and the upper half will descend2 but as gravitation1 in this case also1 favours the descending part and opposes the rising part1 more of the plank will descend than rise1 and consequently the plank will be lowered in the middle by contraction as well as by expansion4 ,thus1 as the plank changes its temperature1 it must1 according to ,mr4 ,moseley's theory1 descend or be deflected in the middle1 step by step--and this not by gravitation alone1 but chiefly by the motive power of heat4 ,i do not1 of course1 mean to assert that the descent of the plank was caused by heat2 but ,i assert that ,mr4 ,mathews's experiment does not necessarily prove 7and this is all that is required in the meantime7 that gravitation alone was the cause of the deflection of the plank4 ,neither does this experiment prove that the ice was deflected without shearing2 for although the weight of the plank was not sufficient to shear the ice1 as ,mr4 ,mathews1 ,i presume1 admits1 yet ,mr4 ,moseley would reply that the weight of the ice1 assisted by the motive power of heat1 was perfectly sufficient4 ,i shall now briefly refer to ,mr4 ,ball's principal objections to ,canon ,moseley's proof that a glacier cannot shear by its weight alone4 ,one of his chief objections is that ,mr4 ,moseley has assumed the ice to be homogeneous in structure1 and that pressures and tensions acting within it1 are not modified by the varying constitution of the mass4#cja ,although there is1 no doubt1 some force in this objection 7for we have probably good reason to believe that ice will shear1 for example1 more easily along certain planes than others71 still ,i can hardly think that ,canon ,moseley's main conclusion can ever be materially affected by this objection4 ,the main question is this1 ,can the ice of the glacier shear by its own weight in the way generally supposed8 ,now the shearing force of ice1 take it in whatever direction we may1 so enormously exceeds that required by ,mr4 ,moseley in order to allow a glacier to descend by its weight only1 that it is a matter of indifference whether ice be regarded as homogeneous in structure or not4 ,mr4 ,ball objects also to ,mr4 ,moseley's imaginary glacier lying on an even slope and in a uniform rectangular channel4 ,he thinks that an irregular channel and a variable slope would be more favourable to the descent of the ice4 ,but surely if the work by the weight of the ice be not equal to the work by the resistance in a glacier of uniform breadth and slope1 it must be much less so in the case of one of irregular shape and slope4 ,that a relative displacement of the particles of the ice is involved in the motion of a glacier1 is admitted1 of course1 by ,mr4 ,ball2 but he states that the amount of this displacement is but small1 and that it is effected with extreme slowness4 ,this may be the case2 but if the weight of the ice be not able to overcome the mutual cohesion of the particles1 then the weight of the ice cannot produce the required displacement1 however small it may be4 ,mr4 ,ball then objects to ,mr4 ,moseley's method of determining the unit of shear on this ground3--,the shearing of the ice in a glacier is effected with extreme slowness2 but the shearing in ,canon ,moseley's experiment was effected with rapidity2 and although it required #ge lbs4 to shear one square inch of surface in his experiment1 it does not follow that #ge lbs4 would be required to shear the ice if done in the slow manner in which it is effected in the glacier4 8,in short10 says ,mr4 ,ball1 8to ascertain the resistance opposed to very slow changes in the relative positions of the particles1 so slight as to be insensible at short distances1 ,mr4 ,moseley measures the resistance opposed to rapid disruption between contiguous portions of the same substance40 ,there is force in this objection2 and here we arrive at a really weak point in ,canon ,moseley's reasoning4 ,his experiments show that if we want to shear ice quickly a weight of nearly #abj lbs4 is required2 but if the thing is to be done more slowly1 #ge lbs4 will suffice4#cjb ,in short1 the number of pounds required to shear the ice depends1 to a large extent1 on the length of time that the weight is allowed to act2 the longer it is allowed to act1 the less will be the weight required to perform the work4 8,i am curious to know10 says ,mr4 ,mathews1 when referring to this point1 8what weight would have sheared the ice if a day had been allowed for its operation40 ,i do not know what would have been the weight required to shear the ice in ,mr4 ,moseley's experiments had a day been allowed2 but ,i feel pretty confident that1 should the ice remain unmelted1 and sufficient time be allowed1 shearing would be produced without the application of any weight whatever4 ,there are no weights placed upon a glacier to make it move1 and yet the ice of the glacier shears4 ,if the shearing is effected by weight1 the only weight applied is the weight of the ice2 and if the weight of the ice makes the ice shear in the glacier1 why may it not do the same thing in the experiment8 ,whatever may be the cause which displaces the particles of the ice in a glacier1 they1 as a matter of fact1 are displaced without any weight being applied beyond that of the ice itself2 and if so1 why may not the particles of the ice in the experiment be also displaced without the application of weights8 ,allow the ice of the glacier to take its own time and its own way1 and the particles will move over each other without the aid of external weights1 whatever may be the cause of this2 well1 then1 allow the ice in the experiment to take its own time and its own way1 and it will probably do the same thing4 ,there is something here unsatisfactory4 ,if1 by the unit of shear1 be meant the pressure in pounds that must be applied to the ice to break the connection of one square inch of two surfaces frozen together and cause the one to slip over the other1 then the amount of pressure required to do this will depend upon the time you allow for the thing being done4 ,if the thing is to be done rapidly1 as in some of ,mr4 ,moseley's experiments1 it will take1 as he has shown1 a pressure of about #abj lbs42 but if the thing has to be done more slowly1 as in some other of his experiments1 #ge lbs4 will suffice4 ,and if sufficient time be allowed1 as in the case of glaciers1 the thing may be done without any weight whatever being applied to the ice1 and1 of course1 ,mr4 ,moseley's argument1 that a glacier cannot descend by its weight alone1 falls to the ground4 ,but if1 by the unit of shear1 be meant not the weight or pressure necessary to shear the ice1 but the amount of work required to shear a square inch of surface in a given time or at a given rate1 then he might be able to show that in the case of a glacier 7say the ,mer de ,glace7 the work of all the resistances which are opposed to its descent at the rate at which it is descending is greater than the work of its weight1 and that consequently there must be some cause1 in addition to the weight1 urging the glacier forward4 ,but then he would have no right to affirm that the glacier would not descend by its weight only2 all that he could affirm would simply be that it could not descend by its weight alone at the rate at which it is descending4 ,mr4 ,moseley's unit of shear1 however1 is not the amount of work performed in shearing a square inch of ice in a given time1 but the amount of weight or pressure requiring to be applied to the ice to shear a square inch4 ,but this amount of pressure depends upon the length of time that the pressure is applied4 ,here lies the difficulty in determining what amount of pressure is to be taken as the real unit4 ,and here also lies the radical defect in ,canon ,moseley's result4 ,time as well as pressure enters as an element into the process4 ,the key to the explanation of this curious circumstance will1 ,i think1 be found in the fact that the rate at which a glacier descends depends in some way or other upon the amount of heat that the ice is receiving4 ,this fact shows that heat has something to do in the shearing of the ice of the glacier4 ,but in the communication of heat to the ice time necessarily enters as an element4 ,there are two different ways in which heat may be conceived to aid in shearing the ice3 7#a47 we may conceive that heat acts as a force along with gravitation in producing displacement of the particles of the ice2 or 7#b47 we may conceive that heat does not act as a force in pushing the particles over each other1 but that it assists the shearing processes by diminishing the cohesion of the particles of the ice1 and thus allowing gravitation to produce displacement4 ,the former is the function attributed to heat in ,canon ,moseley's theory of glacier-motion2 the latter is the function attributed to heat in the theory of glacier-motion which ,i ventured to advance some time ago4#cjc ,it results1 therefore1 from ,canon ,moseley's own theory1 that the longer the time that is allowed for the pressure to shear the ice1 the less will be the pressure required2 for1 according to his theory1 a very large proportion of the displacement is produced by the motive power of heat entering the ice2 and1 as it follows of course1 other things being equal1 the longer the time during which the heat is allowed to act1 the greater will be the proportionate amount of displacement produced by the heat2 consequently the less will require to be done by the weight applied4 ,in the case of the glacier1 ,mr4 ,moseley concludes that at least thirty or forty times as much work is done by the motive power of heat in the way of shearing the ice as is done by mere pressure or weight4 ,then1 if sufficient time be allowed1 why may not far more be done by heat in shearing the ice in his experiment than by the weight applied8 ,in this case how is he to know how much of the shearing is effected by the heat and how much by the weight8 ,if the greater part of the shearing of the ice in the case of a glacier is produced1 not by pressure1 but by the heat which necessarily enters the ice1 it would be inconceivable that in his experiments the heat entering the ice should not produce1 at least to some extent1 a similar effect4 ,and if a portion of the displacement of the particles is produced by heat1 then the weight which is applied cannot be regarded as the measure of the force employed in the displacement1 any more than it could be inferred that the weight of the glacier is the measure of the force employed in the shearing of it4 ,if the weight is not the entire force employed in shearing1 but only a part of the force1 then the weight cannot1 as in ,mr4 ,moseley's experiment1 be taken as the measure of the force4 ,how1 then1 are we to determine what is the amount of force required to shear ice8 in other words1 how is the unit of shear to be determined8 ,if we are to measure the unit of shear by the weight required to produce displacement of the particles of the ice1 we must make sure that the displacement is wholly effected by the weight4 ,we must be certain that heat does not enter as an element in the process4 ,but if time be allowed to elapse during the experiment1 we can never be certain that heat has not been at work4 ,it is impossible to prevent heat entering the ice4 ,we may keep the ice at a constant temperature1 but this would not prevent heat from entering the ice and producing molecular work4 ,true that1 according to ,moseley's theory of glacier-motion1 if the temperature of the ice be not permitted to vary1 then no displacement of the particles can take place from the influence of heat2 but according to the molecular theory of glacier-motion1 which will shortly be considered1 heat will aid the displacement of the particles whether the temperature be kept constant or not4 ,in short1 it is absolutely impossible in our experiments to be certain that heat is not in some way or other concerned in the displacement of the particles of the ice4 ,but we can shorten the time1 and thus make sure that the amount of heat entering the ice during the experiments is too small to affect materially the result4 ,we cannot in this case say that all the displacement has been effected by the weight applied to the ice1 but we can say that so little has been done by heat that1 practically1 we may regard it as all done by the weight4 ,this consideration1 ,i trust1 shows that the unit of shear adopted by ,canon ,moseley in his calculations is not too large4 ,for if in half an hour1 after all the work that may have been done by heat1 a pressure of #ge lbs4 is still required to displace the particles of one square inch1 it is perfectly evident that if no work had been done by heat during that time1 the force required to produce the displacement could not have been less than #ge lbs4 ,it might have been more than that2 but it could not have been less4 ,be this1 however1 as it may1 in determining the unit of shear we cannot be permitted to prolong the experiment for any considerable length of time1 because the weight under which the ice might then shear could not be taken as the measure of the force which is required to shear ice4 ,by prolonging the experiment we might possibly get a unit smaller than that required by ,canon ,moseley for a glacier to descend by its own weight4 ,but it would be just as much begging the whole question at issue to assume that1 because the ice sheared under such a weight1 a glacier might descend by its weight alone1 as it would be to assume that1 because a glacier shears without a weight being placed upon it1 the glacier descends by its weight alone4 ,but why not determine the unit of shear of ice in the same way as we would the unit of shear of any other solid substance1 such1 as iron1 stone1 or wood8 ,if the shearing force of ice be determined in this manner1 it will be found to be by far too great to allow of the ice shearing by its weight alone4 ,we shall be obliged to admit either that the ice of the glacier does not shear 7in the ordinary sense of the term71 or if it does shear1 that there must1 as ,canon ,moseley concludes1 be some other force in addition to the weight of the ice urging the glacier forward4 ,the fact that the rate of descent of a glacier depends upon the amount of heat which it receives1 proves that heat must be regarded either as a cause or as a necessary condition of its motion2 what1 then1 is the necessary relationship between heat and the motion of the glacier8 ,if heat is to be regarded as a cause1 in what way does the heat produce motion8 ,i shall now briefly refer to one or two theories which have been advanced on the subject4 ,let us consider first that of ,canon ,moseley4 ,canon ,moseley's ,theory4--,he found1 from observations and experiments1 that sheets of lead1 placed upon an inclined plane1 when subjected to variations of temperature1 tend to descend even when the slope is far less than that which would enable it to slide down under the influence of gravitation4 ,the cause of the descent he shows to be this4 ,when the temperature of the sheet is raised1 it expands1 and1 in expanding1 its upper portion moves up the slope1 and its lower portion down the slope2 but as gravitation opposes the upward and favours the downward motion1 more of the sheet moves down than up1 and consequently the centre of gravity of the sheet is slightly lowered4 ,again1 when the sheet is cooled1 it contracts1 and in contracting the upper portion moves downwards and the lower portion upwards1 and here again1 for the same reason1 more of the sheet moves downwards than upwards4 ,consequently1 at every change of temperature there is a slight displacement of the sheet downwards4 8,now a theory of the descent of glaciers10 says ,canon ,moseley1 8which ,i have ventured to propose myself1 is that they descend1 as the lead in this experiment does1 by reason of the passage into them and the withdrawal of the sun's rays1 and that the dilatation and contraction of the ice so produced is the proximate cause of their descent1 as it is of that of the lead40#cjd ,the fundamental condition in ,mr4 ,moseley's theory of the descent of solid bodies on an incline1 is1 not that heat should maintain these bodies at a high temperature1 but that the temperature should vary4 ,the rate of descent is proportionate1 not simply to the amount of heat received1 but to the extent and frequency of the variations of temperature4 ,as a proof that glaciers are subjected to great variations of temperature1 he adduces the following3--8,all alpine travellers10 he says1 8from ,de ,saussure to ,forbes and ,tyndall1 have borne testimony to the intensity of the solar radiation on the surfaces of glaciers4 #8,i scarcely ever1' says ,forbes1 #8remember to have found the sun more piercing than at the ,jardin4' ,this heat passes abruptly into a state of intense cold when any part of the glacier falls into shadow by an alteration of the position of the sun1 or even by the passing over it of a cloud40#cje ,mr4 ,moseley is here narrating simply what the traveller feels1 and not what the glacier experiences4 ,the traveller is subjected to great variations of temperature2 but there is no proof from this that the glacier experiences any changes of temperature4 ,it is rather because the temperature of the glacier is not affected by the sun's heat that the traveller is so much chilled when the sun's rays are cut off4 ,the sun shines down with piercing rays and the traveller is scorched2 the glacier melts on the surface1 but it still remains 8cold as ice40 ,the sun passes behind a cloud or disappears behind a neighbouring hill2 the scorching rays are then withdrawn1 and the traveller is now subjected to radiation on every side from surfaces at the freezing-point4 ,it is also a necessary condition in ,mr4 ,moseley's theory that the heat should pass easily into and out of the glacier2 for unless this were the case sudden changes of temperature could produce little or no effect on the great mass of the glacier4 ,how1 then1 is it possible that during the heat of summer the temperature of the glacier could vary much8 ,during that season1 in the lower valleys at least1 everything1 with the exception of the glacier1 is above the freezing-point2 consequently when the glacier goes into the shade there is nothing to lower the ice below the freezing-point2 and as the sun's rays do not raise the temperature of the ice above the freezing-point1 the temperature of the glacier must therefore remain unaltered during that season4 ,it therefore follows that1 instead of a glacier moving more rapidly during the middle of summer than during the middle of winter1 it should1 according to ,moseley's theory1 have no motion whatever during summer4 ,the following1 written fifteen years ago by ,professor ,forbes on this very point1 is most conclusive3--8,but how stands the fact8 ,mr4 ,moseley quotes from ,de ,saussure the following daily ranges of the temperature of the air in the month of ,july at the ,col du ,gant and at ,chamouni1 between which points the glacier lies3 ,at the ,col du ,gant #dbeg ,raumur4 ,at ,chamouni #ajjib ,and he assumes #8the same mean daily variation of temperature to obtain throughout the length' and depth8 #8of the ,glacier du ,gant which ,de ,saussure observed in ,july at the ,col du ,gant4' ,but between what limits does the temperature of the air oscillate8 ,we find1 by referring to the third volume of ,de ,saussure's #8,travels1' that the mean temperature of the coldest hour 7#d ,a4,m47 during his stay at the ,col du ,gant was #ccjc ,fahrenheit1 and of the warmest 7#b ,p4,m47 #dbfa ,f4 ,so that even upon that exposed ridge1 between #b1jjj and #c1jjj feet above where the glacier can be properly said to commence1 the air does not1 on an average of the month of ,july1 reach the freezing-point at any hour of the night4 ,consequently the range of temperature attributed to the glacier is between limits absolutely incapable of effecting the expansion of the ice in the smallest degree40#cjf ,again1 during winter1 as ,mr4 ,ball remarks1 the glacier is completely covered with snow and thus protected both from the influence of cold and of heat1 so that there can be nothing either to raise the temperature of the ice above the freezing-point or to bring it below that point2 and consequently the glacier ought to remain immovable during that season also4 8,there can be no doubt1 therefore10 ,mr4 ,moseley states1 8that the rays of the sun1 which in those alpine regions are of such remarkable intensity1 find their way into the depths of the glacier4 ,they are a power1 and there is no such thing as the loss of power4 ,the mechanical work which is their equivalent1 and into which they are converted when received into the substance of a solid body1 accumulates and stores itself up in the ice under the form of what we call elastic force or tendency to dilate1 until it becomes sufficient to produce actual dilatation of the ice in the direction in which the resistance is weakest1 and by its withdrawal to produce contraction4 ,from this expansion and contraction follows of necessity the descent of the glacier40#cjg ,when the temperature of the ice is below the freezing-point1 the rays which are absorbed will1 no doubt1 produce dilatation2 but during summer1 when the ice is not below the freezing-point1 no dilatation can possibly take place4 ,all physicists1 so far as ,i am aware1 agree that the rays that are then absorbed go to melt the ice1 and not to expand it4 ,but to this ,mr4 ,moseley replied as follows3--8,to this there is the obvious answer that radiant heat does find its way into ice as a matter of common observation1 and that it does not melt it except at its surface4 ,blocks of ice may be seen in the windows of ice-shops with the sun shining full upon them1 and melting nowhere but on their surfaces4 ,and the experiment of the ice-lens shows that heat may stream through ice in abundance 7of which a portion is necessarily stopped in the passage7 without melting it1 except on its surface40 ,but what evidence is there to conclude that if there is no melting of the ice in the interior of the lens there is a portion of the rays 8necessarily stopped0 in the interior8 ,it will not do to assume a point so much opposed to all that we know of the physical properties of ice as this really is4 ,it is absolutely essential to ,mr4 ,moseley's theory of the motion of glaciers1 during summer at least1 that ice should continue to expand after it reaches the melting-point2 and it has therefore to be shown that such is the case2 or it need not be wondered at that we cannot accept his theory1 because it demands the adoption of a conclusion contrary to all our previous conceptions4 ,but1 as a matter of fact1 it is not strictly true that when rays pass through a piece of ice there is no melting of the ice in the interior4 ,experiments made by ,professor ,tyndall show the contrary4#cjh ,there is1 however1 one fortunate circumstance connected with ,canon ,moseley's theory4 ,it is this3 its truth can be easily tested by direct experiment4 ,the ice1 according to this theory1 descends not simply in virtue of heat1 but in virtue of change of temperature4 ,try1 then1 ,hopkins's famous experiment1 but keep the ice at a constant temperature2 then1 according to ,moseley's theory1 the ice will not descend4 ,let it be observed1 however1 that although the ice under this condition should descend 7as there is little doubt but it would71 it would show that ,mr4 ,moseley's theory of the descent of glaciers is incorrect1 still it would not in the least degree affect the conclusions which he lately arrived at in regard to the generally received theory of glacier-motion4 ,it would not prove that the ice sheared1 in the way generally supposed1 by its weight only4 ,it might be the heat1 after all1 entering the ice1 which accounted for its descent1 although gravitation 7the weight of the ice7 might be the impelling cause4 ,according to this theory1 the glacier1 like the sheet of lead1 must expand and contract as one entire mass1 and it is difficult to conceive how this could account for the differential motion of the particles of the ice4 ,professor ,james ,thomson's ,theory4--,it was discovered by this physicist that the freezing-point of water is lowered by pressure4 ,the extent of the lowering is equal to #jjge centigrade for every atmosphere of pressure4 ,as glacier ice is generally about the melting-point1 it follows that when enormous pressure is brought to bear upon any given point of a glacier a melting of the ice at that particular spot will take place in consequence of the lowering of the melting-point4 ,the melting of the ice will1 of course1 tend to favour the descent of the glacier1 but ,i can hardly think the liquefaction produced by pressure can account for the motion of glaciers4 ,it will help to explain the giving way of the ice at particular points subjected to great pressure1 but ,i am unable to comprehend how it can account for the general descent of the glacier4 ,conceive a rectangular glacier of uniform breadth and thickness1 and lying upon an even slope4 ,in such a glacier the pressure at each particular point would remain constant1 for there would be no reason why it should be greater at one time than at another4 ,suppose the glacier to be #ejj feet in thickness2 the ice at the lower surface of the glacier1 owing to pressure1 would have its melting-point permanently lowered one-tenth of a degree centigrade below that of the upper surface2 but the ice at the lower surface would not1 on this account1 be in the fluid state4 ,it would simply be ice at a slightly lower temperature4 ,true1 when pressure is exerted the ice melts in consequence of the lowering of the melting-point1 but in the case under consideration there would1 properly speaking1 be no exertion of pressure1 but a constant statical pressure resulting from the weight of the ice4 ,but this statical condition of pressure would not produce fluidity any more than a statical condition of pressure would produce heat1 and consequently motion could not take place as a result of fluidity4 ,in short1 motion itself is required to produce the fluidity4 ,i need not here wait to consider the sliding theories of ,de ,saussure and ,hopkins1 as they are now almost universally admitted to be inadequate to explain the phenomena of glacier-motion1 seeing that they do not account for the displacement of the particles of the ice over one another4 ,according to the dilatation theory of ,m4 ,charpentier1 a glacier is impelled by the force exerted by water freezing in the fissures of the ice4 ,a glacier he considers is full of fissures into which water is being constantly infiltrated1 and when the temperature of the air sinks below the freezing-point it converts the water into ice4 ,the water1 in passing into ice1 expands1 and in expanding tends to impel the glacier in the direction of least resistance4 ,this theory1 although it does not explain glacier-motion1 as has been clearly shown by ,professor ,j4 ,d4 ,forbes1 nevertheless contains one important element which1 as we shall see1 must enter into the true explanation4 ,the element to which ,i refer is the expansive force exerted on the glacier by water freezing4 ,,chapter ,,xxxi4 ,,the ,,physical ,,cause ,,of ,,the ,,motion ,,of ,,glaciers4--,,the ,,molecular ,,theory4 ,present ,state of the ,question4--,heat necessary to the ,motion of a ,glacier4--,ice does not shear in the ,solid ,state4--,motion of a ,glacier molecular4--,how ,heat is transmitted through ,ice4--,momentary ,loss of ,shearing ,force4--,the ,rationale of ,regelation4--,the ,origin of 8,crevasses40--,effects of ,tension4--,modification of ,theory4--,fluid ,molecules crystallize in ,interstices4--,expansive ,force of crystallizing ,molecules a ,cause of ,motion4--,internal molecular ,pressure the chief ,moving ,power4--,how ,ice can excavate a ,rock ,basin4--,how ,ice can ascend a ,slope4--,how deep ,river ,valleys are striated across4--,a remarkable ,example in the ,valley of the ,tay4--,how ,boulders can be carried from a lower to a higher ,level4 ,the condition which the perplexing question of the cause of the descent of glaciers has now reached seems to be something like the following4 ,the ice of a glacier is not in a soft and plastic state1 but is solid1 hard1 brittle1 and unyielding4 ,it nevertheless behaves in some respects in a manner very like what a soft and plastic substance would do if placed in similar circumstances1 inasmuch as it accommodates itself to all the inequalities of the channel in which it moves4 ,the ice of the glacier1 though hard and solid1 moves with a differential motion2 the particles of the ice are displaced over each other1 or1 in other words1 the ice shears as it descends4 ,it had been concluded that the mere weight of the glacier is sufficient to shear the ice4 ,canon ,moseley has investigated this point1 and shown that it is not4 ,he has found that for a glacier to shear in the way that it is supposed to do1 it would require a force some thirty or forty times as great as the weight of the glacier4 ,consequently1 for the glacier to descend1 a force in addition to that of gravitation is required4 ,what1 then1 is this force8 ,it is found that the rate at which the glacier descends depends upon the amount of heat which it is receiving4 ,this shows that the motion of the glacier is in some way or other dependent upon heat4 ,is heat1 then1 the force we are in search of8 ,the answer to this1 of course1 is1 since heat is a force necessarily required1 we have no right to assume any other till we see whether or not heat will suffice4 ,in what way1 then1 does heat aid gravitation in the descent of the glacier8 ,in what way does heat assist gravitation in the shearing of the ice8 ,there are two ways whereby we may conceive the thing to be done3 the heat may assist gravitation to shear1 by pressing the ice forward1 or it may assist gravitation by diminishing the cohesion of the particles1 and thus allow gravitation to produce motion which it otherwise could not produce4 ,every attempt which has yet been made to explain how heat can act as a force in pushing the ice forward1 has failed4 ,the fact that heat cannot expand the ice of the glacier may be regarded as a sufficient proof that it does not act as a force impelling the glacier forward2 and we are thus obliged to turn our attention to the other conception1 viz41 that heat assists gravitation to shear the ice1 not by direct pressure1 but by diminishing the cohesive force of the particles1 so as to enable gravitation to push the one past the other4 ,but how is this done8 ,does heat diminish the cohesion by acting as an expansive force in separating the particles8 ,heat cannot do this1 because it cannot expand the ice of a glacier2 and besides1 were it to do this1 it would destroy the solid and firm character of the ice1 and the ice of the glacier would not then1 as a mass1 possess the great amount of shearing-force which observation and experiment show that it does4 ,in short it is because the particles are so firmly fixed together at the time the glacier is descending1 that we are obliged to call in the aid of some other force in addition to the weight of the glacier to shear