,,transcriber',s ,,note ,italic text is denoted by underscores4 ,footnote anchors are denoted by number1 and the footnotes have been placed at the end of the book4 ,the tables in this book are best viewed using a monospace font4 ,some minor changes to the text are noted at the end of the book4 ,,the ,,evolution ,,of ,,climate ,,the ,,evolution ,,of ,,climate ,,by ,c4 ,e4 ,p4 ,,brooks1 ,m4,sc41 ,f4,r4,a4,i41 ,f4,r4,met4,soc4 ,,with ,a ,,preface ,,by ,g4 ,c4 ,,simpson1 ,d4,sc41 ,f4,r4,s41 ,,director ,,of ,,the ,,meteorological ,,office ,,london3 ,,benn ,,brothers1 ,,limited #h ,,bouverie ,,street1 ,e4,c4#d #aibb ,,preface ,geologists very early in the history of their science1 in fact as soon as fossils began to be examined1 found indisputable evidence of great variations in climate4 ,the vegetation which resulted in the coal measures could have grown only in a sub-tropical climate1 while over these are vast remains of ice-worn boulders and scratched rocks which obviously have been left by ice existing under polar conditions4 ,such records were not found only in one region1 but cropped up in juxtaposition in many parts of the world4 ,remains of sub-tropical vegetation were found in ,spitzbergen1 and remains of an extensive ice-sheet moving at sea-level from the south were clearly recognized in central and northern ,india4 ,at first it was simply noticed that the older fossils generally indicated a warmer climate1 and it was considered that the early climate of a globe cooling from the molten state would be warm and moist1 and so account for the observed conditions4 ,it was recognized that the ice remains were relatively recent1 and so far as a cause for the ,ice ,age was sought it was considered that astronomical changes would be sufficient4 ,it was only when geologists began to find records of ice ages far anterior to the ,carboniferous ,age1 and astronomers proved by incontrovertible observations and calculations that changes in the earth's orbit1 or its inclination to that orbit1 could not account for the ice ages1 that the importance and inexplicability of the geological evidence for changes of climate came to be clearly recognized4 ,during the last few years much study has been given to 8paloclimatology10 but such a study is extremely difficult4 ,only a very small fraction of the total surface of the earth can be geologically examined1 and of that fraction a still smaller proportion has up to the present been studied in detail4 ,there has been a great tendency to study intently a small region and then to generalize4 ,the method of study which has to be employed is extremely dangerous4 ,a geological horizon is determined by the fossils it contains4 ,wherever fossils of a certain type are found the strata are given the same label4 ,isolated patches correlated by their fossils are found in different parts of the world1 and it is frequently assumed not only that these rocks were laid down at the same time1 but that the conditions which they indicate existed over the whole of the earth's surface simultaneously4 ,thus geologists tell us that the climate of the ,carboniferous ,age was warm and damp2 of the ,devonian ,age cool and dry2 of the ,eocene ,age very warm2 of the ,ice ,age very cold4 ,but has the geologist given sufficient attention to the climatic zones during the various geological climates8 ,it is true that the geologist has definitely expressed the view that in certain ages climatic zones did not exist2 but from a meteorological point of view it is difficult to see how the climate could have been even approximately the same in all parts of the world if solar radiation determined in the past as in the present the temperature of the surface of the earth4 ,the climatic zones of the various geological periods will need much closer study in the future2 the data hardly exist at present1 and the great area covered by the ocean will always make the study difficult and the conclusions doubtful4 ,admitting1 for the sake of argument only1 large changes in average conditions1 but with zonal variations of the same order of magnitude as those existing to-day1 the slow changes from period to period will cause any given climatic state to travel slowly over the surface of the earth1 and this will so complicate the problem as to make it doubtful whether any conclusions can be reached so long as the same criteria are used to determine both the geological epoch and the climatic conditions4 ,these considerations apply more particularly to the earlier records1 while ,mr4 ,brooks has confined his work chiefly to the later records1 beginning with those of the ,great ,ice ,age1 in which climatic zones are clearly indicated by the limits of the ice2 but in this problem one cannot confine one's attention to a portion of the record1 for the test of any explanation must be its sufficiency to explain all the past changes of climate4 ,one will not be satisfied with an explanation of the ,great ,ice ,age which does not explain at the same time the records of earlier ice ages1 of which there is indubitable evidence in the ,permo-,carboniferous and ,pre-,cambrian periods1 and the records of widespread tropical or sub-tropical conditions in the ,carboniferous and ,eocene ,ages4 ,whether ,mr4 ,brooks' theory for the cause of the recent changes of climate satisfies this criterion must be left to each reader to decide4 ,as ,mr4 ,brooks says1 the literature on this subject is now immense1 and it is most unsatisfactory literature to digest and summarize4 ,in the first place1 many of the original observations which can be used in the study of past climates are hidden away in masses of purely geological descriptions1 and a great deal of mining has to be done to extract the climatic ore4 ,then1 again1 most of the writers who have made a special study of climatic changes have had their own theoretical ideas and most of their evidence has been ex parte4 ,to take a single example1 for one paper discussing dispassionately the evidence for changes in climate during the historical period1 there have been ten to prove either that the climate has steadily improved1 steadily deteriorated1 changed in cycles or remained unchanged4 ,it is extremely difficult to arrive at the truth from such material1 and still more difficult to summarize the present state of opinion on the subject4 ,it may be complained that ,mr4 ,brooks has himself adopted this same method and has written his book around his own theory4 ,but was there any alternative8 ,there are so many theories and radically different points of view that no writer could confine himself to the observations and say what these indicate1 for the indications are so very different according to each theory in turn4 ,and new theories are always being propounded2 since ,mr4 ,brooks commenced to write this book1 ,wegener has put forward his revolutionary theory according to which the polar axis has no stability1 and the continents are travelling over the face of the globe like debris on a flood4 ,where is there solid ground from which to discuss climatic changes if the continents themselves can travel from the equator to the pole and back again in the short period of one or two geological epochs8 ,mr4 ,brooks has studied deeply geology1 anthropology1 and meteorology1 and he has considerable mathematical ability4 ,by applying the latter to the results of his studies he has developed a theory for the cause of climatic changes based on changes of land and sea area1 and on changes of elevation of land surfaces1 and naturally he has made this theory the basis of his work4 ,that there will be some who are not able to agree with him as to the sufficiency of the causes he invokes1 or who may even question whether he also has not taken for granted what others dispute1 goes without saying2 but all will agree that he has presented a difficult subject in a clear and concise way1 and that meteorologists 7and may ,i add geologists87 owe to him a deep debt of gratitude4 ,g4 ,c4 ,,simpson4 ,,contents ,,page ,,preface #e ,,introduction #aa ,i4 ,,factors ,,of ,,climate ,,and ,,the ,,causes ,,of ,,climatic ,,fluctuations #ae ,,ii4 ,,the ,,climatic ,,record ,,as ,a ,,whole #cb ,,iii4 ,,conditions ,,before ,,the ,,quaternary ,,ice ,,age #db ,,iv4 ,,the ,,great ,,ice ,,age #dg ,v4 ,,the ,,glacial ,,history ,,of ,,northern ,,and ,,central ,,europe #ee ,,vi4 ,,the ,,mediterranean ,,regions ,,during ,,the ,,glacial ,,period #fh ,,vii4 ,,asia ,,during ,,the ,,glacial ,,period #gf ,,viii4 ,,the ,,glacial ,,history ,,of ,,north ,,america #hf ,,ix4 ,,central ,,and ,,south ,,america #ig ,x4 ,,africa #ajc ,,xi4 ,,australia ,,and ,,new ,,zealand #aji ,,xii4 ,,the ,,glaciation ,,of ,,antarctica #aad ,,xiii4 ,,the ,,close ,,of ,,the ,,ice ,,age--,,the ,,continental ,,phase #aah ,,xiv4 ,,the ,,post-,,glacial ,,optimum ,,of ,,climate #abg ,,xv4 ,,the ,,forest ,,period ,,of ,,western ,,europe #acf ,,xvi4 ,,the 8,,classical0 ,,rainfall ,,maximum1 #ahjj ,b4,c4 ,,to ,a4,d4 #ejj #adj ,,xvii4 ,,the ,,climatic ,,fluctuations ,,since ,a4,d4 #ejj #adi ,,xviii4 ,,climatic ,,fluctuations ,,and ,,the ,,evolution ,,of ,,man #aei ,,xix4 ,,climate ,,and ,,history #afb ,,appendix--,,the ,,factors ,,of ,,temperature #aff ,,index #afi ,,introduction ,the following study is an attempt to reconstruct in some detail the sequence of climatic changes through which the world passed during that important stage of its geological history which is variously known as the ,ice ,age or ,glacial ,period1 the ,pleistocene1 the ,quaternary1 or the ,human ,period4 ,that time saw the growth of humanity from a primitive stage but little removed from the higher animals to the beginnings of a complicated civilization1 and it saw that human life spread from its cradle or cradles to the ends of the earth2 it saw the configuration of the globe passing through a series of modifications which ended by establishing the physical geography of the present day4 ,finally1 it saw a series of startling changes of climate which almost merit the term 8,revolutions0 of the old catastrophic geologists1 at the conclusion of which we can trace the gradual development of the climatic conditions of the present day4 ,in short1 it is a period of immense interest which has a personal application lacking in the remoter parts of geological time1 and for that reason it is worthy of the fullest study4 ,on the geological side the literature of the ,ice ,age is immense1 and is beyond the power of any one man to master4 ,volumes might be1 and not infrequently have been1 written on the glacial geology of areas limited to a few square miles1 or even on the deposits of a single section4 ,on the archological side the literature is not yet so voluminous1 but is technical and conflicting in a high degree4 ,it is only when we seek the contributions of competent meteorologists that we find a serious gap in the literature4 ,nor is this surprising1 for meteorologists are still so much occupied with the present vagaries of the weather1 that few of them have time to extend their researches into the geological past4 ,yet this is eminently a case where the past is the key to the present1 and it may be that the solution of many problems which meteorologists have hitherto faced in vain will yet be suggested by studies of the climatic changes of the ,ice ,age4 ,the writer's excuse for setting down his views is that he is intensely interested in all three sciences--geology1 anthropology1 and meteorology4 ,the combination of these three subjects naturally ended in specialization on their common meeting place1 and led him to hope that he could assist his fellow geologists and anthropologists by acquainting them with some of the bearings of meteorology on their subject1 and could open out to his fellow meteorologists a fascinating branch of their science4 ,the ,quaternary1 however1 was not the only geological period to exhibit the phenomena of an ,ice ,age1 and in order that we may more fully understand the status of the ,quaternary ,ice ,age in the long succession of geological climates1 and also to avoid the charge of presenting part of the evidence only1 a brief discussion of the climates of the earlier periods has been attempted4 ,the plan of the work is as follows3 ,chapter ,i deals generally with the causes of climatic fluctuations and with the meteorology of an ,ice ,age4 ,chapter ,,ii gives a brief account of the climatic record as a whole1 and ,chapter ,,iii deals with the ,tertiary period considered as leading up to the ,quaternary ,ice ,age4 ,chapter ,,iv discusses the subdivisions of the ,glacial period1 and the conflict between advocates of one and of repeated glaciations4 ,chapters ,v to ,,xii give brief accounts1 from the standpoint of a meteorologist1 of the glacial history of ,northern ,europe1 the ,mediterranean ,region1 ,asia1 ,north and ,south ,america1 ,africa1 ,australia1 and the ,south ,polar regions4 ,in ,chapters ,,xiii to ,,xv post-,glacial climatology is considered4 ,chapters ,,xvi and ,,xvii deal with the major climatic fluctuations of the 8historic0 period1 and finally1 in ,chapters ,,xviii and ,,xix1 is a short discussion of the influence of climate on the evolution and history of man4 ,a brief bibliography concludes each chapter4 ,,the ,,evolution ,,of ,,climate ,,chapter ,i ,,factors ,,of ,,climate ,,and ,,the ,,causes ,,of ,,climatic ,,fluctuations ,the climate of any point on the earth's surface depends on a complex of factors1 some of them due to influences arriving from outside the earth1 and others purely terrestrial4 ,since any variations of climate must be due to a change in one or more of these1 it is necessary1 before we can discuss changes of climate1 to consider briefly what the factors are4 ,the only important extra-terrestrial factor of climate is the amount of radiant energy which reaches the borders of the earth's atmosphere from the heavenly bodies--that is1 from the sun1 for the moon and stars can be ignored in this connexion4 ,the only other conceivable factor is the arrival of meteorites1 bringing kinetic energy which is converted into heat1 and introducing cosmic dust into the atmosphere2 but it is highly improbable that this is of appreciable effect4 ,the amount of solar radiation#a which reaches the earth depends in the first place on the total radiation emitted by the sun1 and in the second place on the distance of the earth from the sun1 both of which quantities are variable4 ,it has been calculated that if other factors remained unchanged an increase of ten per cent4 in the solar radiation would raise the mean temperature of the earth's surface by about #g ,c41 or between #ab and #ac ,f41 with1 of course1 a corresponding fall for a decrease4 ,after the sun's radiation reaches the outer limits of the earth's atmosphere its nature and intensity are modified by the composition of the air through which it passes4 ,in general the air itself is very transparent to the small wave-lengths which make up the solar rays1 but the presence of fine dust1 whether of volcanic or of cosmic origin1 has been shown by ,humphreys to be a distinct hindrance to their passage1 so that volcanic eruptions of an explosive nature1 such as that of ,krakatoa in #ahhc1 ,la ,soufrire 7,st4 ,vincent7 in #aijb1 or ,katmai 7,alaska7 in #aiab1 may result in a fall of temperature over the world as a whole4 ,the temperature of the earth is determined by the balance between the radiation received from the sun and the terrestrial radiation to space1 and a decrease in the latter would be as effective in raising the mean temperature as an increase in the former4 ,the use of glass for greenhouses depends on this principle2 for glass is transparent to heat rays of small wave-length1 but is largely opaque to the rays of greater wave-length which make up terrestrial radiation4 ,certain constituents of the atmosphere1 especially water-vapour1 carbon dioxide and ozone1 are effective in this way1 and variations in the amount of these gases present may affect the temperature4 ,the angle at which the sun's rays strike the earth's surface is a highly important factor4 ,within the ,tropics the sun at midday is nearly vertical throughout the year1 and the mean temperature in these regions is correspondingly high2 on the other hand1 during the long polar night the sun is not seen for half the year1 and very low temperatures prevail4 ,there is thus a seasonal variation of the heat received from the sun in middle and high latitudes1 the extent of which depends on the 8obliquity of the ecliptic10 i4e4 the inclination of the earth's axis to the plane of its orbit round the sun1 and any changes in this factor must alter the seasonal variation of climate4 ,further1 since the climate of any place depends so closely on its latitude1 it follows that if the latitude changes the climate will change4 ,a ship can change its latitude at will1 but we are accustomed to regard the position of the 8firm ground beneath our feet0 relatively to the poles as fixed within narrow limits4 ,this stability has1 however1 been questioned from time to time1 mainly on evidence derived from paloclimatology1 and theories of climatic change have been based on the wanderings of continents and oceans4 ,finally1 local climate is intimately bound up with the distribution of land and sea1 and the marine and atmospheric currents resulting therefrom1 and on elevation above sea-level1 both of which factors1 as we shall see1 have suffered very wide variations in the geological past4 ,nearly all the theories which have been put forward to account for geological changes of climate1 and especially the occurrence of the last or ,quaternary ,ice ,age1 are based on the abnormal variation of one or other of the above factors1 and we may consider them briefly in turn4 ,very few have ever been taken seriously4 ,in the first place1 we can at once dismiss fluctuations in the radiation emitted by the sun as a cause of great changes of climate4 ,it is true that many small fluctuations are traceable directly to this cause1 such as the eleven-year periodicity of temperature and rainfall2 but these fluctuations are1 and must be1 greater at the equator than at the poles1 while the fall of temperature during the ,glacial period reached its maximum near the poles and was least at the equator4 ,moreover1 there is not the slightest direct evidence in support of such a theory1 and it can only be admitted when all other hypotheses have failed4 ,the 8astronomical0 theory of the cause of climatic fluctuations is associated chiefly with the name of ,james ,croll4 ,croll's theory connects abnormal variations of climate with variations1 firstly of the eccentricity of the earth's orbit1 and secondly of the ecliptic4 ,in periods of high eccentricity the hemisphere with winter in aphelion is cold because the long severe winter is far from being balanced by the short hot summer2 at the same time the opposite hemisphere enjoys a mild equable climate4 ,this theory commanded instant respect1 and still finds a place in the text-books1 but difficulties soon began to appear4 ,the evidence strongly suggests that glacial periods did not alternate in the two hemispheres1 but were simultaneous over the whole earth2 even on the equator the snow-line was brought low down4 ,moreover1 on ,mars the largest snow-cap appears on the hemisphere with its winter in perihelion4 ,although ,croll's reasoning was beautifully ingenious he gave very few figures2 while the date which he gives for the conclusion of the ,ice ,age1 #hj1jjj years ago1 has been shown by recent research to be far too remote1 #ae1jjj years being nearer the mark4 ,croll's theory has recently been revived in an altered form by ,r4 ,spitaler1 a ,czecho-,slovakian meteorologist1 who calculated the probable alteration in the mean temperature of each latitude under maximum eccentricity 7#j4ggge7 and maximum obliquity 7#bg #dh71 the distribution of land and water remaining unchanged4 ,the results are shown in the attached table1 where - means that the temperature was so much below the present mean1 and that it was so much above4 ---------------------------------------- ------------------ ,aphelion ,december4 ,aphelion ,june4 ---------------------------------------- ----------- ,winter4 ,summer4 ,year4 ,winter4 ,summer4 ,year4 ---------------------------------------- ----------- ,f4 ,f4 ,f4 ,f4 ,f4 ,f4 ,n4 #fj -#i #ae -#a -#e -#d -#a #cj -#ac #ac -#b #a -#h -#b ,equator -#h #d -#b #a -#f -#b ,s4 #cj -#f #a -#b #c -#e -#b #fj -#b -#a -#a #a -#b -#a ---------------------------------------- ------------------ ,spitaler claims that these differences are sufficient to cause a glacial period in the hemisphere with winter in aphelion1 but from this point his theory departs widely from ,croll's4 ,during the long severe winter great volumes of sea water are brought to a low temperature1 and1 owing to their greater weight1 sink to the bottom of the ocean1 where they remain cold and accumulate from year to year4 ,but the water warmed during the short hot summer remains on the surface1 where its heat is dissipated by evaporation and radiation4 ,thus1 throughout the cold period1 lasting about #aj1jjj years1 the ocean in that hemisphere is steadily growing colder1 and this mass of cold water is sufficient to maintain a low temperature through the whole of the following period of #aj1jjj years with winter in perihelion1 which would otherwise be a genial interval4 ,in this way a period of great eccentricity becomes a glacial period over the whole earth1 but with crests of maximum intensity alternating in the two hemispheres4 ,unfortunately the numerical basis of this theory is not presented1 and it seems incredible that a deficiency of temperature could be thus maintained through so long a period4 ,further1 the difficulty about chronology remains1 and the work brings the astronomical theory no nearer to being a solution of the ,ice ,age problem than was ,croll's4 ,the theory which connects fluctuations of climate on a geological scale with changes in the composition of the earth's atmosphere is due to ,tyndall and ,arrhenius1 and was elaborated by ,chamberlin4 ,the theory supposed that the earth's temperature is maintained by the 8blanketing0 effect of the carbon dioxide in the atmosphere4 ,this acts like the glass of a greenhouse1 allowing the sun's rays to enter unhindered1 but absorbing the heat radiated from the earth's surface and returning some of it to the earth instead of letting it pass through to be lost in space4 ,consequently1 any diminution in the amount of carbon dioxide present would cause the earth to radiate away its heat more freely1 so reducing its temperature4 ,but it is now known that the terrestrial radiation which this gas is capable of absorbing is taken up equally readily by water-vapour1 of which there is always sufficient present1 and variations of carbon dioxide cannot have any appreciable effect4 ,brief mention may be made here of a theory put forward by ,humphreys1 who attributed glaciation to the presence of great quantities of volcanic dust in the atmosphere4 ,it would require an enormous output of volcanic dust to reduce the temperature sufficiently2 but in any case the relation1 if any1 between vulcanicity and temperature during the geological ages is rather the reverse of that supposed by ,humphreys1 periods of maximum volcanic action coinciding more frequently with high temperatures than with low4 ,perhaps the best comment on ,humphreys' theory is that in #aijb ,f4 ,frech produced its exact opposite1 warm periods being associated with an excess of vulcanicity and cold periods with a diminution4 ,the theory which attributes climatic changes in various countries to variations in the position of the poles has been adduced in two main forms4 ,the first is known as the ,pendulation ,theory1 and supposes the existence of two 8oscillation poles0 in ,ecuador and ,sumatra4 ,the latitude of these points remains unchanged1 and the geographical poles swing backwards and forwards along the meridian of #aj ,e4 midway between them4 ,varying distances from the pole cause changes of climate1 and the movements of the ocean1 which adjusts itself to the change of pole more rapidly than the land1 causes the great transgressions and regressions of the sea and the elevation and subsidence of the land4 ,an alternative form put forward by ,p4 ,kreichgauer1 and recently brought up again by ,wegener1 explains the apparent variations in the position of the pole1 not through a motion of the earth's axis1 but by the assumption that the firm crust has moved over the earth's core so that the axis1 remaining firm in its position1 passes through different points of the earth's crust4 ,the cause of these movements is the centrifugal force of the great masses of the continents1 which are distributed symmetrically about the earth4 ,imagine a single large continent resting on a sub-fluid magma in temperate latitudes4 ,centrifugal force acting on this continent tends to drive it towards the equator4 ,there is thus a tendency for the latitude of ,europe to decrease4 ,similar forces acting through geological ages have caused the poles and equator to wander at large over the earth's surface1 and also caused the continents to shift their positions relatively to one another4 ,according to ,wegener1 in the ,oligocene there was only a single enormous continent1 ,america being united to ,europe and ,africa on the one hand1 and through ,antarctica to ,australia on the other2 while the ,deccan stretched south-westwards nearly to ,africa4 ,the poles were in ,alaska and north of the ,falkland ,islands4 ,the treatment in ,kreichgauer's original book is speculative and at times fanciful2 ,wegener's treatise appears to demand more respectful attention1 but is open to some vital objections4 ,in the first place1 theories of this class demand that the glaciation occurred in different regions at widely different times1 whereas we shall see in the following pages that the evidence points very strongly to a double glaciation during the ,quaternary occurring simultaneously over the whole earth4 ,this objection1 which was fatal to ,croll's theory in its original form1 is equally fatal to theories of pole-wandering as an explanation of the ,quaternary ,ice ,age4 ,secondly1 we know that the last phase of this glaciation1 known as the ,wisconsin stage in ,america and the ,wurmian in ,europe1 was highly developed only #bj1jjj years ago1 and probably reached its maximum not more than #cj1jjj years ago4 ,in the last #ejjj years there has been no appreciable change of latitude1 at least in ,eurasia2 and it seems impossible for the extensive alterations required in the geography of the world by ,wegener's theory to have taken place in so short a time4 ,the great glaciation of the ,permian period1 referred to in the next chapter1 is a totally different matter4 ,during this time the ice-sheets appear to have reached their maximum area1 and to have extended to sea-level1 in countries which are at present close to the equator1 while lands now in high latitudes remained unglaciated4 ,it is true that at the present day glaciers exist at high latitudes under the equator itself1 and given a ridge sufficiently steep and a snowfall sufficiently heavy such glaciers would possibly extend to sea-level2 but even these conditions would not give rise to the enormous deposits of true boulder-clay which have been discovered1 and there seems no way of avoiding the supposition of an enormous difference in the position of the pole relatively to the continents at this time4 ,wegener's theory alone1 however1 requires that glaciation should always have been proceeding in some part of the globe 7unless both poles were surrounded by wide expanses of ocean71 which is hard to reconcile with the extremely definite and limited glaciations which geological research has demonstrated4 ,in these circumstances we may tentatively explain the pre-,tertiary glacial periods by combining ,wegener's theory of the movements of continents and oceans as a whole with the theory of changes of elevation and of land and sea distribution which is outlined below4 ,that is to say1 we may suppose that the positions of the continents and oceans have changed1 relatively both to each other and to the poles1 slowly but more or less continuously throughout geological time2 while at certain periods the land and sea distribution became favourable for extensive glaciation of the regions which at that time were in high latitudes4 ,the geographical theory1 which states that the ,ice ,age was brought about by elevation in high latitudes1 and by changes in the land and sea distribution1 though never seriously challenged1 has suffered until recently from a lack of precision4 ,the present author attempted to remedy this by a close mathematical study of the relation of temperature to land and sea distribution at the present day4 ,the method at attack was as follows3 from the best available isothermal charts of all countries the mean temperature reduced to sea-level was read off for each intersection of a ten-degree square of latitude and longitude1 for ,january and ,july1 from #gj ,n4 to #fj ,s4 latitude2 this gave #ejd values of temperature for each of these months4 ,round each point was next drawn a circle with an angular radius of ten degrees1 divided into east and west semicircles4 ,the area of each semicircle was taken as #ajj1 and by means of squared paper the percentage of land to the east and land to the west were calculated2 finally1 in each month the percentage of the whole circle occupied by land1 ice1 or frozen sea was calculated1 this figure naturally being greater in winter than in summer4 ,the projection used was that of the 8octagonal globe10 published by the ,meteorological ,office1 which shows the world in five sections1 the error nowhere exceeding six per cent4 ,these figures were then analysed mathematically1 and from them the effects on temperature of land to the east1 land to the west1 and ice were calculated4 ,the detailed numerical results are set out in an ,appendix2 it is sufficient here to give the following general conclusions3 7#a7 ,in winter the effect of land to the west is always to lower temperature4 7#b7 ,in winter the effect of land to the east is almost negligible1 that is to say1 the eastern shore of a continent is almost as cold as the centre of the continent4 ,the only important exception to this rule is #gj ,n41 which may be considered as coming within a belt of polar east winds4 7#c7 ,in summer the general effect of land1 whether to the east or west1 is to raise temperature1 but the effect is nowhere anything like so marked as the opposite effect in winter4 7#d7 ,the effect of ice is always to lower temperature4 7#e7 ,for every latitude a 8basal temperature0 can be found4 ,this is the temperature found near the centre of an ocean in that latitude4 ,this 8basal temperature0 is a function