the ice4 ,heat does not cause displacement of the particles by making the ice soft and plastic2 for we know that the ice of the glacier is not soft and plastic1 but hard and brittle4 ,the shearing-force of the ice of the moving glacier is found to be by at least from thirty to forty times too great to permit of the ice being sheared by the mere force of gravitation2 how1 then1 is it that gravitation1 without the direct assistance of any other force1 can manage to shear the ice8 ,or to put the question under another form3 heat does not reduce the shearing-force of the ice of a glacier to something like #acaic lb4 per square inch of surface1 the unit required by ,mr4 ,moseley to enable a glacier to shear by its weight2 the shearing-force of the ice1 notwithstanding all the heat received1 still remains at about #ge lbs42 how1 then1 can the glacier shear without any other force than its own weight pushing it forward8 ,this is the fundamental question2 and the true answer to it must reveal the mystery of glacier-motion4 ,we are compelled in the present state of the problem to admit that glaciers do descend with a differential motion without any other force than their own weight pushing them forward2 and yet the shearing-force of the ice is actually found to be thirty or forty times the maximum that would permit of the glacier shearing by its weight only4 ,the explanation of this apparent paradox will remove all our difficulties in reference to the cause of the descent of glaciers4 ,there seems to be but one explanation 7and it is a very obvious one71 viz4 that the motion of the glacier is molecular4 ,the ice descends molecule by molecule4 ,the ice of a glacier is in the hard crystalline state1 but it does not descend in this state4 ,gravitation is a constantly acting force2 if a particle of the ice lose its shearing-force1 though but for the moment1 it will descend by its weight alone4 ,but a particle of the ice will lose its shearing-force for a moment if the particle loses its crystalline state for the moment4 ,the passage of heat through ice1 whether by conduction or by radiation1 in all probability is a molecular process2 that is1 the form of energy termed heat is transmitted from molecule to molecule of the ice4 ,a particle takes the energy from its neighbour ,a on the one side and hands it over to its neighbour ,b on the opposite side4 ,but the particle must be in a different state at the moment it is in possession of the energy from what it was before it received it from ,a1 and from what it will be after it has handed it over to ,b4 ,before it became possessed of the energy1 it was in the crystalline state--it was ice2 and after it loses possession of the energy it will be ice2 but at the moment that it is in possession of the passing energy is it in the crystalline or icy state8 ,if we assume that it is not1 but that in becoming possessed of the energy1 it loses its crystalline form and for the moment becomes water1 all our difficulties regarding the cause of the motion of glaciers are removed4 ,we know that the ice of a glacier in the mass cannot become possessed of energy in the form of heat without becoming fluid2 if it can be shown that the same thing holds true of the ice particle1 we have the key to the mystery of glacier-motion4 ,a moment's reflection will suffice to convince any one that if the glacier ice in the mass cannot receive energy in the form of heat without melting1 the same must hold true of the ice particles1 for it is inconceivable that the ice in the mass could melt and yet the ice particles themselves remain in the solid state4 ,it is the solidity of the particles which constitutes the solidity of the mass4 ,if the particles lose their solid form the mass loses its solid form1 for the mass has no other solidity than that which is possessed by the particles4 ,the correctness of the conclusion1 that the weight of the ice is not a sufficient cause1 depends upon the truth of a certain element taken for granted in the reasoning1 viz4 that the shearing-force of the molecules of the ice remains constant4 ,if this force remains constant1 then ,canon ,moseley's conclusion is undoubtedly correct1 but not otherwise2 for if a molecule should lose its shearing-force1 though it were but for a moment1 if no obstacle stood in front of the molecule1 it would descend in virtue of its weight4 ,the fact that the shearing-force of a mass of ice is found to be constant does not prove that the same is the case in regard to the individual molecules4 ,if we take a mass of molecules in the aggregate1 the shearing-force of the mass taken thus collectively may remain absolutely constant1 while at the same time each individual molecule may be suffering repeated momentary losses of shearing-force4 ,this is so obvious as to require no further elucidation4 ,the whole matter1 therefore1 resolves itself into this one question1 as to whether or not the shearing-force of a crystalline molecule of ice remains constant4 ,in the case of ordinary solid bodies we have no reason to conclude that the shearing-force of the molecules ever disappears1 but in regard to ice it is very different4 ,if we analyze the process by which heat is conducted through ice1 we shall find that we have reason to believe that while a molecule of ice is in the act of transmitting the energy received 7say from a fire71 it loses for the moment its shearing-force if the temperature of the ice be not under #cb ,f4 ,if we apply heat to the end of a bar of iron1 the molecules at the surface of the end have their temperatures raised4 ,molecule ,a at the surface1 whose temperature has been raised1 instantly commences to transfer to ,b a portion of the energy received4 ,the tendency of this process is to lower the temperature of ,a and raise that of ,b4 ,b then1 with its temperature raised1 begins to transfer the energy to ,c4 ,the result here is the same2 ,b tends to fall in temperature1 and ,c to rise4 ,this process goes on from molecule to molecule until the opposite end of the bar is reached4 ,here in this case the energy or heat applied to the end of the bar is transmitted from molecule to molecule under the form of heat or temperature4 ,the energy applied to the bar does not change its character2 it passes right along from molecule to molecule under the form of heat or temperature4 ,but the nature of the process must be wholly different if the transferrence takes place through a bar of ice at the temperature of #cb4 ,suppose we apply the heat of the fire to the end of the bar of ice at #cb1 the molecules of the ice cannot possibly have their temperatures raised in the least degree4 ,how1 then1 can molecule ,a take on1 under the form of heat1 the energy received from the fire without being heated or having its temperature raised8 ,the thing is impossible4 ,the energy of the fire must appear in ,a under a different form from that of heat4 ,the same process of reasoning is equally applicable to ,b4 ,the molecule ,b cannot accept of the energy from ,a under the form of heat2 it must receive it under some other form4 ,the same must hold equally true of all the other molecules till we reach the opposite end of the bar of ice4 ,and yet1 strange to say1 the last molecule transmits in the form of heat its energy to the objects beyond2 for we find that the heat applied to one side of a piece of ice will affect the thermal pile on the opposite side4 ,the question is susceptible of a clear and definite answer4 ,when heat is applied to a molecule of ice at #cb1 the heat applied does not raise the temperature of the molecule1 it is consumed in work against the cohesive forces binding the atoms or particles together into the crystalline form4 ,the energy then must exist in the dissolved crystalline molecule1 under the statical form of an affinity--crystalline affinity1 or whatever else we may call it4 ,that is to say1 the energy then exists in the particles as a power or tendency to rush together again into the crystalline form1 and the moment they are allowed to do so they give out the energy that was expended upon them in their separation4 ,this energy1 when it is thus given out again1 assumes the dynamical form of heat2 in other words1 the molecule gives out heat in the act of freezing4 ,the heat thus given out may be employed to melt the next adjoining molecule4 ,the ice-molecules take on energy from a heated body by melting4 ,that peculiar form of motion or energy called heat disappears in forcing the particles of the crystalline molecule separate1 and for the time being exists in the form of a tendency in the separated particles to come together again into the crystalline form4 ,but it must be observed that although the crystalline molecule1 when it is acting as a conductor1 takes on energy under this form from the heated body1 it only exists in the molecule under such a form during the moment of transmission2 that is to say1 the molecule is melted1 but only for the moment4 ,when ,b accepts of the energy from ,a1 the molecule ,a instantly assumes the crystalline form4 ,b is now melted2 and when ,c accepts of the energy from ,b1 then ,b also in turn assumes the solid state4 ,this process goes on from molecule to molecule till the energy is transmitted through to the opposite side and the ice is left in its original solid state4 ,this1 as will be shown in the ,appendix1 is the rationale of ,faraday's property of regelation4 ,this is no mere theory or hypothesis2 it is a necessary consequence from known facts4 ,we know that ice at #cb cannot take on energy from a heated body without melting2 and we know also equally well that a slab of ice at #cb1 notwithstanding this1 still1 as a mass1 retains its solid state while the heat is being transmitted through it4 ,this proves that every molecule resumes its crystalline form the moment after the energy is transferred to the adjoining molecule4 ,this point being established1 every difficulty regarding the descent of the glacier entirely disappears2 for a molecule the moment that it assumes the fluid state is completely freed from shearing-force1 and can descend by virtue of its own weight without any impediment4 ,all that the molecule requires is simply room or space to advance in4 ,if the molecule were in absolute contact with the adjoining molecule below1 it would not descend unless it could push that molecule before it1 which it probably would not be able to do4 ,but the molecule actually has room in which to advance2 for in passing from the solid to the liquid state its volume is diminished by about #a_/aj1 and it consequently can descend4 ,true1 when it again assumes the solid form it will regain its former volume2 but the question is1 will it go back to its old position8 ,if we examine the matter thoroughly we shall find that it cannot4 ,if there were only this one molecule affected by the heat1 this molecule would certainly not descend2 but all the molecules are similarly affected1 although not all at the same moment of time4 ,let us observe what takes place1 say1 at the lower end of the glacier4 ,the molecule ,a at the lower end1 say1 of the surface1 receives heat from the sun's rays2 it melts1 and in melting not only loses its shearing-force and descends by its own weight1 but it contracts also4 ,b immediately above it is now1 so far as ,a is concerned1 at liberty to descend1 and will do so the moment that it assumes the liquid state4 ,a by this time has become solid1 and again fixed by shearing-force2 but it is not fixed in its old position1 but a little below where it was before4 ,if ,b has not already passed into the fluid state in consequence of heat derived from the sun1 the additional supply which it will receive from the solidifying of ,a will melt it4 ,the moment that ,b becomes fluid it will descend till it reaches ,a4 ,b then is solidified a little below its former position4 ,the same process of reasoning is in a similar manner applicable to every molecule of the glacier4 ,each molecule of the glacier consequently descends step by step as it melts and solidifies1 and hence the glacier1 considered as a mass1 is in a state of constant motion downwards4 ,the fact observed by ,professor ,tyndall that there are certain planes in the ice along which melting takes place more readily than others will perhaps favour the descent of the glacier4 ,we have in this theory a satisfactory explanation of the origin of 8crevasses0 in glaciers4 ,take1 for example1 the transverse crevasses formed at the point where an increase in the inclination of the glacier takes place4 ,suppose a change of inclination from1 say1 #d to #h in the bed of the glacier4 ,the molecules on the slope of #h will descend more rapidly than those above on the slope of #d4 ,a state of tension will therefore be induced at the point where the change of inclination occurs4 ,the ice on the slope of #h will tend to pull after it the mass of the glacier moving more slowly on the slope above4 ,the pull being continued1 the glacier will snap asunder the moment that the cohesion of the ice is overcome4 ,the greater the change of inclination is1 the more readily will the rupture of the ice take place4 ,every species of crevasse can be explained upon the same principle4#cji ,this theory explains also why a glacier moves at a greater rate during summer than during winter2 for as the supply of heat to the glacier is greater during the former season than during the latter1 the molecules will pass oftener into the liquid state4 ,as regards the denuding power of glaciers1 ,i may observe that1 though a glacier descends molecule by molecule1 it will grind the rocky bed over which it moves as effectually as it would do did it slide down in a rigid mass in the way generally supposed2 for the grinding-effect is produced not by the ice of the glacier1 but by the stones1 sand1 and other materials forced along under it4 ,but if all the resistances opposing the descent of a glacier1 internal and external1 are overcome by the mere weight of the ice alone1 it can be proved that in the case of one descending with a given velocity the amount of work performed in forcing the grinding materials lying under the ice forward must be as great1 supposing the motion of the ice to be molecular in the way ,i have explained1 as it would be supposing the ice descended in the manner generally supposed4 ,of course1 a glacier could not descend by means of its weight as rapidly in the latter case as in the former2 for1 in fact1 as ,canon ,moseley has shown1 it would not in the latter case descend at all2 but assuming for the sake of argument the rate of descent in both cases to be the same1 the conclusion ,i have stated would follow4 ,consequently whatever denuding effects may have been attributed to the glacier1 according to the ordinary theory1 must be equally attributable to it according to the present explanation4 ,this theory1 however1 explains1 what has always hitherto excited astonishment1 viz41 why a glacier can descend a slope almost horizontal1 or why the ice can move off the face of a continent perfectly level4 ,this is the form in which my explanation was first stated about half-a-dozen years ago4#caj ,there is1 however another element which must be taken into account4 ,it is one which will help to cast additional light on some obscure points connected with glacial phenomena4 ,ice is evidently not absolutely solid throughout4 ,it is composed of crystalline particles1 which1 though in contact with one another1 are1 however1 not packed together so as to occupy the least possible space1 and1 even though they were1 the particles would not fit so closely together as to exclude interstices4 ,the crystalline particles are1 however1 united to one another at special points determined by their polarity1 and on this account they require more space2 and this in all probability is the reason1 as ,professor ,tyndall remarks1 why ice1 volume for volume1 is less dense than water4 8,they 7the molecules7 like the magnets10 says ,professor ,tyndall1 8are acted upon by two distinct forces2 for a time1 while the liquid is being cooled1 they approach each other1 in obedience to their general attraction for each other4 ,but at a certain point new forces1 some attractive some repulsive1 emanating from special points of the molecules1 come into play4 ,the attracted points close up1 the repelled points retreat4 ,thus the molecules turn and rearrange themselves1 demanding as they do so more space1 and overcoming all ordinary resistance by the energy of their demand4 ,this1 in general terms1 is an explanation of the expansion of water in solidifying40#caa ,it will be obvious1 then1 that when a crystalline molecule melts1 it will not merely descend in the manner already described1 but capillary attraction will cause it to flow into the interstices between the adjoining molecules4 ,the moment that it parts with the heat received1 it will of course resolidify1 as has been shown1 but it will not solidify so as to fit the cavity which it occupied when in the fluid state4 ,for the liquid molecule in solidifying assumes the crystalline form1 and of course there will be a definite proportion between the length1 breadth1 and thickness of the crystal2 consequently it will always happen that the interstice in which it solidifies will be too narrow to contain it4 ,the result will be that the fluid molecule in passing into the crystalline form will press the two adjoining molecules aside in order to make sufficient room for itself between them1 and this it will do1 no matter what amount of space it may possess in all other directions4 ,the crystal will not form to suit the cavity1 the cavity must be made to contain the crystal4 ,and what holds true of one molecule1 holds true of every molecule which melts and resolidifies4 ,this process is therefore going on incessantly in every part of the glacier1 and in proportion to the amount of heat which the glacier is receiving4 ,this internal molecular pressure1 resulting from the solidifying of the fluid molecules in the interstices of the ice1 acts on the mass of the ice as an expansive force1 tending to cause the glacier to widen out laterally in all directions4 ,conceive a mass of ice lying on a flat horizontal surface1 and receiving heat on its upper surface1 say from the sun2 as the heat passes downwards through the mass1 the molecules1 acting as conductors1 melt and resolidify4 ,each fluid molecule solidifies in an interstice1 which has to be widened in order to contain it4 ,the pressure thus exerted by the continual resolidifying of the molecules will cause the mass to widen out laterally1 and of course as the mass widens out it will grow thinner and thinner if it does not receive fresh acquisition on its surface4 ,in the case of a glacier lying in a valley1 motion1 however1 will only take place in one direction4 ,the sides of the valley prevent the glacier from widening2 and as gravitation opposes the motion of the ice up1 and favours its motion down the valley1 the path of least resistance to molecular pressure will always be down the slope1 and consequently in this direction molecular displacement will take place4 ,molecular pressure will therefore produce motion in the same direction as that of gravity4 ,in other words1 it will tend to cause the glacier to descend the valley4 ,the lateral expansion of the ice from internal molecular pressure explains in a clear and satisfactory manner how rock-basins may be excavated by means of land-ice4 ,it also removes the difficulties which have been felt in accounting for the ascent of ice up a steep slope4 ,the main difficulty besetting the theory of the excavation of rock-basins by ice is to explain how the ice after entering the basin manages to get out again--how the ice at the bottom is made to ascend the sloping sides of the basin4 ,pressure acting from behind1 it has been argued by some2 but if the basin be deep and its sides steep1 this will simply cause the ice lying above the level of the basin to move forward over the surface of the mass filling it4 ,this conclusion is1 however1 incorrect4 ,the ice filling the basin and the glacier overlying it are united in one solid mass1 so that the latter cannot move over the former without shearing2 and although the resistance to motion offered by the sloping sides of the basin may be much greater than the resistance to shear1 still the ice will be slowly dragged out of the basin4 ,however1 in order to obviate this objection to which ,i refer1 the advocates of the glacial origin of lake-basins point out that the length of those basins in proportion to their depth is so great that the slope up which the ice has to pass is in reality but small4 ,this no doubt is true of lake-basins in general1 but it does not hold universally true4 ,but the theory does not demand that an ice-formed lake-basin cannot have steep sides4 ,we have incontestable evidence that ice will pass up a steep slope2 and1 if ice can pass up a steep slope1 it can excavate a basin with a steep slope4 ,that ice will pass up a steep slope is proved by the fact that comparatively deep and narrow river valleys are often found striated across1 while hills which stood directly in the path of the ice of the glacial epoch are sometimes found striated upwards from their base to their summit4 ,some striking examples of stri running up hill are given by ,professor ,geikie in his 8,glacial ,drift of ,scotland40 ,i have myself seen a slope striated upwards so steep that one could not climb it4 ,a very good example of a river valley striated across came under my observation during the past summer4 ,the ,tay1 between ,cargill and ,stanley 7in the centre of the broad plain of ,strathmore71 has excavated1 through the ,old ,red ,sandstone1 a channel between #bjj and #cjj feet in depth4 ,the channel here runs at right angles to the path taken during the glacial epoch by the great mass of ice coming from the ,north-west ,highlands4 ,at a short distance below ,cargill1 the trap rising out of the bed of the river is beautifully ice-grooved and striated1 at right angles to the stream4 ,a trap-dyke1 several miles in length1 crosses the river about a mile above ,stanley1 forming a rapid1 known as the ,linn of ,campsie4 ,this dyke is moutonne and striated from near the ,linn up the sloping bank to the level of the surrounding country1 showing that the ice must have ascended a gradient of one in seven to a height of #cjj feet4 ,from what has been already stated in reference to the resolidifying of the molecules in the interstices of the ice1 the application of the molecular theory to the explanation of the effects under consideration will no doubt be apparent4 ,take the case of the passage of the ice-sheet across a river valley4 ,as the upper surface of the ice-sheet is constantly receiving heat from the sun and the air in contact with it1 there is consequently a transferrence of heat from above downwards to the bottom of the sheet4 ,this transferrence of heat from molecule to molecule is accompanied by the melting and resolidifying of the successive molecules in the manner already detailed4 ,as the fluid molecules tend to flow into adjoining interstices before solidifying and assuming the crystalline form1 the interstices of the ice at the bottom of the valley are constantly being filled by fluid molecules from above4 ,these molecules no sooner enter the interstices than they pass into the crystalline form1 and become1 of course1 separated from their neighbours by fresh interstices1 which new interstices become filled by fluid molecules1 which1 in turn1 crystallize1 forming fresh interstices1 and so on4 ,the ice at the bottom of the valley1 so long as this process continues1 is constantly receiving fresh additions from above4 ,the ice must therefore expand laterally to make room for these additions1 which it must do unless the resistance to lateral expansion be greater than the force exerted by the molecules in crystallizing4 ,but a resistance sufficient to do this must be enormous4 ,the ice at the bottom of the valley cannot expand laterally without passing up the sloping sides4 ,in expanding it will take the path of least resistance1 but the path of least resistance will always be on the side of the valley towards which the general mass of the ice above is flowing4 ,it has been shown 7,chapter ,,xxvii47 that the ice passing over ,strathmore must have been over #b1jjj feet in thickness4 ,an ice-sheet #b1jjj feet in thickness exerts on its bed a pressure of upwards of #ea tons per square foot4 ,when we reflect that ice under so enormous a pressure1 with grinding materials lying underneath1 was forced by irresistible molecular energy up an incline of one in seven1 it is not at all surprising that the hard trap should be ground down and striated4 ,we can also understand how the softer portions of the rocky surface over which the ice moved should have been excavated into hollow basins4 ,we have also an explanation of the transport of boulders from a lower to a higher level1 for if ice can move from a lower to a higher level1 it of course can carry boulders along with it4 ,the bearing which the foregoing considerations of the manner in which heat is transmitted through ice have on the question of the cause of regelation will be considered in the ,appendix4 ,,appendix4 ,i4 ,,opinions ,,expressed ,,previous ,,to #ahfd ,,regarding ,,the ,,influence ,,of ,,the ,,eccentricity ,,of ,,the ,,earth',s ,,orbit ,,on ,,climate4#cab ,m4 ,,de ,,mairan4 ,m4 de ,mairan1 in an article in the ,memoirs of the ,royal ,academy of ,france#cac 8,on the ,general ,cause of ,heat in ,summer and ,cold in ,winter1 in so far as depends on the internal and permanent ,heat of the ,earth10 makes the following remarks on the influence of the difference of distance of the sun in apogee and perigee3-- 8,cet lment est constant pour les deux solstices2 tandis que les autres 7height of the sun and obliquity of his rays7 y varient raison des latitudes locales2 et il y a encore cela de particulier1 qu'il tend diminuer la valeur de notre t1 et augmenter celle de notre hiver dans l'hmisphre boral o nous sommes1 et tout au contraire dans l'austral4 ,remarquons cependant que de ces mmes distances1 qui constituent ce troisime lment1 nat en partie un autre principe de chaleur tout oppos1 et qui semble devoir temprer les effets du prcdent2 savoir1 la lenteur et la vitesse rciproques du mouvement annuel apparent1 en vertu duquel et du rel qui s'y mle1 le soleil emploie #h jours de plus parcourir les signes septentrionaux4 ,c'est--dire1 que le soleil passe #ahf jours dans notre hmisphre1 et seulement #agh dans l'hmisphre oppos4 ,ce qui1 en gnral1 ne peut manquer de rpandre un pen plus de chaleur sur l't du premier1 et un peu moins sur son hiver40 ,,mr4 ,,richard ,,kirwan4 8pinus1#cad reasoning on astronomical principles1 attributes the inferior temperature of the southern hemisphere to the shorter abode of the sun in the southern tropic1 shorter by seven days1 which produces a difference of fourteen days in favour of the northern hemisphere1 during which more heat is accumulated1 and hence he infers that the temperature of the northern hemisphere is to that of the southern1 as #ahie to #agee1 or as #ad to #ac40--,trans4 of the ,royal ,irish ,academy1 vol4 viii41 p4 #dag4 #ahjb4 ,,sir ,,charles ,,lyell4 8,before the amount of difference between the temperature of the two hemispheres was ascertained1 it was referred by astronomers to the acceleration of the earth's motion in its perihelion2 in consequence of which the spring and summer of the southern hemisphere are shorter by nearly eight days than those seasons north of the equator4 ,a sensible effect is probably produced by this source of disturbance1 but it is quite inadequate to explain the whole phenomena4 ,it is1 however1 of importance to the geologist to bear in mind that in consequence of the precession of the equinoxes1 the two hemispheres receive alternately1 each for a period of upwards of #aj1jjj years1 a greater share of solar light and heat4 ,this cause may sometimes tend to counterbalance inequalities resulting from other circumstances of a far more influential nature2 but1 on the other hand1 it must sometimes tend to increase the extreme of deviation1 which certain combinations of causes produce at distant epochs40--,principles1 ,first ,edition1 #ahcj1 p4 #aaj1 vol4 i4 ,,sir ,,john ,f4 ,,herschel1 ,,bart4 ,the following1 in so far as it relates to the effects of eccentricity1 is a copy of ,sir ,john ,herschel's memoir1 8,on the ,astronomical ,causes which may influence ,geological ,phenomena10 read before the ,geological ,society1 ,dec4 #aeth1 #ahcj4--,trans4 ,geol4 ,soc41 vol4 iii41 p4 #bic1 ,second ,series3-- 8444 ,let us next consider the changes arising in the orbit of the earth itself about the sun1 from the disturbing action of the planets4 ,in so doing it will be obviously unnecessary to consider the effect produced on the solar tides1 to which the above reasoning applies much more forcibly than in the case of the lunar4 ,it is1 therefore1 only the variations in the supply of light and heat received from the sun that we have now to consider4 8,geometers having demonstrated the absolute invariability of the mean distance of the earth from the sun1 it would seem to follow that the mean annual supply of light and heat derived from that luminary would be alike invariable2 but a closer consideration of the subject will show that this would not be a legitimate conclusion1 but that1 on the contrary1 the mean amount of solar radiation is dependent on the eccentricity of the orbit1 and therefore liable to variation4 ,without going at present into any geometrical investigations1 it will be sufficient for the purpose here to state it as a theorem1 of which any one may easily satisfy himself by no very abstruse geometrical reasoning1 that #8the eccentricity of the orbit varying1 the total quantity of heat received by the earth from the sun in one revolution is inversely proportional to the minor axis of the orbit4' ,now since the major axis is1 as above observed1 invariable1 and therefore1 of course1 the absolute length of the year1 it will follow that the mean annual average of heat will also be in the same inverse ratio of the minor axis2 and thus we see that the very circumstance which on a cursory view we should have regarded as demonstrative of the constancy of our supply of solar heat1 forms an essential link in the chain of strict reasoning by which its variability is proved4 8,the eccentricity of the earth's orbits is actually diminishing1 and has been so for ages1 beyond the records of history4 ,in consequence1 the ellipse is in a state of approach to a circle1 and its minor axis being1 therefore1 on the increase1 the annual average of solar radiation is actually on the decrease4 8,so far this is in accordance with the testimony of geological evidence1 which indicates a general refrigeration of climate2 but when we come to consider the amount of diminution which the eccentricity must be supposed to have undergone to render an account of the variation which has taken place1 we have to consider that1 in the first place1 a great diminution of the eccentricity is required to produce any sensible increase of the minor axis4 ,this is a purely geometrical conclusion1 and is best shown by the following table3-- ,eccentricity4 ,minor ,axis4 ,reciprocal or ,ratio of ,heat received4 #jjj #ajjj #ajjj #jje #jiii #ajjb #jaj #jiie #ajje #jae #jihi #ajaa #jbj #jihj #ajba #jbe #jifh #ajcb #jcj #jied #ajdh ,by this it appears that a variation of the eccentricity of the orbit from the circular form to that of an ellipse1 having an eccentricity of one-fourth of the major axis1 would produce only a variation of #c per cent4 on the mean annual amount of solar radiation1 and this variation takes in the whole range of the planetary eccentricities1 from that of ,pallas and ,juno downwards4 8,i am not aware that the limit of increase of the eccentricity of the earth's orbit has ever been determined4 ,that it has a limit has been satisfactorily proved2 but the celebrated theorem of ,laplace1 which is usually cited as demonstrating that none of the planetary orbits can ever deviate materially from the circular form1 leads to no such conclusion1 except in the case of the great preponderant planets ,jupiter and ,saturn1 while for anything that theorem proves to the contrary1 the orbit of the earth may become elliptic to any amount4 8,in the absence of calculations which though practicable have1 ,i believe1 never been made1#cae and would be no slight undertaking1 we may assume that eccentricities which exist in the orbits of planets1 both interior and exterior to that of the earth1 may possibly have been attained1 and may be attained again by that of the earth itself4 ,it is clear that such eccentricities existing they cannot be incompatible with the stability of the system generally1 and that1 therefore1 the question of the possibility of such an amount in the particular case of the earth's orbit will depend on the particular data belonging to that case1 and can only be determined by executing the calculations alluded to1 having regard to the simultaneous effects of at least the four most influential planets1 ,venus1 ,mars1 ,jupiter1 and ,saturn1 not only on the orbit of the earth1 but on those of each other4 ,the principles of this calculation are detailed in the article of ,laplace's work cited4 ,but before entering on a work of so much labour1 it is quite necessary to inquire what prospect of advantage there is to induce any one to undertake it4 8,now it certainly at first sight seems clear that a variation of #c per cent4 only in the mean annual amount of solar radiation1 and that arising from an extreme supposition1 does not hold out such a prospect4 ,yet it might be argued that the effects of the sun's heat is to maintain the temperature of the earth's surface at its actual mean height1 not above the zero of ,fahrenheit's or any other thermometer1 but above the temperature of the celestial spaces1 out of the reach of the sun's influence1 and what that temperature is may be a matter of much discussion4 ,m4 ,fourier has considered it as demonstrated that it is not greatly inferior to that of the polar regions of our own globe1 but the grounds of this decision appear to me open to considerable objection4#caf ,if those regions be really void of matter1 their temperature can only arise1 according to ,m4 ,fourier's own view of the subject1 from the radiation of the stars4 ,it ought1 therefore1 to be as much inferior to that due to solar radiation1 as the light of a starlight night is to that of the brightest noon day1 in other words it should be very nearly a total privation of heat--almost the absolute zero respecting which so much difference of opinion exists1 some placing it at #a1jjj1 some at #e1jjj of ,fahrenheit below the freezing-point1 and some still lower1 in which case a single unit per cent4 in the mean annual amount of radiation would suffice to produce a change of climate fully commensurate to the demands of geologists4#cag 8,without attempting1 however1 to enter further into the perplexing difficulties in which this point is involved1 which are far greater than appear on a cursory view1 let us next consider1 not the mean1 but the extreme effects which a variation in the eccentricity of the earth's orbit may be expected to produce in the summer and winter climates in particular regions of its surface1 and under the influence of circumstances favouring a difference of effect4 ,and here1 if ,i mistake not1 it will appear that an amount of variation1 which we need not hesitate to admit 7at least1 provisionally7 as a possible one1 may be productive of considerable diversity of climate1 and may operate during great periods of time either to mitigate or to exaggerate the difference of winter and summer temperatures1 so as to produce alternately1 in the same latitude of either hemisphere1 a perpetual spring1 or the extreme vicissitudes of a burning summer and a rigorous winter4 8,to show this1 let us at once take the extreme case of an orbit as eccentric as that of ,juno or ,pallas1 in which the greatest and least distances of the sun are to each other as #e to #c1 and consequently the radiations at those distances as #be to #i1 or very nearly as #c to #a4 ,to conceive what would be the extreme effects of this great variation of the heat received at different periods of the year1 let us first imagine in our latitude the place of the perigee of the sun to coincide with the summer solstice4 ,in that case1 the difference between the summer and winter temperature would be exaggerated in the same degree as if three suns were placed side by side in the heavens in the former season and only one in the latter1 which would produce a climate perfectly intolerable4 ,on the other hand1 were the perigee situated in the winter solstice our three suns would combine to warm us in the winter1 and would afford such an excess of winter radiation as would probably more than counteract the effect of short days and oblique sunshine1 and throw the summer season into the winter months4 8,the actual diminution of the eccentricity is so slow1 that the transition from a state of the orbit such as we have assumed to the present nearly circular figure would occupy upwards of #fjj1jjj years1 supposing it uniformly changeable--this1 of course1 would not be the case2 when near the maximum1 however1 it would vary slower still1 so that at that point it is evident a period of #aj1jjj years would elapse without any perceptible change in the state of the data of the case we are considering4 8,now this adopting the very ingenious idea of ,mr4 ,lyell#cah would suffice1 by reason of the combined effect of the precession of the equinoxes and the motion of the apsides of the orbit itself1 to transfer the perigee from the summer to the winter solstice1 and thus to produce a transition from the one to the other species of climate in a period sufficiently great to give room for a material change in the botanical character of country4 8,the supposition above made is an extreme1 but it is not demonstrated to be an impossible one1 and should even an approach to such a state of things be possible1 the same consequences1 in a mitigated degree1 would follow4 ,but if1 on executing the calculations1 it should appear that the limits of the eccentricity of the earth's orbit are really narrow1 and if1 on a full discussion of the very difficult and delicate point of the actual effect of solar radiation1 it should appear that the mean1 as well as the extreme1 temperature of our climates would not be materially affected1--it will be at least satisfactory to know that the causes of the phenomena in question are to be sought elsewhere than in the relations of our planet to the system to which it belongs1 since there does not appear to exist any other conceivable connections between these relations and the facts of geology than those we have enumerated1 the obliquity of the ecliptic being1 as we know1 confined within too narrow limits for its variation to have any sensible influence40--,j4 ,f4 ,w4 ,herschel4 ,the influence which this paper might have had on the question as to whether eccentricity may be regarded as a cause of changes in geological climate appears to have been completely neutralized by the following1 which appeared shortly afterwards both in his 8,treatise0 and 8,outlines of ,astronomy10 showing evidently that he had changed his mind on the subject4 8,it appears1 therefore1 from what has been shown1 the supplies of heat received from the sun will be equal in the two segments1 in whatever direction the line ,,ptq be drawn4 ,they will1 indeed1 be described in unequal times3 that in which the perihelion ,a lies in a shorter1 and the other in a longer1 in proportion to their unequal area2 but the greater proximity of the sun in the smaller segment compensates exactly for its more rapid description1 and thus an equilibrium of heat is1 as it were1 maintained4 8,were it not for this the eccentricity of the orbit would materially influence the transition of seasons4 ,the fluctuation of distance amounts to nearly #a_/cjth of the mean quantity1 and1 consequently1 the fluctuation of the sun's direct heating power to double this1 or #a_/aeth of the whole4444 ,were it not for the compensation we have just described1 the effect would be to exaggerate the difference of summer and winter in the southern hemisphere1 and to moderate it in the northern2 thus producing a more violent alternation of climate in the one hemisphere and an approach to perpetual spring in the other4 ,as it is1 however1 no such inequality subsists1 but an equal and impartial distribution of heat and light is accorded to both40--8,treatise of ,astronomy10 ,cabinet ,cyclopdia1 #cae2 ,outlines of ,astronomy1 #cfh4 8,the fact of a great change in the general climate of large tracts of the globe1 if not of the whole earth1 and of a diminution of general temperature1 having been recognised by geologists1 from their examination of the remains of animals and vegetables of former ages enclosed in the strata1 various causes for such diminution of temperature have been assigned4444 ,it is evident that the mean temperature of the whole surface of the globe1 in so far as it is maintained by the action of the sun at a higher degree than it would have were the sun extinguished1 must depend on the mean quantity of the sun's rays which it receives1 or1 which comes to the same thing1 on the total quantity received in a given invariable time2 and the length of the year being unchangeable in all the fluctuations of the planetary system1 it follows that the total annual amount of solar radiation will determine1 cteris paribus1 the general climate of the earth4 ,now1 it is not difficult to show that this amount is inversely proportional to the minor axis of the ellipse described by the earth about the sun1 regarded as slowly variable2 and that1 therefore1 the major axis remaining1 as we know it to be1 constant1 and the orbit being actually in a state of approach to a circle1 and consequently the minor axis being on the increase1 the mean annual amount of solar radiation received by the whole earth must be actually on the decrease4 ,we have here1 therefore1 an evident real cause of sufficient universality1 and acting in the right direction1 to account for the phenomenon4 ,its adequacy is another consideration40#cai--;,discourse on the ,study of ,natural ,philosophy1 pp4 #adeadg 7#ahcj74 ,,sir ,,charles ,,lyell1 ,,bart4 8,astronomical ,causes of ,fluctuations in ,climate4--,sir ,john ,herschel has lately inquired1 whether there are any astronomical causes which may offer a possible explanation of the difference between the actual climate of the earth's surface1 and those which formerly appear to have prevailed4 ,he has entered upon this subject1 he says1 #8impressed with the magnificence of that view of geological revolutions1 which regards them rather as regular and necessary effects of great and general causes1 than as resulting from a series of convulsions and catastrophes1 regulated by no laws1 and reducible to no fixed principles4' ,geometers1 he adds1 have demonstrated the absolute invariability of the mean distance of the earth from the sun2 whence it would seem to follow that the mean annual supply of light and heat derived from that luminary would be alike invariable2 but a closer consideration of the subject will show that this would not be a legitimate conclusion1 but that1 on the contrary1 the mean amount of solar radiation is dependent on the eccentricity of the earth's orbit1 and1 therefore1 liable to variation4 8,now1 the eccentricity of the orbit1 he continues1 is actually diminishing1 and has been so for ages beyond the records of history4 ,in consequence1 the ellipse is in a state of approach to a circle1 and the annual average of solar heat radiated to the earth is actually on the decrease4 ,so far1 this is in accordance with geological evidence1 which indicates a general refrigeration of climate2 but the question remains1 whether the amount of diminution which the eccentricity may have ever undergone can be supposed sufficient to account for any sensible refrigeration4#cbj ,the calculations necessary to determine this point1 though practicable1 have never yet been made1 and would be extremely laborious2 for they must embrace all the perturbations which the most influential planets1 ,venus1 ,mars1 ,jupiter1 and ,saturn1 would cause in the earth's orbit and in each other's movements round the sun4 8,the problem is also very complicated1 inasmuch as it depends not merely on the ellipticity of the earth's orbit1 but on the assumed temperature of the celestial spaces beyond the earth's atmosphere2 a matter still open to discussion1 and on which ,m4 ,fourier and ,sir ,j4 ,herschel have arrived at very different opinions4 ,but if1 says ,herschel1 we suppose an extreme case1 as if the earth's orbit should ever become as eccentric as that of the planet ,juno or ,pallas1 a great change of climate might be conceived to result1 the winter and summer temperatures being sometimes mitigated and at others exaggerated1 in the same latitudes4 8,it is much to be desired that the calculations alluded to were executed1 as even if they should demonstrate1 as ,m4 ,arago thinks highly probable1 that the mean of solar radiation can never be materially affected by irregularities in the earth's motion1 it would still be satisfactory to ascertain the point40--,principles of ,geology1 ,ninth ,edition1 #ahec1 p4 #abg4 ,m4 ,,arago4 8,can the variations which certain astronomical elements undergo sensibly modify terrestrial climates8 8,the sun is not always equally distant from the earth4 ,at this time its least distance is observed in the first days of ,january1 and the greatest1 six months after1 or in the first days of ,july4 ,but1 on the other hand1 a time will come when the minimum will occur in ,july1 and the maximum in ,january4 ,here1 then1 this interesting question presents itself1--,should a summer such as those we now have1 in which the maximum corresponds to the solar distance1 differ sensibly1 from a summer with which the minimum of this distance should coincide8 8,at first sight every one probably would answer in the affirmative2 for1 between the maximum and the minimum of the sun's distance from the earth there is a remarkable difference1 a difference in round numbers of a thirtieth of the whole4 ,let1 however1 the consideration of the velocities be introduced into the problem1 elements which cannot fairly be neglected1 and the result will be on the side opposite to that we originally imagined4 8,the part of the orbit where the sun is found nearest the earth1 is1 at the same time1 the point where the luminary moves most rapidly along4 ,the demi-orbit1 or1 in other words1 the #ahj comprehended betwixt the two equinoxes of spring-time and autumn1 will then be traversed in the least possible time1 when1 in moving from the one of the extremities of this arc to the other1 the sun shall pass1 near the middle of this course of six months1 at the point of the smallest distance4 ,to resume--the hypothesis we have just adopted would give1 on account of the lesser distance1 a spring-time and summer hotter than they are in our days2 but on account of the greater rapidity1 the sum of the two seasons would be shorter by about seven days4 ,thus1 then1 all things considered1 the compensation is mathematically exact4 ,after this it is superfluous to add1 that the point of the sun's orbit corresponding to the earth's least distance changes very gradually2 and that since the most distant periods1 the luminary has always passed by this point1 either at the end of autumn or beginning of winter4 8,we have thus seen that the changes which take place in the position of the solar orbit1 have no power in modifying the climate of our globe4 ,we may now inquire1 if it be the same concerning the variations which this orbit experiences in its form4444 8,herschel1 who has recently been occupying himself with this problem1 in the hope of discovering the explanation of several geological phenomena1 allows that the succession of ages might bring the eccentricity of the terrestrial orbit to the proportion of that of the planet ,pallas1 that is to say1 to be the #be_/ajj of a semi-greater axis4 ,it is exceedingly improbable that in these periodical changes the eccentricity of our orbit should ever experience such enormous variations1 and even then these twenty-five hundredth parts 7#be_/ajj71 would not augment the mean annual solar radiation except by about one hundredth part 7#a_/ajj74 ,to repeat1 an eccentricity of #be_/ajj would not alter in any appreciated manner the mean thermometrical state of the globe4444 8,the changes of the form1 and of the position1 of the terrestrial orbit are mathematically inoperative1 or1 at most1 their influence is so minute that it is not indicated by the most delicate instruments4 ,for the explanation of the changes of climates1 then1 there only remains to us either the local circumstances1 or some alteration in the heating or illuminating power of the sun4 ,but of these two causes1 we may continue to reject the last4 ,and thus1 in fact1 all the changes would come to be attributed to agricultural operations1 to the clearing of plains and mountains from wood1 the draining of morasses1 c4 8,thus1 at one swoop1 to confine1 the whole earth1 the variations of climates1 past and future1 within the limits of the naturally very narrow influence which the labour of man can effect1 would be a meteorological result of the very last importance40--pp4 #bbabbd1 ,memoir on the 8,thermometrical ,state of the ,terrestrial ,globe10 in the ,edinburgh ,new ,philosophical ,journal1 vol4 xvi41 #ahcd4 ,,baron ,,humboldt4 8,the question10 he says1 8has been raised as to whether the increasing value of this ellipticity is capable during thousands of years of modifying to any considerable extent the temperature of the earth1 in reference to the daily and annual quantity and distribution of heat8 ,whether a partial solution of the great geological problem of the imbedding of tropical vegetable and animal remains in the now cold zones may not be found in these astronomical causes proceeding regularly in accordance with eternal laws8444 ,it might at the first glance be supposed that the occurrence of the perihelion at an opposite time of the year 7instead of the winter1 as1 is now the case1 in summer7 must necessarily produce great climatic variations2 but1 on the above supposition1 the sun will no longer remain seven days longer in the northern hemisphere2 no longer1 as is now the case1 traverse that part of the ecliptic from the autumnal equinox to the vernal equinox1 in a space of time which is one week shorter than that in which it traverses the other half of its orbit from the vernal to the autumnal equinox4 8,the difference of temperature which is considered as the consequence to be apprehended from the turning of the major axis1 will on the whole disappear1 principally from the circumstance that the point of our planet's orbit in which it is nearest to the sun is at the same time always that over which it passes with the greatest velocity4444 8,as the altered position of the major axis is capable of exerting only a very slight influence upon the temperature of the earth2 so likewise the limit of the probable changes in the elliptical form of the earth's orbit are1 according to ,arago and ,poisson1 so narrow that these changes could only very slightly modify the climates of the individual zones1 and that in very long periods40#cba--;,cosmos1 vol4 iv41 pp4 #deh1 #dei4 ,bohn's ,edition4 #aheb4 ,,sir ,,henry ,t4 ,,de ,,la ,,beche4 8,mr4 ,herschel1 viewing this subject with the eye of an astronomer1 considers that a diminution of the surface-temperature might arise from a change in ellipticity of the earth's orbit1 which1 though slowly1 gradually becomes more circular4 ,no calculations having yet been made as to the probable amount of decreased temperature from this cause1 it can at present be only considered as a possible explanation of those geological phenomena which point to considerable alterations in climates40--,geological ,manual4 ,third ,edition4 #ahcc4 p4 #h4 ,,professor ,,phillips4 8,temperature of the ,globe4--,influence of the ,sun4--,no proposition is more certain than the fundamental dependence of the temperature of the surface of the globe on the solar influence4 8,it is1 therefore1 very important for geologists to inquire whether this be variable or constant2 whether the amount of solar heat communicated to the earth is and has always been the same in every annual period1 or what latitude the laws of planetary movements permit in this respect4 8,sir ,john ,herschel has examined this question in a satisfactory manner1 in a paper read to the ,geological ,society of ,london4 ,the total amount of solar radiation which determines the general climate of the earth1 the year being of invariable length1 is inversely proportional to the minor axis of the ellipse described by the earth about the sun1 regarded as slowly variable2 the major axis remaining constant and the orbit being actually in a state of approach to a circle1 and1 consequently1 the minor axis being on the increase1 it follows that the mean annual amount of solar radiation received by the whole earth must be actually on the decrease4 ,the limits of the variation in the eccentricity of the earth's orbit are not known4 ,it is1 therefore1 impossible to say accurately what may have been in former periods of time1 the amount of solar radiation2 it is1 however1 certain that if the ellipticity has ever been so great as that of the orbit of ,mercury or ,pallas1 the temperature of the earth must have been sensibly higher than it is at present4 ,but the difference of a few degrees of temperature thus occasioned1 is of too small an order to be employed in explaining the growth of tropical plants and corals in the polar or temperate zones1 and other great phenomena of ,geology40--,from ,a ,treatise on ,geology1 p4 #aa1 forming the article under that head in the seventh edition of the ,encyclopdia ,britannica4 #ahcg4 ,,mr4 ,,robert ,,bakewell4 8,a change in the form of the earth's orbit1 if considerable1 might change the temperature of the earth1 by bringing it nearer to the sun in one part of its course4 ,the orbit of the earth is an ellipsis approaching nearly to a circle2 the distance from the centre of the orbit to either focus of the ellipsis is called by astronomers #8the eccentricity of the orbit4' ,this eccentricity has been for ages slowly decreasing1 or1 in other words1 the orbit of the earth has been approaching nearer to the form of a perfect circle2 after a long period it will again increase1 and the possible extent of the variation has not been yet ascertained4 ,from what is known respecting the orbits of ,jupiter and ,saturn1 it appears highly probable that the eccentricity of the earth's orbit is confined within limits that preclude the belief of any great change in the mean annual temperature of the globe ever having been occasioned by this cause40--,introduction to ,geology1 p4 #fjj4 #ahch4 ,fifth ,edition4 ,,mrs4 ,,somerville4 8,sir ,john ,herschel has shown that the elliptical form of the earth's orbit has but a trifling share in producing the variation of temperature corresponding to the difference of the seasons40--,physical ,geography1 vol4 ii41 p4 #bj4 ,third ,edition4 ,,mr4 ,l4 ,w4 ,,meech1 ,a4,m4 8,let us1 then1 look back to that primeval epoch when the earth was in aphelion at midsummer1 and the eccentricity at its maximum value--assigned by ,leverrier near to #jggg4 ,without entering into elaborate computation1 it is easy to see that the extreme values of diurnal intensity1 in ,section ,,iv41 would be altered as by the multiplier 77#a e7_/7#a e77#b1 that is #a - #jaa in summer1 and #a #jaa in winter4 ,this would diminish the midsummer intensity by about #i1 and increase the midwinter intensity by #c or #d2 the temperature of spring and autumn being nearly unchanged4 ,but this does not appear to be of itself adequate to the geological effects in question4 8,it is not our purpose1 here1 to enter into the inquiry whether the atmosphere was once more dense than now1 whether the earth's axis had once a different inclination to the orbit1 or the sun a greater emissive power of heat and light4 ,neither shall we attempt to speculate upon the primitive heat of the earth1 nor of planetary space1 nor of the supposed connection of terrestrial heat and magnetism2 nor inquire how far the existence of coal-fields in this latitude1 of fossils1 and other geological remains1 have depended upon existing causes4 ,the preceding discussion seems to prove simply that1 under the present system of physical astronomy1 the sun's intensity could never have been materially different from what is manifested upon the earth at the present day4 ,the causes of notable geological changes must be other than the relative position of the sun and earth1 under their present laws of motion40--8,on the ,relative ,intensity of the ,heat and ,light of the ,sun40 ,smithsonian ,contributions to ,knowledge1 vol4 ix4 ,m4 ,,jean ,,reynaud4 8,la rvolution qui pourrait y causer les plus grands changements thermomtriques1 celle qui porte l'orbite s'largir et se rtrcir alternativement et1 par suite1 la plante passer1 aux poques de prihlie1 plus ou moins prs du soleil1 embrasse une priode de plus de cent mille annes terrestres et demeure comprise dans de si troites limites que les habitants doivent tre peine avertis que la chaleur dcrot1 par cette raison1 depuis une haute antiquit et dcrotra encore pendant des sicles en variant en mme temps dans sa rpartition selon les diverses poques de l'anne4444 ,enfin1 le tournoiement de l'axe du globe s'empreint galement d'une manire particulire sur l'tablissement des saisons qui1 tour de rle1 dans chacun des deux hmisphres1 deviennent graduellement1 durant une priode d'environ vingt-cinq mille ans1 de plus en plus uniformes1 ou1 l'inverse1 de plus en plus dissemblables4 ,c'est actuellement dans l'hmisphre boral que rgne l'uniformit1 et quoique les ts et les hivers y tendent1 ds prsent1 se trancher de plus en plus1 il ne parat pas douteux que la modration des saisons n'y produise1 pendant longtemps encore1 des effets apprciables4 ,en rsum1 de tous ces changements il n'en est donc aucun ni qui suive un cours prcipit1 ni qui s'lve jamais des valeurs considrables2 ils se rglent tous sur un mode de dveloppement presque insensible1 et il s'ensuit que les annes de la terre1 malgr leur complexit virtuelle1 se distinguent par le constance de leurs caractres non-seulement de ce qui peut avoir lieu1 en vertu des mmes principes1 dans les autres systmes plantaires de l'univers1 mais mme de ce qui s'observe dans plusieurs des mondes qui composent le ntre40--,philosophie ,religieuse3 ,terre et ,ciel4 ,m4 ,,adh,,mar4 ,adhmar does not consider the effects which ought to result from a change in the eccentricity of the earth's orbit2 he only concerns himself with those which1 in his opinion1 arise from the present amount of such eccentricity4 ,he admits1 of course1 that both hemispheres receive from the sun equal quantities of heat per annum2 but1 as the southern hemisphere has a winter longer by #afh hours than the corresponding season in the northern hemisphere1 an accumulation of heat necessarily takes place in the latter1 and an accumulation of cold in the former4 ,adhmar also measures the loss of heat sustained by the southern hemisphere in a year by the number of hours by which the southern exceeds the northern winter4 8,the south pole10 he says1 8loses in one year more heat than it receives1 because the total duration of its nights surpasses that of the days by #afh hours2 and the contrary takes place for the north pole4 ,if1 for example1 we take for unity the mean quantity of heat which the sun sends off in one hour1 the heat accumulated at the end of the year at the north pole will be expressed by #afh1 while the heat lost by the south pole will be equal to #afh times what the radiation lessens it by in one hour2 so that at the end of the year the difference in the heat of the two hemispheres will be represented by #ccf times what the earth receives from the sun or loses in an hour by radiation10#cbb and at the end of #ajj years the difference will be #cc1fjj times1 and at the end of #a1jjj years #ccf1jjj times1 or equal to what the earth receives from the sun in #ch years1 and so on during the #aj1jjj years that the southern winter exceeds in length the northern4 ,this1 in his opinion1 is all that is required to melt the ice off the arctic regions1 and cover the antarctic regions with an enormous ice-cap4 ,he further supposes that in about #aj1jjj years1 when our northern winter will occur in aphelion and the southern in perihelion1 the climatic conditions of the two hemispheres will be reversed2 that is to say1 the ice will melt at the south pole1 and the northern hemisphere will become enveloped in one continuous mass of ice1 leagues in thickness1 extending down to temperate regions4 ,this theory1 as shown in ,chapter ,v41 is based upon a misconception regarding the laws of radiant heat4 ,the loss of heat sustained by the southern hemisphere from radiation1 resulting from the greater length of the southern winter1 is vastly over-estimated by ,m4 ,adhmar1 and could not possibly produce the effects which he supposes4 ,but ,i need not enter into this subject here1 as the reader will find the whole question discussed at length in the chapter above referred to4 ,by far the most important part of ,adhemar's theory1 however1 is his conception of the submergence of the land by means of a polar ice-cap4 ,he appears to have been the first to put forth the idea that a mass of ice placed on the globe1 say1 for example1 at the south pole1 will shift the earth's centre of gravity a little to the south of its former position1 and thus1 as a physical consequence1 cause the sea to sink at the north pole and to rise at the south4 ,according to ,adhmar1 as the one hemisphere cools and the other grows warmer1 the ice at the pole of the former will increase in thickness and that at the pole of the latter diminish4 ,the sea1 as a consequence1 will sink on the warm hemisphere where