of the amount of land in the belt of latitude4 ,poleward of latitude #bj an increase of land in the belt lowers the winter basal temperatures very rapidly and raises the summer basal temperature to a less extent4 ,the 8basal temperature0 is important1 since it is the datum line from which we set out to calculate the winter and summer temperatures of any point1 by the addition or subtraction of figures representing the local effect of land in a neighbouring #aj circle4 ,as an illustration of the scale of the temperature variations which may be due to geographical changes1 suppose that the belt between #ej and #gj ,n4 is entirely above the sea4 ,then we have the following theoretical temperatures2 for a point on #fj ,n4 at sea-level3 ,january -#cj ,f42 ,july #gb ,f4 ,data for calculating the effect of ice are rather scanty1 but the following probable figures can be given1 supposing that the belt in question were entirely ice-covered3 ,january -#cj ,f4 7as for land72 ,july #bc ,f4 ,supposing that the belt were entirely oceanic1 the mean temperature in #fj ,n4 would be3 ,january #bi ,f42 ,july #da ,f4 ,these figures show how enormously effective the land and sea distribution really is4 ,from ,appendix it is easy to calculate the probable temperature distribution resulting from any arrangement of land and water masses4 ,since the geography of the more recent geological periods is now known in some detail1 we have thus a means of restoring past climates and discussing the distribution of animals and plants in the light of this knowledge4 ,of course it is not pretended that no other possible causes of great climatic variation exist1 but no others capable of seriously modifying temperature over long periods are known to have been in operation4 ,as we shall see later1 there are solar and other astronomical causes capable of modifying climate slightly for a few decades or even centuries1 but these are insignificant compared with the mighty fluctuations of geological time4 ,in applying the results of this 8continentality0 study to former geological periods the method adopted is that of differences4 ,the present climate is taken as a standard1 and the temperatures of1 for instance1 the ,glacial period are calculated by adding to or subtracting from the present temperatures amounts calculated from the change in the land and sea distribution4 ,this has the advantage of conserving the present local peculiarities1 such as those due to the presence of the ,gulf ,drift1 but such a procedure would be inapplicable for a totally different land and sea distribution1 such as prevailed during the ,carboniferous period4 ,that it is applicable for the ,quaternary is perhaps best shown by the following comparison of temperatures calculated from the distribution of land1 sea and ice with the actual temperatures of the ,ice ,age as estimated by various authorities 7inferred fall73 ---------------------------------------- ----------------------- ,calculated ,fall4 ,locality4 ,author4 ,inferred ,fall4--------------- ,jan4,july4,mean4 ---------------------------------------- --------------------- ,f4 ,f4 ,f4 ,f4 ,scandinavia ,j4 ,geikie ,more than #bj #cf #ah #bg ,east ,anglia ,c4 ,reid #bj #ah #ac #ae ,alps ,penck and ,brckner #aa #ac #i #aa ,japan ,simotomai #g #i #e #g ---------------------------------------- --------------------- ,it is seen that the agreement is quite good4 ,there is one other point to consider1 the effect of height4 ,the existence of a great land-mass generally implies that part of it at least has a considerable elevation1 perhaps #aj1jjj or #bj1jjj feet1 and these high lands lave a very different climate to the neighbouring lowlands4 ,meteorologists have measured this difference in the case of temperature and found that the average fall with height is at the rate of #a ,f4 in #cjj feet4 ,in the lower levels the fall is usually greater in summer than in winter1 but at #cjjj feet it is fairly uniform throughout the year4 ,consequently1 quite apart from any change in climate due to the increased land area1 an elevation of #cjjj feet would result in a fall of temperature of #aj ,f41 winter and summer alike4 ,this reinforces the effect of increased land area and aids in the development of ice-sheets or glaciers4 ,the effect of geographical changes on the distribution of rainfall are much more complicated4 ,the open sea is the great source of the water-vapour in the atmosphere1 and since evaporation is very much greater in the hot than in the cold parts of the globe1 for considerable precipitation over the world as a whole there must be large water areas in the ,tropics4 ,in temperate latitudes the water-vapour is carried over the land by onshore winds1 and some of it is precipitated where the air is forced to rise along the slopes of hills or mountains4 ,some rain falls in thunderstorms and similar local showers1 but the greater part of the rain in most temperate countries is associated with the passage of 8depressions40 ,these are our familiar wind- and rain-storms2 a depression consists essentially of winds blowing in an anti-clockwise direction round an area of low pressure4 ,these centres of low pressure move about more or less irregularly1 but almost invariably from west to east in the temperate regions4 ,they are usually generated over seas or oceans1 and1 since a supply of moist air is essential for their continued existence1 they tend to keep to the neighbourhood of water masses or1 failing that1 of large river valleys4 ,in a large dry area depressions weaken or disappear4 ,their tracks are also very largely governed by the positions of areas of high pressure or anticyclones1 which they tend to avoid1 moving from west to east on the polar side of a large anticyclone and from east to west on the equatorial side4 ,since anticyclones are developed over the great land areas in winter1 this further restricts the paths of depressions to the neighbourhood of the oceans at that season4 ,for all these reasons the tracks of depressions1 and therefore the rainfall1 are intimately connected with the distribution of land and sea4 ,in winter there is little rainfall in the interior of a great land-mass1 except where it is penetrated by an arm of the sea like the ,mediterranean2 on the other hand1 the coasts receive a great deal of rain or snow4 ,the interior receives its rain mostly in spring or summer2 if the coastal lands are of no great elevation this will be plentiful1 but if the coasts are mountainous the interior will be arid1 like the central basins of ,asia4 ,the development of an ice-sheet is equivalent to introducing perpetual winter in the area occupied by the ice4 ,the low temperature maintains high pressure1 and storm-tracks are unable to cross the ice4 ,at the present day depressions rarely penetrate beyond the outer fringe of the ,antarctic continent1 and only the southern extremity of ,greenland is affected by them4 ,since the total energy in the atmosphere is increased by the presence of an ice-sheet1 which affords a greater contrast of temperature between cold pole and equator1 storms will increase in frequency and their tracks must be crowded together on the equatorial side of the ice-sheet4 ,in the southern hemisphere we have great storminess in the 8roaring forties02 south of ,greenland the ,newfoundland banks are a region of great storminess4 ,hence1 when an ice-sheet covered northern and central ,europe the ,mediterranean region must have had a marked increase of storminess with probably rain in summer as well as in winter4 ,but if snow-bearing depressions cannot penetrate an ice-sheet1 it may be asked how the ice-sheet can live4 ,the answer depends on the nature of the underlying country4 ,a land of high relief such as ,antarctica is1 and as ,greenland probably is1 rising to a maximum elevation of many thousand feet near its centre1 draws its nourishment chiefly from the upper currents which flow inward on all sides to replace the cooled air which flows outwards near the surface4 ,these upper currents carry a certain amount of moisture1 partly in the form of vapour1 but partly condensed as cirrus and even cumulus cloud4 ,at low temperatures air is able to hold only a negligible amount of water-vapour1 and this current1 coming in contact with the extremely cold surface of the ice1 is sucked dry1 and its moisture added to the ice-sheet4 ,probably there is little true snowfall1 but the condensation takes place chiefly close to the surface1 forming a frozen mist resembling the 8ice-mist0 of ,siberia4 ,even if the central land is not high enough to reach into the upper current at its normal level1 the surface outflow of cold air will draw the current down to the level of the ice4 ,this will warm it by compression1 but the ice-surface is so cold that such warming makes little difference in the end4 ,this process of condensation ensures that after the ice reaches a certain thickness it becomes independent of topography1 and in fact the centre of the ,scandinavian ice-sheet lay not along the mountain axis1 but some distance to the east of it4 ,it is probably only on the edges of the ice-sheet1 and especially in areas of considerable local relief1 that snowfall of the ordinary type takes place1 associated with moist winds blowing in the front section of depressions which skirt the ice-edge4 ,but when conditions are favourable this source of supply is sufficient to enable these local ice-sheets to maintain an independent life1 merely fusing with the edges of the larger sheet where they meet4 ,examples of such local centres in ,europe were the ,irish and ,scottish glaciers1 and at a later stage the ,lofoten glaciers of the west of ,norway1 and in ,america the ,cordilleran glaciers of ,columbia4 ,penck and ,brckner have demonstrated that in the ,alps the increase of glaciation was due to a fall of temperature and not to an increase of snowfall4 ,the argument is threefold3 firstly1 the lowering of the snow-line was uniform over the whole ,alpine area1 instead of being irregular as it would be if it depended on variations of snowfall2 secondly1 the area and depth of the parent snow-fields which fed the glaciers remained unchanged1 hence the increased length of the glaciers must have been due to decreased melting below the snow-line1 i4e4 to lower temperatures2 thirdly1 the upper limit of tree-growth in ,europe sank by about the same amount as the snow-line4 ,the same conclusion holds for the great ,scandinavian and ,north ,american ice-sheets1 the extension of which was undoubtedly due to a great fall of temperature4 ,in the case of the ,alps the interesting point has come to light that the fall of temperature1 though due in part to increased elevation1 is mainly accounted for by the presence of the ,scandinavian ice-sheet1 which extended its influence for many miles beyond the actual limits of glaciation1 so that its waxings and wanings are faithfully reproduced in those of the ,alpine glaciers1 even to the details of the final retreat after the last maximum4 ,it is only when we turn to tropical and sub-tropical regions that we find variations of temperature unable to account for increased glaciation4 ,not only were the changes of land and sea distribution on a very much smaller scale than further north1 but the ,appendix shows that the temperature value of a corresponding change of land area is also very much less4 ,but the high intertropical mountains--the ,andes and ,kenya and ,kilimanjaro in central ,africa--which to-day bear glaciers1 in ,quaternary times carried much greater ones4 ,we cannot call in a fall of temperature1 for the reason above stated1 and also because at lower levels there is no evidence of colder conditions4 ,in the ,glacial period the marine fauna was the same as to-day1 and mountains which now fall short of the snow-line by a few hundred feet were still unglaciated even then4 ,the only alternative is increased snowfall on the higher mountains4 ,fortunately this fits in well with meteorological theory4 ,the rain and snowfall of tropical regions depends1 first of all1 on the evaporation over the oceans4 ,but evaporation is profoundly influenced by the velocity of the wind2 and the wind1 which in the ,tropics represents the strength of the atmospheric circulation1 depends on the thermal gradient between the equator and the poles2 since there is no evidence of any appreciable change of temperature over the ,tropics as a whole1 while there was a very great fall in cold temperate and polar regions1 the thermal gradient1 and therefore1 ultimately1 the tropical and sub-tropical1 rain and snowfall must have been very greatly increased4 ,hence the increased glaciation of high mountains near the equator1 and hence also the evidence of 8,pluvial periods0 in the sub-tropical arid regions on either side of the equator4 ,thus during ,glacial periods we have3 7#a7 ,elevation in high latitudes caused a great increase of land areas there4 7#b7 ,both elevation and increase of land area resulted in a lowering of temperature1 materially increased by the gradual development of great ice-sheets4 7#c7 ,these ice-sheets caused the development of subsidiary ice-sheets on their southern and western borders4 7#d7 ,the lowering of temperature in high latitudes increased the thermal gradient between equator and poles1 resulting in3 7a7 ,increased snowfall1 and hence increased glaciation on high mountains near the equator4 7b7 ,pluvial periods in the sub-tropical arid regions4 ,,bibliography ,humphreys1 ,w4 ,j4 8,physics of the air40 ,philadelphia1 #aibj4 ,pt4 #d1 pp4 #eef-fbi4 ,chamberlin1 ,t4 ,c4 8,an attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis40 ,journal of ,geology 7,american71 ,vol4 #g1 #ahii1 pp4 #ede-hd1 #ffg-he1 #gea-hg4 ,carbon dioxide theory4 ,croll1 ,j4 8,climate and time in their geological relations40 ,london1 #ahge4 8,discussions on climate and cosmology40 ,london1 #ahhi4 ,eccentricity of earth's orbit4 ,spitaler1 ,r4 8,das ,klima des ,eiszeitalters40 ,prag1 #aiba4 ,lithographed4 ,eccentricity of earth's orbit4 ,reviewed in the ,meteorological ,magazine1 ,london1 ,september1 #aiba4 ,simroth1 ,h4 8,die ,pendulationstheorie40 ,leipzig1 #aijh4 ,kreichgauer1 ,p4 8,die ,aequatorfrage in der ,geologie40 ,steyr1 #aijb4 ,wegener1 ,a4 8,die ,entstehung der ,continente und ,ozeane40 ,die ,wissenschaft1 ,bd4 #ff1 ,braunschweig1 #aibj4 ,kppen1 ,w4 8,ueber ,aenderungen der geographischen ,breiten und des ,klimas in geologischer ,zeit40 ,stockholm1 ,geografiska ,annaler1 #b1 #aibj1 pp4 #bhe-ii4 ,brooks1 ,c4 ,e4 ,p4 8,continentality and temperature40 ,quarterly ,journal of ,royal ,meteorological ,society1 ,vol4 #dc1 #aiag1 p4 #afi2 and #dd1 #aiah1 p4 #bec4 ,influence of land and sea distribution4 ,enquist1 ,f4 8,eine ,theorie ber die ,ursache der ,eiszeit und die geographischen ,konsequenzen derselbe40 ,bull4 ,geol4 ,inst41 ,upsala1 #ac1 #aiae1 ,no4 #b4 ,influence of land and sea distribution4 ,hobbs1 ,w4 ,h4 8,characteristics of existing glaciers40 ,new ,york1 #aiaa4 ,glacial anticyclone4 ,,table ,,of ,,geological ,,formations ,recent ,,quaternary ,pleistocene ,pliocene ,,tertiary or ,miocene ,,cainozoic ,oligocene ,eocene ,cretaceous ,,mesozoic or ,jurassic ,,secondary ,triassic ,permian ,carboniferous ,devonian ,,pal,,ozoic ,silurian ,ordovician ,cambrian ,,proterozoic ,pre-,cambrian ,,chapter ,,ii ,,the ,,climatic ,,record ,,as ,a ,,whole ,it is a remarkable fact that one of the oldest known sedimentary rocks is glacial in origin1 and indicated the presence of an ice-sheet at a very early stage in the earth's history4 ,this is a 8tillite10 or boulder-clay1 discovered by ,prof4 ,coleman at the base of the ,lower ,huronian 7,early ,proterozoic7 of ,canada4 ,it extends in an east and west direction for #ajjj miles across northern ,ontario1 and northward from the northern shore of ,lake ,huron for #gej miles4 ,it rests on a scratched or polished surface of various rocks1 and the included boulders are not always local1 but some have been brought from a considerable distance4 ,all these characters point to a large ice-sheet4 ,traces of ,proterozoic glaciations have been discovered in various other parts of the world1 and some of these may be of the same age as the ,canadian ice-sheet1 but they cannot yet be dated exactly4 ,an interesting example is western ,scotland1 which ,j4 ,geikie considered to have been glaciated by ice from the north-west which has since sunk into the ,north ,atlantic4 ,other glacial remains have no doubt been destroyed or deeply buried1 while some may still await discovery1 and at present we must be content to note the occurrence of a glacial period at this time without attempting any description of the distribution of climates over the globe4 ,followed a long period of milder climate indicated in ,america by thick deposits of limestone with the remains of reef-building organisms and other marine life4 ,this period may have been interrupted at least once by the recurrence of glacial conditions1 but the evidence for this is doubtful4 ,it must be remembered that the duration of the ,proterozoic was very great1 at least as long as all subsequent time1 while the relics of it which are now known to us are few and scattered1 so that much which happened during that time is a closed book4 ,it is not until the very close of the ,proterozoic that we again find indisputable evidence of widespread glacial action4 ,this second great glaciation was placed originally in the earliest ,cambrian 7see table of geological formations at the end of ,chapter ,i71 but later evidence shows that it is slightly older than the oldest deposit which can be referred to this series1 and it may be designated the ,pre-,cambrian glaciation4 ,tillites of this age have been found in the middle ,yangtse region of ,china and in ,south ,australia 7where they extend from #bj miles south of ,adelaide to #ddj miles north1 with an east-west extension of #bjj miles74 ,glacial deposits which probably refer to this period have been found also in ,india1 both in the ,deccan and near ,simla1 over a wide area in ,south ,africa1 and in the extreme north of ,norway4 ,this distribution suggests the presence of two centres of glaciation1 one between ,china1 ,india and ,australia1 and the other north-west of ,europe4 ,the south-eastern of these was the most extensive1 and probably indicates a ring of glaciated continents surrounding the pole1 rather than a single enormous ice-sheet4 ,during the ,cambrian all evidence of glacial action ceases1 and we have1 instead1 evidence of a warm1 fairly uniform climate in the abundant marine life4 ,this continued during the ,ordovician and became accentuated during the ,silurian period1 when reef corals lived in the seas of all parts of the world4 ,terrestrial deposits are curiously lacking in all this series1 and this suggests that in the absence of any great mountain-building and elevation shallow seas extended over almost the whole of the surface1 accompanied by mild oceanic climates extending to high latitudes4 ,at the close of the ,silurian there was a period of mountain-building and the formation of continents4 ,the extinction of numerous species of marine organisms and the rapid evolution of others point to the seas becoming cooler and the stress of life more acute4 ,in the succeeding ,devonian period there is evidence of glacial conditions in ,south ,africa in the form of a thick series of quartzites with striated pebbles up to fifteen inches long1 but no typical boulder-clay has been discovered4 ,there are also some doubtful traces from ,england4 ,the most noteworthy development of the ,devonian in the ,british ,isles is1 however1 a thick deposit of red sandstone 7,old ,red ,sandstone7 of the type that is formed in shallow lagoons or inclosed basins1 and suggesting desert conditions1 so that the rainfall of the ,british ,isles was probably slight4 ,these continental conditions passed away towards the close of the ,devonian period1 and once again extensive warm oceans appear to have spread over a large part of the globe1 associated with the development of reef-building corals4 ,climate continued warm and equable throughout the greater part of the ,carboniferous4 ,the important feature of this period is the great system of coal-beds which extends through ,north ,america and ,europe to ,china1 with northern and southern limits in #hj ,n4 7north-east ,greenland and ,spitzbergen7 and #ae ,s4 7,zambesi ,river74 ,wegener1 summing up the evidence1 and considering especially the absence of annual rings in the trees1 concludes that the coal-beds are the remains of the tropical rain-forest when the equator lay across ,europe some #cj degrees north of its present position4 ,towards the close of the ,carboniferous period great mountain-building set in1 resulting in the formation of the famous ,gondwanaland1 including south and central ,africa1 southern ,asia1 part of ,australia and possibly ,brazil4 ,from a consideration of the glacial evidence1 however1 it appears1 as will be seen later1 that this was probably a ring of neighbouring and partly adjoining land areas rather than a single enormous continent4 ,at the same time the climate became cooler1 and a hardier vegetation1 known as the ,glossopteris flora1 developed in the southern hemisphere1 including woody trees with annual rings indicating seasons4 ,the large insects of the coal forests which did not undergo a metamorphosis were replaced by smaller types which did pass through such a stage2 this change of habit is considered to be due to the winters having become severe1 so that the insects learnt to hibernate through them4 ,in the early ,permian1 ,gondwanaland was occupied by great ice-sheets1 remains of which in the form of tillites of great thickness1 ice-worn surfaces and striated boulders have been found in ,south ,africa1 ,belgian ,congo1 and ,togoland1 ,tasmania and widely separated parts of ,australia1 peninsular and north-western ,india1 and probably also ,afghanistan4 ,in ,india the glacial stri show that the ice-sheet was moving north1 while in ,south ,africa it was moving south1 i4e4 away from the present equator in both cases4 ,widespread glacial remains have been found also in ,brazil1 northern ,argentine and the ,falkland ,islands1 and there are probable traces near ,boston in ,north ,america1 in ,armenia1 the ,urals and the ,alps1 and possibly also in ,england4 ,wegener's reconstruction of the geography of this period places the south pole a little to the south-east of ,south ,africa1 surrounded by a great continent composed of the junction of ,africa1 ,south ,america1 ,antarctica1 ,australia1 and an extended ,deccan added to by smoothing out the folds of the ,himalayas4 ,this great circumpolar continent he considers to have been the site of an immense ice-cap4 ,the ,north ,pole lay in the ,pacific ,ocean1 so that almost all the remaining land areas enjoyed temperate or tropical climates4 ,it is admitted that this peculiar distribution of glacial remains apparently necessitates a position of the pole somewhere near that described by ,wegener1 but the theory of a single polar ice-cap extending beyond #ej latitude on nearly all sides presents difficulties4 ,from the mechanism of the supply of snow to an ice-sheet described in the preceding chapter it follows that1 except close to the edges1 all the moisture precipitated must be brought in by upper currents4 ,but even if we take into account the increase in the strength of the atmospheric circulation due to the introduction of an ice-cap1 there is a limit to the supply of moisture by this process4 ,all such moisture has to cross the periphery1 and with increasing radius2 the number of square miles of area to each mile of periphery becomes greater1 slowly at first1 then more and more rapidly4 ,we shall see in ,chapter ,,viii that even the ,north ,american ,quaternary ice-sheet became unwieldy from this cause1 and suffered several changes of centre4 ,hence it seems that the rapprochement of the continents in ,permo-,carboniferous times need not have been so complete as ,wegener supposes1 the glacial phenomena being more readily explicable by a ring of continents surrounding a polar sea1 as in the case of the ,quaternary glaciation of the northern hemisphere4 ,the local ,permian glaciations of ,europe and ,north ,america1 some of which fell close to ,wegener's equator1 are easily explicable as due to mountain glaciers similar to those of ,ruwenzori and other tropical mountains during the ,quaternary4 ,there were interglacial periods in ,south ,africa1 ,brazil and ,new ,south ,wales1 which increase the resemblance between the ,permian and ,quaternary ,ice ,ages4 ,in ,upper ,permian times there was a widespread development of arid climates1 especially in the present temperate parts of ,north ,america and ,europe4 ,wegener attributes this to the northerly position of the equator bringing the sub-tropical desert belt 7,sahara1 ,arizona7 to these regions4 ,in the ,trias these conditions gradually gave place to another period of widespread warm shallow seas1 with abundant marine life and corals extending over a large part of the world1 even to ,arctic ,alaska4 ,in the ,united ,states there are the remains of the forests of this period1 in which the tree-trunks show very little evidence of annual rings1 indicating that the seasonal changes were slight1 so that the climate had again become mild and oceanic4 ,in the ,lias 7,lower ,jurassic71 there was crustal movement and volcanic action accompanied by land-formation and a gradual lowering of temperature4 ,there was a great reduction in the abundance and geographical range of corals1 and most of the species of insects are of dwarf types4 ,there is1 however1 no evidence of glacial action4 ,the ,upper ,jurassic period appears to have been warmer than the ,lias4 ,insects of a large size and corals again attained a very wide distribution1 but there is enough difference in the marine faunas of different regions to indicate a greater development of climatic zones than in the extremely oceanic periods such as the late ,triassic4 ,schuchert points out that the plants of ,louis ,philippe ,land in #fc ,s4 are the same1 even to species1 as those of ,yorkshire4 ,in the ,cretaceous period the climate was at first similar to that of the ,jurassic1 and trees grew in ,alaska1 ,greenland and ,spitzbergen4 ,these trees1 however1 show marked annual rings1 indicating a considerable differentiation of seasons1 while trees of this age found in ,egypt are devoid of rings4 ,towards the close of the ,cretaceous there were many crustal movements and great volcanic outbursts1 accompanied by a considerable reduction of temperature1 which led to the extinction of many forms of life and the rapid evolution of others4 ,there is no evidence of glacial action during the ,cretaceous1 however1 though at the beginning of the ,eocene there was a local glaciation of the ,san ,juan ,mountains of ,colorado4 ,according to ,w4 ,w4 ,atwood this glaciation was double1 the first stage being of the ,alpine mountain glacier type1 separated by an interglacial from the second stage1 which was of the ,piedmont type 7mountain glaciers spreading out on the plain at the foot of the mountain74 ,this ,eocene glaciation has been found nowhere else1 however1 and the climate of the ,tertiary1 which is discussed more fully in the next chapter1 was in general warm and oceanic1 becoming rigorous towards its close4 ,summing up1 we find that in the geological history of the earth two main types of climate seem to have alternated4 ,following on periods of great crustal movement1 and the formation of large land areas1 the general climate was cool1 with a marked zonal distribution of temperature1 culminating during at least four periods in the development of great sheets of inland ice4 ,it is in such a period1 though1 fortunately1 not at its worst1 that we are living at present4 ,during quiescent periods1 on the other hand1 when these continents largely disappeared beneath the sea1 climate became mild and equable1 and approached uniformity over a great part of the world4 ,at these times1 as soon as the surface water of the sea in high latitudes began to cool1 it sank to the bottom1 and its place was taken by warmer water from lower latitudes4 ,the oceanic circulation was very complete1 but there were practically no cold surface currents4 ,instead1 there was probably a general drift of the surface waters from low to high latitudes 7with an easterly trend owing to rotation of the earth71 and a return drift of cooled water along the floor of the ocean4 ,the formation of sea-ice near the poles became impossible1 while the widespread distribution of marine life was facilitated4 ,the alternation of periods of crustal deformation with periods of quiescence has frequently been noticed1 and has been termed the 8geological rhythm40 ,it may be attributed to the gradual accumulation of small strains during a quiescent period until the breaking point is reached1 when earth-movements take place until equilibrium is restored1 when the process is repeated4 ,the gradual erosion of the land by river and wave-action and the consequent shifting of the load provides a certain amount of stress2 but this is local1 and calls for local readjustments only4 ,a more generally effective agency may be the gradual slowing down of the earth's rotation under the influence of tidal friction4 ,the mechanism of this process was described by ,a4 ,e4 ,h4 ,love 78,nature10 #id1 #aiad1 p4 #bed73 8,the surface of the ocean1 apart from waves and tides1 is at any time a figure of equilibrium answering to the speed of rotation at the time1 more oblate when the speed is greater1 less oblate when it is slower4 ,let us imagine that the lithosphere also is at some time a figure of equilibrium answering to the speed of rotation at that time4 ,if the speed remained constant1 the lithosphere would retain this figure1 and the matter within it would remain always in the same configuration without having to support any internal tangential stress4 ,now suppose that the speed of rotation gradually diminishes4 ,the surface of the ocean will gradually become less and less oblate4 ,the lithosphere also will gradually become less oblate1 but not to such an extent as to make it a figure of equilibrium answering to the diminished speed of rotation1 while the matter within it will get into a state of gradually increasing internal tangential stress4 ,the effect on the distribution of land and water will be that the depth of the ocean will gradually diminish in lower latitudes and increase in higher latitudes1 the latitudes of no change being #ce #af ,n4 and ,s4 8,the internal tangential stress in the matter within the lithosphere may increase so much that it can no longer be supported4 ,if this happens a series of local fractures will take place1 continuing until the lithosphere is again adjusted much more nearly to a figure of equilibrium1 which will be less oblate than the original figure4 ,the effect on the distribution of land and water will be that the depth of the ocean will increase rather rapidly and spasmodically in lower latitudes and diminish in higher latitudes4 8,accordingly1 the kind of geological change which the theory of tidal friction would lead us to expect is a sort of rhythmic sequence1 involving long periods of comparative quiescence1 marked by what ,suess calls #8positive movements of the strand1' in the higher latitudes1 and #8negative movements' in the lower1 alternating with comparatively short periods of greater activity1 marked by rise of the land around the poles and subsidences in the equatorial regions40 ,the main periods of adjustment under this scheme fall at the beginning and end of the ,proterozoic1 in the ,permo-,carboniferous and in the ,quaternary4 ,the two latter at least were periods of great earth-movement1 while the two former were also continental periods1 since the land-masses were large and high enough to develop ice-sheets4 ,the difficult question raised by the low latitudes in which the ,pre-,cambrian and ,permo-,carboniferous glaciations were chiefly developed cannot yet be regarded as solved1 but the geological facts speak strongly in favour of ice-sheets rather than mountain glaciers1 and practically speaking it is meteorologically impossible for large ice-sheets to extend to sea-level in the ,tropics while the rest of the world enjoys a temperate climate4 ,the only escape seems to be to assume a position of the ,south ,pole somewhere between ,africa1 ,india and ,australia throughout the whole of the ,proterozoic and ,palozoic periods4 ,on the other hand1 from the ,jurassic onwards1 there is no real support to the hypothesis that the positions of the poles were other than they are now4 ,wegener's explanation of the ,quaternary ,ice ,age we have seen to be untenable4 ,the period of transition appears to lie in the later ,permian and ,triassic4 ,the ,proterozoic and ,permo-,carboniferous glacial periods were much less definite in the north than in the south-east2 but such as they were they appear to have been most severe in the east of ,north ,america1 where the ice was coming from the north2 there are also some glacial traces in ,europe4 ,this indicates that the position of the ,north ,pole cannot have been in the ,north ,pacific ,ocean1 which is antipodal to the ,south ,indian ,ocean4 ,hence it seems that what we have to consider is not so much the wanderings of the poles at large among the continents as the break-off at the close of the ,palozoic period of portions of the ,antarctic continent and their drift northwards towards the equator4 ,without going into the mathematics of the question1 it seems just possible that the periodic overloading of circumpolar continents by large ice-masses could have this effect in the course of time1#b but the suggestion is put forward tentatively for consideration rather than as a definite hypothesis4 ,we must be thankful that in the next chapter we are on safer ground4 ,,bibliography ,coleman1 ,a4 ,p4 8,climates and physical conditions of the early ,pre-,cambrian40 ,geol4 ,mag4 7#f71 ,vol4 #a1 #aiad1 p4 #dff4 ,eckardt1 ,w4 ,r4 8,paloklimatologie40 ,sammlung ,goschen1 ,leipzig1 #aiaj4 ,geikie1 ,j4 8,the ,evolution of ,climate40 ,edinburgh1 ,scot4 ,geogr4 ,mag4 7#f71 #ahij1 p4 #eg4 ,grabau1 ,a4 ,w4 8,principles of ,stratigraphy40 ,new ,york1 #aiac1 pp4 #gd1 et seq4 ,neumayr1 ,m4 8,ueber klimatischen ,zonen whrend der ,jura- und ,kreidezeit40 ,wien1 ,denkschr4 ,ak4 ,sci41 #dg1 #ahhc1 p4 #baa4 ,ramsay1 ,w4 8,orogenesis und ,klima40 ,ofvers af ,finska ,vetenskaps4 ,soc4 ,forb41 #eb1 #aiji-aj1 ,a1 ,no4 #aa4 ,helsingfors1 #aiaj4 ,schuchert1 ,c4 8,climates of ,geologic ,time1 ,in3 ,the climatic factor as illustrated in arid ,america10 by ,ellsworth ,huntington4 ,washington1 #aiad1 ,pt4 #b4 ,,chapter ,,iii ,,conditions ,,before ,,the ,,quaternary ,,ice ,,age ,the third of the great periods into which the geological record is divided is known as the ,tertiary4 ,throughout most of its length it appears to have been characterized by remarkably mild and equable climatic conditions extending into comparatively high latitudes1 so that the west coast of ,greenland1 for instance1 had a flora of almost sub-tropical aspect4 ,since the plants in question--chiefly palms and cycads--are not of identical species with their present-day representatives1 it is unsafe to base numerical estimates of the temperature upon them1 but it is at least obvious that these regions were warmer than they are at present4 ,let us glance for a moment at the geography of the ,tertiary period4 ,the most noticeable point is a great expanse of sea over south-eastern ,europe1 including the ,mediterranean countries1 extending away over the ,black ,sea and ,caspian1 and stretching in a great arm to the ,arctic ,ocean1 south of ,novaya ,zemlya4 ,the geology of the archipelago north of ,canada is not yet well known1 but it seems probable that there was a considerable area of ,tertiary ocean there also4 ,the sea further encroached on the present boundaries of ,north ,america1 both east and west1 and on the north-eastern coast of ,asia4 ,bearing in mind the principles set out in the first chapter1 we can infer from these changes a great increase in the winter temperature of the regions along the ,arctic circle4 ,the increase reached a maximum on the west of ,greenland and in western ,siberia1 but the west coast of ,alaska also had a decidedly warm climate in the late ,miocene and ,pliocene4 ,the basin of the ,arctic ,ocean1 which already existed at that stage1 was raised to a temperature considerably higher than the present by three great streams of warm water flowing into it4 ,if1 as seems probable1 the ,bering ,strait was deeper1 and the submarine ridge across the ,north ,atlantic less pronounced1 the obstacles to the outflow of cold water along the ocean floor were much less than now4 ,finally1 the winter temperatures of the land-masses to the south1 and especially ,siberia1 being already very much less severe owing to the sea over ,europe1 the temperature of the water of the great rivers flowing into the ,arctic was not so low4 ,for these reasons the development of ice in the ,arctic ,ocean was very much diminished1 and possibly entirely absent1 allowing a great amelioration of the climate of ,greenland1 the rigor of which is at present much enhanced by the ice which flows down the ,greenland ,sea and round ,cape ,farewell4 ,the cumulative effect of all these changes--greater water area1 greater inflow of warm surface water1 less inflow of cold river water1 less ice-development--must have been a mild equable rainy climate1 entirely suitable to a rich vegetation4 ,the sub-tropical aspect of that vegetation should not be stressed1 for it was probably as much an expression of the geological age of the period in question as of its climate4 ,the objection may be raised that at the present time the sub-antarctic islands in the great ,southern ,ocean have the most maritime climate in the world1 but are not by any means places of opulent vegetation4 ,the difference is entirely accounted for by the presence of the great ice-bearing ,antarctic continent4 ,its effect is twofold4 ,firstly1 the glaciers shed into the ,southern ,ocean an immense quantity of ice and ice-cold water annually1 which must have an appreciable effect on temperature4 ,secondly1 the presence of this ice-covered continent and the floating ice in its neighbourhood extending as far as the sixtieth parallel1 by forming a marked contrast with the warmer waters further north1 greatly intensifies the strength of the atmospheric circulation in these regions1 resulting in the development of a great succession of severe storms which sweep the sub-antarctic islands4 ,there are no great land-masses to break the force of the wind1 and these latitudes are among the stormiest1 windiest regions of the earth--gale succeeding gale1 winter and summer alike2 and it is largely to the extraordinary power of the wind that we must attribute the desolate appearance of the islands4 ,the picture we have drawn of the high northern latitudes in early ,tertiary times is vastly different4 ,a great warm ocean occupied the ,arctic regions1 fed by three ocean currents analogous to the ,gulf ,drift1 and the fall of temperature was gradual from the tropic to the pole4 ,the return colder currents were mainly along the ocean floor and with little ice-formation the storms were few and not severe4 ,on the western shores of the continents mild rain-bearing south-west winds prevailed1 and a quiet moist warm atmosphere existed which was especially favourable to plant life4 ,this favourable state of affairs lasted until well on in the ,miocene1 and then changes set in4 ,the land and sea distribution underwent essential modifications4 ,the great ,tertiary continent or archipelago which is believed to have existed in the western ,pacific1 and whose last remaining summits now form the scattered islands of that ocean1 gradually subsided1 and in its place elevation began in higher latitudes4 ,bering ,strait became narrow and shallow1 and was probably for a time entirely closed1 while the connexion between the ,arctic and ,indian ,oceans was closed permanently1 leaving in its lowest areas a chain of great inland seas and lakes1 of which the ,caspian and ,aral ,seas are now the greatest representatives4 ,the ,canadian ,archipelago was probably raised above its present level1 and formed a great northern extension of the ,american continental area4 ,the changes in the ,atlantic also were very extensive4 ,the ,west ,indies were the site of a large and lofty ,antillean continent2 further north a considerable land-mass existed east of ,newfoundland2 ,greenland was joined on the west to the extended ,american continent1 and considerably enlarged to the south-east4 ,iceland1 though it remained an island1 was elevated and probably nearly doubled in area1 and between ,iceland and the north of ,scotland was developed a great submarine ridge1 which may or may not have risen above the sea in places4 ,the ,british ,isles became a solid block of land1 united with continental ,europe across the ,english ,channel and the great plain which is now the ,north ,sea4 ,scandinavia was elevated by more than a thousand feet1 and the elevation extended at least as far as ,spitzbergen4 ,the ,murman area had a considerable extension4 ,in eastern ,asia the ,sea of ,okhotsk was land and ,japan was united to the mainland4 ,in the southern hemisphere our knowledge is not nearly so detailed4 ,the presence of marine ,middle-,tertiary beds with temperate mollusca in ,graham ,land and of plant-bearing beds in ,seymour ,island point to a smaller ,antarctic continent and very much warmer conditions at this time in the ,south as well as in the ,north ,polar regions4 ,for the close of the ,tertiary1 however1 we have strong grounds in the distribution of animals and plants for assuming that the ,antarctic continent was greatly increased in size1 with promontories uniting it to ,australia on the one hand and to ,south ,america on the other4 ,new ,zealand was largely increased in area1 and ,south ,africa probably extended further polewards4 ,the sub-antarctic islands attained a much greater area4 ,conditions were ripe for the ,ice ,age in the southern as well as the northern hemisphere4 ,,bibliography ,kerner von ,marilaun1 ,f4 8,synthese der morphogenen ,winterklimate ,europas zur ,tertirzeit40 ,wien1 ,sitz,ber4 ,k4 ,akad4 ,wiss1 #abb1 #aiac1 pp4 #bcc-ih4 ,osborn1 ,h4 ,f4 8,the age of mammals in ,europe1 ,asia and ,north ,america40 #hvo4 ,new ,york1 #aiaj4 ,nathorst1 ,a4 ,g4 8,on the fossil floras of the ,arctic regions as evidence of geological climates40 ,london1 ,bot4 ,j4 #b1 #aiac1 pp4 #aig-bjb2 and ,washington1 ,report ,smithsonian ,inst41 #aiaa4 ,dall1 ,w4 ,h4 8,on climatic conditions at ,nome1 ,alaska1 during the ,pliocene40 ,amer4 ,j4 ,sci41 ser4 #d1 ,vol4 #bc1 #aijg1 p4 #deg4 ,nansen1 ,f4 8,the bathymetrical features of the ,north ,polar seas1 with a discussion of the continental shelves and previous oscillations of the shore-line40 ,norwegian ,n4 ,polar ,exped41 #ahic-if4 ,scientific ,results1 ,vol4 #d4 ,spencer1 ,j4 ,w4 8,reconstruction of the ,antillean continent40 ,bull4 ,amer4 ,geol4 ,soc41 #f1 #ahie1 pp4 #ajc-dj4 ,wilckens1 ,d4 8,die ,mollusken der antarktischen ,tertirformation40 ,wiss4 ,ergebn4 der ,schwed4 ,sudpolar ,exped41 #aija-c1 ,bd4 #c1 #aiaa4 ,hedley1 ,c4 8,the palographical relations of ,antarctica40 ,london1 ,proc4 ,linnan ,soc41 #abd1 #aiaa-b1 p4 #hj4 ,,chapter ,,iv ,,the ,,great ,,ice ,,age ,as the land began to rise1 the first effect was an increased snowfall on the higher summits1 and increased rainfall on the rising coast lands4 ,the rivers had an increasing fall towards the sea1 and rapidly carved out deep narrow valleys1 which were later developed by the ice into the great fiords of ,norway and other heavily glaciated regions4 ,but on the whole the first beginnings of the ,ice ,age occurring towards the close of the ,pliocene period are obscure1 and are likely always to remain so1 for the simple reason that the advancing and retreating ice-sheets have wiped out most of the evidence of the conditions which immediately preceded their advent4 ,the deteriorations of the climate had begun long before the geographical changes outlined at the close of the last chapter were complete1 for mollusca of the ,pliocene beds in ,east ,anglia indicate progressive refrigeration of the ,north ,sea at the same time as it became increasingly shallow4 ,at the close we have great shell-banks with northern species which must have been piled up by powerful easterly winds2 these easterly winds show that the storm-tracks had been driven south of their present course and suggest that the glacial anticyclone already existed over ,scandinavia4 ,at the present day similar shell-banks are forming on the coast of ,holland under the influence of the prevailing westerly winds4 ,the next series of deposits in this region are fresh-water 8forest beds10 attributed to a greatly extended ,rhine1 and belong to the period when the ,north ,sea had become a plain4 ,it is no part of the plan of this work to go over the geological ground of the ,quaternary ,ice ,age1 which has already been so frequently and so efficiently covered4 ,all ,i can hope to do is to give a brief general account of the succession of climatic changes involved1 necessarily incomplete since so much of the world is at present insufficiently explored for glacial traces4 ,but a certain amount of explanatory introduction is necessary4 ,in ,europe and ,north ,america there are distinct traces of several separate glaciations with 8interglacial0 periods when the climate approached or became even warmer than the present4 ,the time-relations of these glaciations are not yet fully worked out1 but there seems little doubt that they were contemporaneous in the two continents4 ,the correlation is not perfect1 however1 since the ,united ,states geologists recognized altogether five glaciations4 ,the explanation appears to be that the equivalent of the ,rissian glaciation in ,america is double2 two stages1 the ,illinoian and ,iowan1 being recognizable1 separated by a retreat of the ice4 ,the series is as follows3 ---------------------------------------- ----------------------- ,alps4 ,northern ,europe4 ,north ,america4 ,date4 ,b4,c4 ---------------------------------------- ----------------------- ,i ,gunz 8 ,jerseyan or 8 ,nebraskan ,,ii ,mindel ,lower ,diluvium ,kansan #dcj1jjj-cgj1jjj ,,iii ,riss ,middle ,diluvium ,illinoian #acj1jjj-ajj1jjj ,iowan ,,iv ,wurm ,upper ,diluvium ,wisconsin #dj1jjj- #ah1jjj ---------------------------------------- ----------------------- ,the correlation is based on the amount of weathering and erosion which the various deposits have undergone4 ,the time which has elapsed since the glaciers of the last or ,wurm stage were in active retreat has been estimated by comparing the growth of peat-bogs1 river-deltas1 etc41 during historical times with that since the last retreat of the ice4 ,but the most conclusive method is due to the ,swedish geologist ,baron de ,geer1 who has actually counted the years since the ice in its final retreat left any particular point between ,ragunda and the south of ,sweden4 ,the work is based on the idea that the lamination observed in certain marine and lacustrine clays in ,sweden is seasonal1 the thick coarse layers being due to the floods produced by the rapid melting of the ice in summer1 and the thinner and finer layers being due to the partial cessation of melting in winter4 ,by correlating one section with another it is possible to date any particular layer with great exactness1 and further to prove the existence of several great climatic fluctuations during the retreat4 ,the topmost limit of the section is given by the surface of the old floor of ,lake ,ragunda in ,jemtland1 which received its waters from one of the permanent glaciers and was accidentally drained in #agif4 ,de ,geer finds that the edge of the last great ice-sheets lay over southern ,scania about #ab1jjj years ago1 and further estimates #hjjj years for the retreat across the ,baltic4 ,these results are in general agreement with those obtained by other methods1 and we may accordingly1 with some confidence1 put the date when the ice-sheet of the ,wurm glaciation finally left the coast of ,germany at about #ahjjj ,b4,c4 ,this period fixed1 we have a datum for estimating the duration of the interglacial periods4 ,the moraines of the ,wurm glaciation present everywhere a very fresh appearance1 and the chemical change which the boulders they contain have undergone is slight1 while weathering extends to a depth of scarcely a foot4 ,the moraines of the ,riss glaciation are weathered somewhat more deeply1 and those of the ,mindel glaciation very much more4 ,assuming that chemical weathering has proceeded uniformly during the interglacial periods and ceased during the glaciations1 ,penck and ,brckner1 who have studied exhaustively the glaciation of the ,alps1 find that the ,riss-,wurm interglacial lasted about three times as long as the interval between the ,wurm glaciation and the present day1 or #fj1jjj years1 and the ,mindel-,riss interglacial about twelve times as long1 or #bdj1jjj years4 ,no data are available for the ,gunz-,mindel interglacial1 but it is provisionally made equal to the ,riss-,wurm1 another #fj1jjj years4 ,no possibility of such direct measurement of the duration of the glacial periods themselves has yet been found4 ,penck and ,brckner assume that the duration equalled that of the ,riss-,wurm interglacial1 or #fj1jjj years in each case4 ,this seems unnecessarily long4 ,the ,yoldia ,sea1 the deepest part of which coincided with the centre of the ,scandinavian glaciation1 appears to have reached its greatest depth not more than #fjjj years after the maximum of glaciation1 indicating a lag of this period4 ,the subsidence of the land due to the weight of the ice-sheet may have commenced some time before the maximum of glaciation1 but the duration of the subsidence can hardly have been more than #aj1jjj years1 and this is the limit for the second half of the ,wurm glacial period4 ,further1 we know that during the growth of the ice-sheets there was comparatively little melting1 for the rivers then had little power of carrying debris4 ,recent measurements in ,greenland give the rate of ice-growth on the surface of the ice-sheet as #dj cm41 or #ae inches a year2 let us say a foot1 and assume a marginal loss equivalent to half this amount over the whole ice-sheet4 ,this gives us an average increase of six inches a year1 or #aj1jjj years for growth to a maximum thickness of #ejjj feet4 ,on these grounds the estimated duration of the ,rissian glacial period has been reduced to #cj1jjj years1 and that of the ,wurm period to #bb1jjj years4 ,only in the case of the long and complicated ,mindelian period1 which1 as will be seen later1 was virtually a series of overlapping glaciations from various centres1 has the figure of #fj1jjj years been accepted4 ,in the present state of our knowledge no estimate of the duration of the ,gunz-,mindel interglacial can have any value1 and the dates are accordingly carried back only to the ,mindelian4 ,in this way we obtain the time-scale given on page #dh4 ,the fourfold glaciation has been recognized with certainty only in ,europe and ,north ,america1 and even in these countries there is considerable doubt whether the northern ice-sheets shrank back as far as their present narrow limits during the interglacial periods4 ,the long ,mindel-,riss interglacial1 which was probably the ,chellean stage of flint industry1#c was characterized by a very warmth-loving fauna1 and it is possible1 even probable1 that during this period the glaciers melted completely away1 except on the very highest summits4 ,of the climate of the ,gunz-,mindel interglacial 7termed by ,j4 ,geikie the 8,norfolkian10 from the ,cromer ,forest ,bed71 we have comparatively little evidence4 ,if the suggestion put forward in the following chapter is correct1 the ,gunz-,mindel interglacial was merely a local incident in the glaciation of the ,alps1 and not a true interglacial at all4 ,even the ,cromer ,forest ,bed itself is not conclusive1 since it is a river deposit largely composed of material drifted from lower latitudes4 ,the ,riss-,wurm interglacial 7,j4 ,geikie's 8,neudeckian07 nowhere gives us evidence of a climate as warm as the present1 and as regards the ,scandinavian and ,canadian ice-sheets may have been merely an extensive and prolonged oscillation of the ice-edge4 ,as regards the glaciation of ,norway1 the question has been investigated recently by ,h4 ,w4 son ,ahlmann1 who has published a long and detailed paper in ,english in volumes #a and #b of the ,swedish ,geographiska ,annalen4 ,he concludes that the morphology of ,norway1 without reference to stratigraphical or biological data1 gives conclusive evidence of two glaciations4 ,the first of these was the greater1 and between that time and the second smaller glaciations there occurred an interglacial period of such considerable length that the greater part of the present gorges was then formed by fluvial erosion4 ,we may1 accordingly1 consider the ,ice ,age as fourfold or double1 according to the point of view from which we regard it4 ,in the ,alps and other mountain ranges on the borders of the great northern ice-sheets1 which respond very readily to small changes1 it was fourfold4 ,in the peripheral regions of the northern ice-sheets themselves it has an appearance of being threefold or fourfold4 ,in the more central regions of these great ice-sheets1 where response to climatic change is very slow1 there is no evidence of more than two glaciations2 but in these regions1 where the destructive effect of the ice reached its maximum1 it is only by the merest chance that evidence of interglacial periods is preserved at all4 ,and finally1 in all other parts of the world we have evidence of only two glaciations at most4 ,there is one deposit which is of considerable importance in the study of interglacial climates1 and that is the loess4 ,loess is an exceedingly fine-grained homogeneous deposit resulting from the gradual accumulation of wind-blown dust on a surface sparsely covered with vegetation4 ,it is to be seen accumulating at the present day in parts of south-east ,russia and central ,asia4 ,its formation1 except in closed basins1 needs a climate of the steppe character1 with not much rainfall1 and especially with a long dry season4 ,now loess was very extensively developed in ,europe during the ,quaternary4 ,its occurrence is peculiar1 since it is found most widely developed resting on the deposits of the ,rissian glaciation1 and is never found resting on the moraines of the ,wurm glaciation4 ,a little loess is found below the ,riss moraines1 and it has also been found between the ,riss and ,wurm moraines4 ,in the pre-,rissian loess an implement of ,acheulian age was discovered in #aiaj at ,achenheim 7,alsace71 by ,r4 ,r4 ,schmidt and ,p4 ,wernert1 indicating that the deposit was formed towards the close of the ,chellean industry1 when the climate was already cold and dry4 ,in the same section the younger loess seems to fill completely the ,riss-,wurm interglacial1 since ,mousterian implements were found at the base and ,aurignacian implements in the middle4 ,the younger loess contains remains of the jerboa and other rodents at present inhabiting the ,siberian steppes4 ,it is therefore reasonable to conclude that steppe conditions prevailed in central ,europe through practically the whole of the ,riss-,wurm interglacial1 and the same probably applies to the corresponding pre-,wisconsin interglacial in ,america4 ,but if a steppe climate prevailed in central ,germany there must have been very severe conditions in ,scandinavia1 and probably the ice-sheet maintained a quite considerable area there throughout the whole period1 though without encroaching on the ,baltic basin4 ,in ,north ,america the loess was deposited by westerly winds1 indicating that the ice-development was not sufficient to impose anticyclonic conditions in place of the present prevailing westerly winds1 and the same appears to be true of ,europe4 ,similar climatic conditions were developed for a short time at the close of the ,wurm glaciation1 but without any appreciable development of loess4 7,see ,chapter ,,xiii47 ,,bibliography ,wright1 ,w4 ,b4 8,the ,quaternary ,ice-age40 ,london1 ,macmillan1 #aiad4 ,brooks1 ,c4 ,e4 ,p4 8,the correlation of the ,quaternary deposits of the ,british ,isles with those of the continent of ,europe40 ,ann4 ,rep4 ,smithsonian ,inst41 #aiag1 pp4 #bgg-cge4 de ,geer1 ,g4 8,a thermographical record of the late ,quaternary climate40 ,ber4 ,internat4 ,geologenkongr41 ,stockholm1 #aiaj4 8,die ,vernderungen des ,klimas10 p4 #cjc4 ----4 8,a geochronology of the last #ab1jjj years40 ,ber4 ,internat4 ,geologenkongr41 ,stockholm1 #aiaj1 ,vol4 #a1 p4 #bda4 ,penck1 ,a41 and ,brckner1 ,e4 8,die ,alpen in ,eiszeitalter40 ,leipzig1 #c ,vols41 #aija-i4 ,ahlmann1 ,h4 ,w41 son4 8,geomorphological studies in ,norway40 ,stockholm1 ,geografiska ,annaler1 #a1 #aiai1 pp4 #a-aeg1 #aic-beb4 ,richthofen1 ,f4 8,on the mode of origin of the loess40 ,geol4 ,mag41 #ahhb1 p4 #bic4 ,,chapter ,v ,,the ,,glacial ,,history ,,of ,,northern ,,and ,,central ,,europe ,the literature of the glacial period in ,europe is stupendous and is1 further1 of a highly contradictory nature4 ,space does not permit of any summary of the great conflict between the monoglacialists and the polyglacialists2 it is sufficient to say that the latter often went to extremes and so laid themselves open to defeat1 but the twofold nature of the glaciation is now widely accepted4 ,it must be understood1 however1 that the following summary represents the views of a certain section of geologists only1 views which are not universally held4 ,in the ,british ,isles especially1 where the remains of the maximum glaciation completely dominate those of all the others1 the theory of a single glaciation still largely prevails4 ,when ice began to accumulate on the rising ,scandinavian plateau it naturally formed at first on the ,norwegian mountains near the ,atlantic1 which was the chief source of snowfall4 ,these mountain glaciers spread rapidly down the steep seaward slopes to the west and more slowly down the gentler landward slopes to the east4 ,at this stage the centre of the ice-sheet1 and consequently the centre of the glacial anticyclone1 as soon as the latter developed a definite existence1 lay quite near the ,norwegian coast4 ,under anticyclonic conditions the circulation of the winds round the centre is in the same direction as the motion of the hands of a watch1 combined with an outward inclination at an angle of about thirty to forty-five degrees4 ,consequently1 while the centre lay in ,norway1 due north of the ,alps1 the prevailing winds in the latter must have been from north-east1 and therefore very cold4 ,accordingly1 this stage is probably contemporaneous with the ,gunz glaciation of the ,alps4 ,in the same way1 over the ,north ,sea area the winds must have been easterly1 causing the currents which piled up the great shell-banks of the ,east ,anglian coast1 already referred to as marking the end of the ,tertiary and beginning of the ,quaternary period4 ,but the ice which reached the northern ,north ,sea broke up into icebergs not far from the coast1 and floated away1 while that which moved east into the north of ,sweden could only be dissipated by melting and ablation1 processes which we have reason to believe went on very slowly4 ,hence ice began to accumulate and spread over a wide area east of the main ,scandinavian mountain chain4 ,fresh snow was deposited directly on this ice-surface1 until it gradually overtopped the mountains which originally gave rise to it1 and reversed the flow1 so that the ice actually moved uphill across the mountain chain4 ,as the center of the ice-sheet moved eastward the glacial anticyclone moved with it1 and this new position to the eastward caused an alteration in the direction of the prevailing winds over the rest of ,europe4 ,the ,alps were now south-west of the anticyclonic centre1 and the winds in that district accordingly became easterly instead of north-easterly4 ,of course1 the glacial anticyclone was now more intense1 but in summer in central ,europe easterly winds are naturally so much warmer than north-easterly winds that at first this increase in intensity was not enough to counterbalance the change in direction1 and there was a slight improvement in the ,alpine climate4 ,in the same way1 over the ,north ,sea district the prevailing winds had now become south-easterly instead of easterly1 which would make for a slight rise of temperature1 as also would the occasional depressions which would be able to make their way in from the westward1 bringing warm moist air from the ,atlantic and occasional rainfall4 ,by this time the process of elevation had converted the ,north ,sea floor into an extensive plain4 ,from ,sweden and the ,gulf of ,bothnia the ice spread out in all directions1 extending in the east to the foot of the ,ural ,mountains1 which formed an independent centre of glaciation2 in the south-east over a large part of ,european ,russia1 where it reached as far south as latitude #dj in the ,dnieper valley2 in the south over almost the whole of ,germany as far as the ,riesengebirge and ,harz ,mountains2 and in the south-east over the whole of ,holland and the ,north ,sea basin4 ,it should be noted that ,holland and ,denmark were glaciated1 not by ,norwegian ice1 but by ice from the ,baltic sheet which had crossed southern ,sweden4 ,the ,north ,sea