the ice is decreasing and rise on the cold hemisphere where the ice is increasing4 ,and1 again1 in #aj1jjj years1 when the climatic conditions of the two hemispheres are reversed1 the sea will sink on the hemisphere where it formerly rose1 and rise on the hemisphere where it formerly sank1 and so on in like manner through indefinite ages4 ,adhmar1 however1 acknowledges to have derived the grand conception of a submergence of the land from the shifting of the earth's centre of gravity from the following wild speculation of one ,bertrand1 of ,hamburgh3-- 8,bertrand de ,hambourg1 dans un ouvrage imprim en #agii et qui a pour titre3 ,renouvellement priodique des ,continents1 avait dj mis cette ide1 que la masse des eaux pouvait tre alternativement entrane d'un hmisphre l'autre par le dplacement du centre de gravit du globe4 ,or1 pour expliquer ce dplacement1 il supposait que la terre tait creuse et qu'il y avait dans son intrieur un gros noyau d'aimant auquel les comtes par leur attraction communiquaient un mouvement de va-et-vient analogue celui du pendule40--,rvolutions de la ,mer1 p4 #da4 ,the somewhat extravagant notions which ,adhmar has advanced in connection with his theory of submergence have very much retarded its acceptance4 ,amongst other remarkable views he supposes the polar ice-cap to rest on the bottom of the ocean1 and to rise out of the water to the enormous height of twenty leagues4 ,again1 he holds that on the winter approaching perihelion and the hemisphere becoming warm the ice waxes soft and rotten from the accumulated heat1 and the sea now beginning to eat into the base of the cap1 this is so undermined as1 at last1 to be left standing upon a kind of gigantic pedestal4 ,this disintegrating process goes on till the fatal moment at length arrives1 when the whole mass tumbles down into the sea in huge fragments which become floating icebergs4 ,the attraction of the opposite ice-cap1 which has by this time nearly reached its maximum thickness1 becomes now predominant4 ,the earth's centre of gravity suddenly crosses the plain of the equator1 dragging the ocean along with it1 and carrying death and destruction to everything on the surface of the globe4 ,and these catastrophes1 he asserts1 occur alternately on the two hemispheres every #aj1jjj years4--,rvolutions de la ,mer1 pp4 #cafcbh4 ,adhmar's theory has been advocated by ,m4 ,le ,hon1 of ,brussels1 in a work entitled ,priodicit des ,grands ,dluges4 ,bruxelles et ,leipzig1 #aheh4 ,,ii4 ,,on ,,the ,,nature ,,of ,,heat-,,vibrations4#cbc ,from the ,philosophical ,magazine for ,may1 #ahfd4 ,in a most interesting paper on 8,radiant ,heat10 by ,professor ,tyndall1 read before the ,royal ,society in ,march last1 it is shown conclusively that the period of heat-vibrations is not affected by the state of aggregation of the molecules of the heated body2 that is to say1 whether the substance be in the gaseous1 the liquid1 or1 perhaps1 the solid condition1 the tendency of its molecules to vibrate according to a given period remains unchanged4 ,the force of cohesion binding the molecules together exercises no effect on the rapidity of vibration4 ,i had arrived at the same conclusion from theoretical considerations several years ago1 and had also deduced some further conclusions regarding the nature of heat-vibrations1 which seem to be in a measure confirmed by the experimental results of ,professor ,tyndall4 ,one of these conclusions was1 that the heat-vibration does not consist in a motion of an aggregate mass of molecules1 but in a motion of the individual molecules themselves4 ,each molecule1 or rather we should say each atom1 acts as if there were no other in existence but itself4 ,whether the atom stands by itself as in the gaseous state1 or is bound to other atoms as in the liquid or the solid state1 it behaves in exactly the same manner4 ,the deeper question then suggested itself1 viz41 what is the nature of that mysterious motion called heat assumed by the atom8 ,does it consist in excursions across centres of equilibrium external to the atom itself8 ,it is the generally received opinion among physicists that it does4 ,but ,i think that the experimental results arrived at by ,professor ,tyndall1 as well as some others which will presently be noticed1 are entirely hostile to such an opinion4 ,the relation of an atom to its centre of equilibrium depends entirely on the state of aggregation4 ,now if heat-vibrations consist in excursions to and fro across these centres1 then the period ought to be affected by the state of aggregation4 ,the higher the tension of the atom in regard to the centre1 the more rapid ought its movement to be4 ,this is the case in regard to the vibrations constituting sound4 ,the harder a body becomes1 or1 in other words1 the more firmly its molecules are bound together1 the higher is the pitch4 ,two harp-cords struck with equal force will vibrate with equal force1 however much they may differ in the rapidity of their vibrations4 ,the vis viva of vibration depends upon the force of the stroke2 but the rapidity depends1 not on the stroke1 but upon the tension of the cord4 ,that heat-vibrations do not consist in excursions of the molecules or atoms across centres of equilibrium1 follows also as a necessary consequence from the fact that the real specific heat of a body remains unchanged under all conditions4 ,all changes in the specific heat of a body are due to differences in the amount of heat consumed in molecular work against cohesion or other forces binding the molecules together4 ,or1 in other words1 to produce in a body no other effect than a given rise of temperature1 requires the same amount of force1 whatever may be the physical condition of the body4 ,whether the body be in the solid1 the fluid1 or the gaseous condition1 the same rise of temperature always indicates the same quantity of force consumed in the simple production of the rise4 ,now1 if heat-vibrations consist in excursions of the atom to and fro across a centre of equilibrium external to itself1 as is generally supposed1 then the real specific heat of a solid body1 for example1 ought to decrease with the hardness of the body1 because an increase in the strength of the force binding the molecules together would in such a case tend to favour the rise in the rapidity of the vibrations4 ,these conclusions not only afford us an insight into the hidden nature of heat-vibrations1 but they also appear to cast some light on the physical constitution of the atom itself4 ,they seem to lead to the conclusion that the ultimate atom itself is essentially elastic4#cbd ,for if heat-vibrations do not consist in excursions of the atom1 then it must consist in alternate expansions and contractions of the atom itself4 ,this again is opposed to the ordinary idea that the atom is essentially solid and impenetrable4 ,but it favours the modern idea1 that matter consists of forces of resistance acting from a centre4 ,professor ,tyndall in a memoir read before the ,royal ,society 8,on a new ,series of ,chemical ,reactions produced by ,light10 has subsequently arrived at a similar conclusion in reference to the atomic nature of heat-vibrations4 ,the following are his views on the subject3-- 8,a question of extreme importance in molecular physics here arises3--,what is the real mechanism of this absorption1 and where is its seat8 8,i figure1 as others do1 a molecule as a group of atoms1 held together by their mutual forces1 but still capable of motion among themselves4 ,the vapour of the nitrite of amyl is to be regarded as an assemblage of such molecules4 ,the question now before us is this3--,in the act of absorption1 is it the molecules that are effective1 or is it their constituent atoms8 ,is the vis viva of the intercepted waves transferred to the molecule as a whole1 or to its constituent parts8 8,the molecule1 as a whole1 can only vibrate in virtue of the forces exerted between it and its neighbour molecules4 ,the intensity of these forces1 and consequently the rate of vibration1 would1 in this case1 be a function of the distance between the molecules4 ,now the identical absorption of the liquid and of the vaporous nitrite of amyl indicates an identical vibrating period on the part of liquid and vapour1 and this1 to my mind1 amounts to an experimental demonstration that the absorption occurs in the main within the molecule4 ,for it can hardly be supposed1 if the absorption were the act of the molecule as a whole1 that it could continue to affect waves of the same period after the substance had passed from the vaporous to the liquid state40--,proc4 of ,roy4 ,soc41 ,no4 #aje4 #ahfh4 ,professor ,w4 ,a4 ,norton1 in his memoir on 8,molecular ,physics10#cbe has also arrived at results somewhat similar in reference to the nature of heat-vibrations4 8,it will be seen10 he says1 8that these 7,mr4 ,croll's7 ideas are in accordance with the conception of the constitution of a molecule adopted at the beginning of the present memoir 7p4 #aic71 and with the theory of heat-vibrations or heat-pulses deduced therefrom 7p4 #aif740cbf ,,iii4 ,,on ,,the ,,reason ,,why ,,the ,,difference ,,of ,,reading ,,between ,a ,,thermometer ,,exposed ,,to ,,direct ,,sunshine ,,and ,,one ,,shaded ,,diminishes ,,as ,,we ,,ascend ,,in ,,the ,,atmosphere4#cbg ,from the ,philosophical ,magazine for ,march1 #ahfg4 ,the remarkable fact was observed by ,mr4 ,glaisher1 that the difference of reading between a black-bulb thermometer exposed to the direct rays of the sun and one shaded diminishes as we ascend in the atmosphere4 ,on viewing the matter under the light of ,professor ,tyndall's important discovery regarding the influence of aqueous vapour on radiant heat1 the fact stated by ,mr4 ,glaisher appears to be in perfect harmony with theory4 ,the following considerations will perhaps make this plain4 ,the shaded thermometer marks the temperature of the surrounding air2 but the exposed thermometer marks not the temperature of the air1 but that of the bulb heated by the direct rays of the sun4 ,the temperature of the bulb depends upon two elements3 7#a7 the rate at which it receives heat by direct radiation from the sun above1 the earth beneath1 and all surrounding objects1 and by contact with the air2 7#b7 the rate at which it loses heat by radiation and by contact with the air4 ,as regards the heat gained and lost by contact with the surrounding air1 both thermometers are under the same conditions1 or nearly so4 ,we therefore require only to consider the element of radiation4 ,we begin by comparing the two thermometers at the earth's surface1 and we find that they differ by a very considerable number of degrees4 ,we now ascend some miles into the air1 and on again comparing the thermometers we find that the difference between them has greatly diminished4 ,it has been often proved1 by direct observation1 that the intensity of the sun's rays increases as we rise in the atmosphere4 ,how then does the exposed thermometer sink more rapidly than the shaded one as we ascend8 ,the reason is obviously this4 ,the temperature of the thermometers depends as much upon the rate at which they are losing their heat as upon the rate at which they are gaining it4 ,the higher temperature of the exposed thermometer is the result of direct radiation from the sun4 ,now1 although this thermometer receives by radiation more heat from the sun at the upper position than at the lower1 it does not necessarily follow on this account that its temperature ought to be higher4 ,suppose that at the upper position it should receive one-fourth more heat from the sun than at the lower1 yet if the rate at which it loses its heat by radiation into space be1 say1 one-third greater at the upper position than at the lower1 the temperature of the bulb would sink to a considerable extent1 notwithstanding the extra amount of heat received4 ,let us now reflect on how matters stand in this respect in regard to the actual case under our consideration4 ,when the exposed thermometer is at the higher position1 it receives more heat from the sun than at the lower1 but it receives less from the earth2 for a considerable part of the radiation from the earth is cut off by the screen of aqueous vapour intervening between the thermometer and the earth4 ,but1 on the whole1 it is probable that the total quantity of radiant heat reaching the thermometer is greater in the higher position than in the lower4 ,compare now the two positions in regard to the rate at which the thermometer loses its heat by radiation4 ,when the thermometer is at the lower position1 it has the warm surface of the ground against which to radiate its heat downwards4 ,the high temperature of the ground thus tends to diminish the rate of radiation4 ,above1 there is a screen of aqueous vapour throwing back upon the thermometer a very considerable part of the heat which the instrument is radiating upwards4 ,this1 of course1 tends greatly to diminish the loss from radiation4 ,but at the upper position this very screen1 which prevented the thermometer from throwing off its heat into the cold space above1 now affects the instrument in an opposite manner2 for the thermometer has now to radiate its heat downwards1 not upon the warm surface of the ground as before1 but upon the cold upper surface of the aqueous screen intervening between the instrument and the earth4 ,this of course tends to lower the mercury4 ,we are now in a great measure above the aqueous screen1 with nothing to protect the thermometer from the influence of cold stellar space4 ,it is true that the air above is at a temperature little below that of the thermometer itself2 but then the air is dry1 and1 owing to its diathermancy1 it does not absorb the heat radiated from the thermometer1 and consequently the instrument radiates its heat directly into the cold stellar space above1 some hundreds of degrees below zero1 almost the same as it would do were the air entirely removed4 ,the enormous loss of heat which the thermometer now sustains causes it to fall in temperature to a great extent4 ,the molecules of the comparatively dry air at this elevation1 being very bad radiators1 do not throw off their heat into space so rapidly as the bulb of the exposed thermometer2 consequently their temperature does not 7for this reason7 tend to sink so rapidly as that of the bulb4 ,hence the shaded thermometer1 which indicates the temperature of those molecules1 is not affected to such an extent as the exposed one4 ,hence also the difference of reading between the two instruments must diminish as we rise in the atmosphere4 ,this difference between the temperature of the two thermometers evidently does not go on diminishing to an indefinite extent4 ,were we able to continue our ascent in the atmosphere1 we should certainly find that a point would be reached beyond which the difference of reading would begin to increase1 and would continue to do so till the outer limits of the atmosphere were reached4 ,the difference between the temperatures of the two thermometers beyond the limits of the atmosphere would certainly be enormous4 ,the thermometer exposed to the direct rays of the sun would no doubt be much colder than it had been when at the earth's surface2 but the shaded thermometer would now indicate the temperature of space1 which1 according to ,sir ,john ,herschel and ,m4 ,pouillet1 is more than #bjj ,fahrenheit below zero4 ,it follows also1 from what has been stated1 that even under direct sunshine the removal of the earth's atmosphere would tend to lower the temperature of the earth's surface to a great extent4 ,this conclusion also follows as an immediate inference from the fact that the earth's atmosphere1 as it exists at present charged with aqueous vapour1 affects terrestrial radiation more than it does radiation from the sun2 for the removal of the atmosphere would increase the rate at which the earth throws off its heat into space more than it would increase the rate at which it receives heat from the sun2 therefore its temperature would necessarily fall until the rate of radiation from the earth's surface exactly equalled the rate of radiation to the surface4 ,let the atmosphere again envelope the earth1 and terrestrial radiation would instantly be diminished2 the temperature of the earth's surface would therefore necessarily begin to rise1 and would continue to do so till the rate of radiation from the surface would equal the rate of radiation received by the surface4 ,equilibrium being thus restored1 the temperature would remain stationary4 ,it is perfectly obvious that if we envelope the earth with a substance such as our atmosphere1 that offers more resistance to terrestrial radiation than to solar1 the temperature of the earth's surface must necessarily rise until the heat which is being radiated off equals that which is being received from the sun4 ,remove the air and thus get quit of the resistance1 and the temperature of the surface would fall1 because in this case a lower temperature would maintain equilibrium4 ,it follows1 therefore1 that the moon1 which has no atmosphere1 must be much colder than our earth1 even on the side exposed to the sun4 ,were our earth with its atmosphere as it exists at present removed to the orbit of ,venus or ,mars1 for example1 it certainly would not be habitable1 owing to the great change of temperature that would result4 ,but a change in the physical constitution of the atmospheric envelope is really all that would be necessary to retain the earth's surface at its present temperature in either position4 ,,iv4 ,,remarks ,,on ,,mr4 ,j4 ,y4 ,,buchanan',s ,,theory ,,of ,,the ,,vertical ,,distribution ,,of ,,temperature ,,of ,,the ,,ocean4#cbh ,since the foregoing was in type1 a paper on the 8,vertical ,distribution of ,temperature of the ,ocean10 by ,mr4 ,j4 ,y4 ,buchanan1 chemist on board the ,challenger1 has been read before the ,royal ,society4#cbi ,in that paper ,mr4 ,buchanan endeavours to account for the great depth of warm water in the middle of the ,north ,atlantic compared with that at the equator1 without referring it to horizontal circulation of any kind4 ,the following is the theory as stated by ,mr4 ,buchanan3-- 8,let us assume the winter temperature of the surface-water to be #fj ,f4 and the summer temperature to be #gj ,f4 ,if we start from midwinter1 we find that1 as summer approaches1 the surface-water must get gradually warmer1 and that the temperature of the layers below the surface must decrease at a very rapid rate1 until the stratum of winter temperature1 or #fj ,f41 is reached2 in the language of the isothermal charts1 the isothermal line for degrees between #gj ,f4 7if we suppose that we have arrived at midsummer7 and #fj ,f4 open out or increase their distance from each other as the depth increases4 ,let us now consider the conditions after the summer heat has begun to waver4 ,during the whole period of heating1 the water1 from its increasing temperature1 has been always becoming lighter1 so that heat communication by convection with the water below has been entirely suspended during the whole period4 ,the heating of the surface-water has1 however1 had another effect1 besides increasing its volume2 it has1 by evaporation1 rendered it denser than it was before1 at the same temperature4 ,keeping in view this double effect of the summer heat upon the surface-water1 let us consider the effect of the winter cold upon it4 ,the superficial water having assumed the atmospheric temperature of1 say #fj ,f41 will sink through the warmer water below it1 until it reaches the stratum of water having the same temperature as itself4 ,arrived here1 however1 although it has the same temperature as the surrounding water1 the two are no longer in equilibrium1 for the water which has come from the surface1 has a greater density than that below at the same temperature4 ,it will therefore not be arrested at the stratum of the same temperature1 as would have been the case with fresh water2 but it will continue to sink1 carrying of course its higher temperature with it1 and distributing it among the lower layers of colder water4 ,at the end of the winter1 therefore1 and just before the summer heating recommences1 we shall have at the surface a more or less thick stratum of water having a nearly uniform temperature of #fj ,f41 and below this the temperature decreasing at a considerable but less rapid rate than at the termination of the summer heating4 ,if we distinguish between surface-water1 the temperature of which rises with the atmospheric temperature 7following thus1 in direction at least1 the variation of the seasons71 and subsurface-water1 or the stratum immediately below it1 we have for the latter the1 at first sight1 paradoxical effect of summer cooling and winter heating4 ,the effect of this agency is to diffuse the same heat to a greater depth in the ocean1 the greater the yearly range of atmospheric temperature at the surface4 ,this effect is well shown in the chart of isothermals1 on a vertical section1 between ,madeira and a position in lat4 #c #h ,n41 long4 #ad #di ,w4 ,the isothermal line for #de ,f4 rises from a depth of #gdj fathoms at ,madeira to #bdj fathoms at the above-mentioned position4 ,in equatorial regions there is hardly any variation in the surface-temperature of the sea2 consequently we find cold water very close to the surface all along the line4 ,on referring to the temperature section between the position lat4 #c #h ,n41 long4 #ad #di ,w41 and ,st4 ,paul's ,rocks1 it will be seen that1 with a surface-temperature of from #ge ,f4 to #gi ,f41 water at #ee ,f4 is reached at distances of less than #ajj fathoms from the surface4 ,midway between the ,azores and ,bermuda1 with a surface-temperature of #gj ,f41 it is only at a depth of #djj fathoms that we reach water of #ee ,f40 ,what ,mr4 ,buchanan states will explain why the mean annual temperature of the water at the surface extends to a greater depth in the middle of the ,north ,atlantic than at the equator4 ,it also explains why the temperature from the surface downwards decreases more rapidly at the equator than in the middle of the ,north ,atlantic2 but1 if ,i rightly understand the theory1 it does not explain 7and this is the point at issue7 why at a given depth the temperature of the water in the ,north ,atlantic should be higher than the temperature at a corresponding depth at the equator4 ,were there no horizontal circulation the greatest thickness of warm water would certainly be found at the equator and the least at the poles4 ,the isothermals would in such a case gradually slope downwards from the poles to the equator4 ,the slope might not be uniform1 but still it would be a continuous downward slope4 ,v4 ,,on ,,the ,,cause ,,of ,,the ,,cooling ,,effect ,,produced ,,on ,,solids ,,by ,,tension4#ccj ,from the ,philosophical ,magazine for ,may1 #ahfd4 ,from a series of experiments made by ,dr4 ,joule with his usual accuracy1 he found that when bodies are subjected to tension1 a cooling effect takes place4 8,the quantity of cold10 he says1 8produced by the application of tension was sensibly equal to the heat evolved by its removal2 and further1 that the thermal effects were proportional to the weight employed40#cca ,he found that when a weight was applied to compress a body1 a certain amount of heat was evolved2 but the same weight1 if applied to stretch the body1 produced a corresponding amount of cold4 ,this1 although it does not appear to have been remarked1 is a most singular result4 ,if we employ a force to compress a body1 and then ask what has become of the force applied1 it is quite a satisfactory answer to be told that the force is converted into heat1 and reappears in the molecules of the body as such2 but if the same force be employed to stretch the body1 it will be no answer to be told that the force is converted into cold4 ,cold cannot be the force under another form1 for cold is a privation of force4 ,if a body1 for example1 is compressed by a weight1 the vis viva of the descending weight is transmitted to the molecules of the body and reappears under that form of force called heat2 but if the same weight is applied so as to stretch or expand the body1 not only does the force of the weight disappear without producing heat1 but the molecules which receive the force lose part of that which they already possessed4 ,not only does the force of the weight disappear1 but along with it a portion of the force previously existing in the molecules under the form of heat4 ,we have therefore to inquire1 not merely into what becomes of the force imparted by the weight1 but also what becomes of the force in the form of heat which disappears from the molecules of the body itself4 ,that the vis viva of the descending weight should disappear without increasing the heat of the molecules is not so surprising1 because it may be transformed into some other form of force different from that of heat4 ,for it is by no means evident priori that heat should be the only form under which it may exist4 ,but it is somewhat strange that it should cause the force previously existing in the molecules in the form of heat also to change into some other form4 ,when a weight1 for example1 is employed to stretch a solid body1 it is evident that the force exerted by the weight is consumed in work against the cohesion of the particles1 for the entire force is exerted so as to pull them separate from each other4 ,but the cooling effect which takes place shows that more force disappears than simply what is exerted by the weight2 for the cooling effect is caused by the disappearance of force in the shape of heat from the body itself4 ,the force exerted by the weight disappears in performing work against the cohesion of the particles of the body stretched4 ,but what becomes of the energy in the form of heat which disappears from the body at the same time8 ,it must be consumed in performing work of some kind or other4 ,the force exerted by the weight cannot be the cause of the cooling effect4 ,the transferrence of force from the weight to the body may be the cause of a heating effect--an increase of force in the body2 but this transferrence of force to the body cannot be the cause of a decrease of force in the body4 ,if a decrease of force actually follows the application of tension1 the weight can only be the occasion1 not the cause of the decrease4 ,in what manner1 then1 does the stretching of the body by the weight become the occasion of its losing energy in the shape of heat8 ,or1 in other words1 what is the cause of the cooling effects which result from tension8 ,the probable explanation of the phenomenon seems to be this3 if the molecules of a body are held together by any force1 of whatever nature it may be1 which prevents any further separation taking place1 then the entire heat applied to such a body will appear as temperature2 but if this binding force becomes lessened so as to allow further expansion1 then a portion of the heat applied will be lost in producing expansion4 ,all solids at any given temperature expand until the expansive force of their heat exactly balances the cohesive force of their molecules1 after which no further expansion at the same temperature can possibly take place while the cohesive force of the molecules remains unchanged4 ,but if1 by some means or other1 the cohesive force of the molecules become reduced1 then instantly the body will expand under the heat which it possesses1 and of course a portion of the heat will be consumed in expansion1 and a cooling effect will result4 ,now tension1 although it does not actually lessen the cohesive force of the molecules of the stretched body1 yet produces1 by counteracting this force1 the same effect2 for it allows the molecules an opportunity of performing work of expansion1 and a cooling effect is the consequence4 ,if the piston of a steam-engine1 for example1 be loaded to such an extent that the steam is unable to move it1 the steam in the interior of the cylinder will not lose any of its heat2 but if the piston be raised by some external force1 the molecules of the steam will assist this force1 and consequently will suffer loss of heat in proportion to the amount of work which they perform4 ,the very same occurs when tension is applied to a solid4 ,previous to the application of tension1 the heat existing in the molecules is unable to produce any expansion against the force of cohesion4 ,but when the influence of cohesion is partly counteracted by the tension applied1 the heat then becomes enabled to perform work of expansion1 and a cooling effect is the result4 ,,vi4 ,,the ,,cause ,,of ,,regelation4#ccb ,there are two theories which have been advanced to explain ,regelation1 the one by ,professor ,faraday1 and the other by ,professor ,james ,thomson4 ,according to ,professor ,james ,thomson1 pressure is the cause of regelation4 ,pressure applied to ice tends to lower the melting-point1 and thus to produce liquefaction2 but the water which results is colder than the ice1 and refreezes the moment it is relieved from pressure4 ,when two pieces of ice are pressed together1 a melting takes place at the points in contact1 resulting from the lowering of the melting-point2 the water formed1 re-freezing1 joins the two pieces together4 ,the objection which has been urged against this theory is that regelation will take place under circumstances where it is difficult to conceive how pressure can be regarded as the cause4 ,two pieces of ice1 for example1 suspended by silken threads in an atmosphere above the melting-point1 if but simply allowed to touch each other1 will freeze together4 ,professor ,j4 ,thomson1 however1 attributes the freezing to the pressure resulting from the capillary attraction of the two moist surfaces in contact4 ,but when we reflect that it requires the pressure of a mile of ice--#ace tons on the square foot--to lower the melting-point one degree1 it must be obvious that the lowering effect resulting from capillary attraction in the case under consideration must be infinitesimal indeed4 ,the following clear and concise account of ,faraday's theory1 ,i quote from ,professor ,tyndall's 8,forms of ,water30-- 8,faraday concluded that in the interior of any body1 whether solid or liquid1 where every particle is grasped1 so to speak1 by the surrounding particles1 and grasps them in turn1 the bond of cohesion is so strong as to require a higher temperature to change the state of aggregation than is necessary at the surface4 ,at the surface of a piece of ice1 for example1 the molecules are free on one side from the control of other molecules2 and they therefore yield to heat more readily than in the interior4 ,the bubble of air or steam in overheated water also frees the molecules on one side2 hence the ebullition consequent upon its introduction4 ,practically speaking1 then1 the point of liquefaction of the interior ice is higher than that of the superficial ice4444 8,when the surfaces of two pieces of ice1 covered with a film of the water of liquefaction1 are brought together1 the covering film is transferred from the surface to the centre of the ice1 where the point of liquefaction1 as before shown1 is higher than at the surface4 ,the special