glacier extended across ,east ,anglia as far as ,cambridge1 while a northern branch of it swept across ,caithness and the ,orkney and ,shetland ,islands1 but most of the ,british ,isles were glaciated from independent centres--the ,scottish ,highlands1 the ,pennines1 ,cumberland1 ,wales and northern ,ireland4 ,with the growth of the glaciated area1 and particularly with its extension south-westward across the ,north ,sea1 the ,alpine climate again became very severe1 and the local glaciers and ,piedmont ice-sheets of the ,alps reached their maximum development in the ,mindelian4 ,at the same time the central plateau of ,france developed a local plateau glacier of its own1 and the ,pyrenees underwent their first and greatest glaciation1 no traces of the ,gunzian having been found in this range4 ,the ,british ,isles show an interesting outward migration of the local centres of maximum ice-development4 ,the ,scandinavian glacier which invaded ,east ,anglia extended arctic anticyclonic conditions across the ,north ,sea1 and induced a heavy snowfall over the high lands of ,great ,britain4 ,these1 in consequence1 developed independent glaciers1 which on their eastern sides fused with the ,scandinavian glacier and1 partly by deflecting its flow1 partly by intercepting some of its snowfall1 pushed it back into the ,north ,sea plain4 ,the ,scottish glaciers became strong enough to encroach on ,ireland1 partly in the north-east1 and partly by way of the ,irish ,sea and ,st4 ,george's ,channel 7then a valley7 on to the south-east4 ,this further extension of the cold area enabled the ,irish glaciers to develop1 and these in turn pushed back the ,scottish glaciers until ,ireland was solely glaciated by ,irish ice4 ,the southern margin of the ice-sheet did not extend beyond the ,thames valley1 but at some stage the ,english ,channel carried floating ice1 which formed the deposits of ice-borne boulders1 of which that at ,selsey is a well-known example4 ,this great ice-sheet nowhere formed marked terminal moraines1 but its deposits fade away in thin beds of stiff boulder-clay4 ,this absence of moraines is probably connected with the great thickness of the ice-sheets1 which did not leave any appreciable nunataks or rocky 8islands0 exposed in its path1 so that there was nothing to give rise to detritus on the surface of the ice4 ,all the transportation had to be carried on beneath the ice-sheets1 and these1 penetrating into comparatively low latitudes where the sun is powerful in summer1 would suffer gradual melting and ablation for some distance from their margins4 ,near the actual ice-limit the motion must have been slow and the thickness of the ice small1 so that conditions were against the accumulation of thick beds of detritus4 ,on the borders of the ice-sheet the climate cannot have been over-rigorous1 for pre-,chellean man was able to live almost up to the ice-edge4 ,the air must have been extremely cold1 and there was a belt of high arctic climate round the ice1 but in the south and south-west this appears to have been very narrow1 and sub-arctic conditions1 no worse than those in which many races live to-day1 prevailed not very far from the ice4 ,the configuration of the ice-surface largely explains this4 ,a high steeply sloping wall of ice causes intensely violent winds1 carrying dense clouds of drift-snow--blizzards1 in fact1 similar to those now experienced in parts of ,antarctica under similar circumstances1 which sweep the land bare of all life for a considerable distance4 ,but a low and gradually sloping surface1 such as seems to have existed near the borders of the maximum glaciation1 favours instead comparatively gentle winds without much drift snow4 ,it is only on the north-west ice-ridge1 where ice-cliffs fronted the sea and where severe storms from the ,atlantic were frequent in winter1 that blizzards occurred4 ,when the land in ,scandinavia began to sink under the ice-load more rapidly than the supply of snow could build up the surface of the ice-sheet the force which pushed out the ice in all directions from the centre gradually died away1 and the ice-masses over the ,north ,sea area--now probably again below sea-level--and the low grounds of ,europe were left derelict1 with no resources but the snowfall on their own surfaces4 ,under these conditions they melted away more or less rapidly4 ,while these derelict ice-masses were still large1 the auxiliary peripheral centres in the ,alps1 ,pyrenees and ,british ,isles maintained an independent existence for a while1 probably with fluctuations similar to those which marked the close of the last glaciation in the ,alps1 though the evidence of these has now been wiped away4 ,it is even likely that the beginnings of the weakening of the central source of supply helped the ,british ice to divert the ,scandinavian ice into the ,north ,sea4 ,had there been any powerful rivers bearing great masses of detritus from the south1 as there are in ,siberia1 some of these derelict ice-sheets might have been preserved for a time1 at least1 as 8fossil ice10 but in western ,europe conditions were not favourable for this4 ,with the disappearance of the ice-sheets the general climate of ,europe must have passed through a series of stages of amelioration1 of which traces can be found here and there1 though the details are lost to us4 ,ultimately temperate conditions again prevailed2 and for a very long time1 approaching a quarter of a million years1 ,europe cannot have differed greatly from present climatic conditions4 ,in ,scandinavia the mammoth roamed in forests of birch1 pine and spruce2 further south the mammoth is absent1 and we find instead more southern forms--,elephas antiquus1 resembling the ,indian elephant1 ,rhinoceros merckii1 a southern form1 the sabre-toothed tiger1 cave-lion1 cave-bear and cave-hyna1 wolf1 beaver1 horse and various forms of deer1 while the flora included even such warmth-loving trees as the fig4 ,obviously1 during part of this interglacial period1 the climate must have been even warmer than the present4 ,let us glance for a moment at the probable conditions4 ,one of the dominant features in the present weather of ,europe is the accumulation of floating ice in the ,arctic basin4 ,this keeps the temperature low and the pressure high--forms in fact during the spring and summer months a temporary glacial anticyclone similar in kind to1 though of less intensity than1 that which has been described as covering the ,scandinavian ice-sheet4 ,this anticyclone maintains on its southern edges a belt of easterly winds1 and these winds enter into the general circulation of the earth4 ,their effect is to push southward the permanent storm-centres normally situated near ,iceland and the ,aleutian ,islands1 and it is these storm-centres which play a large part in causing the rainy weather of northern and central ,europe4 ,but occasionally--as in the remarkable spring and summer of #aiba--these conditions break down4 ,the ,arctic ,ocean becomes unusually ice-free and warm1 the pressure falls1 and in consequence the storm-centres move northward4 ,europe comes under the influence of the permanent anticyclones of sub-tropical latitudes1 rain-bearing storms pass far to the northward1 and we have a dry warm summer of the ,mediterranean type4 ,this is presumably what happened during the long warm ,mindel-,riss interglacial4 ,for some reason1 possibly connected with a temporary widening and deepening of the ,bering ,strait1 the waters of the ,arctic ,ocean became warmer and the amount of floating ice less4 ,pressure became lower in the polar basin and therefore higher over the ,atlantic and ,europe1 and fine warm conditions prevailed in ,europe as the normal climate instead of only as an occasional event4 ,this warm interval was finally brought to a close by the renewed elevation of ,scandinavia1 and the ice-sheets began to develop again1 heralded by a period of dry steppe climate4 ,this time1 however1 the conditions were different2 the elevation was not so great1 and was more local4 ,hence the resulting glaciation was less intense2 it filled the ,baltic basin and extended some distance on to the ,north ,german plain and into ,holland4 ,it failed to reach the coast of ,britain1 but that it extended some way across the ,north ,sea plain is indicated by the peculiar distribution of the ,newer ,drift of ,britain1 to be referred to later4 ,in the north of ,norway the slope of the ice towards the sea was very steep1 so that many of the coastal hills extended above it as nunataks4 ,the ice extended into the channel between the mainland and the ,lofoten ,islands 7then a peninsula71 but according to ,ahlmann these islands were an independent centre of local glaciation1 as the ,british ,isles had been during the preceding period1 and the local ice met the main ice-sheet in the fiords4 ,on the coast of ,nordland sufficient land lay bare to harbour a small ,arctic flora1 and ,vaero1 the southernmost island of ,lofoten1 had only small hanging snow-banks4 ,the interpretation of the ,british glacial deposits is still very much under discussion1 but it seems probable that the ,scottish highlands formed a subsidiary centre which glaciated the whole of ,scotland and north-east ,england1 sending a stream south-eastward1 which was prevented from spreading across the ,north ,sea plain by the presence of ,scandinavian ice to the east and impinged on the coast of ,yorkshire and ,lincolnshire1 just reaching the northern extremity of ,norfolk4 ,many ,british geologists regard this development as the concluding phase of a single glaciation of ,britain1 but the differences in the amount of weathering undergone are against such an interpretation4 ,at the same time there were local glaciers in ,cumberland1 ,wales and ,ireland4 ,in ,england limits of this glaciation are characterized by a well-marked series of end-moraines1 which indicate that the ice carried much surface detritus1 and probably ended in a steep cliff4 ,in ,scandinavia1 on the other hand1 the centre of glaciation again lay over the low ground well to the east of the mountains1 and the ice which reached ,germany and ,denmark was still largely free of surface detritus1 and so did not form marked end-moraines4 ,there was a difference1 however4 ,on this occasion1 owing to the local nature of the elevation in ,scandinavia1 the ice-sheet did not extend its borders so far to the eastward1 and the glaciation of ,asia1 as described in ,chapter ,,vii1 was slight4 ,europe came more under the influence of cold north-easterly and northerly winds1 and life on the ice-borders was not so easy as during the preceding glaciation4 ,man could still live near the ice1 but he took to making his home in caves1 and to clothing himself in skins for warmth4 ,after the ice had reached its ,rissian maximum of glaciation the climate improved somewhat4 ,the ice-edge retreated1 leaving ,denmark and the ,german coast1 and vacating the ,baltic basin1 but not disappearing altogether from ,scandinavia4 ,at ,rixdorf1 near ,berlin1 there is a bed of gravel deposited in this 8interglacial10 containing numerous and well-preserved bones of the mammoth1 woolly rhinoceros1 aurochs1 bison1 horse1 reindeer1 red deer and other species of ,cervus1 musk ox and wolf--a cold temperate to sub-arctic fauna4 ,in south ,germany fresh-water mollusca indicate that the summers in that district were almost as warm as at present1 but the winters were probably severe4 ,as described in the preceding chapter this 8interglacial0 was the time of loess formation par excellence1 with a continental climate and steppe conditions over much of central ,europe4 ,investigations at ,skrumhede in ,denmark show that this recession of the ice was accompanied by1 and presumably due to1 a fall in the level of the land relatively to that of the sea1 for at the beginning of the oscillation the land lay about #cej feet above its present level1 sinking gradually to only #cj feet above present4 ,even at its best during this interglacial the climate was almost sub-arctic in ,denmark4 ,in northern ,finland1 on the eastern edge of the ice-sheet1 there was also an 8interglacial10 with a slight improvement in the climate accompanying a temporary submergence4 ,but in ,scandinavia there are no traces of any interglacial deposits of this period1 and considering the cold climates which prevailed in ,denmark and ,north ,germany1 it seems probable that ,scandinavia continued to be glaciated during the whole period4 ,the mode of life among ,mousterian men1 who lived during this 8interglacial10 also points to a severe climate4 ,for at this time man did not live in the open1 but in caves and rock-shelters1 and the practice of wearing the fur skins of animals as a protection against the cold1 begun in the preceding ,rissian glacial period1 was not discontinued4 ,after the temporary subsidence had ceased1 elevation again set in1 causing a readvance of the ice-sheets and glaciers4 ,the limits fell short of those of the preceding maximum1 and the climate was not so severe1 but in its general character it resembled that of the preceding maximum1 but was much stormier1 and there were probably frequent blizzards of the ,antarctic type1 carrying drift-snow4 ,the new ice-sheet carried more surface detritus than its predecessors1 presumably because all the high ground was not covered1 and it formed high terminal moraines4 ,the close association of cold ice and irregular masses of bare sand and stones1 strongly heated by the summer sun1 set up a belt of powerful convection very favourable for the development of blizzards2 possibly there was something in the nature of an ice-cliff down which the cold winds could blow with great strength4 ,at any rate1 man found the near neighbourhood of the ice unpleasant1 and went1 so that there are no contemporaneous human implements near the moraines4 ,the limits of the ,scandinavian ice-sheet ran from the ,norwegian coast across ,denmark from north to south1 through ,north ,germany and northern ,russia1 and included ,finland4 ,the ice probably did not extend far across the ,north ,sea plain1 and in the ,british ,isles there was no ice-sheet1 but the high mountains of ,scotland1 ,ireland1 ,wales and ,cumberland bore small local glaciers1 which were long enough to reach the sea in the ,scottish highlands4 ,the ,alps bore considerable glaciers1 indicating a depression of the snow-line of about #cejj feet1 corresponding to a temperature #aa ,f4 lower than the present4 ,after this ice-development had reached its maximum limits and remained there for perhaps a thousand years1 retreat set in1 and the ,scandinavian ice once more withdrew from ,germany and ,denmark to the ,baltic basin4 ,but its edge was never far from the ,german coast1 and occasionally readvanced across it1 for numerous fossiliferous deposits are intercalated in boulder-clay4 ,the fauna and flora1 which are well known1 point to an arctic climate4 ,at its best the mean temperature of ,july rose to about #ej ,f41 and there was a vegetation period of three or four months with an average temperature of about #dj ,f41 but these relatively mild conditions lasted at most for a few decades or perhaps a century at a time1 and the winters were severe throughout4 ,the duration of the whole of this 8,baltic ,interstadial0 was from one to two thousand years4 ,next followed the final readvance of the ice forming the great 8,baltic0 moraines which fringe the ,baltic coast of ,germany1 turning northward in the west into ,denmark and in the east into ,finland4 ,there was a corresponding re-development of glaciers in the ,alps 7,bhl stage7 and in the mountains of ,ireland and ,scotland1 though these probably failed to reach the sea even in ,scotland4 ,this period gave us a repetition of the climate of the preceding maxima4 ,in this case we have definite evidence of the presence of a belt of easterly winds on the southern side of the ice-sheet1 in a series of 8barkans0 or fossil dunes in ,holland1 ,germany and ,galicia4 ,these dunes were formed of fine ice-deposited material1 and they are crescent-shaped1 with their convexities to the east1 indicating that they were built by strong easterly winds4 ,a moment's consideration will show the truth of the latter statement4 ,suppose there is an isolated round hillock of sand exposed to strong easterly winds4 ,the sand grains will travel up the easterly windward slope of the hillock and roll down the westerly leeward side4 ,in this way the whole hillock will advance very slowly westwards4 ,but in the centre1 where the hillock reaches its greatest height1 the grains will take longer to reach the highest point than near the edges1 where they have not to rise so high4 ,at the edges a strong gust will carry some of the heavier grains right over the dune1 while nearer the centre they will be left half-way1 and when the gust ceases will perhaps roll back to their original position4 ,in this way the margins of the dune will advance westward more rapidly than the centre1 producing the crescent shape with the convex side to the east4 ,at the time of their formation these dunes must have had their steepest side to the westward1 but the westerly winds which have prevailed during the last few thousand years have succeeded in modifying that detail1 without destroying the general shape of the dunes1 and the steepest slopes are now on the eastern side4 ,the preservation of the original shape1 in spite of the subsequent development of westerly winds1 is due in part to the coating of vegetation1 which protected the dunes as soon as more favourable conditions occurred1 and probably in part to the lesser velocity of the westerlies4 ,if the period of east winds and dune formation had been long enough1 we might have had another deposit of loess1 but it was short1 and vegetation1 which is necessary to the genesis of true loess1 had no time to establish itself before the climate changed again with the final retreat of the ice4 ,the climate of this period in ,rumania has been ably described by ,g4 ,murgoci3 8,in general the prevailing climate of the time of the formation of loessoid soils and blown sands must have been that which is named by ,e4 de ,martonne the aralian climate1 a dry climate with some rain in spring to call forth a poor and transient vegetation and to maintain the flowing water in rivers and lakes4 ,the temperature with great extremes1 in summer up to #abj ,f4 and in winter below #bj ,f41 was the characteristic of this climate2 the atmosphere was very dry in the hot season1 but in the rest of the year there was some humidity in the air and moisture in the soil1 the water of the subsoil being not very deep4 ,the atmospheric precipitation in this region was caused by the south-west wind just as at present2 but the dominant wind giving the character of a dry continental climate was the north-east wind 7,crivat7 which has left its traces in the fossil dunes of the ,baragan40 ,a history of the changes of climate in ,europe which followed the maximum of the last readvance of the ice-sheet must be left to later chapters4 ,,bibliography ,brooks1 ,c4 ,e4 ,p4 8,the correlation of the ,quaternary deposits of the ,british ,isles with those of the continent of ,europe40 ,ann4 ,rep4 ,smithsonian ,inst41 #aiag1 pp4 #bgg-cge4 ,full list of references4 ,penck1 ,a41 and ,brckner1 ,e4 8,die ,alpen in ,eiszeitalter40 #c ,vols4 ,leipzig1 #aija-i4 ,gagel1 ,c4 8,die ,beweise fr eine mehrfache ,vereisung ,norddeutschlands in diluvialer ,zeit40 ,geol4 ,rundschau1 #d1 #aiac1 p4 #ci4 ,wahnschaffe1 ,f4 8,die ,oberflchengestaltung des norddeutschen ,flachlandes40 ,stuttgart1 #aiaj4 ,svastos1 ,r4 8,le postglaciare dans l',europe centrale du nord et orientale40 ,ann4 ,sci4 ,univ4 ,jassy1 #d1 #aijh1 p4 #dh4 ,,chapter ,,vi ,,the ,,mediterranean ,,regions ,,during ,,the ,,glacial ,,period ,our knowledge of the history of the ,mediterranean basin during the ,glacial period is not nearly so complete as is that of the more northern regions1 chiefly for the reason that during most of the period the land lay above its present level1 and except for local glaciers in the mountain regions there was no ice to leave us a record of the changing climates4 ,most of what we do know relates to the relatively brief periods of submergence4 ,at the beginning of the ,glacial period the sea lay some #ejj feet above its present level1 and we can trace the first appearance of a northern marine fauna4 ,this stage is known as the ,calabrian2 it is divided into two horizons--a lower1 in which northern forms are still rare1 and an upper1 in which they are becoming abundant4 ,the most typical species are two mollusca whose present habitat is the coast of ,iceland--,chlamys 7,pecten7 islandicus and ,cyprina islandica4 ,the ,calabrian beach is not found on the coast of ,spain or at ,gibraltar1 and in ,algeria it probably occurs at a lower level4 ,this suggests that the subsidence at this period was local1 and the western lands stood up as a barrier against the ,atlantic4 ,there must have been a channel of some sort1 however1 on the site of the present ,straits of ,gibraltar1 to provide an inlet for the immigrating northern mollusca4 ,in the ,maritime ,alps1 and again in the eastern ,mediterranean1 the ,calabrian beaches are at a much greater height owing to local elevation4 ,after the formation of the ,calabrian beach the whole ,mediterranean region was elevated above its present level4 ,this elevation must be contemporaneous with the period of maximum elevation in north-west ,europe associated with the great ,mindelian glaciation4 ,it is suggested that the 8sill0 of the outlet channel at ,gibraltar was raised above the level of the ,atlantic1 and the ,mediterranean became1 first a closed salt lake1 and then a pair of lakes1 the eastern fresh draining into the western1 which was salt1 the two being separated by a ridge of land between ,italy and ,tunis4 ,this period of elevation was long enough for a great deal of denudation to take place4 ,even in the ,mediterranean this was a time of severe climate4 ,on the eastern side of ,gibraltar there are breccias1 known as the 8,older ,limestone ,agglomerate10 which reach a thickness of #ajj feet in places1 and are now much weathered4 ,similar agglomerates are found in ,malta4 ,these resemble the 8head0 of the south of ,england1 and appear to be due to frost action in a severe climate4 ,in ,corsica there are traces of four periods of mountain glaciation1 and the two oldest of these are provisionally correlated with the ,gunzian and ,mindelian of the ,alps4 ,in the ,balkan highlands there are traces of two distinct glaciations3 the older1 which was the more general and reached the greater intensity1 probably corresponding to the ,mindelian4 ,in the ,atlas ,mountains there are great boulder moraines which seem to belong to three distinct glaciations1 the oldest extending to about #bjjj feet above sea-level1 and the second terminating at about #djjj feet1 while the third glaciation consisted of small valley glaciers only4 ,towards the close of the ,mindelian glacial period the land sank or the ocean rose again1 and the waters of the ,atlantic poured in1 bringing with them a great number of high northern and ,arctic mollusca4 ,the theory has been put forward that this influx was in the nature of a debacle and carved out a deep gorge through the present ,straits of ,gibraltar4 ,the beaches deposited by this sea lie at a height of #bej to #ccj feet above the present sea-level4 ,the fauna resembles that inhabiting the northernmost parts of ,europe at the present day1 and the waters must have been several degrees colder than at present4 ,this stage is termed the ,sicilian4 ,as the climate improved the land gradually rose again1 and the next general raised beach lies at a height of only about #ajj feet in southern ,italy 7except where it has been elevated by local earth-movements74 ,further west it lies still nearer the present sea-level--twenty feet in the ,balearic ,islands and only seven feet on the coast of ,spain4 ,on the coast of ,algeria and ,tunis this beach is found at a height of about forty-five feet4 ,the beach contains no trace of the northern fauna found in the ,sicilian stage2 instead it is marked by an assemblage of mollusca of a sub-tropical aspect1 including ,strombus bubonius1 ,mytilus senegalensis and ,cardita senegalensis4 ,the bones of large mammals are also found1 including the hippopotamus and southern forms of elephant 7,e4 antiquus7 and rhinoceros 7,rh4 merckii74 ,this warm stage corresponds to the ,chellean interglacial fauna of northern ,europe1 though so far as ,i am aware no ,chellean implements have been found associated with it4 ,about this time the ,older ,limestone ,agglomerate of ,gibraltar had been worn into caves1 in which are found the bones of ibex1 wild boar1 leopard1 spotted hyena1 ,rhinocerus leptorhinus1 ,elephas meridionalis1 lion1 southern lynx1 bear1 wolf1 stag1 horse1 etc41 so that the rock must have been covered by a rich vegetation1 and must have had a greater extent than now1 and a connexion with the continent of ,africa4 ,this is said to have been followed by a submergence of about #gjj feet with numerous oscillations4 ,this submergence1 if it is really attributable to the interglacial1 must have been extremely local1 and possibly it is much older4 ,after the warm ,chellean period the ,mediterranean region rose again1 probably contemporaneously with the rise which caused the ,rissian glaciation of northern ,europe4 ,but the climate was nothing like so severe as in the ,sicilian4 ,we have no old beaches containing a molluscan fauna of this period1 but at the ,grotte au ,prince near ,mentone1 investigated by ,m4 ,boule1 the ,strombus beach is overlain by a bed of cemented pebbles and 8hearths0 containing ,mousterian implements and bones of a temperate fauna4 ,the ,newer ,limestone ,agglomerate on the east of ,gibraltar may have been formed during this period4 ,the ,mediterranean lands remained above their present level until the close of the ,glacial period4 ,each glaciation of northern ,europe must have been a time of greater rainfall as well as of lower temperature in the ,mediterranean4 ,the glacial anticyclone in the north displaced the storms from the ,atlantic1 which now mostly either skirt the north-west coast of ,norway or pass across ,denmark into the ,baltic4 ,these storms had to take a more southerly course1 and entered the ,mediterranean basin either across the south of ,france or in the neighbourhood of ,gibraltar3 tracks which are still occasionally followed in winter4 ,these storms brought a rainfall much heavier than the present1 and of a different character4 ,the ,mediterranean is now a 8winter rain region10 and the north of ,africa is entirely rainless for several months in the summer4 ,but during the 8,pluvial periods0 it is probable that rain fell throughout the year1 though the winter still had more than the summer4 ,the winter rains were in the form of steady falls of long duration1 such as we experience now in ,england1 while the summer rains fell in short1 heavy showers1 perhaps accompanied by thunder4 ,the ,older ,pluvial period1 which corresponds to the ,mindelian glaciation1 had these conditions in their greatest development4 ,depressions cannot live long without a supply of moisture1 either from the sea or from transpiring vegetation1 and at present such winter storms as enter the ,mediterranean are almost confined to its surface1 and on the ,african side rarely penetrate more than one hundred miles inland4 ,but at the period of greatest elevation the shrunken ,mediterranean offered no such great attraction1 and with a comparatively well-watered ,sahara the storms were able to pass much further south4 ,consequently1 northern ,africa possessed a number of large and permanent rivers which reached the sea4 ,it was along these rivers and their banks that the fauna still inhabiting the ,saharan oases made its way1 to be isolated there by the decrease of the rainfall1 so that crocodiles and many species of fish now live in isolated pools and in rivers which lose themselves in the sand4 ,in ,egypt and ,syria the first ,pluvial period is double1 corresponding to the ,gunz and ,mindel glaciations1 with an intervening phase of feeble desert conditions1 during which1 however1 the rainfall remained greater than the present4 ,the second stage1 corresponding to the ,mindelian1 indicates very great activity2 at this time the ,jordan ,sea 7,dead ,sea7 reached its greatest area1 extending to the northern end of the ,sea of ,tiberias4 ,conditions in ,egypt at this time are very interesting4 ,south of ,cairo the alluvial ,nile muds are at most thirty to thirty-five feet thick1 and ten feet of this thickness has been deposited since the time of ,ramesis ,,ii4 ,if the rate of deposition has been uniform1 this gives a period of only #ad1jjj years for the deposition of the whole thickness of the muds4 ,the theory put forward by ,hume and ,craig 7,british ,association ,report1 #aiaa1 p4 #chb7 is briefly as follows3 ,the mud deposits of the ,nile valley are carried down with the flood waters of the ,blue ,nile1 ,atbara1 etc4 ,these rivers rise in the highlands of ,abyssinia1 where they are fed by the rains of the south-west monsoon4 ,the incidence of the monsoon is determined by a number of factors1 prominent among which is the temperature of southern ,asia4 ,during the winter1 at present1 the low temperature of the ,himalayan and ,tibetan region results in a great outflow of cold air1 which strikes the coast of ,africa as the cool dry north-east monsoon4 ,during this time there is very little rain in ,abyssinia4 ,it is only when the ,asiatic land-mass warms up in summer that the south-west monsoon is established4 ,but during the ,glacial period1 as we shall see1 there was a great development of snow and ice on the ,himalayas4 ,the result was that winter conditions1 i4e4 the north-east monsoon1 prevailed more or less throughout the year1 and the rivers which feed the ,nile contained only a small volume of water4 ,hence they lost themselves in the desert before reaching ,cairo1 and the ,nile in its present form did not exist4 ,on the other hand1 the westerly winds which at present bring a moderate winter rainfall to the coast of ,syria were greatly increased in intensity and extended further south1 replacing the dry north and south winds now occupying the ,nile valley4 ,the northerly winds prevailing in the ,nile valley in summer are associated with the low pressure area over the neighbourhood of the ,persian ,gulf1 which in turn is due to the extremely high temperature experienced there4 ,even at the present day the highest hills of ,sinai penetrate above the north winds into a westerly current1 and a moderate fall of temperature over the ,persian ,gulf would inhibit the north winds in the ,nile valley altogether and allow the westerly winds to reach the surface4 ,these strong westerly winds brought a heavy rainfall to the hills1 now almost rainless1 between the ,nile and the ,red ,sea4 ,powerful streams descended the western slopes of these hills1 bringing great quantities of debris1 which formed delta-terraces forty of fifty feet thick where the streams debouched on to the ,egyptian plain4 ,these are especially well developed at ,oina1 the meeting place of several dry valleys from the hills1 and it is remarkable that they actually cross the present site of the ,nile valley and reach the desert on its western side1 additional evidence that the ,nile was not then in existence4 ,these gravel terraces contain numerous stone implements of early 7pre-,chellean7 types1 showing that at this time ,egypt had sufficient rainfall of its own to support human life4 ,the moist westerly winds carried the climate of the ,mediterranean coast far into the desert4 ,for instance1 in the oasis of ,khargeh1 in latitude #be1 grew the evergreen oak and other plants not now found south of ,corsica and southern ,france4 ,the ,mindelian ,pluvial period was followed by a long dry period corresponding to the ,chellean1 when desert conditions supervened4 ,the ,nile as we know it first appeared during this period4 ,terraces were formed on the sides of the valley1 probably during the submergence which produced the ,strombus beaches of the western ,mediterranean2 these contain ,chellean implements4 ,during the succeeding elevation the ,nile cut its bed below the present level4 ,the ,rissian glaciation of northern ,europe is represented in ,egypt by a second rainy period1 the ,lesser ,pluvial period4 ,rain again fell on the ,red ,sea hills1 forming a newer set of gravel terraces1 but these are much smaller than the great ,mindelian terraces4 ,no terraces are known representing the ,wurmian period1 and the country does not seem to have been inhabited at this time4 ,probably the climate was semi-desert1 with not enough rainfall of its own to support human life1 and yet without the fertilizing ,nile floods to enable human life to exist without rainfall4 ,as has been said1 the present regime did not begin until the last glaciation was nearly over1 about #ab1jjj ,b4,c4 ,,bibliography ,gignoux1 ,m4 8,les formations marines pliocnes et quaternaires de l',italie du ,sud et de la ,sicilie40 ,ann4 l',univ4 ,lyon1 n4a41 ,vol4 #a1 fasc4 #cf1 ,paris1 #aiaa1 pp4 #fic4 ,depret1 ,c4 8,les anciennes lignes de rivage de la cte franaise de la ,mediterrane40 ,bull4 ,soc4 ,geol4 de ,france1 ser4 #d1 ,vol4 #f1 pp4 #bjg-cj4 ,douvill1 ,r4 8,espagne10 ,handbuch regional ,geol41 ,h4 #g1 #aiaa4 7,includes ,gibraltar and ,balearic ,is47 ,hume1 ,w4 ,f41 and ,craig1 ,j4 ,i4 8,the ,glacial period and climatic change in ,north-east ,africa40 ,rep4 ,brit4 ,assoc41 #aiaa1 p4 #chb4 ,,chapter ,,vii ,,asia ,,during ,,the ,,glacial ,,period ,the great area of ,asia is at present but little explored for glacial traces1 but a certain amount of evidence has been collected1 and the data from the various mountain districts are consistent enough to map out the general trend of the history of the continent during the ,ice ,age4 ,the earth-movements which brought about the present configuration of ,asia were completed as regards their major details by the close of the ,tertiary period4 ,these movements left a number of great basins closed in on all sides by enormous mountain walls2 at first all these basins contained lakes1 and the subsequent geographical history has consisted largely in the gradual silting up of the lakes and the development of more and more arid conditions4 ,the fluctuations of the ,ice ,age were superposed on this secular desiccation1 but except in northern ,siberia the part played by glaciation in the history of the country has been relatively small4 ,consider for a moment the relief of ,asia4 ,the orographic centre may be taken as the great ,pamir plateau1 the 8,roof of the ,world10 with an average elevation exceeding the height of ,mont ,blanc1 diversified by ranges of mountains exceeding #be1jjj feet in places4 ,east of this is the great plateau of ,tibet1 #aj1jjj to #ag1jjj feet1 bounded on the south by the mighty ,himalayas1 and on the north by the mountains of ,kuen ,lun4 ,on the north the ,pamir plateau is bounded by the ,alai range1 passing north-east into the ,tian-,shan mountains1 rising to #bd1jjj feet in ,khan-tengri4 ,still further north-east comes the ,altai range1 with an elevation of #ijjj feet4 ,east of ,lake ,baikal lie a series of ranges averaging #hjjj feet in height1 and passing into the ,stanovoi range of eastern ,siberia and the mountains of ,kamchatka4 ,the ,himalayas1 owing to their heavy snowfall derived from the south-west monsoon1 bear numerous great glaciers1 but with the series of ranges extending from the ,pamirs to north-east ,siberia the case is different4 ,these ranges all rise above the snow-line in places1 but owing to the scanty snowfall they bear at most a few small glaciers on their northern sides1 and none at all on the slopes which face towards the deserts of western ,china1 and in all cases the glaciation is very slight in comparison with their elevation4 ,this distribution was characteristic also of the ,ice ,age4 ,in the ,pamirs there is evidence of two periods when the glaciers had a greater extent2 in the first they extended to a level of #ejjj feet1 in the second to #gjjj feet4 ,the present limit of the glaciers lies at about #aj1jjj feet4 ,the first glaciation was remote1 for the moraines are worn and weathered1 but the second was much more recent1 for the moraines are fresh1 and in some cases there are still masses of 8dead0 ice buried beneath great accumulations of debris and occasionally exposed by slips4 ,in the ,tian-,shan mountains there are remains of two glaciations4 ,the earlier was the greater1 and the glaciers descended well below #aj1jjj feet4 ,this glaciation was followed by a long interval1 when the erosion of the rivers converted the ,u-shaped glacial valleys into ,v-shaped gorges4 ,a second glaciation descended to a level of #aj1jjj feet1 and again developed ,u-valleys to this level2 the end-moraines of these glaciers are young and fresh-looking4 ,in the ,altai range there were also two glacial periods4 ,in the older and greater the snow-line was depressed by #cjjj feet4 ,the glaciers attained a length of twelve miles and descended to a level of only #cjjj feet above the sea4 ,the second glaciation was less extensive4 ,so far we have been dealing with small mountain glaciers only4 ,but in north-eastern ,siberia we find a different state of affairs4 ,the ,stanovoi and ,verkhoiansk mountains were heavily glaciated1 and during the first glaciation were probably the centre of an actual ice-sheet similar to that of ,scandinavia4 ,the ice descended the valleys of the rivers ,yana1 ,indijirka and ,kolyma and covered the ,new ,siberian ,islands1 which were at that time connected with the mainland4 ,the upper valley of the ,lena was also heavily glaciated by an ice-sheet moving southward1 probably from the ,patom highlands4 ,when this glaciation drew to a close the source of supply among the mountains ceased1 and the ice on the lowlands and in the lower parts of the river valleys was left stranded as 8dead0 ice4 ,when the mountains became free of ice1 the re-born rivers carried great quantities of moraine-clay and other debris with them1 and flooding the ice-surface over wide areas deposited their load above the ice4 ,in course of time the remains of the ice-sheet were deeply covered by a layer of earth and stones1 which prevented the ice from melting and preserved it to the present day4 ,this is the probable origin of the well-known 8fossil ice0 of ,siberia4 ,other theories have been put forward1 such as the freezing of ground water during the winter1 but none are satisfactory1 and that given here was generally adopted by ,russian geologists4 ,during the long warm interglacial which followed1 the surface of the thick earth-layer covering the ice bore low-growing herbage in the same way as any other earth-surface4 7,a parallel to this is found in ,alaska1 where the glaciers terminate among the forests1 which actually grow over the moraines covering their snouts47 ,the rivers cut their way down through the earth and ice1 exposing ice-cliffs1 which were quickly buried by talus from above4 ,the mammoth and woolly rhinoceros roamed the land1 and their tusks remain in great numbers as the 8fossil ivory0 of ,siberia and the ,arctic ,ocean4 ,still more remarkable is the fact that mammoths have been found buried entire1 and preserved by the frozen ground to the present day4 ,it is difficult to say how the animals reached such a position1 but most probably they sank into swamps formed during the summer and were quickly frozen4 ,in western ,europe the mammoth and woolly rhinoceros are regarded as indications of severe climate1 but their presence in north-eastern ,siberia in large numbers is evidence of a climate probably somewhat warmer than that of the present day1 especially as regards the length of the vegetation period4 ,probably the winter snowfall also was less than now4 ,it is difficult to see how the fauna could have moved from1 say1 the ,new ,siberian islands into a warmer climate each winter1 for the winter climate becomes markedly more severe as one penetrates south from the ,arctic coast into the interior4 ,it is possible that the mammoth and woolly rhinoceros hibernated during the winter4 ,after this interglacial there came a recrudescence of glacial conditions4 ,in this case1 however1 the ,stanovoi and ,verkhoiansk mountains and the ,patom highlands were not buried in an ice-sheet1 but became the centre of great valley glaciers1 which reproduced the well-known glacial phenomena--corries1 glacial terraces1 ,u-valleys1 etc4 ,the ice extended down the great river valleys1 leaving a typical moraine landscape on either side1 and again reached the ,new ,siberian islands4 ,in course of time the climate ameliorated1 again commencing in the south1 and again the ice of the glaciers was buried4 ,in the ,new ,siberian islands the happenings are summarized very expressively by a rock-section described by ,vollossovitsch4 ,the bottom of the section is formed by the older layer of 8fossil ice40 ,above this is a sandy clay with remains of meadow vegetation and shrubs1 followed by a fine clay with remains of alder and white birch1 and the bones of mammoth and rhinoceros4 ,above this comes another layer of 8fossil ice10 followed by clay with the dwarf birch1 ,arctic willow1 and bones of musk ox1 horse and later mammoth4 ,after this the coastal regions sank beneath the sea for a time and marine clays were formed in a climate somewhat warmer than the present4 ,when the land rose again the conditions resembled those now prevailing4 ,though not part of ,asia1 reference may be made here to the glaciation of ,spitzbergen1 which runs strictly parallel with that of northern ,siberia4 ,the first glaciation was of the 8ice-sheet0 type1 originating in the region north of ,storfjiord1 filling the whole of that fiord and extending south of ,south ,cape4 ,barentz ,land and ,stans ,foreland were at least partially ice-covered4 ,the ice-floor of ,spitzbergen1 which resembles that of ,siberia1 may have originated during this glaciation4 ,this was followed by subsidence to #bcj feet below present level1 and the ice retreated1 giving place to an 8interglacial10 during which frost was very active and largely obliterated the traces of the ice-sheet4 ,this 8interglacial0 was followed by a second extension of the ice1 which affected the valleys and fiords only1 leaving the plateaux free4 ,this again was followed by subsidence and a warm period4 ,in southern ,kamchatka there was a great development of ice1 but in the form of a network of glaciers rather than of an inland ice-sheet4 ,in the east the ice reached the sea1 but on the west it left a zone forty to sixty miles broad1 and up to a thousand feet high unglaciated1 so that there was the same difference then as now between the rainy east side and the drier west side of the peninsula4 ,the present snow-line in the centre of southern ,kamchatka is about #eejj feet1 and at the maximum of the glaciation it must have been fully #cjjj feet lower4 ,this glaciation was followed after an interval by a second1 which was confined to the mountains4 ,the moraines of this glaciation are much fresher than are those of the earlier one4 ,in ,japan the mountains were only just high enough for glaciers to develop in the north4 ,the moraines are old and weathered1 and their meaning has been disputed2 but recent work by ,simotomai and ,oseki seems to have established their glacial origin4 ,the depression of the snow-line necessary to produce them--about #cjjj feet--fits in very well with that observed in adjoining parts of the continent4 ,the phenomena were confined to small hanging glaciers in the ,hida mountains which cut out corries and descended to a level of about #hjjj feet1 leaving small morainic ridges4 ,this glaciation was probably contemporaneous with the earlier and greater glaciation of ,siberia4 ,to the succeeding interglacial may be attributed the marine deposits found near ,tokio containing corals1 at present living some distance further south4 ,no trace of any subsequent glaciation of ,japan has yet been found4 ,j4 ,s4 ,lee has recently called attention to the existence of a glaciated area in northern ,china1 the evidence for which consists of moraines and striated slabs found in southern ,chi-li1 and a glaciated valley with travelled boulders in the north of ,shan-si4 ,the glacial deposits in ,chi-li are closely associated with a layer of quartzite pebbles which continues southward beneath the loess on the eastern side of the ,tai-hang range1 and is attributed to either torrential rain or the melting of glaciers4 ,j4 ,geikie had long ago stated that there once existed ice-masses all over northern ,china1 and considered that the ice came from the ,himalayas4 ,this origin is impossible1 the probable source of the ice being the ,yablonoi mountains in southern ,mongolia4 ,in the ,himalayas the glaciers formerly had a much greater extension4 ,the glaciers at present extend downwards to #aa-ac1jjj feet1 but old moraines are found at #gjjj feet1 and near ,dalhousie on the southern slopes of the ,dholadar range to #dgdj feet4 ,on the northern side of the ,himalayas there was a great development of ice over ,tibet1 but there was not a real ice-sheet such as occurred further north4 ,oldham records three separate periods of glaciation in ,kashmir1 but it is not yet possible to discuss the glacial history of the ,himalayas in detail4 ,the latter is likely to prove complicated1 since the range is still rising1 and has probably been doing so either continually or intermittently throughout the ,quaternary4 ,the great development of ice in ,tibet1 which is now semi-arid1 owing to interception of the rain-bearing winds by the ,himalayan range1 suggests a considerable alteration in the present meteorological conditions4 ,the ,tibetan snowfall was probably due to the ,mediterranean storms1 which now give a small winter rainfall in north-west ,india1 and which during the ,glacial period greatly increased in strength and frequency and occurred throughout the year 7,chapters ,,iv and ,,vi71 giving the ,pluvial period of ,north ,africa4 ,these storms would pass across ,persia and continue to the north of the ,himalayas1 probably breaking up over the ,tibetan plateau4 ,it is evident that1 taking northern ,asia as a whole1 there have been two general glaciations1 of which the first was the more severe1 separated by a long interglacial1 during which1 in ,japan at least1 the climate became appreciably warmer than the present4 ,the first glaciation is related to elevation in the ,arctic basin1 which closed ,bering ,strait and united the ,new ,siberian islands to the mainland4 ,it was almost certainly contemporaneous with the first glaciation 7,gunz-,mindel7 of ,europe4 ,the ice began as glaciers on the mountains as in ,scandinavia1 but1 owing to the scanty supply of snow1 developed more slowly and only reached the dignity of ice-sheets in north-east ,siberia4 ,then followed subsidence below the present level1 wider opening of the ,bering ,strait1 warm ocean currents and a long interglacial4 ,after this there was again elevation and a re-development of ice-sheets1 but apparently once only1 and not twice as in ,europe4 ,this glaciation probably corresponded in point of time more or less with the ,rissian1 for the post-glacial dry of central ,asia appears to have been of enormous period length4 ,there is one other phenomenon which must be considered in connexion with the glacial history of ,asia1 and that is the loess4 ,loess has already been referred to in connexion with the glaciation of ,europe1 but in ,china its development is much greater4 ,richthofen1 who first studied this deposit attentively1 and to whom we owe the olian theory of its origin1 found that it was formerly deposited in ,china over a much greater area than that over which it is accumulating at present1 and attributes this cessation of growth to the heavier rainfall brought by the ,glacial period1 which enabled the rivers to cut back their valleys and drain some of the mountain basins1 formerly enclosed4 ,he considered that loess can accumulate more rapidly in a closed basin1 where occasional floods leave behind them layers of bare sand and mud1 easily dried to dust1 than in a well-drained river valley where floods are rare4 ,in western ,asia outside the limits of glaciation we have further evidence of at least one ,pluvial period in the former far greater extent of all the enclosed lakes1 due partly to greater precipitation and partly to decreased evaporation4 ,the ,caspian ,sea and ,aral ,sea were extended to several times their present size and united into a single sheet of inland water4 ,lake ,lop-,nor was greatly increased in size1 and many of the desert basins1 at present dry1 were the sites of salt lakes4 ,this is especially the case in central ,persia1 where there were large salt or brackish lakes4 ,these ,pluvial conditions have not yet been correlated with the glaciations of ,asia1 but1 by analogy with the conditions in ,america discussed in the next chapter1 there is little doubt that they were contemporaneous with one at least of the glaciations1 and probably there were two main ,pluvial periods coinciding with the two ,glacial periods4 ,at ,baku1 on the shores of the ,caspian river1 ,pumpelly has found old shore lines at heights of #fjj1 #ejj1 and #cjj feet above the present level of the water4 ,still more interesting are the conditions found by ,sven ,hedin in the ,kavir basin of ,persia4 ,here there are lacustrine clays and silts referable to a ,pluvial period covered by beds of almost pure salt1 suggesting a rapid and complete drying up of the lake4 ,above this again are further silts indicating a return of ,pluvial conditions4 ,in addition to this the succession of silts and clays show that there were several minor fluctuations superposed on the main wet periods1 giving ten moist phases altogether4 ,,bibliography ,many of the more important references are in ,russian1 and for these reference is made to summaries in other languages4 ,sevastianov1 ,d4 ,p4 8,on the glaciation of the extreme north-east of ,siberia40 ,j4 #ab ,congr4 ,russ4 ,nat41 ,moscow1 #aiaj1 ,no4 #aj1 p4 #dia4 7,russian1 see ,geol4 ,centralblatt1 #ae1 p4 #bje47 ,riesnitschanko1 ,w4 8,ancient and modern glaciers of the south-western ,altai40 ,mem4 ,russ4 ,geogr4 ,soc41 #dh1 #aiab1 p4 #ceg4 7,russian1 see ,geol4 ,centralblatt1 #ai1 p4 #aca47 ,komarov1 ,w4 8,on the ,quaternary glaciation of ,kamchatka--,travels in ,kamchatka in #aijh-i10 ,vol4 #a 7,russian1 see ,n4 ,j4 ,min41 #aiae1 ,pt4 #b1 ,p4 #aag74 ,merzbacher1 ,g4 8,zur ,eiszeitfrage in der nordwestlichen ,mongolei40 ,peterm4 ,mitt41 ,gotha1 #eg1 #aiaa1 p4 #ah4 ,prinz1 ,gyula4 8,die ,vergletscherung des nrdlichen ,teiles des zentralen ,tien-schan-,gebirges40 ,wien1 ,mitt4 ,k4 ,k4 geogr4 ,gesellsch1 #eb1 #aiji1 p4 #aj4 ,obrutschev1 ,w4 ,a4 8,geological map of ,lena gold-bearing region40 ,st4 ,petersburg1 #aijg4 ,text in ,russian2 see ,geol4 ,centralblatt1 #ab1 pp4 #ejg-i4 ,simotomai1 ,h4 8,die diluviale ,eiszeit in ,japan40 ,berlin1 ,zs4 ,ges4 ,erdkunde1 #aiad1 p4 #ef4 ,oseki1 ,k4 8,some notes on the glacial phenomena in the ,north ,japanese ,alps40 ,edinburgh1 ,scot4 ,geogr4 ,mag41 #ca1 #aiae1 p4 #aac4 ,lee1 ,j4 ,s4 8,note on traces of recent ice-action in ,north ,china40 ,geol4 ,mag41 #ei1 #aibb1 p4 #ad4 ,burrard1 ,s4 ,g41 and ,hayden1 ,h4 ,h4 8,a sketch of the geography and geology of the ,himalaya ,mountains and ,tibet40 ,calcutta1 #aijg-h4 ,hogbm1 ,g4 8,bidrag till ,isfjordsomradets kvartargeologi40 ,geol4 ,foren4 ,stockholm ,forb41 #aiaa4 7,spitsbergen2 rsum in ,german47 ,richthofen1 ,f4 ,freih4 von4 8,china40 #e ,vols41 #aijg-ab4 7,loess1 see ,vol4 #a1 p4 #gd ff47 ,hedin1 ,sven4 8,some physico-geographical indications of post-,pluvial climatic changes in ,persia40 ,internat4 ,geol4 ,congr41 ,stockholm1 #aiaa4 8,die ,vernderung des ,klimas40 ,,chapter ,,viii ,,the ,,glacial ,,history ,,of ,,north ,,america ,the glaciation of ,north ,america was even greater and more complicated than was that of ,europe4 ,it spread from three main centres1 the ,cordilleran or ,rocky ,mountain centre1 the ,keewatin centre west of ,hudson ,bay1 and the ,labradorean centre4 ,vancouver ,island in the west and ,new ,brunswick and ,newfoundland in the east1 were also independent centres of glaciation1 and ice from the latter may have reached the coast of the ,united ,states in places4 ,the ice covered an area of about #d1jjj1jjj square miles1 and the main ice-sheet extended to #ch ,n41 or twelve degrees further south than the ,scandinavian ice-sheet4 ,nine stages are recognized by ,american geologists1 though opinion is divided as to whether all the stages of 8deglaciation0 represent real interglacial periods4 ,the sequence is as follows3 #a4 ,nebraskan1 ,jerseyan or pre-,kansan glaciation4 #b4 ,aftonian deglaciation4 #c4 ,kansan glaciation4 #d4 ,yarmouth deglaciation4 #e4 ,illinoian glaciation4 #f4 ,sangamon deglaciation4 #g4 ,iowan glaciation4 #h4 ,peorian deglaciation4 #i4 ,wisconsin glaciation4 ,on the other hand1 in the northern part of the ,rocky ,mountains there is evidence of only two ,glacial periods1 separated by a single long interglacial1 though perhaps the second glaciation was double4 ,further south1 out of reach of the main ice-sheets1 there are traces of two and in places three separate developments of valley glaciers resembling those of the ,alps4 ,as in the case of ,europe1 the literature of the subject is extensive and conflicting1 but the following summary of the course of events represents the views of most moderate ,american geologists4 ,the ,quaternary period opened with extensive elevation of the whole ,north ,american continent1 which raised the ,rocky ,mountains several thousand feet above their present level and extended the continental area over much of the northern archipelago4 ,in the east ,newfoundland is considered to have been raised at least #ajjj feet1 a movement which converted the banks into dry land and interposed a large cold area in the path of the moisture-bearing southerly winds4 ,as in northern ,europe the high mountains of the west were the first to develop large glaciers1 which coalesced into an ice-sheet1 filling the valleys and rising up the slopes of the mountains until it reached a thickness of #ejjj feet4 ,in ,puget ,sound the ice was #djjj feet thick1 but seawards the slope is very rapid and the ice was unable to extend far from the shore4 ,this ice-sheet extended south-eastwards some distance into the ,united ,states1 forming the first ground-moraine of that district4 ,probably while this ,cordilleran glaciation was still in progress ice began to spread outwards also from the ,labradorean centre1 forming the oldest drift of that region4 ,these oldest deposits are1 however1 not yet well understood4 ,this oldest boulder-clay is separated from the moraines of the main glaciation near its southern limit by river gravels containing the remains of mollusca and large herbivorous mammals--extinct species of horse1 the hairy mammoth of the old world 7,elephas primigenius71 and two other extinct species of elephant1 and also the true ,american mammoth4 ,this is the ,aftonian fauna1 which has been claimed as evidence of an ,interglacial period4 ,that it evidences a retreat of the ice-edge in that particular region is certain1 but that the climate became really temperate is very doubtful4 ,more probably it corresponds to the ,gunz-,mindel 8interglacial0 of the ,alps1 and was formed when the ,cordilleran ice-sheet was retreating1 but before the ,keewatin sheet had reached its maximum4 ,the ,aftonian stage was followed by the ,kansan glaciation1 when the ice-sheets reached their maximum area over the greater part of ,north ,america4 ,the chief centre of glaciation at this stage was the ,keewatin1 west of ,hudson ,bay4 ,while it is certain that the ,keewatin centre reached its maximum later than the ,cordilleran1 geological opinion in ,america is divided as to whether or no the two ice-sheets ever coalesced1 but it is difficult to understand how an independent ice-sheet could have grown up on the comparatively low ground of the ,keewatin centre4 ,most probably the course of events here was an exact parallel of that in the better-known ,scandinavian region--the ,cordilleran ice-sheet extended eastwards over the lower ground until a glacial anticyclone developed east of the ,rockies4 ,when this happened the supply of moisture to the western part of the ice-sheet fell off somewhat1 and the eastern part took on an independent life1 ultimately becoming the main centre of glaciation4 ,it was while these changes were in progress that the southern limit of the ice retreated northwards and the 8,aftonian0 deposits were formed4 ,the next stage 7,kansan7 occurred when the ice from the ,keewatin centre spread outwards in all directions1 and in the south reached the maximum limits of glaciation in ,america4 ,in the west this sheet overlapped on to the ground-moraine of the former ,cordilleran ice1 but the ,rocky ,mountains were too far away and too high for ,keewatin ice to dominate them and overflow them from east to west4 ,instead these mountains must have maintained an extensive glaciation of their own4 ,with the growth of the ,keewatin centre the ,labradorean also decreased1 but more slowly1 and this change was not associated with a retreat of the southern ice-edge1 so that there was no corresponding 8interglacial0 in the east of the ,united ,states4 ,the moraines of these older glaciations resemble those of the early ice-sheets of ,europe in presenting only featureless level surfaces of boulder-clay without morainic ridges1 lakes and the other characteristics of ice-bearing surface detritus1 and there is no doubt that conditions at the southern edge were similar--the climate was severe in winter1 but not insupportable in summer4 ,at the same time it was decidedly more severe than the present1 even as far south as ,florida1 where there are colonies of northern plants1 which migrated southwards during the ,ice ,age1 still living on local cold slopes with a northerly aspect4 ,after the maximum of glaciation the disappearance of the ice took place gradually and chiefly by ablation1 for there are none of the extensive river gravels and flood terraces which we should find had the melting been rapid4 ,it is only in the valleys of the ,rocky ,mountains that such deposits occur1 testifying to conditions such as obtained in the ,alps4 ,the succeeding ,yarmouth stage of deglaciation was very long1 corresponding in this respect to the ,mindel-,riss interglacial of ,europe4 ,the ,kansan moraine was weathered to a depth of ten or twenty feet1 and four-fifths of its surface was removed by the erosion of streams and rivers4 ,in the mountain districts the side streams which had been left occupying 8hanging valleys0 by the over-deepening of the heavily glaciated main valleys1 had time to cut out uniformly graded broad ,v-shaped valleys descending to the level of the main stream4 ,in the ,great ,basin also1 where the periods of high water-level are considered to correspond to the main glaciations1 the interval of low water corresponding to the ,yarmouth stage was very long4 ,a rough estimate of its length is about #bjj1jjj years--somewhat shorter than the ,mindel-,riss4 ,actually1 though the ,kansan and ,mindelian glaciations were approximately contemporaneous1 the subsequent recurrence of glaciation in ,america appears to have preceded slightly that in ,europe4 ,of the climate of this stage we have unfortunately little evidence4 ,old land surfaces of this age are known1 containing deposits of peat and bones of the wood rabbit and common skunk1 but both of these animals have a wide range4 ,perhaps the climate resembled the present during most of the period2 there is no evidence that it was ever warmer1 and it appears quite likely that ice-sheets maintained their existence in the far north through the whole of this stage4 ,after this interglacial there set in a period of renewed elevation in the ,rocky ,mountains and in the ,labrador-,newfoundland centres1 which brought about a recurrence of the glaciation4 ,in the ,rocky ,mountains the ice was not so thick as in the preceding stage1 but all the valleys were occupied to a considerable depth and the ice spread out to the eastward4 ,the ,labrador ice-sheets also developed again1 forming the ,illinoian glaciation1 the moraines of which are found as far west as ,illinois1 but no moraines are known of this age due to the ,keewatin ice-sheet4 ,the latter developed later1 and is classed by some ,american geologists as a separate glaciation1 the ,iowan1 which is only certainly found in northern ,iowa1 but may be represented further east by a thin sheet of boulder-clay overlapping the ,illinoian moraine4 ,the supposed interglacial between the ,illinoian and ,iowan1 the 8,sangamon ,stage10 is represented only by land surfaces formed of the ,illinoian moraine and covered by the loess or locally by the equivalent of the ,iowan moraine1 and there is no evidence that the ice-edge retreated far4 ,other ,american geologists1 including ,f4 ,leverett1 do not recognize the existence of a separate ,iowan glaciation1 and as the amount of weathering and denudation undergone by the two moraines differs very little1 this seems the more natural view4 ,the natural explanation seems to be that this was another case of 8glacial piracy10 the ,keewatin ice-sheet1 owing to its lesser snowfall1 developing more gradually1 and finally diverting the supply of moisture from the ,labradorean ice-sheet1 until it