solidifying power of ice upon water is now brought into play on both sides of the film4 ,under these circumstances1 ,faraday held that the film would congeal1 and freeze the two surfaces together40--,the ,forms of ,water1 p4 #agc4 ,the following appears to be a more simple explanation of the phenomena than either of the preceding3-- ,the freezing-point of water1 and the melting-point of ice1 as ,professor ,tyndall remarks1 touch each other as it were at this temperature4 ,at a hair's-breadth lower water freezes2 at a hair's-breadth higher ice melts4 ,now if we wish1 for example1 to freeze water1 already just about the freezing-point1 or to melt a piece of ice already just about the melting-point1 we can do this either by a change of temperature or by a change of the melting-point4 ,but it will be always much easier to effect this by the former than by the latter means4 ,take the case already referred to1 of the two pieces of ice suspended in an atmosphere above the melting-point4 ,the pieces at their surfaces are in a melting condition1 and are surrounded by a thin film of water just an infinitesimal degree above the freezing-point4 ,the film has on the one side solid ice at the freezing-point1 and on the other a warm atmosphere considerably above the freezing-point4 ,the tendency of the ice is to lower the temperature of the film1 while that of the air is to raise its temperature4 ,when the two pieces are brought into contact the two films unite and form one film separating the two pieces of ice4 ,this film is not like the former in contact with ice on the one side and warm air on the other4 ,it is surrounded on both sides by solid ice4 ,the tendency of the ice1 of course1 is to lower the film to the same temperature as the ice itself1 and thus to produce solidification4 ,it is evident that the film must either melt the ice or the ice must freeze the film1 if the two are to assume the same temperature4 ,but the power of the ice to produce solidification1 owing to its greater mass1 is enormously greater than the power of the film to produce fluidity1 consequently regelation is the result4 ,,vii4 ,,list ,,of ,,papers ,,which ,,have ,,appeared ,,in ,,dr4 ,a4 ,,petermann',s ,,geographische ,,mittheilungen ,,relating ,,to ,,the ,,gulf-,,stream ,,and ,,thermal ,,condition ,,of ,,the ,,arctic ,,regions4 ,the most important memoir which we have on the ,gulf-stream and its influence on the climate of the arctic regions is the one by ,dr4 ,a4 ,petermann1 entitled 8,der ,golfstrom und ,standpunkt der thermometrischen ,kenntniss des nord-atlantischen ,oceans und ,landgebiets im ,jahre #ahgj40 ,geographische ,mittheilungen1 ,band ,,xvi4 #ahgj4 ,dr4 ,petermann has1 in this memoir1 by a different line of argument from that which ,i have pursued in this volume1 shown in the most clear and convincing manner that the abnormally high temperature of the north-western shores of ,europe and the seas around ,spitzbergen is owing entirely to the ,gulf-stream1 and not to any general circulation such as that advocated by ,dr4 ,carpenter4 ,from a series of no fewer than #ajj1jjj observations of temperature in the ,north ,atlantic and in the arctic seas1 he has been enabled to trace with accuracy on his charts the very footsteps of the heat in its passage from the ,gulf of ,mexico up to the shores of ,spitzbergen4 ,the following is a list of the more important papers bearing on the subject which have recently appeared in ,dr4 ,petermann's ,geogr4 ,mittheilungen3-- ,an ,english translation of ,dr4 ,petermann's ,memoir1 and of a few more in the subjoined list1 has been published in a volume1 with supplements1 by the ,hydrographic ,department of the ,united ,states1 under the superintendence of ,commodore ,r4 ,h4 ,wyman4 ,the papers whose titles are in ,english have appeared in the ,american volume4 ,in that volume the principal ,english papers on the subject1 in as far as they relate to the north-eastern extension of the ,gulf-stream1 have also been reprinted4 ,the ,system of ,oceanic ,currents in the ,circumpolar ,basin of the ,northern ,hemisphere4 ,by ,dr4 ,a4 ,mhry4 ,vol4 ,,xiii41 ,part ,,ii4 #ahfg4 ,the ,scientific ,results of the first ,german ,north ,polar ,expedition4 ,by ,dr4 ,w4 von ,freeden4 ,vol4 ,,xv41 ,part ,,vi4 #ahfi4 ,the ,gulf-stream1 and the ,knowledge of the ,thermal ,properties of the ,north ,atlantic ,ocean and its ,continental ,borders1 up to #ahgj4 ,by ,dr4 ,a4 ,petermann4 ,geographische ,mittheilungen1 ,vol4 ,,xvi41 ,part ,,vi4 #ahgj4 ,the ,temperature of the ,north ,atlantic ,ocean and the ,gulf-stream4 ,by ,rear-,admiral ,c4 ,irminger4 ,vol4 ,,xvi41 ,part ,,vi4 #ahgj4 ,meteorological ,observations during a ,winter ,stay on ,bear ,island1 #ahfeahff4 ,by ,sievert ,tobilson4 ,vol4 ,,xvi41 ,part ,,vii4 #ahgj4 ,die ,temperatur-verhltnisse in den arktischen ,regionen4 ,von ,dr4 ,petermann4 ,band ,,xvi41 ,heft ,,vii4 #ahgj4 ,preliminary ,reports of the ,second ,german ,north ,polar ,expedition1 and of minor ,expeditions1 in #ahgj4 ,vol4 ,,xvii4 ,preliminary ,report of the ,expedition for the ,exploration of the ,nova-,zembla ,sea 7the sea between ,spitzbergen and ,nova ,zembla71 by ,lieutenants ,weyprecht and ,payer1 ,june to ,september1 #ahga4 ,by ,dr4 ,a4 ,petermann4 ,vol4 ,,xvii4 #ahga4 ,der ,golfstrom ostwrts vom ,nordkap4 ,von ,a4 ,middendorff4 ,band ,,xvii41 ,heft ,i4 #ahga4 ,kapitn ,e4 ,h4 ,johannesen's ,umfahrung von ,nowaja ,seml im ,sommer #ahgj1 und norwegischer ,finwalfang stlich vom ,nordkap4 ,von ,th4 v4 ,heuglin4 ,band ,,xvii41 ,heft ,i4 #ahga4 ,die ,nordpol-,expeditionen1 das sagenhafte ,gillis-land und der ,golfstrom im ,polarmeere4 ,von ,dr4 ,a4 ,petermann4 #e ,nov4 #ahgj4 ,th4 v4 ,heuglin's ,aufnahmen in ,ost-,spitzbergen4 ,begleitworte zur neuen ,karte dieses ,gebiets4 ,tafel #i4 #ahgj4 ,band ,,xvii41 ,heft ,v4 #ahga4 ,die zweite deutsche ,nordpolar-,expedition1 #ahfigj4 ,schlittenreise an der ,kste ,grnlands nach ,norden1 #h ,mrz#bg ,april1 #ahgj4 ,von ,ober-,lieutenant ,julius ,payer4 ,band ,,xvii41 ,heft ,v4 #ahga4 ,die ,entdeckung des ,kaiser ,franz ,josef-,fjordes in ,ost-,grnland1 ,august1 #ahgj4 ,von ,ober-,lieutenant ,julius ,payer4 ,band ,,xvii41 ,heft ,v4 #ahga4 ,die ,erschliessung eines ,theiles des nrdlichen ,eismeeres durch die ,fahrten und ,beobachtungen der norwegischen ,seefahrer ,torkildsen1 ,ulve1 ,mack ,qvale1 und ,nedrevaag im karischen ,meere1 #ahgj4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xvii41 ,heft ,,iii4 #ahga4 ,die zweite deutsche ,nordpolar-,expedition1 #ahfigj4 ,schlittenreise nach ,ardencaple ,inlet1 #hbi ,mai1 #ahgj4 ,von ,ober-,lieutenant ,julius ,payer4 ,band ,,xvii41 ,heft ,,xi4 #ahga4 ,ein ,winter unter dem ,polarkreise4 ,von ,ober-,lieutenant ,julius ,payer4 ,band ,,xvii41 ,heft ,,xi4 #ahga4 ,die ,entdeckung eines offenen ,polarmeeres durch ,payer und ,weyprecht im ,september1 #ahga4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xvii41 ,heft ,,xi4 #ahga4 ,james ,lamont's ,nordfahrt1 ,mai-,august1 #ahga4 ,die ,entdeckungen von ,weyprecht1 ,payer1 ,tobiesen1 ,mack1 ,carlsen1 ,ulve1 und ,smyth im ,sommer1 #ahga4 ,stand der ,nordpolarfrage zu ,ende des ,jahres #ahga4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xvii41 ,heft ,,xii4 #ahga4 ,das ,innere von ,grnland4 ,von ,dr4 ,robert ,brown4 ,band ,,xvii41 ,heft ,x4 #ahga4 ,captain ,t4 ,torkildsen's ,cruise from ,troms to ,spitzbergen1 ,july #bf to ,september #bf1 #ahga4 ,vol4 ,,xviii4 #ahgb4 ,the ,sea north of ,spitzbergen1 and the most northern ,meteorological ,observations4 ,vol4 ,,xviii4 #ahgb4 ,results of the ,observations of the ,deep-sea ,temperature in the ,sea between ,greenland1 ,northern ,europe1 and ,spitzbergen4 ,by ,professor ,h4 ,mhn4 ,vol4 ,,xviii4 #ahgb4 ,the ,norwegian ,cruises to ,nova ,zembla and the ,kara ,sea in #ahga4 ,vol4 ,,xviii4 #ahgb4 ,the ,cruises in the ,polar ,sea in #ahgb4 ,vol4 ,,xviii4 #ahgb4 ,the ,cruise of ,smyth and ,ulve1 ,june #ai to ,september #bg1 #ahga4 ,vol4 ,,xviii4 #ahgb4 ,die fnfmonatliche ,schiffbarkeit des sibirischen ,eismeeres um ,nowaja ,semlja1 erwiesen durch die norwegischen ,seefahrer in #ahfi und #ahgj1 ganz besonders aber in #ahga4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xviii41 ,heft ,x4 #ahgb4 ,die neuen norwegischen ,aufnahmen des nordstlichen ,theiles von ,nowaja ,semlja durch ,mack1 ,drma1 ,carlsen1 u4 ,a41 #ahga4 ,von ,dr4 ,petermann4 ,band ,,xviii41 ,heft ,x4 #ahgb4 ,nachrichten ber die sieben zurckgekehrten ,expeditionen unter ,graf ,wiltschek1 ,altmann1 ,johnsen1 ,nilsen1 ,smith1 ,gray1 ,whymper2 die drei berwinterungs-,expeditionen2 die ,amerikanische1 ,schwedische1 sterreichisch-,ungarische2 und die zwei neuen3 die norwegische ,winter-,expedition und diejenige unter ,kapitn ,mack4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xviii41 ,heft ,,xii4 #ahgb4 ,konig ,karl-,land im ,osten von ,spitzbergen und seine ,erreichung und ,aufnahme durch norwegische ,schiffer im ,sommer #ahgb4 ,von ,professor ,h4 ,mhn4 ,band ,,xix41 ,heft ,,iv4 #ahgc4 ,resultate der ,beobachtungen angestellt auf der ,fahrt des ,dampfers 8,albert0 nach ,spitzbergen im ,november und ,dezember1 #ahgb4 ,von ,professor ,mhn4 ,band ,,xix41 ,heft ,,vii4 #ahgc4 ,die amerikanische ,nordpolar-,expedition unter ,c4 ,f4 ,hall1 #ahgac4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xix41 ,heft ,,viii4 #ahgc4 ,die ,trift der ,hall'schen ,nordpolar-,expedition1 #af ,august bis #ae ,oktober1 #ahgb1 und die ,schollenfahrt der #bj bis zum #cj ,april1 #ahgc4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xix41 ,heft ,x4 #ahgc4 ,das offene ,polarmeer besttigt durch das ,treibholz an der ,nordwestkste von ,grnland4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xx41 ,heft ,v4 #ahgd4 ,das arktische ,festland und ,polarmeer4 ,von ,dr4 ,joseph ,chavanne4 ,band ,,xx41 ,heft ,,vii4 #ahgd4 ,die ,umkehr der ,hall'schen ,polar-,expedition nach den ,aussagen der ,offiziere4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xx41 ,heft ,,vii4 #ahgd4 ,die zweite sterreichisch-ungarische ,nordpolar-,expedition unter ,weyprecht und ,payer1 #ahgbd4 ,von ,dr4 ,a4 ,petermann4 ,band ,,xx41 ,heft ,x4 #ahgd4 ,beitrge zur ,klimatologie und ,meteorologie des ,ost-polar-,meeres4 ,von ,professor ,mhn4 ,band ,,xx41 ,heft ,v4 #ahgd4 ,kapitn ,david ,gray's ,reise und ,beobachtungen im ost-grnlndischen ,meere1 #ahgd1 und seine ,ansichten ber den besten ,weg zum ,nordpol4 ,original-,mittheilungen an ,a4 ,petermann1 d4,d41 ,peterhead1 ,dezember1 #ahgd4 ,band ,,xxi41 ,heft ,,iii4 #ahge4 ,,viii4 ,,list ,,of ,,papers ,,by ,,the ,,author ,,to ,,which ,,reference ,,is ,,made ,,in ,,this ,,volume4 ,on the ,influence of the ,tidal ,wave on the ,earth's ,rotation and on the ,acceleration of the ,moon's ,mean ,motion4--,phil4 ,mag41 ,april1 #ahfd4 ,on the ,nature of ,heat-vibrations4--,phil4 ,mag41 ,may1 #ahfd4 ,on the ,cause of the ,cooling ,effect produced on ,solids by ,tension4--,phil4 ,mag41 ,may1 #ahfd4 ,on the ,physical ,cause of the ,change of ,climate during ,geological ,epochs4--,phil4 ,mag41 ,august1 #ahfd4 ,on the ,physical ,cause of the ,submergence of the ,land during the ,glacial ,epoch4--,the ,reader1 ,september #bnd and ,october #adth1 #ahfe4 ,on ,glacial ,submergence4--,the ,reader1 ,december #bnd and #ith1 #ahfe4 ,on the ,eccentricity of the ,earth's ,orbit4--,phil4 ,mag41 ,january1 #ahff4 ,glacial ,submergence on the ,supposition that the ,interior of the ,globe is in a ,fluid ,condition4--,the ,reader1 ,january #acth1 #ahff4 ,on the ,physical ,cause of the ,submergence and ,emergence of the ,land during the ,glacial ,epoch1 with a ,note by ,professor ,sir ,william ,thomson4--,phil4 ,mag41 ,april1 #ahff4 ,on the ,influence of the ,tidal ,wave on the ,motion of the ,moon4--,phil4 ,mag41 ,august and ,november1 #ahff4 ,on the ,reason why the ,change of ,climate in ,canada since the ,glacial ,epoch has been less complete than in ,scotland4--,trans4 ,geol4 ,soc4 of ,glasgow1 #ahff4 ,on the ,eccentricity of the ,earth's ,orbit1 and its ,physical ,relations to the ,glacial ,epoch4--,phil4 ,mag41 ,february1 #ahfg4 ,on the ,reason why the ,difference of ,reading between a ,thermometer exposed to direct ,sunshine and one shaded diminishes as we ascend in the ,atmosphere4--,phil4 ,mag41 ,march1 #ahfg4 ,on the ,change in the ,obliquity of the ,ecliptic2 its ,influence on the ,climate of the ,polar ,regions and ,level of the ,sea4--,trans4 ,geol4 ,soc4 of ,glasgow1 vol4 ii41 p4 #agg4 ,phil4 ,mag41 ,june1 #ahfg4 ,remarks on the ,change in the ,obliquity of the ,ecliptic1 and its ,influence on ,climate4--,phil4 ,mag41 ,august1 #ahfg4 ,on certain ,hypothetical ,elements in the ,theory of ,gravitation and generally received ,conceptions regarding the ,constitution of ,matter4--,phil4 ,mag41 ,december1 #ahfg4 ,on ,geological ,time1 and the probable ,date of the ,glacial and the ,upper ,miocene ,period4--,phil4 ,mag41 ,may1 ,august1 and ,november1 #ahfh4 ,on the ,physical ,cause of the ,motions of ,glaciers4--,phil4 ,mag41 ,march1 #ahfi4 ,scientific ,opinion1 ,april #adth1 #ahfi4 ,on the ,influence of the ,gulf-stream4--,geol4 ,mag41 ,april1 #ahfi4 ,scientific ,opinion1 ,april #bast and #bhth1 #ahfi4 ,on ,mr4 ,murphy's ,theory of the ,cause of the ,glacial ,climate4--,geol4 ,mag41 ,august1 #ahfi4 ,scientific ,opinion1 ,september #ast1 #ahfi4 ,on the ,opinion that the ,southern ,hemisphere loses by ,radiation more ,heat than the ,northern1 and the supposed ,influence that this has on ,climate4--,phil4 ,mag41 ,september1 #ahfi4 ,scientific ,opinion1 ,september #bith and ,october #fth1 #ahfi4 ,on ,two ,river ,channels buried under ,drift belonging to a ,period when the ,land stood several hundred feet higher than at present4--,trans4 ,geol4 ,soc4 of ,edinburgh1 vol4 i41 p4 #ccj4 ,on ,ocean-currents3 ,ocean-currents in ,relation to the ,distribution of ,heat over the ,globe4--,phil4 ,mag41 ,february1 #ahgj4 ,on ,ocean-currents3 ,ocean-currents in ,relation to the ,physical ,theory of ,secular ,changes of ,climate4--,phil4 ,mag41 ,march1 #ahgj4 ,the ,boulder ,clay of ,caithness a ,product of ,land-ice4--,geol4 ,mag41 ,may and ,june1 #ahgj4 ,on the ,cause of the ,motion of ,glaciers4--,phil4 ,mag41 ,september1 #ahgj4 ,on ,ocean-currents3 ,on the ,physical ,cause of ,ocean-currents4 ,examination of ,lieutenant ,maury's ,theory4--,phil4 ,mag41 ,october1 #ahgj4 ,on the ,transport of the ,wastdale ,granite ,boulders4--,geol4 ,mag41 ,january1 #ahga4 ,on a ,method of determining the ,mean ,thickness of the ,sedimentary ,rocks of the ,globe4--,geol4 ,mag41 ,march1 #ahga4 ,mean ,thickness of the ,sedimentary ,rocks4--,geol4 ,mag41 ,june1 #ahga4 ,on the ,age of the ,earth as determined from ,tidal ,retardation4--,nature1 ,august #bdth1 #ahga4 ,ocean-currents3 ,on the ,physical ,cause of ,ocean-currents4 ,examination of ,dr4 ,carpenter's ,theory4--,phil4 ,mag41 ,october1 #ahga4 ,ocean-currents3 ,further ,examination of the ,gravitation ,theory4--,phil4 ,mag41 ,february1 #ahgd4 ,ocean-currents3 ,the ,wind ,theory of ,oceanic ,circulation4--,phil4 ,mag41 ,march1 #ahgd4 ,ocean-currents4--,nature1 ,may #bast1 #ahgd4 ,the ,physical ,cause of ,ocean-currents4--,phil4 ,mag41 ,june1 #ahgd4 ,american ,journal of ,science and ,art1 ,september1 #ahgd4 ,on the ,physical ,cause of the ,submergence and ,emergence of the ,land during the ,glacial ,epoch4--,geol4 ,mag41 ,july and ,august1 #ahgd4 ,,index4 ,absolute heating-power of ocean-currents1 #bc amount of heat received from the sun per day1 #bf ,adhmar1 ,m41 theory founded upon a mistake in regard to radiation1 #ha1 #he on submergence1 #cfh on influence of eccentricity on climate1 #edb ,arial currents increased in action by formation of snow and ice1 #gf function of1 stated1 #ea heat conveyed by1 #bg ,africa1 ,south1 glacial and inter-glacial periods of1 #bdb boulder clay of ,permian age1 #cjj ,age and origin of the sun1 #cdf ,air1 on absorption of rays by1 #ei when humid1 absorbs rays which agree with it in period1 #ei when perfectly dry incapable of absorbing radiant heat1 #ei ,airy1 ,professor1 earth's axis of rotation permanent1 #g ,aitken's1 ,mr41 experiment on density of polar water1 #abi ,aland islands1 striation of1 #ddg ,alternate cold and warm periods1 #bcf ,allermuir1 striations on summit of1 #dda ,america1 low temperature in ,january1 #gb thickness of ice-sheet of ,north1 #cha ,anderson1 ,captain ,sir ,james1 never observed a stone on an iceberg1 #bhb ,antarctic regions1 mean summer temperature of1 below freezing-point1 #fc ,antarctic ice-cap1 probable thickness of1 #cge diagram representing thickness of1 #cgg thickness of1 estimated from icebergs1 #chd ,antarctic snowfall1 estimates of1 #chb ,aphelion1 glacial conditions at maximum when winter solstice is at1 #gg ,arago1 ,m41 on influence of eccentricity on climate1 #ecf ,arctic climate1 influence of ocean-currents on1 during glacial period1 #bfj ,arctic regions1 influence of ,gulf-stream on climate of1 #de mean summer temperature of1 #fc ,arctic regions1 amount of heat received by1 per unit surface1 #aie warm periods best marked in1 #beh warm inter-glacial periods in1 #behbfe state of1 during glacial period1 #bfj evidence of warm periods in1 #bfa occurrence of recent trees in1 #bfa1 #bfe evidence of warm inter-glacial periods1 #bic warm climate during ,old ,red ,sandstone period in1 #bie glacial period during ,carboniferous age in1 #big warm climate during ,permian period in1 #cja list of papers relating to1 #eef ,arctic ,ocean1 area of1 #aie according to gravitation theory ought to be warmer than ,atlantic in torrid zone1 #aie heat conveyed into1 by currents1 compared with that received by it from the sun1 #aie blocked up with polar ice1 #ddd ,armagh1 boulder beds of1 #bii ,arran1 ,island of1 glacial conglomerate of ,permian age in1 #bii ,astronomical causes of change of climate1 #aj ,astronomy and geology1 supposed analogy between1 #cee ,atlantic1 atmospheric pressure on middle of1 #cc inability of1 to heat the south-west winds without the ,gulf-stream1 #cd mean annual temperature of1 #cf mean temperature of1 raised by ,gulf-stream1 #cf1 #dj isothermal lines of1 compared with those of the ,pacific1 #df area of1 from equator to ,tropic of ,cancer1 #aid inquiry whether the area of1 is sufficient to supply heat according to ,dr4 ,carpenter's theory1 #aid ,atlantic1 ,north1 heat received by1 from torrid zone by currents1 #aid according to ,dr4 ,carpenter's theory ought to be warmer in temperate regions than in the torrid zone1 #aie great depth of warm water in1 #aih ,north1 an immense whirlpool1 #baf above the level of equator1 #bba probable antiquity of1 #cfg from ,scandinavia to ,greenland probably filled with ice1 #dea ,atmosphere-pressure in ,atlantic a cause of south-west winds1 #cc ,atmosphere1 on difference between black-bulbed and shaded thermometer in upper strata of1 #edg ,australia1 evidence of ice-action in conglomerate of1 #bie ,ayrshire1 ice-action during ,silurian period in1 #bic ,bakewell1 ,mr4 ,r41 on influence of eccentricity on climate1 #edj ,banks's ,land1 discovery of ancient forest in1 #bfa ,professor ,heer1 on fossilized wood of1 #cji ,ball1 ,mr41 objection to ,canon ,moseley's results1 #eja ,baltic current1 #aga ,baltic1 glaciation of islands in1 #ddh ,baltic glacier1 passage of1 over ,denmark1 #ddi ,bath1 grooved rock surfaces of1 #dfd ,bay-ice grinds but does not striate rocks1 #bgg ,belcher1 ,sir ,e41 tree dug up by1 in latitude #ge ,n41 #bfc carboniferous fossils found in arctic regions by1 #bih ,belle-,isle1 ,strait of1 observations on action of icebergs in1 #bgf ,bell1 ,mr4 ,a41 on ,mediterranean forms in glacial bed at ,greenock1 #bed ,belt1 ,mr4 ,thomas1 theory of the cause of glacial epochs1 #dae ,bennie1 ,mr4 ,james1 on surface geology1 #dfh on deposits filling buried channel1 #dhf ,blanford1 ,mr41 on ice-action during ,carboniferous age in ,india1 #big ,borings1 evidence of inter-glacial beds from1 #bed examination of drift by1 #dfg journals of1 #dhc1 #dhd ,boulder clays of former glacial epochs1 why so rare1 #bfi a product of land-ice1 #bhd if formed from icebergs must be stratified1 #bhd scarcity of fossils in1 #bhe formed chiefly from rock on which it lies1 #bhe of ,caithness a product of land-ice1 #dce on summit of ,allermuir1 #dda ,boulders1 how carried from a lower to a higher level1 #ebg ,boussingault on absorption of carbon by vegetation1 #dbh ,britain1 climate of1 affected most by south-eastern portion of ,gulf-stream1 #cc ,brown1 ,dr4 ,r41 cited on ,greenland ice-sheet1 #cgh1 #chj on inland ice of ,greenland1 #bhd on cretaceous formation of ,greenland1 #cje on ,miocene beds of the ,disco district1 #caj ,brown1 ,mr4 ,robert1 on growth of coal plants1 #dba ,brown and ,dickeson1 on sediment of ,mississippi1 #ccj ,buchan1 ,mr41 on atmosphere-pressure in the ,atlantic1 #cc on force of the wind1 #bbj ,buchanan1 ,mr4 ,j4 ,y41 on vertical distribution of heat of the ocean1 #eej ,buckland1 ,dr41 observations by1 on occurrence of red chalk on ,cotteswold hills1 #dei ,buff1 ,professor1 on oceanic circulation1 #ade ,buried river channels1 #dff channel from ,kilsyth to ,grangemouth1 #dfh section at ,grangemouth1 #dgd from ,kilsyth to ,clyde1 #dha not excavated by sea nor by ice1 #dfi other examples of1 #dhhdid ,caithness1 difficulty of accounting for the origin of the boulder clay of1 #dce ,caithness1 boulder clay of1 a product of land-ice1 #dce boulder clay not formed by icebergs1 #dcg theories regarding the origin of the boulder clay of1 #dcg why the ice was forced over it1 #ddd ,professor ,geikie and ,b4 ,n4 ,peach on path of ice over1 #dec ,cambrian conglomerate of ,islay1 #bib ,campbell1 ,mr41 observations of1 on icebergs1 #bgf on supposed striation of rocks by large icebergs1 #bgh evidence that river-ice does not striate rocks1 #bgi ,canada1 change of climate less complete than in ,scotland1 #ga ,carboniferous period of arctic regions1 #bih evidence of glacial epoch during1 #bifbih temperate climate of1 #dbb ,carboniferous limestone1 mode of formation1 #dcc ,carpenter's1 ,dr41 objections examined1 #ada theory1 mechanics of1 #ade idea of a vertical circulation stated1 #aec ,carpenter's1 ,dr41 radical error in theory of1 #aee on difference of density between waters of ,atlantic and ,mediterranean1 #afh theory1 inadequacy of1 #aia estimate of thermal work of ,gulf-stream1 #aii ,charpentier's1 ,m41 theory of glacier-motion1 #eac ,carse clays1 date of1 #dje ,cattegat1 ice-markings on shore of1 #ddf ,cave and river deposits1 #bea ,chalk1 erratic blocks found in1 #cjd dbris1 conclusion of ,mr4 ,searles ,wood1 #dfj ,challenger's temperature-soundings at equator1 #aai crucial test of the wind and gravitation theories1 #bbj ,chambers1 ,dr4 ,robert1 on striated pavements1 #bee observations on glaciation of ,gothland1 #ddf ,champlain ,lake1 inter-glacial bed of1 #bda ,chapelhall1 ancient buried channel at1 #dia inter-glacial sand-bed1 #bdd ,chart showing the agreement between system of currents and system of winds1 #bab ,christianstadt1 crossed by ,baltic glacier1 #dej ,circulation without difference of level1 #agf ,climate1 ,secular changes of1 intensified by reaction of physical causes1 #ge1 #gf affected most by temperature of the surface of ground1 #hh ocean-currents in relation to1 #bbf cold conditions of1 inferred from absence of fossils1 #bhh cold condition of1 difficulty of determining1 from fossil remains1 #bhi warm1 of arctic regions during ,old ,red ,sandstone period1 #bie rough sketch of the history of1 during the last #fj1jjj years1 #dji of ,coal period inter-glacial in character1 #dbj alternate changes of1 during ,coal period1 #dbf ,climates1 ,mr4 ,j4 ,geikie on difficulty of detecting evidence of ancient glacial conditions1 #bhi evidence of1 from ancient sea-bottoms1 #bhi ,coal an inter-glacial formation1 #dbj ,coal beds1 alternate submergence and emergence during formation of1 #dbd preservation of1 by submergence1 #dbf ,coal period1 flatness of the land during1 #dcj ,coal plants1 conditions necessary for1 preservation of1 #dbc ,coal seams1 thickness of1 indicative of length of inter-glacial periods1 #dbh ,coal seams1 time occupied in formation of1 #dbi ,coal strata1 on absence of ice-action in1 #dbi ,coal measures1 oscillations of sea-level during formation of1 #dbe ,cold periods best marked in temperate regions1 #beh ,colding1 ,dr41 oceanic circulation1 #ie ,confusion of ideas in reference to the agency of polar cold1 #agi ,continental ice1 inadequate conceptions of1 #che absence of1 during glacial epochs of ,coal period1 #dcb ,contorted drift near ,musselburgh1 #dfe ,cook1 ,captain1 description of ,sandwich ,land by1 #fj on ,south ,georgia1 #fj ,cornwall1 striated rocks of1 #dfd ,cotteswold hills1 red chalk from ,yorkshire found on1 #dei ,couthony1 ,mr41 on action of icebergs1 #bge ,coutts1 ,mr4 ,j41 on buried channel1 #dic ,craig1 ,mr4 ,robert1 on inter-glacial beds at ,overton ,hillhead and ,crofthead1 #bdg ,craiglockhart hill1 inter-glacial bed of1 #bde 8,crawling0 theory considered1 #ejg 8,crevasses10 origin of1 according to molecular theory1 #eba ,cretaceous period1 evidence of ice-action during1 #cjccje ,cretaceous age1 evidence of warm periods during1 #cjd ,cretaceous formation of ,greenland1 #cje ,crofthead1 inter-glacial bed at1 #bdh ,cromer forest bed1 #bej ,crosskey1 ,rev4 ,mr41 comparison of ,clyde and ,canada shell beds1 #ga on southern shells in ,clyde beds1 #bec ,croydon1 block of granite found in chalk at1 #cjc ,crucial test of the wind and gravitation theories1 #bbj ,crystallization1 force of1 a cause of glacier-motion1 #ebc ,currents1 effects of their stoppage on temperatures of equator and poles1 #db produced by saltness neutralize those produced by temperature1 #ajf ,dalager1 excursion in ,greenland by1 #cgh ,dana1 ,professor1 on action of icebergs1 #bge on striations by icebergs1 #bge on thickness of ice-sheet of ,north ,america1 #cha ,darwin1 ,mr41 on alternate cold and warm periods1 #bca on migration of plants and animals during glacial epoch1 #cie on peat of ,falkland ,islands1 #dbb ,date of the #dj-;foot beach1 #dji ,date when conditions were favourable to formations of the ,carse clay1 #dji ,davis' ,straits1 current of1 #acb ,dawkins1 ,mr4 ,boyd1 on the animals of cave and river deposits1 #bea ,dawson1 ,principal1 on esker of ,carboniferous age1 #bif on habitats of coal plants1 #dbd ,deflection of ocean-currents chief cause of change of climate1 #fh ,de la ,beche1 ,sir ,h4 ,t41 on influence of eccentricity on climate1 #eci ,de ,mairan1 on influence of eccentricity on climate1 #ebh ,denmark1 crossed by ,baltic glacier1 #ddideb ,denudation1 method of measuring rate of1 #cbi as a measure of geological time1 #cbi measured by sediment of ,mississippi1 #ccj subarial rate of1 #cca law which determines rate of1 #ccc marine1 trifling1 #ccg ,deposition1 rates of1 generally adopted1 quite arbitrary1 #cfj rate of1 determined by rate of denudation1 #cfb range of1 restricted to a narrow fringe surrounding the continents1 #cfd area of1 #cfe during glacial epoch probably less than present1 #cff ,deposits from icebergs cannot be wholly unstratified1 #dcg ,despretz1 tables by1 of temperature of maximum density of sea-water1 #aag ,desor1 ,m41 on tropical fauna of the ,eocene formation in ,switzerland1 #cjf ,derbyshire1 breaks in limestone of1 marks of cold periods1 #dcd ,derbyshire limestone a product of inter-glacial periods1 #dcd ,devonshire1 boulder clay discovered in1 #dfc ,diagram illustrating descent of water from equator to poles1 #aee showing variations of eccentricity1 #cac illustrative of fluidity of interior of the earth1 #cif showing formation of coal beds1 #dbf ,dick1 ,mr41 chalk flints in boulder clay1 #ded ,dick1 ,mr4 ,r41 on buried channel1 #dia ,difference of level essential to gravitation theory1 #agf ,dilatation of sea-water by increase of temperature calculated by ,sir ,john ,herschel1 #aaf ,disco district1 ,dr4 ,r4 ,brown cited on ,miocene beds of1 #caj ,disco ,island1 ,upper ,miocene period of1 #cjgcjh ,distribution1 how effected by ocean-currents1 #bca ,dove1 ,professor1 method of constructing normal temperature tables by1 #dj on mean annual temperature1 #dja ,dover1 mass of coal imbedded in chalk found at1 #cjc ,drayson1 ,lieutenant-,colonel1 on obliquity of ecliptic1 #daj ,drayson1 ,lieutenant-,colonel1 theory of the cause of the glacial epoch1 #daj ,drift1 examination by borings1 #dfg ,drumry1 deep surface deposits at1 #dhb ,dubuat's1 ,m41 experiments1 #ahb experiments by1 on water flowing down an incline1 #abj ,duncan1 ,captain1 on under current in ,davis' ,strait1 #acd ,drnten lignite beds1 #bdj ,drnten beds an example of inter-glacial coal formation1 #dcc ,durham1 buried river channel at1 #dhh ,earth's axis of rotation permanent1 #g ,earth1 mean temperature of1 increased by water at equator1 #cj not habitable without ocean-currents1 #ed mean temperature of1 greatest in aphelion1 #gg1 #gh centre of gravity of1 effects of ice-cap on1 #cgj1 #cga ,eccentricity of the earth's orbit1 ,mr4 ,stockwell's researches regarding1 #ed primary cause of change of climate1 #ed primary cause of glacial epochs1 #gg how it affects the winds1 #bbh tables of1 #cadcba its influence on temperature1 #cbc explanation of tables of1 #cbd ,de ,marian1 on influence of1 on climate1 #ebh ,sir ,j4 ,f4 ,herschel1 on influence of1 on climate1 #ebi pinus1 on influence of1 on climate1 #ebi ,r4 ,kirwan1 on influence of1 on climate1 #ebi of planetary orbits1 superior limits as determined by ,lagrange1 ,leverrier1 and ,mr4 ,stockwell1 #eca ,sir ,charles ,lyell1 on influence of1 on climate1 #ebi1 #ece ,m4 ,arago1 on influence of1 on climate1 #ecf ,baron ,humboldt1 on influence of1 on climate1 #ech ,sir ,h4 ,t4 de la ,beche1 on influence of1 on climate1 #eci ,professor ,phillips1 on influence of1 on climate1 #eci ,mrs4 ,somerville1 on influence of1 on climate1 #edj ,l4 ,w4 ,meech1 on influence of1 on climate1 #edj ,mr4 ,r4 ,bakewell1 on influence of1 on climate1 #edj ,m4 ,jean ,reynaud1 on influence of1 on climate1 #eda ,m4 ,adhmar1 on influence of1 on climate1 #edb ,equator1 reduction of level by denudation1 #ccf ,ecliptic1 supposed effect of a change of obliquity of1 #h changes of1 effects on climate1 #cihdag obliquity of1 ,lieutenant-,colonel ,drayson on1 #daj ,emergence1 physical cause of1 #cfh ,england1 inter-glacial beds of1 #bdi glacial origin of ,old ,red ,sandstone of1 #bid ice-action during ,permian period in1 #bih ,north of1 ice-sheet of1 #def ice-sheet of ,south of1 #dfc ,eocene period1 total absence of fossils in flysch1 #bhf glacial epoch of1 #cje ,eocene and ,miocene periods1 date of1 #ceg ,equator1 heat received per square mile at1 #bf temperature of earth increased by water at1 #cj and poles1 effects of stoppage of currents on temperature of1 #db surface-currents warmer than the under currents1 #ib heat transferred by currents from southern hemisphere compared with that received by land at1 #ic temperature soundings at1 #aai temperature of sea at1 decreases most rapidly at the surface1 #aai heat received by the three zones compared with that received by the1 #aid migration across1 #bcd glaciation of1 #bcd ,equatorial current1 displacement of1 #bbi ,erratic blocks in stratified rocks1 evidence of former land-ice1 #bfi in chalk1 #cjd why not found in coal strata1 #dcb ,erratics extend further south in ,america than in ,europe1 #gb ,etheridge1 ,r41 jun41 on glacial conglomerate in ,australia of ,old ,red ,sandstone age1 #bie ,europe1 influence of ,gulf-stream on climate of1 #ca effect of deflection of ,gulf-stream on condition of1 #fh glacial condition of1 if ,gulf-stream was stopped1 #ga river systems of1 unaltered since glacial period1 #cic ,faraday1 ,professor1 on cause of regelation1 #eed ,faroe ,islands glaciated by land-ice from ,scandinavia1 #dej ,ferrel1 ,mr41 on ,dr4 ,carpenter's theory1 #abf argument from the tides1 #ahd ,findlay1 ,mr4 ,a4 ,g41 objection by1 considered1 #ca1 #bjc estimate of heat conveyed by ,gulf-stream1 #bjf ,fisher1 ,rev4 ,o41 on the trail of ,norwich1 #bea on glacial submergence1 #chg ,fitzroy1 ,admiral1 on temperature of ,atlantic1 #cf ,fluid molecules crystallize in interstices1 #ebc ,fluvio-marine beds of ,norwich1 #bej 8,flysch0 of ,eocene period1 absence of fossils in1 #bhf of ,switzerland of glacial origin1 #cjf ,fogs prevent the sun's heat from melting ice and snow in arctic regions1 #fj ,forbes1 ,professor ,j4 ,d41 method adopted by1 of ascertaining temperatures1 #dh on temperature of equator and poles1 #dh on the conductivity of different kinds of rock1 #hf on underground temperature1 #hf experiments by1 on the power of different rocks to store up heat1 #hf ,forest bed of ,cromer1 #bej ,former glacial periods1 #bffcaj why so little known of1 #bff geological evidence of1 #bib ,france1 evidence of ice-action during ,carboniferous period in1 #bif ,fraserburgh1 glaciation of1 #dej crossed by ,north ,sea ice1 #ded ,fundamental problem of geology1 #a ,ganges1 amount of sediment conveyed by1 #cca ,gases1 radiation of1 #ch ,gastaldi1 ,m41 on the ,miocene glacial epoch of ,italy1 #cjf ,geikie1 ,professor1 on geological agencies1 #a on inter-glacial beds of ,scotland1 #bdc remarks on inter-glacial beds1 #bde on striated pavements1 #bef on ice-markings on ,scandinavian coast1 #bha striated stones found in carboniferous conglomerate by1 #bif on sediment of ,european rivers1 #ccb on modern denudation1 #ccb suggestion regarding the loess1 #deb on striation of ,caithness1 #dec on buried channel at ,chapelhall1 #dia and ,mr4 ,james1 on glacial conglomerate of ,lower ,carboniferous age1 #bif ,geikie1 ,mr4 ,james1 on ,crofthead inter-glacial bed1 #bdh on the gravels of ,switzerland1 #bfh on difficulty of recognising former glacial periods1 #bhi on ,cambrian conglomerate of north-west of ,scotland1 #bic on ice-action in ,ayrshire during ,silurian period1 #bic on boulder conglomerate of ,sutherland1 #cja on buried channels1 #dib ,geogr4 ,mittheilungen1 list of papers in1 relating to arctic regions1 #eef ,geological agencies climatic1 #b ,geological principle1 nature of1 #d ,geological climates1 theories of1 #f ,geological time1 #caacei measurable from astronomical data1 #caa why it has been over-estimated1 #cbe method of measuring1 #cbh1 #cbi ,professor ,ramsay on1 #cdc ,geology1 fundamental problem of1 #a a dynamical science1 #e and astronomy1 supposed analogy between1 #cee ,german ,polar ,expedition on density of polar water1 #aea list of papers relating to1 #eef ,german ,ocean once dry land1 #dgi ,germany1 ,professor ,ramsay on ,permian breccia of1 #cjj ,gibraltar current1 ,dr4 ,carpenter's theory of1 #afg cause of1 #bae ,glacial conditions increased by reaction of various physical causes1 #ge reach maximum when winter solstice arrives at aphelion1 #gg ,glacial epoch1 date of1 #cbg circumstances which show recent date of1 #cda ,mr4 ,belt's theory of cause of1 #dae ,glacial epochs dependent upon deflection of ocean-currents1 #fh caused primarily by eccentricity1 #gg why so little known of1 formerly1 #bff boulder clays of former1 why so rare1 #bfi geological evidence of former1 #bib ,glacial period in ,america more severe than in ,western ,europe1 #gc mean temperature of the earth greatest at aphelion during1 #gh records of1 fast disappearing1 #bgj of the ,eocene formation1 #cje ,glacial periods1 indirect evidence of1 in ,eocene and ,miocene formations1 #bhg difficulty of determining1 from fossil remains1 #bhi ,glacial submergence resulting from displacement of the earth's centre of gravity1 #chi ,glaciation a cause of submergence1 #cij remains of1 found chiefly on land surfaces1 #bfg of ,scandinavia inexplicable by theory of local glaciers1 #ddh ,glacier des ,bois1 #dig ,glacier-motion1 ,canon ,moseley's theory of1 #ejg ,professor ,james ,thomson's theory of1 #eab ,m4 ,charpentier's theory of1 #eac molecular1 #eaf ,glacier-motion1 present state of the question1 #ead molecular theory of1 #eadebg heat necessary to1 #eae due to force of crystallization1 #ebc due chiefly to internal molecular pressure1 #ebc ,glaciers1 pressure exerted by1 #bgd physical cause of the motion of1 #dieebg difficulties in accounting for motion of1 #die ,glasgow1 actual ,january temperature of1 #bh above normal1 #gb ,godwin-,austen1 ,mr41 on ice-action during the ,carboniferous period in ,france1 #bif on evidence of ice-action during ,cretaceous period1 #cjc on mass of coal found in chalk at ,dover1 #cjd on the flatness of the land during ,coal period1 #dcj ,gothland1 glaciation of1 #ddf ,grangemouth1 buried river channel at1 #dfh surface-drift of1 #dhd ,gravitation1 the whole work of1 performed by descent of water down the slope1 #aed of sun's mass1 #cdh insufficient to account for sun's heat1 #cdi1 #cej ,gravitation theory1 its relation to the theory of ,secular changes of climate1 #ig three modes of determining it1 #aae mechanics of1 #ade of the ,gibraltar current1 #afg inadequacy of1 #aia crucial test of1 #bbj of the sun's heat1 #cdfcee ,gravity1 force of1 impelling water from equator to poles1 #aai1 #abj force of1 insensible at a short distance below the surface1 #abj work performed by1 #aej diagram illustrating the action of1 in producing currents1 #aee amount of work performed by1 due solely to difference of temperature between equatorial and polar waters1 #afd specific difference in1 between water of ,atlantic and ,mediterranean insufficient to produce currents1 #afi centre of1 displacement1 by polar ice-cap1 #cfh ,greenland1 summer warm if free from ice1 #ei receives as much heat in summer as ,england1 #ff continental ice free from clay or mud1 #bhd ,north1 warm climate during ,oolitic period in1 #cjb ,cretaceous formation of1 #cje ,greenland1 evidence of warm conditions during ,miocene period in1 #cjg ,professor ,heer cited on ,miocene flora of1 #cjh1 #cji state of1 during glacial period1 #bei effect of removal of ice from1 #bfj ,greenland ice-sheet1 probable thickness of1 #cgh invaded the ,american continent1 #dde ,greenland inland ice1 #cgi ,gulf-stream1 estimate of its volume1 #bd ,united ,states' coast survey of1 #bd absolute amount of heat conveyed by1 #be1 #bf heat conveyed by1 compared with that carried by arial currents1 #bg heat conveyed by1 compared with that received by the frigid zone from the sun1 #bg influence on climate of ,europe1 #ca efficiency of1 due to the slowness of its motion1 #cb climate of ,britain influenced by south-eastern portion of1 #cc heat conveyed by1 compared with that derived by temperate regions from the sun1 #cd heat of1 expressed in foot-pounds of energy1 #ce mean temperature of ,atlantic increased one-fourth by1 #cf the only current that can heat arctic regions1 #de influence of1 on climate of arctic regions1 #de the compensating warm current1 #df palontological objections to influence of1 #ec agencies which deflect the1 in glacial periods1 #fi result1 if stopped1 #ga large portion of the heat derived from southern hemisphere1 #id ,lieut4 ,maury on propulsion of1 by specific gravity1 #ajb contradictory nature of1 the causes supposed by ,lieut4 ,maury for the1 #aaj higher temperature of1 considered by ,lieut4 ,maury as the real cause of its motion1 #aaa amount of heat conveyed by1 not over-estimated1 #aig amount of heat conveyed by1 #aib amount of heat conveyed by1 compared with that by general oceanic circulation1 #aid heat conveyed by1 compared with that received by torrid zone from the sun1 #aid heat conveyed by1 into ,arctic ,ocean compared with that received by it from the sun1 #aie ,capt4 ,nares's observations of1 #aih ,dr4 ,carpenter's estimate of the thermal work of1 #aii ,gulf-stream1 volume and temperature of1 according to ,mr4 ,a4 ,g4 ,findlay1 #bjc1 #bjf erroneous notion regarding depth of1 #bjg list of papers relating to1 #eef ,haughton1 ,professor1 on recent trees in arctic regions1 #bfc on fragments of granite in carboniferous limestone1 #bif on coal beds of arctic regions1 #bih on ,ammonites of ,oolitic period in arctic regions1 #cjc ,hayes1 ,dr41 on ,greenland ice-sheet1 #cgi ,heat received from the sun per day1 #bf received by temperate regions from the sun1 #cd radiant1 absorbed by ice remains insensible1 #fj sun's1 amount of1 stored up in ground1 #hg transferred from southern to northern hemisphere1 #ic internal1 supposed influence of1 #agf received by the three zones compared with that received by the equator1 #aid amount radiated from the sun1 #cdf received by polar regions #aa1gjj years ago1 #djc necessary to glacier-motion1 #eae how transmitted through ice1 #eag ,heat-vibrations1 nature of1 #edd ,heath1 ,mr4 ,d4 ,d41 on glacial submergence1 #chg ,heer1 ,professor1 on ,drnten lignite beds1 #bda on ,miocene flora of ,greenland1 #cjhcaj on ,miocene flora of ,spitzbergen1 #cji ,hills1 ice-markings on summits of1 as evidence of continental ice1 #deh ,helmholtz's gravitation theory of sun's heat1 #cdh ,henderson1 ,mr4 ,john1 on inter-glacial bed at ,redhall quarry1 #bdg ,herschel1 ,sir ,john1 on influence of eccentricity1 #aa estimate of the ,gulf-stream by1 #be on the amount of the sun's heat1 #bf on inadequacy of specific gravity to produce ocean-currents1 #aaf his objections to specific gravity not accepted1 #aag on influence of eccentricity on climate1 #ebi ,home1 ,mr4 ,milne1 on buried river channels1 #dgh ,hooker1 ,sir ,w41 on tree dug up by ,capt4 ,belcher1 #bfd ,hooker1 ,dr41 on preponderance of ferns among coal plants1 #dba ,horne1 ,mr4 ,j41 on conglomerates of ,isle of ,man1 #bie ,hoxne1 inter-glacial bed of1 #bda ,hudson's ,bay1 low mean temperature of1 in ,june1 #fb ,hull1 ,professor1 on ice-action during ,permian age in ,ireland1 #bii on equable temperature of ,coal period1 #dba on estuarine origin of coal measures1 #dbd ,hull1 buried channel at1 #dhi ,humboldt1 ,baron1 on loss of heat from radiation1 #hb on rate of growth of coal1 #dbi on influence of eccentricity on climate1 #ech ,humphreys and ,abbot on sediment of ,mississippi1 #ccj ,ice1 latent heat of1 #fj ,ice1 effects of removal of1 from polar regions1 #fd heat absorbed by1 employed wholly in mechanical work1 #fj slope necessary for motion of continental1 #cge does not shear in the solid state1 #eaf how heat is transmitted through1 #eag how it can ascend a slope1 #ebe how it can excavate a rock basin1 #ebe ,icebergs do not striate sea-bottom1 #bgb markings made by1 are soon effaced1 #bgc exerting little pressure perform little work1 #bgc behaviour of1 when stranded1 #bgd action of1 on sea-bottoms1 #bgd rocks ground smooth1 but not striated by1 #bgf stones seldom seen on1 #bha evidence of1 in ,miocene formation of ,italy1 #cjg comparative thickness of arctic and antarctic1 #cha great thickness of antarctic1 #chb ,ice-cap1 effects of1 on the earth's centre of gravity1 #cfi probable thickness of antarctic1 #cge evidence from icebergs as to thickness of antarctic1 #chcche ,ice-markings1 modern1 observed by ,sir ,charles ,lyell1 #bhj ,ice-sheet1 probable thickness of in ,greenland1 #chj of north of ,england1 #def ,ice-worn pebbles found on summit of ,allermuir1 #dda ,iceland1 lignite of ,miocene age in1 #cjh probably glaciated by land-ice from ,north ,greenland1 #dea ,india1 evidences of glacial action of ,carboniferous age in1 #big ,indian ,ocean1 low temperature at bottom1 #abc ,internal heat1 no influence on climate1 #f supposed influence of1 #agf ,inter-tropical regions1 greater portion of moisture falls as rain1 #bi ,inter-glacial bed at ,slitrig1 #bdc at ,chapelhall1 #bdd of ,craiglockhart hill1 #bde at ,kilmaurs1 #bdh ,inter-glacial beds1 ,professor ,geikie on1 #bdc of ,drnten1 #bdj of ,scotland1 #bdc of ,england1 #bdi at ,norwich1 #bej evidence of1 from borings1 #bed ,inter-glacial character of cave and river deposits1 #bea ,inter-glacial climate during ,old ,red ,sandstone period in arctic regions1 #bie ,inter-glacial periods1 #bcf reason why overlooked1 #bcg of ,switzerland1 #bci evidence of1 from shell-beds1 #beb evidence from striated pavements of1 #bee reasons why so few vestiges remain of1 #beg in arctic regions1 #behbfe of ,silurian age in arctic regions1 #bic of ,carboniferous age in arctic regions1 #big of ,eocene formation in ,switzerland1 #cjf formation of coal during1 #dbj length of1 indicated by thickness of coal-seams1 #dbh ,inglefield1 ,captain1 erect trees found in ,greenland by1 #cji ,ireland1 on ice-action during ,permian age in1 #bii ,isbister1 ,mr41 on carboniferous limestone of arctic regions1 #big ,islay1 ,cambrian conglomerate of1 #bib ,italy1 glacial epoch of ,miocene period in1 #cjf ,jack1 ,mr4 ,r4 ,l41 on deflection of ice across ,england1 #dfa ,jamieson1 ,mr4 ,t4 ,f41 on boulder clay of ,caithness1 #dce opinion that ,caithness was glaciated by floating ice1 #dcg on thickness of ice in the north ,highlands1 #dci glaciation of headland of ,fraserburgh1 #dej1 #dee ,january temperature of ,glasgow and ,cumberland1 difference between1 #gb ,jeffreys1 ,mr4 ,gwyn1 on ,swedish glacial shell beds1 #bec ,johnston1 ,dr4 ,a4 ,keith1 on coast-line of the globe1 #ccg ,joule's1 ,dr41 experiments on the thermal effect of tension1 #eeb ,judd1 ,mr41 on boulders of ,jurassic age in the ,highlands1 #cjb ,jukes1 ,mr41 on warm climate of ,north ,greenland during ,oolitic period1 #cjb ,july1 why hotter than ,june1 #hi ,kane1 ,dr41 on mean temperature of ,von ,rensselaer ,harbour1 #fb ,karoo beds1 glacial character of1 #cja evidence of subtropical during deposition of1 #cja ,kelvin1 ancient bed of1 #dha ,kielsen1 ,mr41 excursion upon ,greenland ice-sheet1 by1 #cgh ,kilmours1 inter-glacial bed at1 #bdh ,kirwan1 ,richard1 on influence of eccentricity on climate1 #ebi ,kyles of ,bute1 southern shell bed in1 #bec ,labrador1 mean temperature of1 for ,january1 #gb ,mr4 ,packard on glacial phenomena of1 #bhb ,lagrange1 ,m41 on eccentricity of the earth's orbit1 #ed table of superior limits of eccentricity1 #eca ,land at equator would retain the heat at equator1 #cj radiates heat faster than water1 #ia elevation of1 will not explain glacial epoch1 #cia submergence and emergence during glacial epoch1 #cfhcig successive upheavals and depressions of1 #cia ,land-ice necessarily exerts enormous pressure1 #bgd evidence of former1 from erratic blocks on stratified deposits1 #bfi ,land-surfaces1 remains of glaciation found chiefly on1 #bfg 7ancient7 scarcity of1 #bfh ,laplace1 ,m41 on obliquity of ecliptic1 #cih ,laughton1 ,mr41 on cause of ,gibraltar current1 #bae ,leith ,walk1 inter-glacial bed at1 #bdf ,leverrier1 ,m41 on superior limit of eccentricity1 #ed on obliquity of ecliptic1 #cih table1 by1 of superior limits of eccentricity1 #eca formul1 of1 #cab ,lignite beds of ,drnten1 #bdj ,loess1 origin of1 #deb ,london1 temperature of1 raised #dj degrees by ,gulf-stream1 #dc ,lomonds1 ice-worn pebbles found on1 #dci ,lubbock1 ,sir ,j41 on cave and river deposits1 #beb ,lucy1 ,mr4 ,w4 ,c41 on glaciation of ,west ,somerset1 #dfc on northern derivation of drift on ,cotteswold hills1 #dfj ,lyell's1 ,sir ,c41 theory of the effect of distribution of land and water1 #h on action of river-ice1 #bhj on tropical character of the fauna of the ,cretaceous formation1 #cje on warm conditions during ,miocene period in ,greenland1 #cjg on influence of eccentricity1 #cbd on sediment of ,mississippi1 #cca on comparison of existing rocks with those removed1 #cfb on submerged areas during ,tertiary period1 #cib on change of obliquity of ecliptic1 #dah on climate best adapted for coal plants1 #dbj on influence of eccentricity on climate1 #ebi1 #ece ,mackintosh1 ,mr41 observations on the glaciation of ,wastdale ,crag1 #deg ,magellan1 ,straits of1 temperature at midsummer1 #fa ,mahony1 ,mr4 ,j4 ,a41 on ,crofthead inter-glacial bed1 #bdh ,mlar ,lake crossed by ice1 #ddg ,man1 ,isle of1 ,mr4 ,cumming on glacial origin of ,old ,red ,sandstone of1 #bid ,mars1 uncertainty as to its climatic condition1 #hj objection from present condition of1 #gi ,marine denudation trifling1 #ccg ,markham1 ,clements1 on density of ,gulf-stream water1 #abi on motion of icebergs in ,davis' ,straits1 #acc ,martins's1 ,professor ,charles1 objections1 #gi ,mathews1 ,mr41 on ,canon ,moseley's experiment1 #dii ,maury1 ,lieutenant1 his estimate of the ,gulf-stream1 #be his theory examined1 #ie on temperature as a cause of difference of specific gravity1 #ajb on difference of saltness as a cause of ocean-currents1 #ajc discussion of his views of the causes of ocean-currents1 #ajd his objection to wind theory of ocean-currents1 #baa ,mc,clure1 ,captain1 discovery of ancient forest in ,banks's ,land1 #bfa ,mecham1 ,lieutenant1 discovery of recent trees in ,prince ,patrick's ,island1 #bfa ,mechanics of gravitation theory1 #ade ,mediterranean shells in glacial shell bed of ,udevalla1 #bec shells in glacial beds at ,greenock1 #bed ,meech1 ,mr41 on amount of sun's rays cut off by the atmosphere1 #bf on influence of eccentricity on climate1 #edj ,melville ,island1 summer temperature of1 #fe discovery of recent trees in1 #bfb plants found in coal of1 #bih ,mer de ,glace1 ,professor ,tyndall's observations on1 #dih ,meteoric theory of sun's heat1 #cdg ,method of measuring rate of denudation1 #cbi ,miller1 ,hugh1 on absence of hills in the land of the ,coal period1 #dca ,migration of plants and animals1 how influenced by ocean-currents1 #bca across equator1 #bcd ,millichen1 remarkable section of drift at1 #dhc ,miocene glacial period1 #bhf ,miocene period1 glacial epoch of1 in ,italy1 #cjf ,miocene1 warm period of1 in ,greenland1 #cjg ,miocene and ,eocene periods1 date of1 #ceg ,mississippi1 amount of sediment in1 #ccj volume of1 #ccj ,mitchell1 ,mr41 on cause of ,gulf-stream1 #aca ,molecular theory of origin of ,crevasses10 #eba modification of1 #ebc ,moore1 ,mr4 ,j4 ,carrick1 on ice-action of ,silurian age in ,wigtownshire1 #bic ,moore1 ,mr4 ,charles1 on grooved rocks in ,bath district1 #dfd ,morlot1 ,m41 on inter-glacial periods of ,switzerland1 #bdj ,moseley1 ,canon1 experiment to determine unit of shear1 #dih on motion of glaciers1 #dih unit of shear uncertain1 #ejd his theory examined1 #ejg ,motion of the sea1 how communicated to a great depth1 #acf ,motion in space1 origin of sun's heat1 #cec ,mhry1 ,m41 on circumpolar basin1 #acc1 #eef ,mundsley1 freshwater beds of1 #bej ,muncke on the expansion of sea-water1 #aah ,murchison1 ,sir ,r41 on southern shells at ,worcester1 #bec on trees in arctic regions1 #bfb on striation of islands in the ,baltic1 #ddh ,murphy's1 ,mr41 theory1 #ff ,musselburgh1 section of contorted drift near1 #dfe ,nares1 ,captain1 on low temperature of antarctic regions1 #fd discovery of great depth of warm water in ,north ,atlantic1 #aih estimate of volume and temperature of ,gulf-stream1 #aih temperature soundings by1 #aai1 #bbb thermal condition of ,southern ,ocean1 #bbe ,natal1 boulder clay of1 #cjj ,newberry1 ,professor1 on inter-glacial peat-bed of ,ohio1 #bdi on boulder of quartzite found in seam of coal1 #bif ,nicholson1 ,dr41 on ,wastdale ,crag1 #deg ,nicol1 ,professor1 on inter-glacial buried channel1 #bdd ,nordenskjld1 ,professor1 on inland ice of ,greenland1 #cgi ,north ,sea rendered shallow by drift deposits1 #ddc ,northern seas probably filled with land-ice during glacial period1 #dch ,northern hemisphere1 condition of1 when deprived of heat from ocean-current1 #fh ,norway1 southern species in glacial shell beds1 #bec ,norwich ,crag1 its glacial character1 #bdi ,norwich fluvio-marine beds1 #bej ,norwich inter-glacial beds1 #bej ,obliquity of ecliptic1 its effects on climate1 #cihdai change of1 influence on sea-level1 #djc ,lieutenant-,colonel ,drayson on1 #daj ,mr4 ,belt on change of1 #dae ,sir ,charles ,lyell on change of1 #dah ,ocean1 imperfect conception of its area1 #ace condition of1 inconsistent with the gravitation theory1 #acf low temperature at bottom a result of under currents1 #adb circulation1 pressure as a cause of1 #ahg antiquity of1 #cfg ,ocean-currents1 absolute heating power of1 #bc influence of1 on normal temperatures overlooked1 #dj maximum effects of1 reached at equator and poles1 #di compensatory at only one point1 #di heating effects of1 greatest at the poles1 #ej cooling effects of1 greatest at equator1 #ej earth not habitable without1 #ea result of deflection into ,southern ,ocean1 #fh palontological objections against influence of1 #ec deflection of1 the chief cause of changes of climate1 #fh how deflected by eccentricity1 #fi deflected by trade-winds1 #gj temperature of southern hemisphere lowered by transference of heat to northern hemisphere by1 #ib take their rise in the ,southern ,ocean1 #ib cause of1 never specially examined by physicists1 #ie if due to specific gravity1 strongest on cold hemisphere1 #ig if due to eccentricity1 strongest on warm hemisphere1 #ig if due to specific gravity1 act only by descent1 #ii mode by which specific gravity causes1 #ajj1 #aja the true method of estimating the amount of heat conveyed by1 #bjg due to system of winds1 #bab system of1 agrees with the system of the winds1 #bac how they mutually intersect1 #bai in relation to climate1 #bbf direction of1 depends on direction of winds1 #bbg causes which deflect1 affect climate1 #bbh in relation to distribution of plants and animals1 #bca effects of1 on ,greenland during glacial period1 #bfj pinus on influence of eccentricity on climate1 #ebi ,ohio inter-glacial beds1 #bdi ,old ,red ,sandstone1 evidence of ice-action in conglomerate of1 #bid1 #bie ,oolite of ,sutherlandshire1 #ded ,oolitic period1 evidence of ice-action during1 #cjacjc warm climate in ,north ,greenland during1 #cjb ,organic remains1 absence of1 in glacial conglomerate of ,upper ,miocene period1 #bhf ,organic life1 paucity of1 a characteristic of glacial periods1 #bhg ,orkney ,islands1 glaciated by land-ice1 #ddd ,osborne1 ,captain1 remarks on recent forest trees in arctic regions1 #bfb1 #bfc ,oudemans1 ,dr41 on planet ,mars1 #hj ,overton ,quarry1 inter-glacial bed in1 #bdg ,pacific ,ocean1 depth of1 #adg ,packard1 ,mr41 on glacial phenomena of ,labrador1 #bhb ,page1 ,professor1 on temperate climate of ,coal period1 #dbb on character of coal plants1 #dba on old watercourse at ,hailes quarry1 #dij ,palontological objections against influence of ocean-currents1 #ec ,palontological evidence of last glacial period1 #bhe ,parry1 ,captain1 discovery of recent trees in ,melville ,island by1 #bfb ,peach1 ,mr4 ,c4 ,w41 on inter-glacial bed at ,leith ,walk1 #bdf on boulder clay of ,caithness1 #dcf on striated rock surfaces in ,cornwall1 #dfd ,peach1 ,mr4 ,b4 ,n41 on striation of ,caithness1 #dec ,pengelly1 ,mr4 ,w41 on raised beaches1 #djg ,perigee1 nearness of sun in1 cause of snow and ice1 #gd ,perihelion1 warm conditions at maximum when winter solstice is at1 #gg ,permian period1 evidence of ice-action in1 #bihcjc ,perthshire hills1 ice-worn surfaces at elevations of #b1bjj feet on the1 #ddj ,petermann1 ,dr4 ,a41 on ,dr4 ,carpenter's theory1 #ach on thermal condition of the sea1 #ach chart of ,gulf-stream and ,polar current1 #bai ,geogr4 ,mittheilungen of1 list of papers in relation to arctic regions1 #eef ,phillips1 ,professor1 on influence of eccentricity on climate1 #eci ,poisson's theory of hot and cold parts of space1 #g ,polar regions1 effect of removal of ice from1 #fd influence of ice on climate1 #fd low summer temperature of1 #ff ,polar cold considered by ,dr4 ,carpenter the primum mobile of ocean-currents1 #agc confusion of ideas regarding its influence1 #ahj influence of1 according to ,dr4 ,carpenter1 #ahj ,polar ice-cap1 displacement of the earth's centre of gravity by1 #cfh ,port ,bowen1 mean temperature of1 #fc ,portobello1 striated pavements near1 #bee1 #bef ,post-tertiary formations1 hypothetical thickness of1 #cff ,pouillet1 ,m41 on the amount of the sun's heat1 #bf on amount of sun's rays cut off by the atmosphere1 #bf ,pratt1 ,archdeacon1 on glacial submergence1 #chg ,prestwich1 ,professor1 on ,hoxne inter-glacial bed1 #bda ,pressure as a cause of circulation1 #ahg ,principles of geology1 nature of1 #d ,prince ,patrick's ,island1 discovery of recent tree in1 #bfa ,radiation1 rate of1 increases with increase of temperature1 #cg of gases1 #ch the way by which the earth loses heat1 #ci how affected by snow covering the ground1 #eh how affected by humid air1 #ei accelerated by increased formation of snow and ice1 #ge ,raised beaches1 date of1 #djg ,mr4 ,pengelly on1 #djg ,ramsay1 ,professor1 on glacial origin of ,old ,red ,sandstone of ,north of ,england1 #bid on ,old ,red ,sandstone1 #cfg on geological time1 #cdc on ice-action during ,permian period1 #bih on boulders of ,permian age in ,natal1 #cja on thickness of stratified rocks of ,britain1 #bfg1 #cfa ,redhall ,quarry1 inter-glacial bed in1 #bdg ,red ,sea1 why almost rainless1 #cj ,regelation1 rationale of1 #ebj1 #eed ,professor ,james ,thomson on cause of1 #eed ,professor ,faraday on cause of1 #eed ,regnault1 ,m41 on specific heat of sandstone1 #hf ,reynaud1 ,jean1 on influence of eccentricity on climate1 #eda ,rhine1 ancient1 bed in ,german ,ocean1 #dhj ,ridge between ,capes ,trafalgar and ,spartel1 influence of1 #afg ,rink1 ,dr41 on inland ice of ,greenland1 #chj ,river-ice1 effect of1 #bgi ,river-ice does not produce striations1 #bgi ,river systems1 carrying-power measure of denudation1 #ccf ,river valleys1 how striated across1 #ebe ,robertson1 ,mr4 ,david1 on ,crofthead and ,hillhead inter-glacial beds1 #bdg1 #bdh on foraminifera in red clay1 #dhe ,rock-basins1 how excavated by ice1 #ebe ,rocks removed by denudation1 #cfa ,ross1 ,capt4 ,sir ,james1 on ,south ,shetland1 #fa on temperature of antarctic regions in summer1 #fc ,sandwich ,land1 description by ,capt4 ,cook1 #fj cold summers of1 not due to latitude1 #fd ,salter1 ,mr41 on carboniferous fossils of arctic regions1 #bih on warm climate of ,north ,greenland during ,oolitic period1 #cjb ,saltness of the ocean1 difference of1 as a cause of motion1 #ajc in direct opposition to temperature in producing ocean-currents1 #ajd ,scandinavian ice1 track of1 #ddg ,scandinavian ice-sheet in the ,north ,sea1 #ddd ,scoresby1 ,dr41 on condition of arctic regions in summer1 #eh1 #fb on density of ,gulf-stream water1 #abi ,scotland1 inter-glacial beds of1 #bdcbdi evidence of ice-action in carboniferous conglomerate of1 #bif buried under ice1 #dci ice-sheet of1 in ,north ,sea1 #ddb why ice-sheet was so thick1 #deb ,sea1 height of1 at equator above poles1 #aai rise of1 due to combined effect of eccentricity and obliquity1 #djc bottoms not striated by icebergs1 #bgb ,sea and land1 present arrangement indispensable to life1 #eb ,sea-level1 oscillations of1 in relation to distribution1 #cid oscillations of1 during formation of coal measures1 #dbd raised1 by melting of antarctic ice-cap1 #chh influence of obliquity of ecliptic on1 #djc ,section of ,mid-,atlantic1 #bbb ,section across antarctic ice-cap1 #cgg ,sedimentary rocks existing fragmentary1 #cfa of the globe1 mean thickness of1 hitherto unknown1 #cfa how mean thickness might be determined1 #cfb mean thickness of1 over-estimated1 #cfd ,shearing-force of ice1 #dif momentary loss of1 #eah ,shetland islands glaciated by land-ice from ,scandinavia1 #dej ,shetland1 ,south1 glacial condition of1 #fa ,shell-beds1 evidence of warm inter-glacial periods from1 #beb ,shells of the boulder clay of ,caithness1 #dej ,shore-ice1 striations produced by1 in ,bay of ,fundy1 #bhj ,silurian period1 ice-action in ,ayrshire during1 #bic evidence in ,wigtownshire of ice-action during1 #bic ,slitrig1 inter-glacial bed of1 #bdc ,slope of surface of maximum density has no power to produce motion1 #abj from equator to pole1 erroneous view regarding1 #abj ,smith1 ,mr4 ,leigh1 temperature soundings1 #abi ,smith1 ,mr41 of ,jordanhill1 on striated pavements1 #bef ,snow1 how radiation is affected by1 #eh common in summer in arctic regions1 #fb rate of accumulation of1 increased by sun's rays being cut off by fogs1 #ge formation increased by radiation1 #ge ,somerset1 ,west1 glaciation of1 #dfc ,somerville1 ,mrs41 on influence of eccentricity on climate1 #edj ,south ,africa1 glaciation of1 #bdb boulder clay of ,permian age in1 #cjj ,south of ,england ice-sheet1 #dfc ,south ,shetland1 glacial condition of1 at mid summer1 #fa ,south-west winds1 heat conveyed by1 not derived from equatorial regions1 #bh heat conveyed by1 derived from ,gulf-stream1 #bh ,southern hemisphere1 present extension of ice on1 due partly to eccentricity1 #gh why colder than northern1 #haib absorbs more heat than the northern1 #ij lower temperature of1 due to ocean-currents1 #ib surface currents from1 warmer than under currents to1 #ib glacial and inter-glacial periods of1 #bdb ,southern ,ocean1 thermal condition of1 #bbe ,specific gravity can act only by causing water to descend a slope1 #ii mode of action in causing ocean-currents1 #ajj inadequacy of1 to produce ocean-currents demonstrated by ,sir ,john ,herschel1 #aaf ,spitzbergen1 ,gulf-stream and under current at1 #acd ,miocene flora of1 #cji ,stellar space1 temperature of1 #ce received temperature of1 probably too high1 #ci ,stewart1 ,professor ,balfour1 experiment on radiation1 #cg on cause of glacial cold1 #gi ,stirling1 ,mr41 on old watercourse near ,grangemouth1 #dha ,st4 ,john's ,river1 action of ice on banks of1 #bgi ,st4 ,lawrence1 action of ice on bank of river1 #bgi ,stockwell1 ,mr41 on eccentricity of earth's orbit1 #ed on obliquity of ecliptic1 #cii table of superior limits of eccentricity1 #eca ,stone1 ,mr41 on eccentricity of the earth's orbit1 #cbb ,stow1 ,g4 ,w41 on glacial beds of ,south ,africa1 #bdb on ,karoo beds1 #cja ,stri1 direction of1 show the clay of ,caithness came from the sea1 #dcf ,striations obliterated rather than produced by icebergs1 #bgd ,striated pavements why so seldom observed1 #bef evidence of inter-glacial periods from1 #bee ,striated stones found in conglomerate of ,lower ,carboniferous age by ,professor ,geikie1 #bif in ,permian breccias1 #bii in the glacial conglomerate of the ,superga1 ,turin1 #cjf ,stratified rocks may be formed at all possible rates1 #cfj rate of formation of1 as estimated by ,professor ,huxley1 #cfc ,struve1 ,m41 formula of obliquity of ecliptic1 #djd ,subarial denudation1 rate of1 #cca ,submarine forests1 #dji 7ancient71 coal seams the remains of1 #dbh ,submergence1 physical causes of1 #cfh coincident with glaciation1 #chi of land resulting from melting of antarctic ice-cap1 #chi how affected by fluidity of interior of the earth1 #cie necessary for preservation of coal plants1 #dbc frequent during formation of coal beds1 #dbf ,subsidence insufficient to account for general submergence1 #cij necessary to accumulation of coal seams1 #dbg ,sun supposed by some to be a variable star1 #h maximum and minimum distance of1 #ee rays of1 cut off by fogs in ice-covered regions1 #fj nearness in perigee a cause of snow and ice1 #gd total amount of heat radiated from1 #cdf age and origin of1 #cdf source of its energy1 #cdg heat of1 origin and chief source of1 #cdi originally an incandescent mass1 #cej energy of1 may have originally been derived from motion in space1 #cee ,surface currents which cross the equator warmer than the compensatory under currents1 #ib ,surface currents from poles to equator1 according to ,maury1 produced by saltness1 #ajh ,sutherland1 ,dr41 observations by1 on stranding of icebergs1 #bge testimony1 that icebergs do not striate rocks1 #bgh on the boulder clay of ,natal1 #cjj ,sutherland1 boulder conglomerate of ,oolitic period of1 #cjb ,sweden1 ,southern1 shells in glacial shell beds of1 #bec ,switzerland1 inter-glacial period of1 #bci ,m4 ,morlat on inter-glacial periods of1 #bdj gravels of1 by ,mr4 ,james ,geikie1 #bfh ,eocene glacial epoch in1 #cje ,table of ,june temperatures in different latitudes1 #fe soundings in temperate regions1 #bbb ,tables of eccentricity1 #cadcba of eccentricity1 explanation of1 #cbb ,tay1 valley of1 striated across1 #ebf ancient buried channel of1 #dij ,temperate regions1 cold periods best marked in1 #beh ,temperature of space1 #ecb reasons why it should be reconsidered1 #ci ,temperature 7mean7 of equator and poles compared1 #da why so low in polar regions during summer1 #ff how difference of specific gravity is caused by1 #ajb higher1 of the waters of ,gulf-stream considered by ,lieutenant ,maury as the real causes of its motion1 #aaa of sea at equator decreases most rapidly at the surface1 #aai of ,greenland in ,miocene period1 #caj of poles when obliquity was at its superior limit1 #djb ,tension1 effect of1 on ice1 #ebb the cause of the cooling effect produced by1 #eeb ,tertiary period1 climate of1 error in regard to1 #bhh ,thermal condition of ,southern ,ocean1 #bbe ,thibet1 table-land of1 #dah ,thomson1 ,professor ,james1 on cause of regelation1 #eed theory of glacier-motion1 #eab ,thomson1 ,mr4 ,james1 on glacial conglomerate in ,arran1 #bii on ice-action in ,cambrian conglomerate of ,islay1 #bib ,thomson1 ,professor ,wyville1 on ,dr4 ,carpenter's theory1 #abi cited1 #acj thermal condition of the sea1 #ach ,thomson1 ,sir ,w41 amount of internal heat passing through earth's crust1 #adb on limit to age of the globe1 #cdc on influence of ice-cap on sea-level1 #cgb climate not affected by internal heat1 #f earth's axis of rotation permanent1 #g on volume and mass of the sun1 #cdg ,tidal wave1 effect of friction1 #ccf ,tides1 supposed argument from1 #ahd ,time1 geological1 #caacei as represented by geological phenomena1 #cbf represented by existing rocks1 #cfa ,torrid zone1 annual quantity of heat received by1 per unit of surface1 #aid ,towncroft farm1 section of channel at1 #dgd ,towson1 ,mr41 on icebergs of ,southern ,ocean1 #chc ,trade-winds 7anti71 heat conveyed by1 over-estimated1 #bh 7anti7 derive their heat from the ,gulf-stream1 #cb of warm hemisphere overborne by those of cold hemisphere1 #gj causes which determine the strength of1 #gj strongest on glaciated hemisphere1 #gj reaction upon trade-winds by formation of snow and ice1 #gf influence of1 in turning ocean-currents on warm hemisphere1 #ig do not explain the antarctic current1 #baa ,tiddeman on ,north of ,england ice-sheet1 #deh displacement of1 #bcj ,transport of boulders and rubbish the proper function of icebergs1 #bha ,trafalgar1 effect of ridge between ,capes ,spartel and on ,gibraltar current1 #afg ,turner1 ,professor1 on arctic seal found at ,grangemouth1 #dhe ,tylor1 ,alfred1 on denudation of ,mississippi basin1 #ccc ,tyndall1 ,professor1 on heat in aqueous vapour1 #bi on sifted rays1 #dg on diathermancy of air1 #ei on glacial epoch1 #gh ,udevalla1 ,mediterranean shell in glacial shells1 bed of1 #bec ,under currents to southern hemisphere colder than surface currents from1 #ib produced by saltness1 flow from equator to poles1 #ajf account for cold water at equator1 #abd1 #adb in ,davis' ,strait1 #acd take path of least resistance1 #acj why considered improbable1 #ace difficulty regarding1 obviated1 #bag theory of1 #bag ,underground temperature1 ,professor ,j4 ,d4 ,forbes on1 #hf ,underground temperature exerts no influence on the climate1 #hh absolute amount of heat derived from1 #adb supposed influence of1 #agf ,uniformity1 modern doctrine of1 #cbe ,united ,states' coast survey of ,gulf-stream1 #bd hydrographic department1 papers published by1 #eef ,unstratified boulder clay must be the product of land-ice1 #dcg ,upsala and ,stockholm striated by ,baltic glacier1 #ddg ,vertical circulation1 ,lieutenant ,maury's theory of1 #ajh according to ,dr4 ,carpenter1 #aec ,vertical descent of polar column caused by extra pressure of water upon it1 #aed effects of1 and slope1 the same1 whether performed simultaneously or alternately1 #aei of polar column illustrated by diagram1 #afj ,vertical distribution of heat in the ocean1 ,mr4 ,buchanan's theory1 #eej ,vogt1 ,professor1 on ,drnten lignite bed1 #bda ,warm hemisphere made warmer by increased reaction of physical causes1 #gf ,warm periods best marked in arctic regions1 #beh in arctic regions1 evidence of1 #bfa better represented by fossils than cold periods1 #bhh evidence of1 during ,cretaceous age1 #cjd ,warm inter-glacial periods in arctic regions1 #behbfe ,water at equator the best means of distributing heat derived from the sun1 #cj ,water1 a worse radiator than land1 #ia ,wastdale granite boulders1 difficulty of accounting for transport of1 #def ,wastdale ,crag glaciated by continental ice1 #deg ,weibye1 ,m41 striation observed by1 #bhj ,wilkes1 ,lieutenant1 on cold experienced in antarctic regions in summer1 #fc ,wellington ,sound1 ancient trees found at1 #bfe ,winter-drift of ice on coast of ,labrador1 #bgf ,west winds1 moisture of1 derived from ,gulf-stream1 #bi ,wind1 work in impelling currents1 #bai ,winds1 ocean-currents produced by1 #bab system of1 agrees with the system of ocean-currents1 #bac ,wind theory of oceanic circulation1 #baj crucial test of1 #bbj ,wigtownshire1 ice-action during ,silurian age1 #bic ,work performed by descent of polar column1 #aeg ,wood1 ,mr4 ,nicholas1 on buried channel1 #dhh ,wood1 ,jun41 ,mr4 ,searles1 middle drift1 #bej on occurrence of chalk dbris in south-west of ,england1 #dfj ,woodward1 ,mr4 ,h4 ,b41 on boulder clay in ,devonshire1 #dfc ,wunsch1 ,mr4 ,e4 ,a41 on glacial conglomerate in ,arran1 #bii ,yare1 ancient buried channel of1 #dhi ,young1 ,mr4 ,j41 objection considered1 #dhb ,yorkshire drift common in south of ,england1 #dfj ,zenger1 ,professor1 on the moon's influence on climate1 #cbd ,,the ,,end4 ,,printed ,,by ,,virtue ,,and ,,co41 ,,city ,,road1 ,,london4 ,,the ,,great ,,ice ,,age1 ,,and ,,its ,,relation ,,to ,,the ,,antiquity ,,of ,,man4 ,by ,,james ,,geikie1 ,f4,r4,s4,e41 ,f4,g4,s41 c41 of ,h4,m4 ,geological ,survey4 ,with ,maps1 ,charts1 and numerous illustrations4 ,demy #hvo1 #bds4 8,there is a great charm in the well-balanced union of cultivated powers of observation and analytical method1 with considerable imagination and much poetical feeling1 which runs through the pages of this volume4444 ,we have indicated but imperfectly the philosophical spirit which marks every step of inquiry into the wonders of this #8,great ,ice ,age1' and we strongly recommend the volume to all who are prepared to read thoughtfully1 and weigh the evidences of truth carefully1 in the assurance of finding that there are indeed1 #8,sermons in ,stones4'0--,athenum4 8,every step in the process is traced with admirable perspicuity and fullness by ,mr4 ,geikie4444 ,this book will mark an epoch in the scientific study of the ,ice ,age40--,saturday ,review4 8,the book shows everywhere the marks of acute observation1 wide research1 and sound reasoning4 ,it presents in a readable form the chief features of the great ,ice ,age1 and illustrates them very amply from those great tracts of ,scotland in which glaciation has left its most distinct and most enduring marks40--,spectator4 8,no one can peruse this most interesting book without feeling grateful to ,mr4 ,geikie for his masterly summing-up of the evidence1 and appreciating the spirit of scientific candour with which he states his conclusions4 ,at once in respect of its matter and its tone1 the work forms a valuable contribution to our scientific literature40--,scotsman4 8,by far the most important contribution to the chapter of ,geological inquiry that has yet appeared4 ,we can assure our readers that they will find in ,mr4 ,geikie's book an admirable and satisfactory summary of the present condition of opinion on some of the most interesting of geological questions which are here discussed in an agreeable and readable manner40--,westminster ,review4 8,this work1 without any sacrifice of scientific accuracy and completeness1 is so clear1 and so free from technicalities1 as to be intelligible to any reader of ordinary education4 ,for knowledge and command of his subject1 for skill in the arrangement of his facts1 and for the clearness with which he reasons out his conclusions1 ,mr4 ,geikie occupies a high place as a scientific writer40--,academy4 8,the most comprehensive and lucid interpretation that has been given of the ,great ,ice ,age40--,edinburgh ,courant4 8,it offers to the student of geology by far the completest account of the period yet published1 and is characterized throughout by refreshing vigour of diction and originality of thought40--,glasgow ,herald4 8,can be cordially recommended both to the geologist and the general reader4 ,the explanations are so full1 and the method of handling so free from technicality1 that with a moderate amount of attention the book may be understood1 and its reasoning followed1 by those who had previously little or no geological knowledge40--,nature4 ,,daldy1 ,,isbister1 ,,co41 #ef1 ,,ludgate ,,hill1 ,,london4 ,,works ,,of ,,travel1 ,,science1 ,,and ,,philosophy4 ,letters from ,abroad4 ,by ,dean ,,alford4 ,second ,edition4 ,crown #hvo1 #gs4 #f;d4 8,as the season approaches1 and the highway of ,italian travel will be thronged again1 we are sure readers who contemplate a trip to ,rome and the ,south1 to ,central or ,northern ,italy1 will find him a kind1 genial1 and entertaining companion1 who will show them what to see1 and how to see it4 ,at any time1 stay-at-home travellers will read the volume with interest1 and the descriptions of the sins and shames of ,rome--still pagan ,rome--will1 we trust1 confirm in many minds a hearty determination to resist the advent of ,romish imposture in our own country40--,eclectic ,review4 ,the ,reign of ,law4 ,by the ,duke of ,,argyll4 ,crown #hvo1 #fs4 ,people's ,edition 7sixteenth71 limp cloth1 #bs4 #f;d4 8,there are few books in which a thoughtful reader will find more that he will desire to remember40--,times4 8,shows a breadth of thought1 a freedom from prejudice1 and a power of clear exposition rare in all ages and all countries4 ,it is as unanswerable as it is attractive40--,pall ,mall ,gazette4 8,a masterly book4444 ,strong1 sound1 mature1 able thought from its first page to its last40--,spectator4 ,primeval ,man4 ,an ,examination of ,some ,recent ,speculations4 ,by the ,duke of ,,argyll4 ,third ,edition4 ,crown #hvo1 #ds4 #f;d4 8,this is perhaps the most clear1 graceful1 pointed1 and precise piece of ethical reasoning published for a quarter of a century4 ,its great end is to show that it is impossible to pursue any investigation of man's history from the purely physical side4 ,its reasoning seems as absolutely conclusive against the upholders of the #8natural selection' theory4 ,the book is worthy of a place in every library1 as skilfully popularising science1 and yet sacrificing nothing either of its dignity or of its usefulness40--,nonconformist4 ,iona4 ,by the ,duke of ,,argyll4 ,with ,illustrations4 ,third ,edition4 ,crown #hvo1 #cs4 #f;d4 8,pleasantly and unaffectedly written1 it is well fitted to discharge what we take to be the main object of such a work1 that of guiding people to a subject and setting them to think about it4 ,we are not ashamed to confess that we put down the ,duke's little book with a wish to know more about ,iona and ,st4 ,columba than we knew when we began it4 ,we thank him for a pretty little book40--,saturday ,review4 ,walks about the ,city and ,environs of ,jerusalem4 ,by ,w4 ,h4 ,,bartlett4 ,with #be ,steel ,engravings and numerous ,woodcut ,illustrations4 ,small #dto1 cloth gilt extra1 #ajs4 #f;d4 ,the ,science of ,gems1 ,jewels1 ,coins1 and ,medals1 ,ancient and ,modern4 ,by ,,archibald ,,billing1 ,m4,d41 ,a4,m41 ,f4,r4,s4 ,with ,illustrations4 ,new and ,cheaper ,edition1 revised and corrected4 ,demy #hvo1 cloth gilt extra1 #bas4 ,holiday ,letters4 ,by ,m4 ,,betham ,,edwards1 ,author of 8,a ,winter with the ,swallows10 c4 ,crown #hvo1 #gs4 #f;d4 8,miss ,edwards' ,letters form a delightful volume4 ,her style is lively and vivid1 touched here and there with a certain quaint and piquant humour1 and instinct with a strong appreciation of the grand and beautiful1 whether in natural scenery or works of ,art40--,daily ,news4 ,sundays ,abroad4 ,by ,,thomas ,,guthrie1 ,d4,d4 ,second ,thousand4 ,crown #hvo1 #cs4 #f;d4 8,many will welcome a volume which gives us1 in ,dr4 ,guthrie's forcible language1 the story of ,savonarola1 the surprising deliverance of the ,medici1 notices of evangelical preachers1 such as ,dr4 ,de ,sanctis at ,florence1 and ,comba in ,venice1 and some very interesting chapters relating to the churches of the ,waldensian valleys40--,graphic4 ,walks in ,rome4 ,by ,,augustus ,j4 ,c4 ,,hare4 ,fourth ,edition4 #b vols4 crown #hvo1 #bas4 8,the best handbook of the city and environs of ,rome ever published4444 ,it cannot be too much commended40--,pall ,mall ,gazette4 ,,by ,,the ,,same ,,author4 ,,days ,,near ,,rome4 ,with more than #ajj ,illustrations by the ,author4 ,second ,edition4 #b vols1 crown #hvo1 #bds4 8,mr4 ,hare is the very paragon of cicerones1 and his writings are the true model of that descriptive literature which is designed to please and to instruct4 ,the amount of information which is crowded into these two delightful volumes is simply marvellous40--,hour4 8,mr4 ,hare probably knows ,italy better than almost any ,englishman living4444 ,the information which it affords will enable any one who cares to see more of the genuine native life of ,italy in a month than most pilgrims to the ,peninsula see in a lifetime40--,world4 ,,wanderings ,,in ,,spain4 ,with ,illustrations by the ,author4 ,third ,edition4 ,crown #hvo1 #ajs4 #f;d4 8,we recollect no book that so vividly recalls the country to those who have visited it1 and we recommend intending tourists to carry it with them as a companion of travel40--,times4 8,here is the ideal book of travel in ,spain1 which exactly anticipates the requirements of everybody who is fortunate enough to be going to that enchanted land1 and which ably consoles those who are not so happy1 by supplying the imagination from the daintiest and most delicious of its stores40--,spectator4 ,a ,year at the ,shore4 ,by ,,philip ,,henry ,,gosse1 ,f4,r4,s4 ,with #cf ,illustrations1 printed in ,colours4 ,third ,thousand4 ,crown #hvo1 #is4 8,a delicious book deliciously illustrated40--,illustrated ,london ,news4 ,walks in ,florence4 ,by ,,susan and ,,joanna ,,horner4 ,with ,illustrations4 ,third ,edition4 #b vols4 crown #hvo1 #bas4 8,no one can read it without wishing to visit ,florence1 and no one ought to visit ,florence without having read it40--,times4 8,a work which1 by the accuracy of its information1 the exactness of its detail1 and the refined taste conspicuous in every page1 proves its authors to be worthy inheritors of the honoured name they bear4 ,henceforward it will be as indispensable to every intelligent visitor to the #8,city of ,flowers1' as ,mr4 ,hare's is for #8,the ,eternal ,city4'0--,guardian4 ,the ,regular ,swiss ,round4 ,in ,three ,trips4 ,by the ,rev4 ,,harry ,,jones1 ,m4,a4 ,with ,illustrations by ,,whymper4 ,small #hvo1 #cs4 #f;d4 8,contains much valuable information for the inexperienced tourist40--,patriot4 8,mr4 ,jones' book will no doubt find and please many readers2 the brisk and pointed style of the book will give pleasure in itself40--,pall ,mall ,gazette4 ,popular ,lectures on ,scientific ,subjects4 ,by ,sir ,,john ,f4 ,w4 ,,herschel1 ,bart4 ,eighth ,thousand4 ,crown #hvo1 #fs4 8,a book of most profound and romantic scientific charm40--,spectator4 ,town ,geology4 ,by ,,charles ,,kingsley4 ,fourth ,thousand4 ,crown #hvo1 #es4 8,a masterpiece of popular scientific exposition40--,echo4 8,the author here compresses within the briefest compass the results of many years' thought and observation1 and illustrates his facts and suggestions with singular felicity of language4 ,not even ,professor ,huxley could convey scientific information in a style more straightforward and transparent40--,pall ,mall ,gazette4 ,god's ,glory in the ,heavens4 ,a ,survey of ,recent ,astronomical ,discovery and ,speculation in connection with the ,religious ,questions to which they give rise4 ,by ,,william ,,leitch1 ,d4,d41 late ,principal of ,queen's ,college1 ,canada4 ,with numerous ,illustrations4 ,fourth ,edition4 ,crown #hvo1 cloth extra1 #ds4 #f;d4 8,we cannot conclude our notice of ,dr4 ,leitch's book without dwelling upon the admirable manner in which the astronomical facts contained in it are blended with practical observations and the highest and most ennobling sentiments4 ,it is thus that books on popular science should ever be written40--,reader4 ,the ,egyptian ,sketchbook4 ,by ,,charles ,g4 ,,leland4 ,post #hvo1 #gs4 #f;d4 8,it confirms its author as chief of all living humorists1 and the first thing the reader will probably do after finishing the last chapter will be to read the sketches all over again40--,hour4 ,eastward3 ,travels in ,egypt1 ,palestine1 and ,syria4 ,by ,,norman ,,macleod1 ,d4,d4 ,with numerous ,illustrations4 ,fifth ,thousand4 ,crown #hvo1 #fs4 8,the most enjoyable book on the ,holy ,land we have ever read40--,nonconformist4 8,this handsome volume1 though not a novel1 is a novelty among books of travel4 ,the genial1 manly spirit of the author gives a human colouring to every scene1 and keeps awake in us as we accompany him an increasing sympathy40--,daily ,news4 ,peeps at the ,far ,east4 ,a ,familiar ,account of a ,visit to ,india4 ,by ,,norman ,,macleod1 ,d4,d4 ,with numerous ,illustrations4 ,second ,thousand4 ,small #dto1 cloth gilt extra1 #bas4 8,it would be difficult to point out in our popular literature a book which in anything like the same compass conveys so full or so instructive a knowledge of ,british ,india4 ,dr4 ,macleod has the gift of insight into character1 and in his intercourse both with natives and ,european residents never fails to establish a kind of freemasonry1 and to draw out the material of thought and subsequent reflection4 ,his work has thus an inner depth and a philosophical value beyond that of a mere record of travel40--,saturday ,review4 ,through ,normandy4 ,by ,mrs4 ,,macquoid1 ,author of 8,patty10 c4 ,with #ij ,illustrations4 ,second ,edition4 ,crown #hvo1 #abs4 8,written in a cheerful spirit1 it leaves a bright and pleasant impression upon the mind2 and while those who already know ,normandy will recognise the truth of her descriptions1 and sympathize with her enthusiasm1 those who are yet in ignorance of its attractions may be stirred by ,mrs4 ,macquoid's advocacy to the amendment of their education40--,saturday ,review4 8,the illustrations are excellent40--,athenum4 ,the ,philosophy of the ,conditioned3 ,sir ,william ,hamilton and ,john ,stuart ,mill4 ,by the late ,h4 ,l4 ,,mansel1 ,d4,d41 ,dean of ,st4 ,paul's4 ,post #hvo1 #fs4 8,this volume is distinguished by the same clearness of style1 cogency of argument1 accuracy of information1 and mastery of the subjects1 which characterize all the other valuable productions of the author1 and is on the points criticized a most successful as well as a most unsparing exposure of ,mill's manifold errors40--,british ,quarterly ,review4 ,the ,human ,intellect4 ,with an ,introduction upon ,psychology and the ,soul4 ,by ,,noah ,,porter1 ,d4,d41 ,,ll4,d41 ,president of ,yale ,college4 ,demy #hvo1 #afs4 8,in this book the best philosophical thinking of our day may be said to culminate4 ,not only is it by far the ablest psychological work that ,america has yet produced1 it is unique among ourselves in its completeness and ability4 ,it is a work of which any school or country might be proud1 and its form as a manual makes it invaluable to students40--,british ,quarterly ,review4 8,dr4 ,porter's work presents us with a more complete and impartial survey of this whole region of inquiry than has ever before been offered to the student4 ,a man might appeal to such a work as a worthy product of a life40--,blackwood's ,magazine4 ,westward by ,rail4 ,a ,journey to ,san ,francisco and ,back1 and a ,visit to the ,mormons4 ,by ,w4 ,f4 ,,rae1 ,author of 8,wilkes1 ,sheridan1 ,fox10 c4 ,with ,map4 ,third and ,cheaper ,edition4 ,small #hvo1 #ds4 #f;d4 8,mr4 ,rae unites the power of a keen and thoughtful observer with the skill and tact of a graphic delineator4 ,the evident candour and singleness of purpose with which he writes make him a trustworthy guide for those who would weigh aright the inducements for or against the longest continuous land journey as yet opened upon our planet40--,saturday ,review4 8,at once the most modern and the most reliable authority on the increasingly important subjects with which it deals40--,westminster ,review4 ,a ,summer in ,skye4 ,by the late ,,alexander ,,smith1 ,author of 8,a ,life ,drama10 8,dreamthorp10 c4 ,with ,illustrations by ,r4 ,t4 ,,pritchett4 ,fourth ,thousand4 ,crown #hvo1 #fs4 8,mr4 ,alexander ,smith speaks of ,boswell's ,journal as #8delicious reading2' his own work1 though after a very different fashion1 affords delicious reading also4 ,his egotism is never offensive2 it is often very charming4 ,if the traveller is sometimes lost in the essayist1 who will not prefer an ,elia to a ,pennant80--,daily ,news4 ,lewsiana2 or1 ,life in the ,outer ,hebrides4 ,by ,w4 ,,anderson ,,smith1 ,author of 8,off the ,chain40 ,with ,illustrations4 ,post #hvo1 #ajs4 #f;d4 8,those who cannot visit these ,outer ,hebrides and discover still unknown beauties with their own eyes1 ought1 as the next best thing1 to view it through the eyes of the author of #8,lewsiana4'0--,scotsman4 8,he is as enthusiastic about the #8,lews' as the author of #8,the ,princess of ,thule' himself4 ,he writes in a light1 agreeable1 and graphic style1 and has the gift of the pencil as well as the pen40--,world4 ,our ,inheritance in the ,great ,pyramid4 ,by ,professor ,c4 ,,piazzi ,,smyth1 ,astronomer ,royal for ,scotland4 ,new and ,enlarged ,edition1 including all the most important ,discoveries up to the ,present ,time4 ,with #ag ,explanatory ,plates4 ,post #hvo1 #ahs4 ,man and ,beast1 ,here and ,hereafter4 ,with ,illustrative ,anecdotes4 ,by the ,rev4 ,j4 ,g4 ,,wood1 ,m4,a41 ,author of 8,homes without ,hands10 c4 #b vols4 post #hvo1 #bas4 8,the book is delightful40--,british ,quarterly ,review4 8,it is filled with anecdotes which are very entertaining40--,saturday ,review4 8,extremely readable and interesting4444 ,if the talk runs on dogs1 cats1 canaries1 horses1 elephants1 or even pigs or ducks1 he who has #8,man and ,beast' at his fingers' end may be sure of a story good enough to cap the best that is likely to be told40--,pall ,mall ,gazette4 ---------------------------------------- ------------------------------ ,,footnotes3 #a ,trans4 of ,edin4 ,geol4 ,soc41 vol4 ii4 p4 #beb4 #b ,phil4 ,mag41 ,january1 #ahfc4 #c ,athenum1 ,september #bb1 #ahfj4 #d ,trans4 ,glasgow ,geol4 ,soc41 vol4 iv41 p4 #cac4 #e ,see ,mr4 ,hopkin's remarks on this theory1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 viii4 #f ,see ,chap4 xxv4 #g ,see ,chap4 iv4 #h 8,treatise on ,astronomy10 #cae2 8,outlines10 #cfh4 #i ,annuaire for #ahcd1 p4 #aii4 ,edin4 ,new ,phil4 ,journ41 ,april1 #ahcd1 p4 #bbd4 #aj 8,cosmos10 vol4 iv4 p4 #dei 7,bohn's ,edition74 8,physical ,description of the ,heavens10 p4 #ccf4 #aa ,phil4 ,mag4 for ,february1 #ahfg1 p4 #abg4 #ab ,the ,gulf-stream at the narrowest place examined by the ,coast ,survey1 and where also its velocity was greatest1 was found to be over #cj statute miles broad and #a1iej feet deep4 ,but we must not suppose that this represents all the warm water which is received by the ,atlantic from the equator2 a great mass flows into the ,atlantic without passing through the ,straits of ,florida4 #ac ,it is probable that a large proportion of the water constituting the south-eastern branch of the ,gulf-stream is never cooled down to #dj2 but1 on the other hand1 the north-eastern branch1 which passes into the arctic regions1 will be cooled far below #dj1 probably below #cj4 ,hence ,i cannot be over-estimating the extent to which the water of the ,gulf-stream is cooled down in fixing upon #dj as the average minimum temperature4 #ad 8,physical ,geography of the ,sea10 #bd1 #fth edition4 #ae 8,physical ,geography10 #ed4 #af ,trans4 of ,roy4 ,soc4 of ,edin41 vol4 xxi41 p4 #eg4 ,phil4 ,mag41 #d1 vol4 ix41 p4 #cf4 #ag 8,smithsonian ,contributions to ,knowledge10 vol4 ix4 #ah 8,heat as a ,mode of ,motion10 art4 #bdj4 #ai ,trans4 ,roy4 ,soc4 of ,edin41 vol4 xxv41 part #b4 #bj ,see 8,smithsonian ,contributions to ,knowledge10 vol4 ix4 #ba 8,meteorology10 section #cf4 #bb ,comptes-,rendus1 ,july #i1 #ahch4 ,taylor's 8,scientific ,memoirs10 vol4 iv41 p4 #dd 7#ahdf74 #bc ,the mean temperature of the ,atlantic between the tropics and the arctic circle1 according to ,admiral ,fitzroy's chart1 is about #fj4 ,but he assigns far too high a temperature for latitudes above #ej4 ,it is probable that #ef is not far from the truth4 #bd ,the probable physical cause of this will be considered in the ,appendix4 #be ,the mean temperature of the equator1 according to ,dove1 is #gig1 and that of the north pole #bc4 ,but as there is1 of course1 some uncertainty regarding the actual mean temperature of the poles1 we may take the difference in round numbers at #hj4 #bf ,trans4 of ,roy4 ,soc4 ,edin41 vol4 xxii41 p4 #ge4 #bg ,connaissance des ,temps for #ahfc 7,additions74 ,lagrange's determination makes the superior limit #jjgfda 7,memoirs of the ,berlin ,academy for #aghb1 p4 #bgc74 ,recently the laborious task of re-investigating the whole subject of the secular variations of the elements of the planetary orbits was undertaken by ,mr4 ,stockwell1 of the ,united ,states4 ,he has taken into account the disturbing influence of the planet ,neptune1 the existence of which was not known when ,leverrier's computations were made2 and he finds that the eccentricity of the earth's orbit will always be included within the limits of #j and #jjfichhh4 ,mr4 ,stockwell's elaborate ,memoir1 extending over no fewer than two hundred pages1 will be found in the eighteenth volume of the 8,smithsonian ,contributions to ,knowledge40 #bh ,when the eccentricity is at its superior limit1 the absolute quantity of heat received by the earth during the year is1 however1 about one three-hundredth part greater than at present4 ,but this does not affect the question at issue4 #bi ,scoresby's 8,arctic ,regions10 vol4 ii41 p4 #cgi4 ,daniell's 8,meteorology10 vol4 ii41 p4 #abc4 #cj ,tyndall1 8,on ,heat10 article #cfd4 #ca ,tyndall1 8,on ,heat10 article #cfd4 #cb ,see ,phil4 ,mag41 ,march1 #ahgj1 p4 #cc ,captain ,cook's 8,second ,voyage10 vol4 ii41 pp4 #bcb1 #bce4 #cd 8,antarctic ,regions10 vol4 ii41 pp4 #cdecdi4 #ce ,ibid41 vol4 i41 p4 #afg4 #cf ,ibid41 vol4 ii41 p4 #cfb4 #cg ,edinburgh ,philosophical ,journal1 vol4 iv41 p4 #bff4 #ch ,scoresby's 8,arctic ,regions10 vol4 i41 p4 #cgh4 #ci ,ibid41 p4 #dbe4 #dj ,see ,meech's memoir 8,on the ,intensity of the ,sun's ,heat and ,light10 8,smithsonian ,contributions10 vol4 ix4 #da 8,antarctic ,regions10 vol4 i41 p4 #bdj4 #db ,challenger ,reports1 ,no4 #b1 p4 #aj4 #dc ,see 8,smithsonian ,contributions10 vol4 ix4 #dd ,quart4 ,journ4 ,geol4 ,soc41 vol4 xxv41 p4 #cej4 #de ,trans4 of ,glasgow ,geol4 ,soc4 for #ahff4 #df ,revue des ,deux ,mondes for #ahfg4 #dg ,letter to the author1 ,february1 #ahgj4 #dh 8,rvolutions de la ,mer10 p4 #cg 7second edition74 #di ,edin4 ,phil4 ,journ41 vol4 iv41 p4 #bfb 7#ahba74 #ej ,phil4 ,mag41 #d1 vol4 xxviii41 p4 #aca4 ,reader1 ,december #bnd1 #ahfe4 #ea ,this point will be found discussed at considerable length in the ,phil4 ,mag4 for ,september1 #ahfi4 #eb ,see ,phil4 ,mag4 for ,october1 #ahgj1 p4 #bei4 #ec ,proceedings of the ,royal ,society1 ,no4 #ach1 p4 #eif1 foot-note4 #ed ,the edition from which ,i quote1 unless the contrary is stated1 is the one published by ,messrs4 ,t4 ,nelson and ,sons1 #ahgj1 which is a reprint of the new edition published in #ahei by ,messrs4 ,sampson ,low and ,co4 #ee 8,physical ,geography10 article #eg4 #ef ,philosophical ,magazine1 vol4 xii4 p4 #a 7#ahch74 #eg 8,mmoires par divers ,savans10 tom4 i41 p4 #cah1 ,st4 ,petersburgh1 #ahca4 ,see also twelfth number of ,meteorological ,papers1 published by the ,board of ,trade1 #ahfe1 p4 #af4 #eh ,dubuat's 8,hydraulique10 tom4 i41 p4 #fd 7#ahaf74 ,see also ,british ,association ,report for #ahcd1 pp4 #dbb1 #dea4 #ei ,see ,proceedings of the ,royal ,society for ,december1 #ahfh1 ,november1 #ahfi4 ,lecture delivered at the ,royal ,institute1 ,nature1 vol4 i41 p4 #dij4 ,proceedings of the ,royal ,geographical ,society1 vol4 xv4 #fj ,trans4 of ,glasgow ,geol4 ,soc4 for ,april1 #ahfg4 ,phil4 ,mag4 for ,february1 #ahfg1 and ,june1 #ahfg 7,supplement74 #fa ,phil4 ,mag4 for ,february1 #ahgj4 #fb 8,the ,depths of the ,sea10 pp4 #cgf and #cgg4 #fc 8,the ,threshold of the ,unknown ,region10 p4 #ie4 #fd ,see 8,physical ,geography of the ,sea10 chap4 ix41 new edition1 and ,dr4 ,a4 ,mhry 8,on ,ocean-currents in the ,circumpolar ,basin of the ,north ,hemisphere40 #fe 8,depths of the ,sea10 ,nature for ,july #bh1 #ahgj4 #ff 8,memoir on the ,gulf-stream10 ,geographische ,mittheilungen1 vol4 xvi4 7#ahgj74 #fg ,dr4 ,carpenter 8,on the ,gulf-stream10 ,proceedings of ,royal ,geographical ,society for ,january #i1 #ahga1 #bi4 #fh ,dr4 ,petermann's ,mittheilungen for #ahgb1 p4 #cae4 #fi ,proceedings of the ,royal ,society1 vol4 xvii41 p4 #ahg1 xviii41 p4 #dfc4 #gj ,the average depth of the ,pacific ,ocean1 as found by the soundings of ,captain ,belknap1 of the ,u4,s4 steamer ,tuscarora1 made during ,january and ,february1 #ahgd1 is about #b1djj fathoms4 ,the depth of the ,atlantic is somewhat less4 #ga ,proceedings of ,royal ,geographical ,society1 vol4 xv41 #bb4 #gb ,it is a well-established fact that in polar regions the temperature of the sea decreases from the surface downwards2 and the ,german ,polar ,expedition found that the water in very high latitudes is actually less dense at the surface than at considerable depths1 thus proving that the surface-water could not sink in consequence of its greater density4 #gc ,proceedings of the ,royal ,society1 vol4 xix41 p4 #bae4 #gd ,nature for ,july #f1 #ahga4 #ge ,since the above objection to the ,gravitation ,theory of the ,gibraltar ,current was advanced three years ago1 ,dr4 ,carpenter