reached a maximum after the latter was already on the wane4 ,both these sheets of drift present similar flat features to the ,kansan sheet1 without morainic ridges4 ,leverett's interpretation of the succession is as follows3 ,the third 7,illinoian-,iowan7 glaciation was followed by a period of moist climate1 when peat-bogs were formed on level poorly-drained surfaces1 while elsewhere coniferous forests developed4 ,this was followed by a period of dry steppe-like conditions with a cold temperate climate1 when the great ,american loess sheet was deposited4 ,this loess sheet extends northwards1 overlapping the ,iowan moraine1 and in places passing under the ,wisconsin drift4 ,the material has come from the west1 and probably most largely from the dry plains east of the ,rocky ,mountains1 from which it diminishes in thickness eastwards4 ,but unlike ,europe this phase of steppe conditions was followed in ,america by a definite interglacial1 when the climate seems to have become rather warmer than the present4 ,in the northern ,states an old land-surface formed on the loess1 and1 termed the ,peorian stage1 is overlain by the ,wisconsin drift2 but near ,toronto1 on the shores of ,lake ,ontario and in the ,don valley1 the gap represented by this land-surface is partly filled by a remarkable series of lacustrine deposits known as the ,toronto stage4 ,the ,lake ,ontario beds indicate a climate slightly colder than the present1 but the ,don valley beds contain plants and animals living in the central ,states1 and refer to conditions more favourable than those now found in the district4 ,the duration of this interglacial has been worked out in a remarkable way by ,a4 ,p4 ,coleman1 who on the basis of wave-action estimated it as #fb1jjj years1 which agrees very closely with the #fj1jjj years found by ,penck and ,brckner in the ,alps4 ,this period was not long enough for streams in the 8hanging valleys0 to cut out uniformly graded valleys down to the main rivers1 and was consequently much shorter than the preceding interglacial4 ,the last glaciation of ,north ,america was the ,wisconsin1 which closely resembles the ,wurmian of ,europe both in its relations to the older glaciations and in the rough topography and unworn character of its moraines4 ,it extended within the limits of the ,kansan drift across fully two-thirds of the continent1 from ,nantucket and ,cape ,cod through ,long ,island1 northern ,new ,jersey1 ,pennsylvania1 southern ,new ,york1 ,ohio1 ,indiana1 ,illinois1 ,michigan1 ,wisconsin1 ,minnesota1 ,iowa and the ,dakotas1 ,manitoba1 ,saskatchewan and ,alberta4 ,at the same time the ,cordilleran centre probably bore increased local valley glaciers4 ,like the ,wurm glaciation1 the ,wisconsin was double4 ,the older moraines are well-marked1 and in places are covered by a foot or two of loess1 though this deposit reaches nothing like the thickness of that overlying the moraines of the earlier glaciations4 ,the moraine under this loess is very little weathered1 so that the time interval was very short2 possibly this loess is redistributed older loess associated with glacial east winds4 ,the ice of the first glaciation melted very slowly and there is very little gravel outwash to the moraines4 ,but 8after the ,wisconsin ice-sheet had reached a position a little outside the limits of the ,great ,lakes the retreat became much more rapid1 and large outwash aprons were formed from which valley trains of gravel led far down the drainage lines4 ,from this position 444 the moraines are practically free from loess-like silts40#d ,from this point onwards the glacial history of ,america is one of irregular retreat1 with occasional halts or even readvances resembling those of the ,scandinavian ice4 ,banded clays are found similar to those used so successfully by ,baron de ,geer in dating the retreat stages of ,scandinavia1 and this geologist has recently been investigating them1 but until his results are worked out no correlation with ,europe can be attempted4 ,a natural clock of another type is provided by ,niagara ,falls1 which are cutting their way back up the gorge at a rate which has been definitely ascertained4 ,taking into account the varying amounts of water which have passed over the falls at different stages of post-glacial geography1 the duration since the region became free of ice has been calculated at about #bj1jjj years1 which agrees closely with the time elapsed since the ,scandinavian ice-sheet left the ,north ,german coast4 ,before leaving ,north ,america it is necessary to give a brief account of the phenomena outside the main centres of glaciation1 and especially of the history of the ,great ,basin between the ,sierra ,nevada and ,wasatch ,mountains4 ,the lowest levels of this basin are at present occupied by several salt lakes without outflow1 of which the largest is the ,great ,salt ,lake1 the level of the water being determined by the balance between inflow of the rivers and evaporation from the surface4 ,twice in the past this balance has been decidedly more favourable1 and then the lakes grew to many times their present size4 ,the two greatest of these old lakes have been fully described under the names of ,lake ,bonneville 7of which the ,great ,salt ,lake is a vestige7 and ,lake ,lahontan1 further to the west4 ,the investigations have shown that before the ,glacial period1 and extending back into an unknown past1 there was a period of great aridity4 ,to this succeeded a long period of high water1 during which1 however1 neither of the lakes overflowed4 ,this stage was followed by a very long period of great aridity1 during which the lakes dried up completely1 and all their soluble matter was deposited and buried by alluvial material4 ,this period was followed by a return of moist conditions1 during which the water reached a higher level than before1 and in the case of ,lake ,bonneville actually overflowed into the ,snake river1 cutting a deep gorge4 ,this period1 however1 was shorter than the preceding moist period4 ,it was followed by an irregular fall interspersed with occasional slight rises1 but ultimately both lakes descended below their present level and probably again dried up completely4 ,both lakes suggest that this low level was followed by a third rise to a height very slightly above the present level1 followed by a slow fall in recent years4 ,the relations of the periods of high water to the glaciations are not clear in these large lakes1 but in the ,mono ,basin1 a small basin further west1 there is no doubt that the two were almost contemporaneous1 high water accompanying the maxima of glaciation and extending some way into the retreat phase4 ,the very long interval between the first and second period of high water1 several times that since the second period1 agrees with this correlation4 ,we find then that south-west of the main glaciated area there was a district of greater precipitation or less evaporation1 or more probably both4 ,this is confirmed by the valley moraines of all this region--,sierra ,nevada1 ,uinta and ,wasatch mountains1 ,medicine ,bow ,range of northern ,colorado1 etc41 all of which indicate two glaciations1 of which the first was the greater1 separated by a very long interval4 ,in several ranges the moraines of the second glaciation are double1 and some geologists consider that there were three ,glacial periods in these regions4 ,in the extremely arid region of ,arizona1 on the other hand1 which is considerably further south1 the evidence of the ,gila conglomerates indicates that while frost was very active1 the increase of precipitation1 though undoubtedly present1 was comparatively slight4 ,this shows that the climatic balance was not greatly disturbed1 the chief effect being an important lowering of temperature1 probably due to cold northerly winds4 ,the ,gila conglomerates are double1 separated by a period representing present-day conditions4 ,summing up the evidences of glacial climate in ,north ,america1 we find a striking similarity to ,europe4 ,in the north elevation and increased land area caused the development of large ice-sheets1 which appeared first in the mountainous regions with a heavy snowfall1 and later spread over the drier plains and plateaux of the interior4 ,this first glaciation was long and complex4 ,owing to the anticyclonic conditions which formed over the ice1 the rain- and snow-bearing depressions were forced to pass further southward1 causing greater snowfall on the mountains and high water-level in the lake basins4 ,this greater snowfall1 together with the cold conditions due to the existence of the ice-sheets to the north1 caused the development of mountain glaciers south of the main glaciated region4 ,in the east there were cold northerly winds which carried a severe climate as far south as ,florida4 ,this ,glacial period was followed by subsidence1 and a long spell of dry1 moderately warm climate lasting perhaps #bjj1jjj years1 after which elevation and glacial conditions again set in4 ,these conditions were not so severe as the first1 and their duration was much less1 while they were broken up by several intervals of temporary recession of the ice1 one of which1 corresponding to the ,riss-,wurm period1 lasted for #fj1jjj years1 and perhaps should be considered as an 8interglacial40 ,this period was marked in its early stages by the deposition of the curious olian deposit known as 8loess10 indicating steppe conditions4 ,after the last glaciation there set in a stage of irregular retreat4 ,,bibliography ,leverett1 ,f4 8,comparison of ,north ,american and ,european glacial deposits40 ,zs4 f4 ,gletscherknde #d1 #aiaj1 pp4 #bhj1 #cbc4 ,wright1 ,w4 ,b4 8,the ,quaternary ,ice ,age40 ,london1 #aiad1 ,chs4 #h-i4 ,attwood1 ,w4 ,w4 8,the glaciation of the ,uinta ,mountains40 ,j4 ,geol41 #ae1 #aijg1 p4 #gij4 ,henderson1 ,j4 8,extinct glaciers of ,colorado40 ,colo4 ,univ4 ,studies1 #c1 #aije1 p4 #ci4 ,gilbert1 ,g4 ,k4 8,lake ,bonneville40 ,washington1 ,u4,s4 ,geol4 ,survey ,monograph ,i1 #ahij4 ,russell1 ,i4 ,c4 8,the geological history of ,lake ,lahontan40 ,washington1 ,u4,s4 ,geol4 ,survey ,monograph ,,xi1 #ahhe4 ,coleman1 ,a4 ,p4 8,an estimate of post-,glacial and interglacial time in ,north ,america40 ,rep4 #ab ,internat4 ,congr4 ,geol41 #aiac1 p4 #dce4 ,,chapter ,,ix ,,central ,,and ,,south ,,america ,the scarcity of data which was bewailed in dealing with ,asia is still more marked in the case of ,south ,america1 and it will be necessary to present the glacial history of that continent in the barest outline only4 ,this is the more unfortunate as the chain of the ,andes1 extending from north of the equator to high southern latitudes1 is of enormous importance in glacial theory1 and especially in the question of simultaneity of glaciation in the two hemispheres4 ,the beginnings of glaciation in ,south ,america are obscure4 ,the distribution of animals shows that towards the close of the ,tertiary the ,falkland ,islands were greatly elevated and were united to ,tierra del ,fuego and ,patagonia1 and this enlarged land area was connected in some way with ,australia and ,tasmania1 but the mode of this latter connexion is not definitely known4 ,this question will be discussed more fully in ,chapter ,,xi2 it is sufficient to say here that the amount of elevation may have reached #ab1jjj feet in ,tierra del ,fuego4 ,equatorwards the elevation diminished1 and near the equator the land probably lay somewhat lower than now4 ,in ,south ,georgia the present glaciers greatly expanded1 until practically the whole island was buried in ice1 and the same is true of the ,falkland ,islands and ,tierra del ,fuego1 only the highest peaks remaining above the ice4 ,in the latter district there is some evidence of two glaciations separated by an interglacial1 the earlier glaciation being due to a regional ice-sheet and the later to smaller valley glaciers4 ,the intricate coast-line of the ,falkland ,islands and ,tierra del ,fuego points to fiord erosion by ice which extended well beyond the present limits of the land1 and can only have occurred during considerable elevation4 ,as to the character of the interglacial1 little is known4 ,in the ,falklands there is a bed of black vegetable soil full of tree-trunks1 indicating the existence of luxuriant forests and a temperate climate4 ,this deposit is overlain by boulder-clay1 and may be either interglacial or pre-glacial1 but since it was formed when the land stood at a comparatively low level1 while we have reason to believe 7see ,chapter ,,xii7 that during the close of the ,tertiary period these islands were greatly elevated1 it is probably an interglacial formation1 and indicates a great amelioration of climate4 ,in ,gable ,island1 ,tierra del ,fuego1 ,halle found beneath boulder-clay a ,quaternary fauna of barnacles and marine mollusca indicating a climate slightly warmer than the present1 and this probably belongs to the same period4 ,to the concluding stages of the ,glacial period in the ,falklands belong the curious 8stone rivers10 great streams of moss-grown boulders which fill the valleys1 and under the influence of temperature changes are probably still slowly advancing4 ,passing further north to the ,andes1 between #ci and #dd south latitude1 the glaciation was not so severe1 and its records are therefore clearer4 ,the first result of elevation was the cutting of deep canyons by the rivers4 ,this was followed1 possibly without much further elevation1 by a fall of temperature1 which in this connexion may be attributed to the extension of the ,antarctic and ,tierra del ,fuego ice-sheets4 ,glaciers now developed and spread down the canyons1 leaving moraines of great volume and height1 associated with all the other criteria of glaciation4 ,the snow-fields from which these glaciers originated lay between #ejjj and #fjjj feet above the sea1 and the snow-line lay at about #cjjj feet instead of above #fjjj as at present4 ,this glaciation was followed by a long interglacial1 during which the glaciers retreated to the highest summits of the ,andes4 ,the length of this period is indicated by the fact that the earlier moraines have been eroded to such an extent that they no longer present distinctly the typical features of glacial topography1 while the materials of which they are composed are decayed to somewhat the same extent as the older moraines of ,north ,america1 the granite boulders especially being rotten and friable4 ,this interglacial was followed by a re-development of the glaciers1 but to nothing like the same extent as formerly2 their moraines are smaller and fresh-looking1 indicating that this glaciation was comparatively recent4 ,still further north1 in latitude #bj-be ,s41 we come to a region of very slight snowfall1 where the snow-line lies higher than anywhere else on the face of the earth4 ,the glaciation here was comparatively unimportant1 the snow-line descending only #afjj to #bejj feet4 ,here ,keidel found moraines of three glacial advances1 and from his description it appears probable that the earliest and greatest was separated by a considerable interval from the two younger1 the interglacial between which was short and not characterized by a return to present-day climatic conditions1 since during this interval there was very little weathering4 ,probably we have here to do with two glaciations1 of which the second was double4 ,in fact1 some writers have described no less than five glacial advances in the ,argentine ,andes1 but most of these are probably merely retreat stadia4 ,in ,peru1 ,w4 ,sievers reports the existence of two glaciations separated by a considerable interval4 ,the present limit of the glaciers is about #ae1bjj feet2 during the first glaciation they descended to about #aa1jjj feet1 and during the second to #ab1hjj feet4 ,the evidence is very complete4 ,in ,ecuador1 ,h4 ,meyer records a similar bipartition4 ,the oldest glaciation is represented by trough-like valleys1 enormous gravel terraces1 and old moraines much weathered2 the limits are far below the present limits of glaciers1 but have been much obscured by subsequent erosion4 ,this glaciation was followed by a long period of steppe climate resembling the present1 during which the loess-like ,cangagua formation was deposited4 ,this in turn was followed by a readvance of the glaciers to a level about #bgjj feet below the present limit4 ,this glaciation is associated with crescent-shaped moraines1 corrie lakes1 hanging valleys and gravel terraces1 covered with vegetation1 but otherwise fresh-looking4 ,the snow-line lay about #afjj feet below the present4 ,probably during the first glaciation the ,andes were invaded by numerous mountain plants and animals related to ,north ,american forms--a valuable piece of evidence which indicates that the glaciation was contemporaneous with that in ,north ,america4 ,in ,columbia and ,venezuela there are traces of ,glacial periods1 but these have not yet been studied in detail4 ,the most northerly evidence of a ,glacial period comes from the ,sierra ,nevada de ,santa ,maria1 near the north coast of ,venezuela in #aa ,n4 ,except in ,tierra del ,fuego and ,patagonia the ice did not extend far from the mountains4 ,but in the eastern ,argentine there is a great series of ,quaternary deposits known as the ,pampean4 ,this formation covers #bjj1jjj square miles1 and consists of at least ninety feet of fine loam without a single pebble 7except for a few thin calcareous layers71 but containing large numbers of complete skeletons of mammals4 ,it raises several interesting problems4 ,apparently it represents the whole course of the ,glacial period4 ,by some geologists it is considered to be a delta deposit of the combined ,parana and ,paraguay rivers1 but the absence of mollusca1 except in a marine intercalation near its summit1 is against this view1 and ,steinmann attributes it to olian agencies and compares it to the loess of ,europe and ,north ,america4 ,if this view is correct the ,pampean represents steppe conditions prevailing on the equatorial side of the ,patagonia-,falkland ,islands ice-sheet4 ,apparently before the incoming of the greatest cold the ,pampas were in part at least forest-clad1 for in the older beds are found peculiar forms of ground-sloths which were adapted for forest life and have been found also in cave-deposits of ,brazil4 ,at the maximum of glacial conditions the ,pampas probably had a steppe climate1 but the disappearance of the forests is to be attributed rather to drought than to cold4 ,elevated glacier-bearing ,andes to the west and ice-sheets to the south would render the ,argentine extremely arid1 and this accounts for the gradual extinction of so many giant forms whose remains are found in the ,pampean deposits4 ,conditions ultimately became too severe even for the horse1 which died out in ,south ,america4 ,the marine transgression which left its mark near the top of the ,pampean is probably post-glacial4 ,in ,brazil1 on the other hand1 there is no evidence that the climate has ever been drier than the present1 and in the semi-arid regions of the north-east it is even probable that during the ,glacial period the climate was moister1 presumably owing to the greater strength of the rain-bearing east and north-east winds4 ,further west in the ,andes the existence of this wet period is borne out by the former greater size of ,lake ,titicaca1 and there seems to be additional evidence to the same effect in the ,chilian deserts4 ,,bibliography ,steinmann1 ,j4 8,diluvium in ,sdamerika40 ,zs4 d4 ,d4 ,geol4 ,gesellsch41 #eh1 #aijf1 p4 #bae4 ,meyer1 ,h4 8,in den ,hochanden von ,ekuador40 ,berlin1 #aijg4 ,sievers1 ,w4 8,reise in ,peru und ,ecuador1 ausgefhrt #aiji40 ,mnchen und ,leipzig1 #aiad4 ,keidel1 ,h4 8,ueber den ,anteil der ,quartaren ,klimaschwankungen an der ,gestaltung der ,gebirgsoberflche in dem ,trockengebiete der mittleren und nrdlichen ,argentinischen ,anden40 ,congr4 ,geol4 ,internat41 #ab1 ,canada1 #aiac1 p4 #geg4 ,willis1 ,bailey4 8,physiography of the ,cordillera de los ,andes between latitudes #ci and #dd ,s40 ,congr4 ,geol4 ,internat41 #ab1 ,canada1 #aiac1 ,p4 #gcc4 ,halle1 ,t4 ,g4 8,on ,quaternary deposits and changes of level in ,patagonia and ,tierra del ,fuego40 ,bull4 ,geol4 ,inst41 ,upsala1 #i1 #aijh-i1 p4 #ic4 ,,chapter ,x ,,africa ,the ,quaternary history of ,africa can unfortunately be dismissed in a very few words4 ,the glaciation of the ,atlas ,mountains has already been referred to in connexion with the ,mediterranean region4 ,further south we have no great mountain chain such as the ,andes extending above the snow-line over the whole extent of the country1 but merely a few isolated peaks4 ,three of these1 all close to the equator1 are known to show traces of a greatly extended glaciation in the past3 ,ruwenzori1 just north of the equator1 on the borders of ,uganda and the ,congo1 reaching an elevation of #af1gid feet1 with the present snow-line at #ae1jjj feet1 and glaciers extending to #aj1jjj feet1 formerly bore glaciers extending down as far as #ebjj feet2 ,kenya1 on the equator in ,kenya ,colony1 height #ag1jdj feet1 present snow-line about #ae1jjj feet1 past snow-line #ab1jjj feet1 and old moraines at #aj1jjj feet2 finally1 ,kilimanjaro1 #c ,s41 on the borders of ,tanganyika territory1 height #ai1cbj feet1 present limit of glaciers #ac1fej feet1 past limit #dhgj feet4 ,further south1 the ,drakensberg ,mountains1 between ,basutoland and ,natal1 were glaciated on their higher summits4 ,in none of these cases have the remains of more than one glaciation been described1 but the mountains are still very little known and this negative evidence is not conclusive4 ,in the neighbourhood of ,ruwenzori there are several peaks1 which approach #ab1jjj feet1 but these were not glaciated1 pointing to a snow-line above this level4 ,unfortunately the latter piece of evidence is of doubtful validity since these mountains are volcanic and possibly of post-glacial age2 we may consider1 however1 that the glaciation of the central ,african mountains was characterized by a great increase in the length of the glaciers with only a slight depression of the snow-line1 conditions showing that the glaciation was due chiefly to an increase of snowfall1 and only in a minor degree to a fall of temperature4 ,this conclusion is borne out by the low-level beds1 which nowhere show an appreciably lower temperature1 but abound in indications of a former greatly increased rainfall4 ,the first of these is the former greater size of the ,african great lakes4 ,abyssinia1 as we have seen1 was probably drier than at present1 but further south the rainfall must have been considerably greater4 ,lake ,kioga stood #fjj feet above its present level and was connected with ,lake ,victoria4 ,lake ,victoria and the smaller lakes were twice their present size1 and most of the broad valleys were filled with water4 ,lake ,magadi is the attenuated relic of a vast sheet of water1 and other great lakes have disappeared entirely4 ,one of these1 in the ,rift valley1 south of ,lake ,naivasha1 has been mapped by ,professor ,gregory and named after ,professor ,suess4 ,part of this decrease of the lakes has undoubtedly taken place within historic times1 and part may be attributed to changes in the drainage1 but there remains enough evidence to show that some time in the ,ice ,age the great lakes were very much larger than the present4 ,mr4 ,e4 ,j4 ,wayland1 the ,government ,geologist of ,uganda1 informs me that in the old basin of ,victoria ,nyanza there are masses of gravel which may be two or three miles in breadth1 the surface of which forms two terraces at different levels4 ,above the level of these is an old peneplain with ancient beach gravels4 ,mr4 ,wayland considers that this peneplain was formed probably during the ,pliocene by the first ,victoria ,nyanza occupying a basin between folds4 ,the initial high level was due to the want of an outlet1 but may have been amplified by other causes4 ,the level of the lake then sank gradually to a considerably lower level1 after which it rose again nearly to its old level and remained there for a considerable time4 ,during this period the great gravel deposits were formed2 they contain flood deposits1 especially near their base4 ,the level of the lake then sank again and this part of the basin was converted into a valley occupied by a river4 ,subsequently the level rose again sufficiently to carve out the lower terrace in the gravels4 ,mr4 ,wayland considers that the upper terrace may also represent a stage distinct from that in which the gravels were actually deposited1 but the upper terrace may be the original surface of the gravels4 ,thus there is evidence of two ,pluvial periods in central ,africa1 of which the first1 probably corresponding with the great extension of the mountain glaciers1 was the greater4 ,from the archological evidence it appears to correspond with the ,mindelian glaciation of ,europe4 ,a second line of evidence has been pointed out by ,c4 ,w4 ,hobley4 ,at the entrance to ,kilindi ,harbour1 ,mombasa1 there is a gap in the coral barrier through which the fresh water from the river finds its way4 ,these gaps are always found opposite the mouths of rivers1 and are due to the inability of the coral polyp to live in fresh or brackish water4 ,in ,pleistocene times the land stood some seventy feet lower relatively to the sea1 and the old channel through the reef at this height is almost double the width of the present channel1 showing that the river then had a greater volume1 i4e4 the rainfall in its basin was greater4 ,but ,africa is noteworthy chiefly for its deserts1 and the most important evidence of climatic change is found in the deserts of ,sahara and ,kalahari4 ,from the time of the ancient ,greeks it had been believed that the ,sahara was formerly the site of a great inland sea1 and the presence of this sea had even been suggested as the cause of the ,ice ,age in ,europe1 but recent investigations have shown that this is not so2 the ,sahara has been land at least throughout the ,tertiary period4 ,there is1 however1 abundant evidence that during the ,quaternary the rainfall was considerably greater than the present4 ,the presence of numerous animals closely associated with water1 such as the hippopotamus and even the crocodile1 in oases now entirely isolated1 shows that these oases were formerly connected with the big rivers4 ,the most definite evidence1 however1 comes from ,lake ,tchad4 ,this was formerly of much greater area1 but ,chudeau and ,freydenberg have made out a whole series of changes from desert conditions in the ,tertiary through pluvial conditions in the ,quaternary back to desert conditions of the present4 ,the sequence is as follows3 #a4 ,a regime of dunes4 #b4 ,a slow transgression causing a long marshy period1 during which numerous plants whose remains are found lived in the period4 #c4 ,a slow regression4 #d4 ,a rapid transgression 7grey loam74 #e4 ,a slow regression 7clayey white loam with traces of roots74 #f4 ,a transgression 7white loam74 #g4 ,establishment of a new dune regime4 ,in the ,chari basin east of ,lake ,tchad are the remains of fish and shells1 and also small pebbles of sandstone and chalcedony1 which are not local1 but must have been brought from the mountains of ,tibesti by the rivers ,egnei and ,toro when their current was much stronger than at present4 ,in ,senegal1 south of the #aeth parallel1 the present dune sands are underlain by an alluvial soil1 indicating moister conditions preceding the present climate4 ,there is no means of dating the moist periods indicated by these phenomena1 but it is reasonable to correlate them with the former extension of the central ,african lakes4 ,passing south to the ,kalahari1 we find evidence of a number of moist stages separated by drier intervals1 but they can apparently be grouped into two main ,pluvial periods1 separated by a long interpluvial with steppe-like conditions4 ,one at least of these ,pluvial periods must be correlated with the former immense extension of ,lake ,ngami and the ,etosha ,pan4 ,from ,cape ,colony1 there is some evidence of moister conditions in the past1 but the ,quaternary variations cannot be separated from those of historic times4 ,before leaving ,africa some reference must be made to an interesting suggestion by ,c4 ,w4 ,hobley1 as to the mechanism of climatic change in tropical countries4 ,he notes that the north-east and south-west monsoons extend to a height of only a few thousand feet4 ,above them are the very steady 8trade winds0 connected with the general circulation of the atmosphere4 ,in ,kenya ,colony these blow from east or a little south of east4 8,their effect is very marked on the high mountains of the interior1 such as ,kenya1 ,kilimanjaro and ,elgon2 in the early morning they are generally quite clear1 but about #aj a4m4 the clouds sweep up from the ,s4,s4,e4 and collect on the mountains and blot them out from view for the rest of the day4 ,these are believed to be clouds borne inland by the trade winds1 and the moisture they carry is precipitated mainly on the south and south-east sides of the mountains40 ,hobley suggests that there was formerly a nearly continuous ridge of high land extending north and south1 and this caught the moisture from the trade winds1 so causing the ,pluvial period1 the evidence for this ridge being the distribution of alpine plants on the now isolated high mountains4 ,an alternative explanation is that the greater strength of the earth's circulation during glacial times caused the trade winds to be much stronger and also to extend to a lower level at the expense of the monsoons1 just as the west winds extended to a lower level in northern ,egypt4 ,this would bring a great deal more moisture to be precipitated on the mountains1 increasing the length of the glaciers and also the volume of the rivers4 ,,bibliography ,scott ,elliott1 ,g4 ,f4 8,the geology of ,mount ,ruwenzori and some adjoining regions of tropical ,africa40 ,q4,j4,g4,s41 #ea1 #ahie1 p4 #ffi4 ,hobley1 ,c4 ,w4 8,the alleged desiccation of ,east ,africa40 ,geogr4 ,journ41 #dd1 #aiad1 p4 #dfg4 ,freydenberg1 ,h4 8,le ,tchad et le ,bassin du ,chari40 ,diss4 ,paris1 #aijh4 ,passarge1 ,h4 8,die ,kalahari40 ,,chapter ,,xi ,,australia ,,and ,,new ,,zealand ,the continent of ,australia has a relatively low relief1 only rising above the snow-line in ,mount ,kosciusko1 and glacial traces have a relatively unimportant development4 ,the history of the region appears to be as follows3 ,in late ,tertiary times the shore-line lay some distance to the east towards ,new ,zealand1 this being a relic of a much earlier connexion between the two lands4 ,towards the close of the ,tertiary earth-movements set in1 which elevated the mountain belt of eastern ,australia and formed a land connexion with ,tasmania and the ,antarctic continent4 ,at the same time the land to the east and the closed basins