appears to have abandoned the theory to a great extent4 ,he now admits 7,proceedings of ,royal ,geographical ,society1 vol4 xviii41 pp4 #caiccd1 #ahgd7 that the current is almost wholly due not to difference of specific gravity1 but to an excess of evaporation in the ,mediterranean over the return by rain and rivers4 #gf ,proceedings of ,royal ,society1 ,no4 #ach1 #bf4 #gg ,proceedings of ,royal ,geographical ,society1 ,january #i1 #ahga4 #gh ,ibid4 #gi ,see #bj1 #cd2 also ,brit4 ,assoc4 ,report for #ahgb1 p4 #di1 and other places4 #hj ,see also to the same effect ,brit4 ,assoc4 ,report1 #ahgb1 p4 #ej4 #ha ,phil4 ,mag4 for ,oct4 #ahga4 #hb ,the actual slope1 however1 does not amount to more than #a in #g1jjj1jjj4 #hc ,proc4 of ,roy4 ,geog4 ,soc41 ,january #i1 #ahga1 #bi4 #hd ,trans4 of ,geol4 ,soc4 of ,glasgow for ,april1 #ahfg2 ,phil4 ,mag4 for ,june1 #ahfg4 #he ,nature1 vol4 i41 p4 #eda4 ,proc4 ,roy4 ,soc41 vol4 xviii41 p4 #dgc4 #hf ,chapter ,,ii4 #hg ,chapter ,,ii4 #hh ,chapter ,,ii4 #hi ,mr4 ,findlay considers that the daily discharge does not exceed #ccc cubic miles 7,brit4 ,assoc4 ,rep41 #ahfi1 p4 #afj74 ,my estimate makes it #cgh cubic miles4 ,mr4 ,laughton's estimate is #fcj cubic miles 7,paper 8,on ,ocean-currents10 ,journal of ,royal ,united-,service ,institution1 vol4 xv474 #ij ,proceedings of the ,royal ,geographical ,society1 vol4 xviii41 p4 #cic4 #ia ,phil4 ,mag4 for ,october1 #ahga1 p4 #bgd4 #ib ,proceedings of the ,royal ,geographical ,society1 vol4 xv4 #ic ,phil4 ,mag41 ,february1 #ahgj4 #id ,brit4 ,assoc4 ,report1 #ahfi1 ,sections1 p4 #afj4 #ie ,journal of ,royal ,united-,service ,institute1 vol4 xv4 #if ,dr4 ,carpenter 7,proc4 of ,roy4 ,geog4 ,soc41 vol4 xviii41 p4 #ccd7 misapprehends me in supposing that ,i attribute the ,gibraltar current wholly to the ,gulf-stream4 ,in the very page from which he derives or could derive his opinion as to my views on the subject 7,phil4 ,mag4 for ,march1 #ahgd1 p4 #ahb71 ,i distinctly state that 8the excess of evaporation over that of precipitation within the ,mediterranean area would of itself produce a considerable current through the ,strait40 ,that the ,gibraltar current is due to two causes1 7#a7 the pressure of the ,gulf-stream1 and 7#b7 excess of evaporation over precipitation in the ,mediterranean1 has always appeared to me so perfectly obvious1 that ,i never held nor could have held any other opinion on the subject4 #ig ,paper read to the ,edinburgh ,botanical ,society on ,january #h1 #ahgd4 #ih ,proc4 ,roy4 ,geog4 ,soc41 vol4 xviii41 p4 #cfb4 ,a more advantageous section might have been chosen1 but this will suffice4 ,the section referred to is shown in ,plate ,,iii4 ,the peculiarity of this section1 as will be observed1 is the thinness of the warm strata at the equator1 as compared with that of the heated water in the ,north ,atlantic4 #ii ,the temperature of column ,c in ,dr4 ,carpenter's section is somewhat less than that given in the foregoing table2 so that1 according to that section1 the difference of level between column ,c and columns ,a and ,b would be greater than my estimate4 #ajj ,captain ,nares's ,report1 ,july #cj1 #ahgd4 #aja ,see ,chapter ,,iv4 #ajb ,phil4 ,mag4 for ,august1 #ahfd1 ,february1 #ahfg1 ,march1 #ahgj2 see ,chap4 ,,iv4 #ajc ,quarterly ,journal of ,science for ,october1 #ahgd4 #ajd ,see a paper by ,m4 ,morlot1 on 8,the ,post-,tertiary and ,quaternary ,formations of ,switzerland40 ,edin4 ,new ,phil4 ,journal1 ,new ,series1 vol4 ii41 #ahee4 #aje ,edin4 ,new ,phil4 ,journ41 ,new ,series1 vol4 ii41 p4 #bh4 #ajf ,vogt's 8,lectures on ,man10 pp4 #cahcba4 #ajg ,see ,mr4 ,prestwich on ,flint ,implements1 ,phil4 ,trans4 for #ahfj and #ahfd4 ,lyell's 8,antiquity of ,man10 ,second ,edition1 p4 #afh4 #ajh ,edin4 ,new ,phil4 ,journ41 ,new ,series1 vol4 ii41 p4 #bh4 ,silliman's ,journ41 vol4 xlvii41 p4 #bei 7#ahdd74 #aji ,quart4 ,journ4 ,geol4 ,soc41 vol4 xxvii41 p4 #ecd4 #aaj ,ibid41 vol4 xxviii41 p4 #ag4 #aaa 8,glacial ,drift of ,scotland10 p4 #ed4 #aab 8,glacial ,drift of ,scotland10 p4 #eh4 #aac ,quart4 ,journ4 ,geol4 ,soc41 vol4 v41 p4 #bb4 #aad 8,glacial ,drift of ,scotland10 p4 #fd4 #aae ,trans4 ,edin4 ,geol4 ,soc41 vol4 ii41 p4 #cia4 #aaf ,trans4 of ,geol4 ,soc4 of ,glasgow1 vol4 iv41 p4 #adf4 #aag ,geol4 ,mag41 vi41 p4 #cia4 #aah ,see 8,memoirs of ,geological ,survey of ,scotland10 ,explanation of sheet #bb1 p4 #bi4 ,see also ,trans4 ,glasgow ,geol4 ,soc41 iv41 p4 #aej4 #aai 8,great ,ice ,age10 p4 #cgd4 #abj 8,great ,ice ,age10 p4 #chd4 #aba 8,geological ,survey of ,ohio1 #ahfi10 p4 #afe4 ,see also 8,great ,ice ,age10 chap4 xxviii4 #abb ,quart4 ,journ4 ,geol4 ,soc41 xxviii41 p4 #dce4 #abc ,brit4 ,assoc4 ,report1 #ahfc4 #abd ,trans4 ,glasgow ,nat4 ,hist4 ,soc41 vol4 i41 p4 #aae4 #abe ,trans4 of the ,geol4 ,soc4 of ,glasgow1 vol4 iii41 p4 #acc4 ,see also 8,great ,ice ,age10 chaps4 xii4 and xiii4 #abf ,chap4 ,,xxix4 #abg ,edin4 ,new ,phil4 ,journ41 vol4 liv41 p4 #bgb4 #abh 8,newer ,pliocene ,geology10 p4 #abi4 ,john ,gray ,co41 ,glasgow4 #abi 8,glacial ,drift of ,scotland10 p4 #fg4 #acj 8,glacial ,drift of ,scotland10 p4 #ab4 #aca ,see ,chapter ,,iv4 #acb 8,discovery of the ,north-,west ,passage10 p4 #bac4 #acc 8,voyage of the ,resolute10 p4 #bid4 #acd ,quart4 ,journ4 ,geol4 ,soc41 vol4 xi41 p4 #edj4 #ace 8,mc,clure's ,north-,west ,passage10 p4 #bad4 ,second ,edition4 #acf 8,british ,association ,report for #ahee10 p4 #cha4 8,the ,last of the ,arctic ,voyages10 vol4 i41 p4 #cha4 #acg ,mr4 ,james ,geikie informs me that the great accumulations of gravel which occur so abundantly in the low grounds of ,switzerland1 and which are1 undoubtedly1 merely the re-arranged materials originally brought down from the ,alps as till and as moraines by the glaciers during the glacial epoch1 rarely or never yield a single scratched or glaciated stone4 ,the action of the rivers escaping from the melting ice has succeeded in obliterating all trace of stri4 ,it is the same1 he says1 with the heaps of gravel and sand in the lower grounds of ,sweden and ,norway1 ,scotland and ,ireland4 ,these deposits are evidently in the first place merely the materials carried down by the swollen rivers that issued from the gradually melting ice-fields and glaciers4 ,the stones of the gravel derived from the demolition of moraines and till1 have lost all their stri and become in most cases well water-worn and rounded4 #ach ,report on ,icebergs1 read before the ,association of ,american ,geologists1 ,silliman's ,journal1 vol4 xliii41 p4 #afc 7#ahdb74 #aci 8,manual of ,geology10 p4 #fgg4 #adj ,quart4 ,journ4 ,geol4 ,soc41 vol4 ix41 p4 #cjf4 #ada ,dana's 8,manual of ,geology10 p4 #fgg4 #adb ,quart4 ,journ4 ,geol4 ,soc41 vol4 ix41 p4 #cjf4 #adc 8,journal10 vol4 i41 p4 #ch4 #add 8,short ,american ,tramp10 pp4 #afh1 #agd4 #ade 8,short ,american ,tramp10 pp4 #bcibda4 #adf 8,travels in ,north ,america10 vol4 ii41 p4 #acg4 #adg ,ibid41 vol4 ii41 p4 #agd4 #adh ,proceedings of the ,royal ,society of ,edinburgh1 ,session #ahfeff1 p4 #ecg4 #adi 8,short ,american ,tramp10 pp4 #gg1 #ha1 #aaa4 #aej 8,second ,visit10 vol4 ii41 p4 #cfg4 #aea 8,memoirs of ,boston ,society of ,natural ,history10 vol4 i4 7#ahfg71 p4 #bbh4 #aeb 8,antiquity of ,man10 p4 #bfh4 ,third ,edition4 #aec 8,great ,ice ,age10 p4 #eab4 #aed ,brit4 ,assoc41 #ahgj1 p4 #hh4 #aee ,quart4 ,journ4 ,geol4 ,soc41 vol4 v41 p4 #aj4 ,phil4 ,mag4 for ,april1 #ahfe1 p4 #bhi4 #aef 8,great ,ice ,age10 p4 #eab4 #aeg ,jukes' 8,manual of ,geology10 p4 #dba4 #aeh ,see also ,quarterly ,journal ,geological ,society1 vol4 xi41 p4 #eaj4 #aei ,the ,reader for ,august #ab1 #ahfe4 #afj 8,history of the ,isle of ,man10 p4 #hf4 ,my colleague1 ,mr4 ,john ,horne1 in his 8,sketch of the ,geology of the ,isle of ,man10 ,trans4 of ,edin4 ,geol4 ,soc41 vol4 ii41 part iii41 considers this conglomerate to be of ,lower ,carboniferous age4 #afa ,see ,selwyn1 8,phys4 ,geography and ,geology of ,victoria40 #ahff4 pp4 #aeaf2 ,taylor and ,etheridge1 ,geol4 ,survey ,vict41 ,quarter ,sheet #ac1 ,n4,e4 #afb ,report on the ,geology of the ,district of ,ballan1 ,victoria4 #ahff4 p4 #aa4 #afc ,atrypa reticularis4 #afd ,quart4 ,journ4 ,geol4 ,soc41 vol4 xii41 p4 #eh4 #afe 8,great ,ice ,age10 p4 #eac4 #aff 8,great ,ice ,age10 p4 #eac4 #afg ,brit4 ,assoc4 ,report for #ahgc4 #afh ,quart4 ,journ4 ,geol4 ,soc41 vol4 xi41 p4 #eai4 #afi ,orthis resupinata4 #agj ,prod4 semireticulatus var4 ,martini4 ,sow4 #aga 8,belcher's ,voyage10 vol4 ii41 p4 #cgg4 #agb 8,journal of a ,boat ,voyage through ,rupert-,land10 vol4 ii41 p4 #bjh4 #agc ,quart4 ,journ4 ,geol4 ,soc41 vol4 xi41 p4 #aig4 #agd ,explanation ,memoir to ,sheet #dg1 8,geological ,survey of ,ireland40 #age ,phil4 ,mag41 vol4 xxix41 p4 #bij4 #agf 8,memoirs of the ,geological ,survey of ,india10 vol4 i41 part i4 #agg ,quart4 ,journ4 ,geol4 ,soc41 vol4 xxvi41 p4 #ead4 #agh ,ibid41 vol4 xxvii41 p4 #edd4 #agi ,phil4 ,mag41 vol4 xxix41 p4 #bij4 #ahj ,journal of the ,royal ,dublin ,society for ,february1 #aheg4 #aha ,quart4 ,journ4 ,geol4 ,soc41 vol4 xi41 p4 #eai4 #ahb 8,the ,last of the ,arctic ,voyages10 by ,captain ,sir ,e4 ,belcher1 vol4 ii41 p4 #chi4 ,appendix ,brit4 ,assoc4 ,report for #ahee1 p4 #gi4 #ahc ,ibid41 vol4 ii41 p4 #cgi4 ,appendix4 #ahd 8,manual of ,geology10 pp4 #cie1 #dic4 #ahe ,appendix to ,mc,clintock's 8,arctic ,discoveries40 #ahf ,quart4 ,journ4 ,geol4 ,soc41 vol4 xiv41 p4 #bfb4 ,brit4 ,assoc4 ,report for #aheg1 p4 #fb4 #ahg ,quart4 ,journ4 ,geol4 ,soc41 vol4 xvi41 p4 #cbg4 ,geologist1 #ahfj1 p4 #ch4 #ahh ,phil4 ,mag41 vol4 xxix41 p4 #bij4 #ahi ,trans4 ,geol4 ,soc4 of ,glasgow1 vol4 v41 p4 #fd4 #aij 8,principles10 vol4 i41 p4 #bji4 ,eleventh ,edition4 #aia 8,memoirs of the ,royal ,academy of ,science of ,turin10 ,second ,series1 vol4 xx4 ,i am indebted for the above particulars to ,professor ,ramsay1 who visited the spot along with ,m4 ,gastaldi4 #aib 8,antiquity of ,man10 ,second ,edition1 p4 #bcg4 #aic ,dr4 ,robert ,brown1 in a recent ,memoir on the ,miocene ,beds of the ,disco ,district 7,trans4 ,geol4 ,soc4 ,glasg41 vol4 v41 p4 #ee71 has added considerably to our knowledge of these deposits4 ,he describes the strata in detail1 and gives lists of the plant and animal remains discovered by himself and others1 and described by ,professor ,heer4 ,professor ,nordenskjld has likewise increased the data at our command 7,transactions of the ,swedish ,academy1 #ahgc72 and still further evidence in favour of a warm climate having prevailed in ,greenland during ,miocene times has been obtained by the recent second ,german polar expedition4 #aid ,the following are ,m4 ,leverrier's formul for computing the eccentricity of the earth's orbit1 given in his 8,memoir0 in the ,connaissance des ,temps for #ahdc3-- ,eccentricity in 7t7 years after ,january #a1 #ahjj h#b l#b where h #jjjjebf ,sin 7gt 7 #jjaffaa ,sin 7g#at #a7 #jjjbcff ,sin 7g#bt #b7 #jjajfbb ,sin 7g#ct #c7 - #jjahibe ,sin 7g#dt #d7 #jjaaghb ,sin 7g#et #e7 - #jjafiac ,sin 7g#ft #f7 and l #jjjjebf ,cos 7gt 7 #jjaffaa ,cos 7g#at #a7 #jjjbcff ,cos 7g#bt #b7 #jjajfbb ,cos 7g#ct #c7 - #jjahibe ,cos 7g#dt #d7 #jjaaghb ,cos 7g#et #e7 - #jjafiac ,cos 7g#ft #f7 g #bbehdb #abf #dc #ae g#a #cgacfd #a #bg #ba #bf g#b #bbdbgc #b #abf #dd #h g#c #ebihi #c #he #dg #de g#d #gegdg #d #ce #ch #dc g#e #agaebg #e #be #aa #cc g#f #aghfcc #f #de #bh #ei #aie ,see ,professor ,c4 ,v4 ,zenger's paper 8,on the ,periodic ,change cf ,climate caused by the ,moon10 ,phil4 ,mag4 for ,june1 #ahfh4 #aif ,phil4 ,mag4 for ,february1 #ahfg4 #aig ,phil4 ,mag4 for ,may1 #ahfh4 #aih ,student's 8,elements of ,geology10 p4 #ia4 ,second ,edition4 #aii ,in an interesting memoir1 published in the ,phil4 ,mag4 for #ahej1 ,mr4 ,alfred ,tylor estimated that the basin of the ,mississippi is being lowered at the rate of one foot in #aj1jjj years by the removal of the sediment2 and he proceeds further1 and reasons that one foot removed off the general surface of the land during that period would raise the sea-level three inches4 ,had it not been that ,mr4 ,tylor's attention was directed to the effects produced by the removal of sediment in raising the level of the ocean rather than in lowering the level of the land1 he could not have failed to perceive that he was in possession of a key to unfold the mystery of geological time4 #bjj ,proc4 ,roy4 ,soc41 ,no4 #aeb1 #ahgd4 #bja ,i have taken for the volume and mass of the sun the values given in ,professor ,sir ,william ,thomson's memoir1 ,phil4 ,mag41 vol4 viii4 7#ahed74 #bjb ,phil4 ,mag41 #d1 vol4 xi41 p4 #eaf 7#ahef74 #bjc ,phil4 ,mag4 for ,july1 #ahgb1 p4 #a4 #bjd 8,principles10 p4 #baj4 ,eleventh ,edition4 #bje 8,principles10 vol4 i41 p4 #ajg4 ,tenth ,edition4 #bjf ,the conception of submergence resulting from displacement of the earth's centre of gravity1 caused by a heaping up of ice at one of the poles1 was first advanced by ,m4 ,adhmar1 in his work 8,rvolutions de la ,mer10 #ahdb4 ,when the views stated in this chapter appeared in the ,reader1 ,i was not aware that ,m4 ,adhmar had written on the subject4 ,an account of his mode of viewing the question is given in the ,appendix4 #bjg ,petermann's ,geog4 ,mittheilungen1 #ahga1 ,heft4 x41 p4 #cgg4 #bjh ,geol4 ,mag41 #ahgb1 vol4 ix41 p4 #cfj4 #bji 8,open ,polar ,sea10 p4 #acd4 #baj ,journal of the ,royal ,geographical ,society1 #ahec1 vol4 xxiii4 #baa 8,physics of ,arctic ,ice10 ,quart4 ,journ4 ,geol4 ,soc4 for ,february1 #ahga4 #bab ,some writers have objected to the conclusion that the antarctic ice-cap is thickest at the pole1 on the ground that the snowfall there is probably less than at lower latitudes4 ,the fact is1 however1 overlooked1 that the greater thickness of an ice-cap at its centre is a physical necessity not depending on the rate of snowfall4 ,supposing the snowfall to be greater at1 say1 lat4 #gj than at #hj1 and greater at #hj than at the pole2 nevertheless1 the ice will continue to accumulate till it is thicker at #hj than at #gj1 and at the pole than it is at #hj4 #bac ,it is a pity that at present no record is kept1 either by the ,board of ,trade or by the ,admiralty1 of remarkable icebergs which may from time to time be met with4 ,such a record might be of little importance to navigation1 but it would certainly be of great service to science4 #bad ,see ,chapter ,,xxvii41 and also ,geol4 ,mag4 for ,may and ,june1 #ahgj1 and ,january1 #ahga4 #bae ,phil4 ,mag4 for ,april1 #ahff1 p4 #cbc4 #baf ,ibid41 for ,march1 #ahff1 p4 #agb4 #bag ,reader1 ,february #aj1 #ahff4 #bah ,in a former paper ,i considered the effects of another cause1 viz41 the melting of polar ice resulting from an increase of the ,obliquity of the ,earth's ,orbit4--,trans4 ,glasgow ,geol4 ,soc41 vol4 ii41 p4 #agg4 ,phil4 ,mag41 ,june1 #ahfg4 ,see also ,chapter ,,xxv4 #bai ,phil4 ,mag4 for ,november1 #ahfh1 p4 #cgf4 #bbj ,phil4 ,mag41 ,november1 #ahfh4 #bba 8,origin of ,species10 chap4 xi4 ,fifth ,edition4 #bbb ,lieutenant-,colonel ,drayson 78,last ,glacial ,epoch of ,geology07 and also ,mr4 ,belt 7,quart4 ,journ4 of ,science1 ,october1 #ahgd7 state that ,leverrier has lately investigated the question as to the extent of the variation of the plane of the ecliptic1 and has arrived at results differing considerably from those of ,laplace2 viz41 that the variation may amount to #d #eb1 whereas1 according to ,laplace1 it amounts to only #a #ba4 ,i fear they are comparing things that are totally different2 viz41 the variation of the plane of the ecliptic in relation to its mean position with its variation in relation to the equator4 ,laplace estimated that the plane of the ecliptic would oscillate to the extent of #d #ec #cc on each side of its mean position1 a result almost identical with that of ,leverrier1 who makes it #d #ea #db4 ,but neither of these geometricians ever imagined that the ecliptic could change in relation to the equator to even one-third of that amount4 ,laplace demonstrated that the change in the plane of the ecliptic affected the position of the equator1 causing it to vary along with it1 so that the equator could never possibly recede further than #a #bb #cd from its mean position in relation to the ecliptic 78,mcanique ,cleste10 vol4 ii41 p4 #hef1 ,bowditch's ,translation2 see also ,laplace's memoir1 8,sur les ,variations de l',obliquit de l'cliptique10 ,connaissance des ,temps for #ahbg1 p4 #bcd71 and ,i am not aware that ,leverrier has arrived at a different conclusion4 #bbc ,memoir on the ,secular ,variations of the ,elements of the ,orbits of the ,planets1 8,smithsonian ,contributions to ,knowledge10 vol4 xvii4 #bbd 8,smithsonian ,contributions to ,knowledge10 vol4 ix4 #bbe 8,distribution of ,heat on the ,surface of the ,globe10 p4 #ad4 #bbf ,chapter ,,iv4 #bbg ,quart4 ,journ4 ,geol4 ,soc41 ,june1 #ahff1 p4 #efd4 #bbh ,quart4 ,journ4 ,geol4 ,soc41 vol4 xxi41 p4 #ahf4 #bbi 8,geological ,observer10 p4 #ddf4 ,see also ,mr4 ,james ,geikie's valuable ,memoir1 8,on the ,buried ,forests and ,peat ,mosses of ,scotland40 ,trans4 of the ,royal ,society of ,edinburgh1 vol4 xxiv41 and ,chambers' 8,ancient ,sea-,margins40 #bcj ,see ,lyell's 8,antiquity of ,man10 ,second ,edition1 p4 #bhb2 8,elements10 ,sixth ,edition1 p4 #afb4 #bca ,in order to determine the position of the solstice-point in relation to the aphelion1 it will not do to assume1 as is commonly done1 that the point makes a revolution from aphelion to aphelion in any regular given period1 such as #ba1jjj years2 for it is perfectly evident that owing to the great irregularity in the motion of the aphelion1 no two revolutions will probably be performed in the same length of period4 ,for example1 the winter solstice was in the aphelion about the following dates3 #aa1gjj1 #cc1cjj1 and #fa1cjj years ago4 ,here are two consecutive revolutions1 the one performed in #ba1fjj years and the other in #bh1jjj years2 the difference in the length of the two periods amounting to no fewer than #f1djj years4 #bcb ,quart4 ,journ4 ,geol4 ,soc41 vol4 xxvii41 p4 #bcb4 ,see also 8,the ,last ,glacial ,epoch of ,geology10 by the same author4 #bcc ,quart4 ,journ4 of ,science1 ,october1 #ahgd4 #bcd ,the longer diameter passes from long4 #ad #bc ,e4 to long4 #afe #cg ,w4 #bce 8,principles10 vol4 i41 p4 #bid4 ,eleventh ,edition4 #bcf ,phil4 ,mag4 for ,august1 #ahfd4 #bcg 8,elementary ,geology10 p4 #cii4 #bch 8,the ,past and ,present ,life of the ,globe10 p4 #ajb4 #bci 8,memoirs of the ,geological ,survey10 vol4 ii41 ,part #b1 p4 #djd4 #bdj 8,coal ,fields of ,great ,britain10 p4 #de4 ,third ,edition4 #bda 8,journal of ,researches10 chap4 xiii4 #bdb 8,coal ,fields of ,great ,britain10 p4 #fg4 #bdc ,see 8,smithsonian ,report for #aheg10 p4 #ach4 #bdd ,quart4 ,journ4 ,geol4 ,soc41 ,may1 #ahfe1 p4 civ4 #bde 8,geology of ,fife and the ,lothians10 p4 #aaf4 #bdf 8,life on the ,earth10 p4 #acc4 #bdg ,quart4 ,journ4 ,geol4 ,soc41 vol4 xi41 p4 #ece4 #bdh ,ibid41 vol4 xii41 p4 #ci4 #bdi ,miller's 8,sketch ,book of ,practical ,geology10 p4 #aib4 #bej ,from ,geological ,magazine1 ,may and ,june1 #ahgj2 with a few verbal corrections1 and a slight re-arrangement of the paragraphs4 #bea ,see ,phil4 ,mag4 for ,november1 #ahfh1 p4 #cgd4 #beb ,see ,phil4 ,mag4 for ,november1 #ahfh1 pp4 #cffcgd4 #bec ,journ4 ,geol4 ,soc41 vol4 xxi41 p4 #afe4 #bed ,specimens of the striated summit and boulder clay stones are to be seen in the ,edinburgh ,museum of ,science and ,art4 #bee ,phil4 ,mag4 for ,april1 #ahff4 #bef 8,tracings of the ,north of ,europe10 #ahej1 pp4 #dhea4 #beg ,quart4 ,journ4 ,geol4 ,soc41 vol4 ii41 p4 #cfd4 #beh 8,tracings of the ,north of ,europe10 by ,robert ,chambers1 pp4 #bei1 #bhe4 8,observations sur les ,phnomnes d',erosion en ,norvge10 by ,m4 ,hrbye1 #aheg4 ,see also ,professor ,erdmann's 8,formations ,quaternaires de la ,sude40 #bei 8,glacial ,drift of ,scotland10 p4 #bi4 #bfj ,geological ,magazine1 vol4 ii41 p4 #cdc4 ,brit4 ,assoc4 ,rep41 #ahfd 7sections71 p4 #ei4 #bfa ,trans4 ,roy4 ,soc4 ,edin41 vol4 vii41 p4 #bfe4 #bfb 8,tracings of ,iceland and the ,faroe ,islands10 p4 #di4 #bfc ,see ,chap4 ,,xxiii4 #bfd ,mr4 ,thomas ,belt has subsequently advanced 7,quart4 ,jour4 ,geol4 ,soc41 vol4 xxx41 p4 #dij71 a similar explanation of the steppes of ,siberia4 ,he supposes that an overflow of ice from the polar basin dammed back all the rivers flowing northward1 and formed an immense lake which extended over the lowlands of ,siberia1 and deposited the great beds of sand and silt with occasional freshwater shells and elephant remains1 of which the steppes consist4 #bfe ,proc4 ,roy4 ,phys4 ,soc41 ,edin41 vols4 ii4 and iii4 #bff ,from ,geol4 ,mag4 for ,january1 #ahga4 #bfg ,quart4 ,journ4 ,geol4 ,soc41 xxvi41 p4 #eag4 #bfh ,british ,assoc4 ,report for #ahfd 7sections71 p4 #fe4 #bfi ,quart4 ,journ4 ,geol4 ,soc41 xxvi41 p4 #ij4 #bgj ,geol4 ,mag41 vii41 p4 #cdi4 #bga ,trans4 ,edin4 ,geol4 ,soc41 vol4 i41 p4 #acf4 #bgb ,geol4 ,mag4 for ,june1 #ahgj4 ,see ,chap4 ,,xxvii4 #bgc ,this was done by ,mr4 ,r4 ,h4 ,tiddeman of the ,geological ,survey of ,england 7,quart4 ,journ4 ,geol4 ,soc4 for ,november1 #ahgb71 and the result established the correctness of the above opinion as to the existence of a ,north of ,england ice-sheet4 ,additional confirmation has been derived from the important observations of ,mr4 ,d4 ,mackintosh1 and also of ,mr4 ,goodchild1 of the ,geological ,survey of ,england4 #bgd ,trans4 ,geol4 ,soc41 vol4 v41 p4 #eaf 7first series74 #bge ,quart4 ,journ4 ,geol4 ,soc41 vol4 xi41 p4 #dib4 8,memoir of the ,country around ,cheltenham10 #aheg4 8,geology of the ,country around ,woodstock10 #ahei4 #bgf ,geol4 ,mag41 vol4 vii41 p4 #dig4 #bgg ,quart4 ,journ4 ,geol4 ,soc41 vol4 xxvi41 p4 #ij4 #bgh ,my colleague1 ,mr4 ,r4 ,l4 ,jack4 #bgi ,the greater portion of this chapter is from the ,trans4 of ,geol4 ,soc4 of ,edinburgh1 for #ahfi4 #bhj ,chapter ,,xv41 p4 #bec4 #bha ,trans4 of the ,geol4 ,soc4 of ,glasgow1 vol4 iii41 part i41 page #acc4 #bhb ,mr4 ,milne ,home has advanced1 in his 8,estuary of the ,firth of ,forth10 p4 #ia1 the theory that this trough had been scooped out during the glacial epoch by icebergs floating through the ,midland valley from west to east when it was submerged4 ,the bottom of the trough1 be it observed1 at the watershed at ,kilsyth1 is #cjj feet above the level of its bottom at ,grangemouth2 and this ,mr4 ,milne ,home freely admits4 ,but he has not explained how an iceberg1 which could float across the shallow water at ,kilsyth1 say1 #ajj feet deep1 could manage to grind the rocky bottom at ,grangemouth1 where it was not less than #djj feet deep4 8,the impetus acquired in the ,kyle at ,kilsyth10 says ,mr4 ,milne ,home1 8would keep them moving on1 and the prevailing westerly winds would also aid1 so that when grating on the subjacent carboniferous rocks they would not have much difficulty in scooping out a channel both wider and deeper than at ,kilsyth40 ,but how could they 8grate on the subjacent carboniferous rocks0 at ,grangemouth1 if they managed to float at ,kilsyth8 ,surely an iceberg that could 8grate0 at ,grangemouth would 8ground0 at ,kilsyth4 #bhc ,trans4 of the ,geol4 ,soc4 of ,glasgow1 vol4 iii41 p4 #ada4 #bhd ,mr4 ,john ,young and ,mr4 ,milne ,home advanced the objection1 that several trap dykes cross the valley of the ,clyde near ,bowling1 and come to so near the present surface of the land1 that the ,clyde at present flows across them with a depth not exceeding #bj feet4 ,i fear that ,mr4 ,young and ,mr4 ,milne ,home have been misinformed in regard to the existence of these dykes4 ,about a mile above ,bowling there are one or two dykes which approach to the river-bank1 and may probably cross1 but these could not possibly cut off a channel entering the ,clyde at ,bowling4 ,in none of the borings or excavations which have been made by the ,clyde ,trustees has the rock been reached from ,bowling downwards4 ,i may also state that the whole ,midland valley1 from the ,forth of ,clyde to the ,firth of ,forth1 has been surveyed by the officers of the ,geological ,survey1 and only a single dyke has been found to cross the buried channels1 viz41 one 7,basalt rock7 running eastward from ,kilsyth to the canal bridge near ,dullatur4 ,but as this is not far from the watershed between the two channels it cannot affect the question at issue4 ,see sheet #ca of ,geological ,survey ,map of ,scotland4 #bhe ,trans4 ,geol4 ,soc4 ,glasgow1 vol4 iv41 p4 #aff4 #bhf 8,great ,ice ,age10 chap4 xiii4 #bhg ,see further particulars in ,mr4 ,bennie's paper on the ,surface ,geology of the district around ,glasgow1 ,trans4 ,geol4 ,soc4 of ,glasgow1 vol4 iii4 #bhh ,see also ,smith's 8,newer ,pliocene ,geology10 p4 #aci4 #bhi ,british ,association ,report for #ahfc1 p4 #hi4 ,geologist for #ahfc1 p4 #chd4 #bij ,see ,geological ,magazine1 vol4 ii41 p4 #ch4 #bia ,proc4 ,geol4 ,soc41 vol4 iii41 #ahdj1 p4 #cdb4 #bib 8,antiquity of ,man0 7,third ,edition71 p4 #bdi4 #bic 8,glacial ,drift of ,scotland10 p4 #fe4 ,trans4 ,geol4 ,soc4 ,glas41 vol4 i41 part #b4 #bid 8,memoir1 ,geological ,survey of ,scotland10 ,sheet #bc1 p4 #db4 #bie ,mr4 ,robert ,dick had previously described1 in the ,trans4 ,geol4 ,soc4 ,edinburgh1 vol4 i41 p4 #cde1 portions of these buried channels4 ,he seems1 however1 to have thought that they formed part of one and the same channel4 #bif ,a description of this channel was read to the ,natural ,history ,society of ,glasgow by ,mr4 ,james ,coutts1 the particulars of which will appear in the ,transactions of the ,society4 #big 8,occasional ,papers10 pp4 #aff1 #bbc4 #bih ,memoir read before the ,royal ,society1 ,january #g1 #ahfi4 #bii 8,alpine ,journal10 ,february1 #ahgj4 #cjj ,phil4 ,mag41 ,january1 #ahgb4 #cja ,phil4 ,mag41 ,july1 #ahgj2 ,february1 #ahga4 #cjb ,philosophical ,magazine for ,january1 #ahgj1 p4 #h2 ,proceedings of the ,royal ,society for ,january1 #ahfi4 #cjc ,philosophical ,magazine for ,march1 #ahfi4 #cjd ,proceedings of ,bristol ,naturalists' ,society1 p4 #cg 7#ahfi74 #cje ,ibid41 vol4 iv41 p4 #cg 7new series74 #cjf ,phil4 ,mag41 ,s4 #d1 vol4 x41 p4 #cjc4 #cjg ,proceedings of the ,bristol ,naturalists' ,society1 vol4 iv41 p4 #ci 7new series74 #cjh ,see ,philosophical ,transactions1 ,december1 #aheg4 #cji ,there is one circumstance tending slightly to prevent the rupture of the glacier1 when under tension1 which ,i do not remember to have seen noticed2 that is1 the cooling effect which is produced in solids1 such as ice1 when subjected to tension4 ,tension would tend to lower the temperature of the ice-molecules1 and this lowering of temperature would have the tendency of freezing them more firmly together4 ,the cause of this cooling effect will be explained in the ,appendix4 #caj ,phil4 ,mag41 ,march1 #ahfi2 ,september1 #ahgj4 #caa 8,forms of ,water10 p4 #abg4 #cab ,see text1 p4 #aj4 #cac ,mathematical and ,physical ,series1 vol4 xxxvi4 7#agfe74 #cad 8,memoirs of ,st4 ,petersburg ,academy10 #agfa4 #cae ,the calculations here referred to were made by ,lagrange nearly half a century previous to the appearance of this paper1 and published in the 8,mmoires de l',acadmie de ,berlin10 for #aghb1 p4 #bgc4 ,lagrange's results differ but slightly from those afterwards obtained by ,leverrier1 as will be seen from the following table2 but as he had assigned erroneous values to the masses of the smaller planets1 particularly that of ,venus1 the mass of which he estimated at one-half more than its true value1 full confidence could not be placed in his results4 ,superior limits of eccentricity as determined by ,lagrange1 ,leverrier1 and ,mr4 ,stockwell3-- ,by ,lagrange4 ,by ,leverrier4 ,by ,mr4 ,stockwell4 ,mercury #jbbbjh #jbbefdf #jbcagahe ,venus #jjhbga #jjhfgaf #jjgjfcbi ,earth #jjgfda #jjgggdg #jjfichhh ,mars #jadgbf #jadbbdc #jacifee ,jupiter #jjfjcf #jjfaedh #jjfjhbgd ,saturn #jjhdjh #jjhdiai #jjhdcbhi ,uranus -- #jjfdfff #jjggifeb ,neptune -- -- #jjadejff ,j4 ,c4 #caf 8,mm4 de l',acad4 royale des ,sciences40 #ahbg4 ,tom4 vii41 p4 #eih4 #cag ,absolute zero is now considered to be only #dic ,fah4 below the freezing-point1 and ,herschel himself has lately determined #bga below the freezing-point to be the temperature of space4 ,consequently1 a decrease1 or an increase of one per cent4 in the mean annual amount of radiation would not produce anything like the effect which is here supposed4 ,but the mean annual amount of heat received cannot vary much more than one-tenth part of one per cent4 ,in short1 the effect of eccentricity on the mean annual supply of heat received from the sun1 in so far as geological climate is concerned1 may be practically disregarded4--,j4 ,c4 #cah 8,principles of ,geology10 p4 #aaj4 8,mr4 ,lyell1 however1 in stating the actual excess of eight days in the duration of the sun's presence in the northern hemisphere over that in the southern as productive of an excess of light and heat annually received by the one over the other hemisphere1 appears to have misconceived the effect of elliptic motion in the passage here cited1 since it is demonstrable that whatever be the ellipticity of the earth's orbit the two hemispheres must receive equal absolute quantities of light and heat per annum1 the proximity of the sun in perigee exactly compensating the effect of its swifter motion4 ,this follows from a very simple theorem1 which may be thus stated3 #8,the amount of heat received by the earth from the sun while describing any part of its orbit is proportional to the angle described round the sun's centre1' so that if the orbit be divided into two portions by a line drawn in any direction through the sun's centre1 the heats received in describing the two unequal segments of the ellipse so produced will be equal40 #cai ,when the eccentricity of the earth's orbit is at its superior limit1 the absolute quantity of heat received by the globe during one year will be increased by only #a_/cjjth part2 an amount which could produce no sensible influence on climate4--,j4 ,c4 #cbj ,sir ,charles has recently1 to a certain extent1 adopted the views advocated in the present volume1 viz41 that the cold of the glacial epoch was brought about not by a decrease1 but by an increase of eccentricity4 7,see vol4 i4 of 8,principles10 tenth and eleventh editions47 ,the decrease in the mean annual quantity of heat received from the sun1 resulting from the decrease in the eccentricity of the earth's orbit--the astronomical cause to which he here refers--could have produced no sensible effect on climate4--,j4 ,c4 #cba ,it is singular that both ,arago and ,humboldt should appear to have been unaware of the researches of ,lagrange on this subject4 #cbb 8,rvolutions de la ,mer10 p4 #cg4 ,second ,edition4 #cbc ,see text1 p4 #cg4 #cbd ,see ,philosophical ,magazine for ,december1 #ahfg1 p4 #deg4 #cbe ,silliman's ,american ,journal for ,july1 #ahfd4 ,philosophical ,magazine for ,september1 #ahfd1 pp4 #aic1 #aif4 #cbf ,philosophical ,magazine for ,august1 #ahfe1 p4 #ie4 #cbg ,see text1 p4 #hj4 #cbh ,see text1 p4 #bbb4 #cbi ,proc4 ,roy4 ,soc41 ,no4 #aeg1 #ahge4 #ccj ,see text1 p4 #ebb4 #cca ,phil4 ,trans4 for #ahei1 p4 #ia4 #ccb ,see text1 p4 #ebg4 ---------------------------------------- ------------------------------ ,transcriber's ,notes3 - ,text enclosed by underscores is in italics 7italics74 - ,blank pages have been removed4 - ,obvious typographical errors have been silently corrected4 - ,some spelling and hyphenation variations have been made consistent4