of central ,australia were also probably developed about this time4 ,the climate was then somewhat warmer than the present1 at least on the east coast1 for the ,australian barrier reef extended further south4 ,probably at this time the ,antarctic ice-sheet did not reach the sea1 and there was none of the floating ice which is such an important factor in cooling the ,southern ,ocean4 ,the next stage was the lowering snow-line on ,kosciusko to about #cjjj feet below the present and the development of extensive glaciers1 which descended to #eejj feet above the sea1 and attained an area of #hj to #ajj square miles and a thickness of at least #ajjj feet4 ,tasmania was also extensively ice-covered1 probably by glaciers which coalesced at low levels1 forming what is known as a 8piedmont0 ice-sheet1 which possibly reached the sea4 ,the lowering of the snow-line in ,tasmania is estimated as #fjjj feet1 corresponding to a fall in temperature of #ah ,f4 ,probably a large part of this fall is accounted for by the increased elevation1 which may have been several thousand feet in ,tasmania and more than a thousand feet even in ,new ,south ,wales4 ,this glaciation1 which was probably dependent on the growth of the ,antarctic ice-sheet1 was followed by a very long interglacial1 the duration of which has been estimated by ,professor ,david as #ajj1jjj to #bjj1jjj years4 ,the old moraines are much weathered and denuded1 resembling in this respect the older moraines of ,europe4 ,no information is available as to the climate of this interglacial period4 ,possibly some of the ,quaternary raised beaches with warmth-loving mollusca found in unglaciated parts of ,australia belong to this period1 and if so the climate was warmer than the present for at least part of the time4 ,the interglacial was followed by uplift and a second much less severe ,glacial period1 characterized by valley glaciers on ,kosciusko and in ,tasmania1 reaching the sea in places on the latter island4 ,it was at the close of this ,glacial period that man reached ,tasmania2 its conclusion is dated by ,prof4 ,david at about #aj1jjj years ago4 ,it was terminated by a period of depression below the present level with a warm climate4 ,in the dry interior of ,australia there is evidence that at one time1 probably during the maximum glaciation1 the rainfall was heavier than the present1 and numerous lakes were developed which have now been dry for a very long time4 ,it is possible that the artesian water supply of ,australia1 which ,gregory considers to be 8fossil water0 accumulated under different conditions from the present1 is a vestige of the rainfall of this period4 ,further north1 in ,java1 the beds in which the famous ,pithecanthropus skeleton was found1 believed to be lower glacial1 contain also plant remains similar to those now found in the ,khassian mountains of ,assam1 one of the rainiest climates in the world4 ,the climate of ,java during the maximum glaciation was thus decidedly rainier1 and probably somewhat cooler than the present4 ,an extraordinary find which may be referred to here is that of ,professor ,neuhauss1 who discovered giant erratics1 scratched and polished1 and moraines at sea-level at the western end of ,huon ,gulf1 ,new ,guinea4 ,the region is very unstable1 and is known to have stood at a very much higher level1 perhaps #aj1jjj feet or more1 in ,quaternary times1 and if the moraines indicate glaciers terminating at #aj1jjj feet above the sea they are explicable by a slight fall of temperature and increase of snowfall4 ,turning now to ,new ,zealand1 we find extensive glacial remains on ,south ,island1 though not on ,north ,island4 ,as in so many other countries1 the ,quaternary opened with great elevation1 which reached at least #aejj feet over the whole group4 ,north and ,south ,islands were united with each other1 with ,stewart ,island and probably also the outlying islands1 even including the ,chatham ,islands1 forming a great land-mass several times the present area of ,new ,zealand4 ,on the southern part of this land-mass extensive glaciers were formed2 on the east these did not reach the present sea-level1 but on the snowy south-west they extended far below it1 so that the terminal moraines are now completely submerged2 possibly they were never formed1 but the debris was floated away seaward on icebergs4 ,further north moraines are found near the present shore-line at many places between ,milford ,sound and ,hokitika1 and morainic mounds cover a large part of the low ground4 ,still further north they retreat inland1 and in the ,nelson ,province are not found below a level of #bjjj feet at the foot of ,lake ,rotoiti4 ,in the south-east a great moraine has been described at the south end of ,lake ,wakatipu and others at the north-east ends of ,lakes ,manapouri and ,te ,anau1 but none are found nearer the sea-coast4 ,the glaciated area of ,new ,zealand was at least ten times the present ice-covered area1 and the ,tasman1 the longest glacier in ,new ,zealand1 was expanded from its present length of #af miles to at least #cj miles4 ,much of the apparent fall of temperature shown by this glaciation was probably due to the great elevation1 but apart from this the ice had a marked influence on climate4 ,outside the limits of glaciation on the east is a thick deposit of typical loess1 which extends up to a level of #ajjj feet on the flanks of the hills4 ,the occurrence of this loess points to a steppe climate with dry1 cold1 southerly winds on the lee side of the glaciated mountains1 and is probably also connected with the increase of land area4 ,further north1 north of ,auckland in ,north ,island1 the present treeless plains were covered by forests2 for ,kauri gum1 apparently very old1 has been found4 ,the sub-antarctic islands--,campbell1 ,antipodes1 etc4--were not covered by either ,new ,zealand or ,antarctic ice1 but were the centres of local severe glaciations of their own4 ,the next stage was a great subsidence1 during which the glaciers retreated4 ,the land sank below its present level1 raised beaches probably of interglacial age being found at various heights ranging from #aj feet above the sea at ,manukau in the centre of ,north ,island to #aej feet at ,taranaki1 #bjj feet at ,cape ,palliser1 #djj feet on the west coast of ,south ,island1 #ejj feet at ,amuri ,bluff1 and even #hjj feet in the entrances to the south-western sounds4 ,this great submergence was associated with the deposition of extensive gravel deposits by the rivers4 ,the interglacial was followed by a second period of elevation4 ,it is not certain how far this went4 ,submerged peat-bogs have been found at a depth of nearly #fjj feet below sea-level near ,canterbury1 but these may belong to the early stages of the interglacial and not to the post-,glacial period4 ,on the other hand1 the submerged forests which are found at many points on the coast of ,new ,zealand are evidently post-glacial and indicate a slight rise above present level4 ,at the same time there was a renewal of the glacial conditions1 but the ice was confined to the valleys and had a much less extent than in the first glaciation4 ,this period seems to have been followed by a slight submergence and a temporary warm period4 ,,bibliography ,david1 ,t4 ,w4 ,e4 8,australasie4 ,les conditions du climat aux poques gologiques40 ,rep4 ,congr4 ,geol4 ,internat41 #aj1 #aijf1 pp4 #bge-ih4 ,sssmilch1 ,c4 ,a4 8,an introduction to the geology of ,new ,south ,wales40 ,sydney1 #aiad4 ,gagel1 ,c4 8,beitrge zur ,geologie von ,kaiser-,wilhelms ,land40 ,beitr4 geol4 ,erforsch4 deutsch4 ,schutzgebieten1 ,berlin1 #aiac1 ,h4 #d4 ,marshall1 ,p4 8,the glaciation of ,new ,zealand40 ,trans4 ,new ,zealand ,inst41 #db1 #aiji1 p4 #ccd4 ,salenka1 ,m4 ,l4 et al4 8,die ,pithecanthropusschichten auf ,java40 ,geol4 und ,palol4 ,ergebnisse der ,trinilexpedition 7#aijg und #aijh74 ,leipzig1 #aiaa4 ,,chapter ,,xii ,,the ,,glaciation ,,of ,,antarctica ,the great ,antarctic continent offers a unique problem to the glacial climatologist1 for here we have a land area with the theoretical snow-line already at sea-level1 and accordingly covered with a thick ice-sheet that leaves only a few mountain ranges and nunataks exposed above its surface1 and yet in the past these ice-sheets and glaciers have attained a thickness several thousand feet greater1 and have extended further north4 ,various suggestions have been made to account for this former extension1 perhaps the most remarkable being that it coincided with a milder and therefore snowier climate4 ,this1 however1 is untenable1 for the ,glacial period of ,graham ,land and the ,south ,orkneys is obviously a southward extension of the ,glacial period of ,tierra del ,fuego1 which was obviously due to a colder climate1 and can be traced northward along the ,andes into tropical regions4 ,a more fruitful suggestion is that as one of the most potent factors in preventing the accumulation of snow is at present the wind1 it was a decrease in the strength of the wind which enabled the ice to reach a greater thickness4 ,this is probably true in a sense1 the decrease of wind force being due to a great increase in the area of the ,antarctic continent during the ,quaternary4 ,we have seen that in the early ,quaternary there was great elevation in the south of ,south ,america and also in ,australia and ,new ,zealand4 ,the amount of this elevation increased southward and was very great near the polar circle4 ,this is borne out by considerations based on the distribution of living and fossil animals1 which point very definitely to a land connexion between ,australia and ,south ,america in ,tertiary and early ,quaternary times1 most probably by way of ,antarctica4 ,the first line of evidence is the distribution of the marsupials1 living and extinct4 ,as is well known the chief home of this type of mammal is now in ,australia and ,new ,guinea1 but in ,tertiary deposits in ,patagonia remains of extinct forms known as ,dasyurids have been found1 which are allied to ,australian forms1 and can only have come from ,australia1 probably via ,tasmania4 ,secondly1 there are two peculiar families of fresh-water fishes1 the ,haplochitonid and ,galaxiid1 the first common to ,australia and ,south ,america1 while one species of the second is found in ,new ,zealand1 ,tasmania1 the ,falkland ,islands and ,patagonia4 ,thirdly1 ,beddard has found an intimate relation between the earthworms of ,new ,zealand1 ,eastern ,australia and ,patagonia4 ,finally there is a curious similarity between the slugs of ,patagonia and those of ,polynesia4 ,what is the explanation of these relationships8 ,assuming that there has been a land connexion1 it can have been either by way of ,antarctica or ,polynesia4 ,the earthworms cannot endure a very severe climate1 but on the other hand there is a total absence of any tropical forms common to ,australia and ,south ,america1 and the general dissimilarity of the faunas shows that the connexion cannot have been available for a very long period4 ,a study of the oceanic depths suggests that the ,antarctic connexion is the more probable4 ,a comparatively slight elevation would connect ,patagonia and the ,falkland ,islands with the ,south ,shetlands and ,graham ,land1 and an elevation of #ab1jjj feet would give a large land connexion between ,australia and the opposite coast of ,antarctica via ,kerguelen4 ,forbes even postulates an immense ,tertiary ,antarctica in which several forms of animals and plants were able to evolve1 but except possibly in the case of the edentates this supposition is not necessary4 ,the course of events may provisionally be taken as follows3 ,in late ,tertiary times an elevation of at least #ab1jjj feet in the ,south ,polar regions caused a great increase in the area of ,antarctica1 which was united to ,south ,america on the one hand and ,australia on the other4 ,the northern shores of this continent were far to the north of their present position1 and though the interior was very cold the coast lands had at first a moderate temperature1 and for a short time allowed animals to migrate from ,australia to ,south ,america or vice versa4 ,but the high mountains of the interior were already glaciated1 and ice-sheets gradually crept down their slopes4 ,owing to the small precipitation the advance of the ice-sheets was slow1 but ultimately1 probably in late ,tertiary times1 they approached the coast1 and the track along which migrations had taken place was closed4 ,the distribution of animals and plants shows quite clearly that the land connexion was maintained into the period of refrigeration4 ,the shores of the continent being further north1 the pressure gradient between the pole and the present coast was less1 and consequently the winds were lighter4 ,this and the diminished loss by calving into glaciers allowed the ice to become thicker than it is now4 ,hedley apparently considers that the migrations referred to above took place in an interglacial period1 but the ,patagonian beds in which the fossil marsupials are found are ,tertiary and not ,quaternary4 ,no direct evidence of an interglacial period has been found in ,antarctica1 nor1 considering the intensity of the glaciation which the country is even now undergoing1 is any such to be expected1 and we can only infer from the bipartition of the ,glacial period in ,australia1 ,new ,zealand and ,south ,america--which1 in ,new ,zealand at least1 was associated with submergence--that there was probably a similar bipartition in ,antarctica4 ,nordenskjold states that the submarine relief showing river erosion which1 in ,tierra del ,fuego1 was developed partly at least in the interglacial period1 is also developed in ,west ,antarctica4 ,it is improbable that the ice ever entirely vanished from the continent4 ,we shall see in ,chapter ,,xiv that even the comparatively brief warm period known as the post-glacial climatic optimum extended to the ,antarctic coast1 and this is additional argument for extending the much greater interglacial oscillation southward beyond its known limits in ,tierra del ,fuego1 ,australia and ,new ,zealand1 but here the matter must be left4 ,,bibliography ,hedley1 ,c4 8,the palographical relations of ,antarctica40 ,london1 ,proc4 ,linnan ,soc41 #abd1 #aiaa-b1 p4 #hj4 ,lydekker1 ,r4 8,a geographical history of mammals40 ,cambridge ,university ,press1 #ahif1 pp4 #abe ff4 ,david1 ,t4 ,w4 ,e4 8,antarctica and some of its problems40 ,london1 ,geogr4 ,j4 #dc1 #aiad1 pp4 #fje-cj4 ,nordenskjold1 ,o4 8,antarktis40 ,handbuch ,regional ,geologie1 ,heft #ae1 #aiac4 ,,chapter ,,xiii ,,the ,,close ,,of ,,the ,,ice ,,age--,,the ,,continental ,,phase ,in ,chapter ,v we left the climatic history of northern ,europe at the point where the ice in its final readvance had once more reached the ,german coast4 ,but ,scandinavia was now sinking1 and the margin of the ice soon began to retreat again4 ,at the same time the ,alpine glaciers diminished in size1 while the ,irish and ,scottish glaciers disappeared4 ,this is the critical period in the change from glacial to temperate conditions1 and1 thanks to the researches of the ,swedish geologists1 and especially ,g4 de ,geer1 ,h4 ,munthe and ,gunnar ,andersson1 we are very well acquainted with it4 ,the change was not uniform2 at first the recession was very slow1 and there were periods when for scores of years the ice-edge remained stationary or even readvanced1 but on the whole the time was one of persistent amelioration4 ,the following description is based chiefly on ,w4 ,b4 ,wright's summary of de ,geer's work4 ,after leaving the coast of ,germany the ice-edge appears to have remained in the western ,baltic1 retreating slowly for some #hjjj years4 ,about #aj1jjj ,b4,c4 it lay along the southern coast of ,sweden1 and during the next #bjjj years it withdrew to about #ei ,n4 ,this was the ,gotiglacial stage4 ,here came a pause1 when1 for #bjj years1 about #hjjj ,b4,c41 owing presumably to a change for the worse in the climate1 the ice-edge remained in one position1 forming a great moraine4 ,then came another period of very rapid retreat1 the ,finiglacial occupying nearly #cjjj years1 followed by a further halt of some duration near ,ragunda1 about #ejjj ,b4,c4 ,after this the ice-sheet split into two portions1 and the ,glacial period is regarded as over4 ,in the ,alps there were similar periods of regression and of halting or readvance4 ,the first1 known as the ,bhlstadium1 corresponded to the ,baltic readvance 7,chapter ,v74 ,the second1 the ,gschnitz-stadium1 with a snow-line #bjjj feet below the present 7i4e4 mean temperature about #f ,f4 lower than now71 has not been dated1 but probably occurred about #hjjj ,b4,c4 ,this was followed by a warmer period1 probably as warm as and drier than the present1 after which the glaciers readvanced about #ejjj ,b4,c4 in the third or ,daun-stadium1 when the snow-line was depressed #ajjj feet 7temperature #c ,f4 lower than now74 ,in the lower ,nile valley the deposition of gravel ceased1 and that of mud began about #hjjj ,b4,c41 indicating that at this time the climate of north-east ,africa reached its present state of dryness4 ,it is at present difficult to give more than a tentative explanation of these oscillations of climate during the ,retreat ,phase4 ,northern ,europe was at the time passing through a complicated series of geographical changes4 ,as the ice left the ,baltic basin the latter became the site of a cold ice-lake1 with narrow outlets to the ,atlantic by way of the ,sound and the ,belts4 ,at this time the recession was slow4 ,then the retreat of the ice opened a connexion with the ,white ,sea1 and elevation closed the outlet to the west4 ,this probably made the waters still colder1 and the ,fennoscandian pause occurred4 ,elevation now closed the connexion with the ,white ,sea1 and an entirely closed-in ice-lake resulted4 ,during this stage the retreat was slow1 until between #gjjj and #fjjj ,b4,c41 when the ice-sheet vacated ,scania1 and direct communication between the ,baltic and the ,atlantic was opened across ,lakes ,wener and ,wetter1 and the climate1 though still arctic at first1 became appreciably warmer by #fjjj ,b4,c4 ,for more than #aj1jjj years of the retreat1 or until #fjjj ,b4,c41 the ice-sheet was still sufficiently large and powerful to maintain a border of ,arctic anticyclonic conditions on its southern edge4 ,during the retreat the mean annual temperature of southern ,sweden increased from #ag ,f4 to #ce ,f41 equivalent to a change from ,north-east ,greenland to ,south ,greenland4 ,the ,july temperature rose to about #dc ,f4 ,on the ,north ,german ,plain still lived the reindeer and the fauna and flora of the sub-,arctic tundras2 the mean annual temperature rose to #de ,f4 by the close of the period4 ,the land flora in ,sweden was entirely xerophilous1 indicating a slight rainfall4 ,there is also geological evidence of a small annual rainfall on the south-west coast of ,norway4 ,this period covers the transition from ,palolithic to ,neolithic culture4 ,it seems probable that the continental character of the climate of the final stages of the retreat phase was slightly increased by astronomical causes1 the obliquity of the ecliptic being probably nearly one degree greater about #gejj ,b4,c4 than it is now4 ,in ,germany and ,sweden this would have the effect of lowering the winter temperature and raising the summer temperature by rather more than #a ,f4 ,while the land was still falling rapidly in the north of ,scandinavia and the ,gulf of ,bothnia1 the coasts of ,germany and ,denmark began to rise1 and about #fjjj ,b4,c4 again closed#e the outlet of the ,baltic1 converting it into a large fresh-water lake1 the ,ancylus lake4 ,a similar lake was formed farther east in central ,finland4 ,at this time the south-west ,baltic lands stood more than #ajj feet higher than at present4 ,the land was probably still largely under the influence of dry easterly winds1 and the shutting out of the ,atlantic accentuated the continental conditions1 and this stage in the climatic history of ,europe is known as the 8,continental ,phase40 ,the winter climate was severe2 at first the summers were not especially warm 7,july temperature about #ed ,f4 in southern ,sweden74 ,this is probably the period of formation of the ,ragunda moraines1 and of a readvance of the glaciers on the ,norwegian side of the divide1 when the snow-line lay #bjj-cjj metres lower than at present2 it was also the time of the ,daun readvance in the ,alps4 ,but as the land sank in the north and rose in the south1 the waters of the ,ancylus lake retreated farther and farther north1 and the summers became hot and dusty1 with a mean ,july temperature of about #fj ,f4 ,everywhere in the ,baltic regions the older ,ancylus beds show a monotonous pine-wood1 but in the upper ,ancylus these are followed closely by a number of plants and shrubs of southern type--black alder1 curled birch1 linden1 etc4 ,the temperature continued to rise1 and oak1 ,norway maple1 ash1 and finally1 in the southernmost parts of ,sweden1 the common maple appeared4 ,the last-named plant has been found below the present level of the sea in ,ystad ,harbour4 ,under the influence of these conditions the remnant of the ,scandinavian ice-sheet again decreased in size1 until it split into two portions1 the break occurring at ,ragunda1 and this is considered by ,scandinavian geologists to mark the end of the ,ice ,age in ,europe4 ,gunnar ,andersson compares the climate of southern ,sweden at this time to the ,baraba ,steppes in western ,siberia1 with an annual rainfall of #ab to #af inches1 but this seems an extreme estimate4 ,the 8,karst0 flora of the limestone areas of south-east ,europe immigrated into eastern ,sweden during this period1 and south-east ,europe probably gives a better idea of the climate of ,sweden during the continental phase4 ,farther east1 in ,finland1 ,kupffer describes the climate as resembling that of central ,russia4 ,in central ,germany the climate was dry1 with a mean temperature in the four summer months of #fc ,f42 it resembled that of south-west ,russia4 ,this period of warm summers began earlier in ,germany than in ,sweden1 and throughout this phase ,scandinavia was occupied by a rich forest flora4 ,the hazel extended several degrees north of its present position1 and to higher levels1 indicating a ,july temperature about #g ,f4 higher than the present4 ,in southern ,norway the pine extended to much greater heights4 ,but the ivy and yew1 whose limits depend on the winter rather than on the summer temperature1 showed no such extension1 indicating that the winters remained severe4 ,in ,denmark there was a dry climate1 fairly warm at the close1 with fir forests1 though western ,denmark is now too wet for this tree4 ,on the coast of ,norway the seas were still cold1 so that there is a contrast between the animal life of the sea and the plant life of the land4 ,the ,alps also became warm and dry1 and were occupied by a xerophilous flora4 ,as the glacial anticyclone decreased in intensity1 depressions from the ,atlantic began to take a more northerly course1 but were held up near the ,british ,isles and materially increased the rainfall4 ,this is the first peat-bog period of these islands1 when the birch and pine forests which had covered the non-glaciated lands during the cold dry period gave way to extensive growths of peat-bogs4 ,southern and eastern ,england1 however1 largely escaped this damp period1 sharing in the dry climate of the ,continent4 ,the absence of storms off the north-west coast of ,norway is shown by the forests which at this period covered all the outermost islands of ,norway as far as ,ingo ,island1 off ,north ,cape4 ,these islands are now barren1 and their afforestation indicates a drier and especially a less stormy climate than the present1 with a decreased frequency of winds from the sea4 ,these conditions were well developed about #ejjj ,b4,c4 ,this is the ,early ,neolithic period4 ,owing to the great development of forests1 this period is sometimes called the ,early ,forest period4 ,the late-glacial history of ,north ,america was equally complicated4 ,consider first the region of the ,st4 ,lawrence ,estuary and the ,great ,lakes4 ,as the ,wisconsin ice-sheet retreated across the present site of the ,lakes1 the latter underwent a remarkable series of fluctuations of area and outflow1 which have been made the subject of brilliant studies by several ,american geologists4 ,the opening stage began when the ice abandoned the high ground south of the lakes1 leaving depressions bounded on the south by the hills and on the north by the ice4 ,the earliest of these in the basins of ,lakes ,erie and ,huron are known as the first and second ,lake ,maumee4 ,these gradually grew in size and coalesced1 forming several series of connected lakes1 to which various names have been given2 thus ,lake ,warren extended well outside the present limits of ,lake ,erie and southern ,huron1 and was held up by ice over ,lake ,ontario and northern ,huron4 ,at a later stage an enormous ,lake ,algonquin extended beyond the combined limits of ,lakes ,superior1 ,michigan and ,huron1 and communicated by broad channels with an enlarged ,lake ,ontario known as ,lake ,iroquois1 and with ,lake ,erie4 ,but even before this time the northern shores of the lakes1 relieved of the major portion of their ice-load1 had begun to rise rapidly1 and ultimately reduced the lakes to their present size4 ,these great areas of ice-cold water1 bathing the southern edges of the ice-sheet1 must have had an unfavourable influence on the climate1 keeping it cold and damp1 and preventing dry continental conditions from becoming established4 ,they probably retarded the ice-retreat in these regions quite considerably1 so that a lobe of ice was left here long after the edge had retreated northwards on either side4 ,at the same time the climate further south was dry1 with olian deposits2 but as the anticyclonic winds blew off the ,atlantic the evidence of drought is not so marked as in ,europe4 ,after this slow retreat had been in progress for a considerable time a submergence1 known as the 8,champlain stage0 set in1 reaching a depth of at least #fjj feet and opening the ,st4 ,lawrence regions wide to the ,atlantic1 which penetrated into ,lake ,ontario4 ,the ice now retreated rapidly under the influence of a maritime climate little colder than the present4 ,in phase this period corresponds to the second ,yoldia ,sea stage of ,scandinavia2 in point of time it was probably somewhat earlier4 ,this was followed by elevation1 the first result of which was to cut off the warm water and cause a sharp fall of temperature exactly analogous to that of the ,ragunda moraines1 but a few thousand years earlier and probably more marked4 ,the continuance of elevation brought on a long continental period of extreme aridity1 when trees grew on the peat-bogs of the eastern ,states1 while the lakes of the ,great ,basin further west were almost or wholly dried up4 ,at the maximum of the continental conditions the summers at least were warmer than at present1 as indicated by the northward extension of various species of plants and fresh-water mollusca4 ,the winters were probably more severe4 ,possibly the great aridity of this period was partly due to a sub-glacial continental anticyclone obstructing the path of depressions across ,america from west to east4 ,the drainage area of the ,great ,basin received hardly any rainfall and was a hopeless desert1 but the ,atlantic ,states were able to grow trees on the old peat-bogs1 probably with rainfall derived from the ,atlantic4 ,by reference to the cutting of ,niagara gorge1 we can infer that the warm dry period began about #fjjj ,b4,c41 so that it corresponds exactly with the continental phase 7,ancylus stage7 of ,europe4 ,this period of aridity was finally ended by a fresh submergence1 the 8,micmac10 which carried the land about twenty feet below its present level4 ,in ,yukon and ,alaska1 where the glaciation was not nearly so severe as further to the south-east1 the depression of the land by the ice-load and consequently the subsequent rise on its removal were not great4 ,there were no complicated geographical changes1 and correspondingly there appear to have been no fluctuations of climate1 but only a gradual passage to present conditions4 ,even in ,iceland there are indications of a dry period following the last glacial maximum1 for tree-trunks1 buried in the peat-bogs1 show that the birch formerly had a much greater extension4 ,it is also quite possible that there was an accentuation of desert conditions in ,asia during the retreat of the glaciers in ,europe and ,north ,america1 which may have played a part in the wave of ,neolithic migration that appears to have overwhelmed the artistic ,palolithic races of western ,europe2 but of this we have as yet no direct evidence4 ,the ,neolithic invasion of ,europe took place along two main routes1 the ,nordics passing from the centre of ,asia north of the ,caspian1 across ,russia to the ,baltic shores1 where they became the ,kitchen-midden people2 and the ,alpine race passing from ,transbaikalia1 south of the ,caspian and ,black ,sea1 into southern ,europe4 ,the ,nordics drove before them an older race1 characterized by the transitional ,maglemose culture1 which passed from east of ,russia to the shores of the ,baltic and ultimately to ,england1 where harpoons of ,maglemose type have been found beneath the peat of ,holderness4 ,in the southern hemisphere the continental phase does not appear to have been so well developed4 ,the uppermost part of the ,pampean loess is possibly post-glacial2 more certainly so are the sand-dunes on the coast near ,buenos ,aires1 in which human remains have been found in association with the bones of some extinct animals4 ,in ,new ,south ,wales1 after the retreat of the glaciers1 there was a period with land a little above its present level1 so that the stools of ,eucalyptus trees are now found ten feet below sea-level2 but there is no evidence as to the climate of this stage4 ,in ,new ,zealand we have no definite post-glacial beds of continental type4 ,the occurrence of xerophilous plants1 such as ,aciphylla1 still living in a climate which is now decidedly moist1 may be a remnant of a continental phase in ,new ,zealand1 or may date back to the steppe conditions of the loess4 ,as to ,antarctica1 we have1 of course1 no evidence4 ,,bibliography ,brooks1 ,c4 ,e4 ,p4 8,the evolution of climate in north-west ,europe40 ,london1 ,q4 ,j4 ,r4 ,meteor4 ,soc41 #dg1 #aiba1 p4 #agc4 ,wright1 ,w4 ,b4 8,the ,quaternary ,ice ,age40 ,london1 #aiad4 7,ch4 #ag1 ,late-glacial changes of level in ,north ,america47 ,bericht ,internat4 ,geologenkongress1 ,stockholm1 #aiaj4 8,die ,vernderungen des ,klimas seit der ,maximum des letzten ,eiszeits40 ,numerous papers1 dealing with ,europe and ,north ,america4 ,munthe1 ,h4 8,studies in the ,late-,quaternary history of southern ,sweden40 ,stockholm1 ,geol4 ,foren4 i ,forh41 #bb1 #aiaj1 pp4 #aaig-abib4 ,antevs1 ,e4 ,on the late-glacial and post-glacial history of the ,baltic4 ,geogr4 ,rev41 ,new ,york1 #ab1 #aibb1 p4 #eba4 ,,chapter ,,xiv ,,the ,,post-,,glacial ,,optimum ,,of ,,climate ,in most of the polar and temperate regions of the world the ,glacial period seems to have been separated from the present by a short interval of slightly more maritime climate4 ,the existence of this phase was the chief point brought out in the great collection of papers communicated to the ,stockholm meeting of the ,international ,geological ,congress1 which has frequently been referred to in this volume4 ,the pioneer work on the subject has been done by the ,scandinavian geologists1 and we may commence with a discussion of this period in the countries bordering on the ,baltic4 ,about #djjj ,b4,c41 at the conclusion of the continental phase referred to in the preceding chapter1 a rapid movement of submergence set in over the whole of the southern ,baltic1 and shortly afterwards the land-bar which had formerly separated the fresh waters of the ,ancylus lake from the ,atlantic gave place to a wide strait1 through which the waters of the ocean flowed into the ,baltic across southern ,sweden4 ,ultimately this channel became wider than the present outlet between ,sweden and ,denmark1 and maritime influences penetrated to all parts of the ,baltic4 ,in recognition of this influence the period was termed by ,blytt the 8,atlantic stage40 ,the much greater freedom with which the waters of the ,atlantic were able to enter is shown by a comparison of the 8isohalines0 of this period with those of the present day4 ,isohalines indicate the degree of saltness of the water2 those of to-day can1 of course1 be measured directly1 and show that in the ,gulf of ,bothnia the water becomes continually less salt as we go northward1 for which reason many species of marine mollusca are unable to live4 ,by studying the distribution of the mollusca in the ,littorina ,sea the isohalines of that period have been reconstructed also1 and show that the salt content was much greater than at the present day1 indicating a greater influx of oceanic waters4 ,if we take a map showing a reconstruction of the geography of ,littorina time1 and apply to it the formul given in the ,appendix1 comparing our results with the inferences of ,scandinavian and north ,german geologists as to the temperature1 we find that there is a remarkably good agreement4 ,many of the palo-botanists comment on the prolongation of the autumn into the present winter1 which is especially characteristic of a more insular climate4 ,the amounts of change in each case are also in good agreement1 except perhaps in the ,christiania region and in north ,denmark1 where the geologists require a greater change than that calculated from the land and sea distribution2 this is probably accounted for by a higher temperature in the waters of the ,atlantic4 ,the maximum change as calculated is shown in south-west ,finland 7winter #f ,f4 warmer1 summer #b ,f4 cooler74 ,finland is described as having at that time the climate of western ,europe1 which we may take as meaning winter #h warmer1 summer #c-d cooler4 ,there was thus a great change from the extreme climate of the continental phase with its hot summers and severe winters and little rain1 to an extremely temperate climate with cool summers1 mild winters and a heavy rainfall4 ,the warmth-loving plants which had begun to immigrate during the later part of the continental phase continued to spread1 and probably the highest average temperatures were reached at the time of maximum submergence1 but now they were accompanied by plants for which a large rainfall is necessary1 and it seems that the average rainfall of southern ,sweden must have been about #dj inches a year4 ,the oak began to dominate the forests in place of the hazel1 and the peat-bogs1 which during the preceding dry period had hardened into a firm surface on which birch and pine were able to take root1 again became moist1 so that the trees were choked by growths of bog-plants4 ,on the shores lived men of the ,transition and ,early ,neolithic4 ,as the land rose again and the ,littorina ,sea decreased in area the climate again became drier and more rigorous4 ,in ,denmark the forests of the ,ancylus period gave place to oak as the land sank1 and there are also remains of two water plants1 the water-nut 7,trapa natans71 which is no longer found in ,denmark1 and ,najas marina1 still living in one isolated locality4 ,northern ,denmark was broken up into islands1 among which marine deposits were formed1 containing the remains of southern mollusca1 many of which are found in the kitchen-middings4 ,most of the wood used by ,neolithic man was oak2 there is little fir and no beech4 ,in ,norway the work of ,c4 ,brgger has made us familiar with the ,tapes beds1 which correspond in point of time to the ,littorina stage of the ,baltic4 ,tapes decussatus is itself a southern species of mollusc1 and it is associated with a very rich warmth-loving fauna4 ,in southern ,norway the geographical conditions were different from those in ,sweden1 for the land reached its lowest level relatively to the sea about the close of the ,glacial period1 and has been rising throughout the post-glacial4 ,the seas show a progressive rise of temperature from #h ,f4 below present at the close of the ,glacial period to #d ,f4 above the present in the older ,tapes beds4 ,the littoral climate at this stage resembled that prevailing at present on the coast of northern ,england4 ,after this1 as the land approached its present level1 the temperature fell again1 and in the upper ,tapes stage was only #b ,f4 above the present4 ,the warm period represented by the ,tapes beds is found at intervals along the west coast of ,norway1 and we again find evidence of a submergence of the land contemporary with the maximum temperature4 ,these conditions extend even as far north as ,troms1 within the ,arctic circle4 ,in ,spitzbergen there are raised beaches #cj to #hj feet above the sea1 containing remains of molluscs and a species of ,fucus1 none of which are now living so far north4 ,on the land there are old peat-bogs of great thickness1 though peat-mosses cannot now grow1 since the ground never thaws below a depth of #f-aj inches4 ,it has been pointed out that a great number of the plants now living in ,spitzbergen are unable to ripen their seeds under present climatic conditions1 though they must have done so in the past4 ,ripe seeds of some species1 in fact1 have been found in the peat-bogs1 which are contemporaneous with the raised beach4 ,there is thus evidence of a very well-marked warm period associated with submergence in ,spitsbergen4 ,in ,franz ,josef ,land1 ,nansen found raised beaches with mussels #aj to #bj feet above the present level2 this shell does not now live so far north4 ,in the ,white ,sea and on the ,murman coast there are also raised beaches with a southern fauna4 ,the warm period shown in the beds of the ,new ,siberian ,islands has already been referred to 7p4 #gi74 ,returning to the ,british ,isles we find that in the south the land was above its present level throughout the whole of the post-glacial period4 ,on the other hand1 a #be-;foot beach is found in north-west ,england 7,formby and ,leasowe marine beds71 but without any evidence as to climate2 the same applies to the #be-;foot beach of ,scotland4 ,it is only when we come to the north-east of ,ireland that we find evidence of conditions appreciably warmer than the present1 in the section of the ,alexandra ,dock1 ,belfast1 where marine clays overlie beds of grey sand and peat4 ,the lower estuarine clay is essentially a littoral clay1 known as the ,scrobicularia zone4 ,it is brownish-blue and sandy1 and contains in abundance the roots and leaves of the grass-wrack 7,zostera marina71 and a vast number of shells of a few species which live between tide-marks1 indicating that the land stood #aj feet or so above its present level at first1 while the climate cannot have differed greatly from that prevailing at the present day4 ,it must have been formed during a period of gradual depression1 for throughout its six feet or more of thickness it preserves identical littoral characters4 ,after a time this depression became more rapid1 and the upper estuarine clay began to form--a light blue clay1 very pure and unctuous1 with a very rich and well-preserved fauna1 known as the ,thracia zone4 ,the fauna has a decidedly southern aspect1 and indicates that the coasts of north-east ,ireland had the present temperature of ,bantry ,bay--an increase of at least #c ,f4 in the mean annual temperature4 ,the ,thracia zone is followed by a bed of yellow shore sand1 indicating re-elevation to about seven feet above the present level4 ,corresponding to the upper estuarine clay are raised beaches at a height of #be feet in north-east ,ireland1 falling to #ae feet at ,dublin1 and to only #f or #g feet in western ,donegal and ,sligo4 ,the mollusca indicate a somewhat higher temperature than the present4 ,in the beaches have been found flint scrapers and arrowheads of early ,neolithic type4 ,looking further westwards1 we find that ,iceland1 which had undergone a slight elevation during the continental phase1 so that peat was formed below present sea-level1 again subsided1 falling to #aj or #ab feet below its present level4 ,during this subsidence the temperature rose1 the greatest warmth coinciding with the lowest level of the land4 ,species from the south-west shores1 where the temperature of the water is directly influenced by the ,gulf ,drift1 extended to the cold northern coast4 ,in some places the marine clays of this period have been ploughed up by a subsequent readvance of the glaciers4 ,from ,greenland comes abundant evidence of a post-glacial warm period coincident with a subsidence of about #hj feet4 ,raised beaches all along the west coast contain mollusca1 some species of which are not now living north of the ,st4 ,lawrence estuary4 ,on the other hand1 some northern species which lived off the west coast during the glacial maximum retreated northwards during this period1 and have not re-established themselves1 though the climate is now suitable4 ,further1 ,k4 ,steenstrup describes the occurrence of 8dead ice0 at several places in ,north ,greenland--masses of ice which have become separated from their parent glaciers owing to rapid recession1 and are now buried in morainic matter4 ,subsequently the ice again advanced1 and in some cases a new glacier has advanced over these masses of 8dead ice40 ,passing to the mainland of ,north ,america1 we find in eastern ,canada colonies of southern mollusca1 especially oysters and quohogs1 separated from their main area of distribution south of ,cape ,cod by a wide area of cold seas--the ,gulf of ,maine and ,bay of ,fundy4 ,at the beginning of the warm phase the land lay slightly below its present level1 but subsequently rose above it4 ,the climate became still warmer1 until its temperature resembled that of the middle ,new ,england ,states4 ,at the same time the rainfall diminished and the peat-bogs were replaced by forests of hardwood trees4 ,in the basin of the ,great ,lakes the warm period is represented by gravel beds in the ,niagara gorge1 which from their position must1 according to the most recent determinations1 have been formed about #djjj to #cjjj ,b4,c4 ,these gravels contain shells of fresh-water mollusca1 especially species of ,unio1 which are not now living in the ,st4 ,lawrence system1 but are found in tributaries of the ,mississippi further south4 ,further south on the eastern coast of the ,united ,states there are marine deposits indicating a slight submergence1 with a climate somewhat warmer than the present4 ,passing to ,south ,america1 we find in southern ,patagonia and ,tierra del ,fuego exactly similar evidence of a post-glacial subsidence with a warmer climate than the present4 ,raised beaches at a height of #ej feet contain mollusca1 some of which are now rare or extinct in that locality1 and in sheltered situations plants are found still living whose nearest neighbours are some way to the north4 ,in the same way1 in southern and eastern ,australia there are beaches a few feet above present level1 containing warmth-loving species of mollusca and indicating a post-glacial warm period4 ,there is some evidence in the distribution of plants and marine mollusca that this warm period extended to ,new ,zealand4 ,raised beaches at a height of #ej to #ahj feet are also known from many places in ,antarctica1 and these contain mollusca1 some of which are not now living south of the sub-antarctic islands4 ,an interesting confirmation of this has been given by ,e4 ,philippi1 from the results of an examination of the sea-floor at four points in about #fc ,s41 #ge-ie ,e41 all within the present limit of pack-ice4 ,the deposit at present forming is poor in pelagic foraminifera1 and consequently contains little lime1 but this deposit is very thin1 and beneath it is a much more calcareous clay especially rich in ,globigerina4 ,the latter deposit is still forming north of the limit of pack-ice1 and ,philippi concludes that at no very distant date the limits of ice were further south1 indicating warmer conditions4 ,it is interesting to note that a similar sequence has been found in the ,norwegian ,north ,sea1 the brown foraminiferous deposit 7in this case containing ,biloculina7 being known to be underlain as well as overlain by an unfossiliferous grey clay attributed to the ,glacial period4 ,finally1 with regard to ,cape ,colony1 ,a4 ,w4 ,rodgers says3 8,it is possible that the presence of marine mollusca belonging to species that are only known in the living state from the coast north of ,pondoland1 in the raised beaches of ,mossel and ,algoa ,bays1 indicates that the sea on the south coast was formerly warmer than now40 ,thus we have evidence of a period of submergence and climates warmer than the present from a large number of places1 including the ,arctic ,ocean and ,greenland1 the temperate coasts of ,north ,america and ,europe1 the ,southern ,ocean and ,antarctica4 ,the stage appears to be missing on the temperate coasts of the ,pacific1 on both the ,asiatic and ,north ,american sides1 and from the whole of the ,tropics4 ,it is fairly certain that the warm period occurred at the same time in eastern ,north ,america and western ,europe2 in the case of the southern hemisphere we have no direct proof of this1 but in all cases the deposits are comparatively recent1 and since they obviously refer to a similar state of affairs we may assume that they are of the same date4 ,in the ,baltic area we know that the great change of level was due largely to a subsidence of the land and only to a small extent to a rise of the sea4 ,but in other parts of the world the amount of submergence was remarkably uniform at places in the same latitude1 and decreased steadily from the polar regions to about latitude #dj-ej1 where it became zero4 ,now such a general change suggests that it was the sea which rose rather than the land which sank1 and points to some general cause which piled up the waters of the oceans in the higher latitudes4 ,a possible cause of this nature has been adduced by ,o4 ,pettersson1 which he terms the 8tide-generating force10 which reached one of its maxima in an #ahjj-year cycle about #cejj ,b4,c4 ,this possibility will be dealt with more fully in ,chapter ,,xvii4 ,,bibliography ,bericht ,internat4 ,geologenkongress1 ,stockholm1 #aiaj4 8,die ,vernderungen des ,klimas seit der ,maximum des letzten ,eiszeits40 ,numerous papers ranging from the ,arctic to the ,antarctic4 ,brooks1 ,c4 ,e4 ,p4 8,the evolution of climate in north-west ,europe40 ,london1 ,q4 ,j4 ,r4 ,meteor4 ,soc41 #dg1 #aiba1 p4 #agc4 ,praeger1 ,r4 ,ll4 8,report on the estuarine clays of the north-east of ,ireland40 ,proc4 ,r4 ,irish ,acad41 ser4 #c1 ,vol4 #b1 #ahib1 pp4 #bab-hi4 ,goldthwait1 ,j4 ,w4 8,the twenty-foot terrace and sea-cliff of the lower ,st4 ,lawrence40 ,amer4 ,j4 ,science1 ser4 #d1 ,vol4 #cb1 #aiaa1 pp4 #bia-cag4 ,cowles1 ,h4 ,c4 8,a remarkable colony of northern plants along the ,apalachicola ,river1 ,florida1 and its significance40 ,rep4 #h ,internal4 ,geogr4 ,congress1 #aijd1 p4 #eii4 ,shimer1 ,h4 ,w4 8,post-glacial history of ,boston40 ,amer4 ,j4 ,science1 ser4 #d1 ,vol4 #dj1 #aiae1 pp4 #dcg-db4 ,halle1 ,t4 ,g4 8,on ,quaternary deposits and changes of level in ,patagonia and ,tierra del ,fuego40 ,bull4 ,geol4 ,inst41 ,upsala1 #i1 #aijh-i1 pp4 #ic-aag4 ,sssmilch1 ,c4 ,a4 8,an introduction to the geology of ,new ,south ,wales10 ,sydney1 #aiad4 ,marshall1 ,p4 8,new ,zealand40 ,handbuch regional ,geologie1 ,heft #e1 #aiaa4 ,,chapter ,,xv ,,the ,,forest ,,period ,,of ,,western ,,europe ,hitherto we have been dealing with climatic changes which can be recognized with more or less certainty over most of the polar and temperate regions of the world1 but we have now to describe a stage which appears to have been peculiar to ,europe and possibly ,asia--the ,forest period4 ,by #cjjj ,b4,c41 or towards the close of the ,neolithic period1 considerable elevation had again taken place over the central latitudes of western ,europe 7the northern parts of ,norway and ,sweden were still several hundred feet below their present level74 ,the southern part of the ,british ,isles1 which had remained slightly elevated since the last ,glacial period1 had now emerged to a height of nearly ninety feet above its present level2 the area of ,ireland had increased appreciably and part of the ,north ,sea was land4 ,the geographical changes were not great1 but they were sufficient to turn the scale in the direction of a continental climate in the ,british ,isles4 ,the more or less complete closing of the ,straits of ,dover1 and the consequent bar to the free circulation of the ,gulf ,drift1 must have had an appreciable effect on the climate in the direction of continentality4 ,at the same time the low level of northern ,norway1 and possibly the persistence of warm conditions in the ,arctic basin1 more and more attracted depressions to the northernmost track1 so that the ,british ,isles especially1 and to a lesser extent ,holland1 ,germany1 southern ,scandinavia and ,russia1 came more persistently under the influence of anticyclonic conditions4 ,the rainfall of these countries diminished1 and the surface of the bogs dried sufficiently to enable forests to grow in the western countries2 in ,germany heath-plants took the place of bog-plants1 while in ,russia steppe conditions supervened4 ,the normal meteorological conditions at this time in fact resembled those of the memorable drought of #aiba1 which was characterized by low pressure and stormy conditions in the ,arctic ,ocean and a belt of high pressure and persistently fine weather across central ,europe4 ,during this phase the winters may have been severe1 but the summers were warmer than the present1 for in the peat-bogs of ,ireland and ,scotland are the remains of trees larger than any now found in the neighbourhood4 ,the ,irish bogs dried so completely that they were extensively inhabited2 corded oak roads have been found at this horizon1 while in #ahhc a two-story log house1 surrounded by an enclosure1 was found in ,drumkelin ,bog1 ,co4 ,donegal2 it was twelve feet square and nine feet in height1 and a roadway led to it across the bog4 ,both house and roadway were entirely constructed of oak4 ,with the hut were found a stone chisel and a flint arrowhead4 ,beneath the floor were fourteen feet of bog1 and above the floor twenty-six feet4 ,this time was also one of relatively little wind movement1 for stools occur even in exposed positions on the mountain slopes of western ,ireland1 where trees will only grow now in sheltered positions near sea-level4 ,further evidence of the very dry climate of this phase is the frequent occurrence of trees apparently in situ beneath the surface of fresh-water lakes1 both in ,ireland and ,scandinavia4 ,i was able to examine one very good example near ,lough ,toome in north-west ,ireland4 ,an unusually dry spring had lowered the surface of the water and a large number of tree-stools were exposed2 when these trees were growing the water-surface must have been at least two feet below the level of the present outlet4 ,most of the lakes in which these stools are found are shallow upland basins with a small drainage area1 and if the present climate became drier they would more or less completely disappear4 ,mr4 ,fairgrieve has noted the action of blown sand on the westward side of broken-off tree-stumps in a submerged forest on the shore in south ,wales1 which1 though not conclusive1 suggests dry conditions4 ,mr4 ,fairgrieve also noted the direction of fall of twenty-one trees1 and found that in the great majority of cases they were blown down by westerly winds4 ,the forest phase was short2 according to the late ,c4 ,reid the land again began to subside shortly after #cjjj ,b4,c41 and by #afjj ,b4,c41 in ,britain at least1 had reached its present level2 this carries us to the beginning of the ,bronze ,age4 ,in connexion with ,ellsworth ,huntington's theory that the dampness of ,ireland lowers the energy of its inhabitants1 it is interesting to note that this dry period apparently corresponds to the legendary ,heroic ,age1 when the vigour of the ,irish reached a level never since attained4 ,civilization in ,scandinavia also seems to have benefited by the drier conditions1 for ,scandinavian technique advanced rapidly to a high level about #ahjj ,b4,c4 ,but though there is evidence of a considerable sea-borne commerce with ,britain and ,ireland1 there appears to have been comparatively little land traffic between different parts of ,scandinavia at this time4 ,in fact1 to primitive man dense forest with thick undergrowth was almost impenetrable4 ,but at the close of the forest phase and the beginning of the peat-bog phase the trees were weakening under conditions becoming unfavourable4 ,such dying forests are marked by the absence of undergrowth and young trees1 and afford safe and easy land communication4 ,accordingly we find that by #aejj ,b4,c4 a considerable traffic had developed across ,scandinavia by land4 ,although we have no direct evidence1 the meteorological conditions suggest very strongly that the dry belt extended across ,russia into ,siberia as a marked period of desiccation1 possibly worse than any droughts of the historic period4 ,at present ,siberia receives its rainfall mainly from depressions which cross ,russia from the ,baltic or ,black ,seas1 and follow a well-marked track north of the central ,asiatic mountains4 ,but during the forest period these tracks were abandoned1 and the majority of the depressions passed north-eastward off the coast of ,norway into the ,arctic ,ocean4 ,the result must have been a great diminution of rainfall over the continent4 ,we shall see later 7,chapter ,,xix7 that this period of drought was of extraordinary importance in human history4 ,for during the moist maritime phase central and eastern ,europe1 and probably also ,asia1 had become extensively peopled by neolithic nomads of ,aryan and ,semitic races1 while the great river valleys of the south were in the possession of dense agricultural populations in a more advanced state of civilization4 ,as the climate became progressively drier and the pasture diminished1 the land was unable to support such a large nomadic population1 and there was a great outburst of raiding and conquering expeditions directed southwards and westwards1 resulting in a succession of empires in the rich ,mesopotamian regions and neighbouring countries1 which form the beginnings of our history4 ,the beginnings of history in ,china also1 about #bejj ,b4,c41 show that at this time the settled peoples of that country were in trouble with the nomads of the interior4 ,,bibliography ,reid1 ,c4 8,submerged forests40 ,cambridge ,university ,press1 #aiac4 ,lewis1 ,f4 ,j4 8,the history of the ,scottish peat-mosses and their relation to the ,glacial period40 ,edinburgh1 ,scot4 ,geogr4 ,mag41 #bb1 #aijf1 p4 #bda4 ,,chapter ,,xvi ,,the 8,,classical0 ,,rainfall ,,maximum1 #ahjj ,b4,c4 ,,to ,a4,d4 #ejj ,about #ahjj ,b4,c41 or the beginning of the ,bronze ,age in ,britain1 the subsiding land finally attained approximately its present level4 ,at the same time the climate of western ,europe deteriorated1 becoming much more humid and rainy1 and there set in a period of intense peat-formation in ,ireland1 ,scotland and northern ,england1 ,scandinavia and ,north ,germany1 known as the ,peat-,bog ,period or ,upper ,turbarian4 ,the peat-beds choked and killed the forests which had developed on the older peat-bogs1 and grew up above the stools and fallen trunks1 so that we have two layers of peat separated by an old forest4 ,the forest level contains neolithic articles1 the peat contains gold collars1 bronze swords and pins1 and other objects of the ,bronze ,age4 ,this growth also went on even over high ground1 which had not previously been covered by peat1 for ,professor ,henry informs us that on ,copped ,mountain1 near ,enniskillen1 and at other places in ,ireland1 ,bronze ,age cairns and tumuli are found resting on rock and covered by several feet of bog4 ,peat-beds on the ,frisian dunes between two layers of blown sand are dated about #ajj ,b4,c41 and some bogs in northern ,france were formed during the ,roman period4 ,there is also some much-disputed contemporary ,latin evidence that at the time of the ,roman occupation the climate of ,britain was damp and boggy1 while ,gibbon 78,decline and ,fall of the ,roman ,empire071 referring to the climate of central ,europe at the beginning of the ,christian era1 points to some evidence that the climate was colder4 ,this is1 that the ,rhine and the ,danube were frequently frozen over1 so that the natives crossed them with cavalry and wagons without difficulty1 although at the present time this never happens4 ,it is possible that this severe climate is referred to in the ,germanic legend of the 8,twilight of the ,gods10 when frost and snow ruled the world for generations4 ,the ,norse sagas point to a similar cold period in ,scandinavia4 ,this lapse of climate occurred in the ,early ,iron ,age1 about #fej to #djj ,b4,c41 when there was a rapid deterioration from the high ,scandinavian civilization of the ,bronze ,age4 ,this deterioration of culture was probably the direct result of the increased severity of the climate4 ,this ,pluvial period has been made the subject of special studies by ,ellsworth ,huntington in several important books and papers2 he finds evidence of a distinctly ,pluvial period in three regions--the ,mediterranean1 central and south-western ,asia1 and an area including the southern ,united ,states and northern ,mexico4 ,in the first of these1 the ,mediterranean1 ,huntington considers that the ,grco-,roman civilizations grew up in a period of increased rainfall which lasted from about #ejj ,b4,c4 to ,a4,d4 #bjj4 ,these states were able to develop in comparative peace because during this time there were no great invasions of nomadic peoples from eastern ,europe or central ,asia1 a fact which points to good rainfall in these comparatively dry regions1 so that their inhabitants had no need to emigrate in quest of a living4 ,in the ,mediterranean itself the heavier rainfall allowed a solid agricultural basis which produced a sturdy race of peasants who made good soldiers4 ,owing to the greater cyclonic control of climate and consequent changeable weather1 these inhabitants were more vigorous in mind and body1 for ,huntington's researches have demonstrated that long spells of monotonous weather1 either fine or rainy1 are unfavourable for human energy4 ,finally the heavier rainfall maintained a perennial flow in the rivers1 giving plentiful supplies of good drinking water4 ,these conditions broke down earlier in ,greece than in ,italy1 as the latter naturally has a heavier rainfall4 ,huntington considers that the decline of ,greece was largely due to malarial poisoning1 the decreasing rainfall causing the river-flow to break down in summer1 leaving isolated pools forming a breeding ground for mosquitoes4 ,after ,a4,d4 #bjj the climate of ,italy also deteriorated4 ,the decrease of rainfall1 combined with gradual exhaustion of the soil1 made wheat-growing more and more difficult for the small agriculturalist1 and the farms came into the hands of large landowners1 who worked them by slave labour1 and in place of wheat either grew vines or olives or raised flocks and herds4 ,the agricultural population gravitated to ,rome and a few other large cities1 and had to be fed by imported wheat4 ,the decline was probably aided by the introduction of malaria1 as in ,greece4 ,in north ,africa and ,palestine the question is more debatable4 ,c4 ,negro1 who has investigated the supposed desiccation of ,cyrenaica1 concludes that there has been no change of climate since ,roman times1 but a careful study of his evidence suggests that his conclusions are open to criticism4 ,all that he has proved is that there has been no marked progressive decrease of rainfall since about ,a4,d4 #bjj2 he has ignored the possibility of great fluctuations before and since that date4 ,in north ,africa it seems difficult to believe that the great cities of antiquity could have existed under present climatic conditions1 but when we turn to ,palmyra in the ,syrian desert we have practically incontrovertible proof in the great aqueducts1 built to carry from the hill-springs to the city large volumes of water which these springs no longer deliver1 so that even where they are intact the aqueducts now carry only the merest trickle4 ,in ,persia we find numerous ruins1 which point to a much greater population two thousand or more years ago4 ,this population lived by agriculture1 and the remains of their irrigation works are now found in regions where running water never comes4 ,even the scanty population of to-day can hardly live on the present rainfall of the country1 and it is unbelievable that the much greater population indicated by these ruined cities could have existed without a very much greater supply of water4 ,the same condition is indicated by the ruined cities of the great deserts of central ,asia4 ,these cities were inhabited by agriculturalists1 and the remains of tilled fields1 terraces and irrigation works abound in places where the supply of brackish water would now be barely sufficient for drinking purposes for such a large population4 ,huntington has also made a careful study of the water-level of the ,caspian ,sea in classical times1 and finds that there was a great period of high water extending from unknown antiquity to about ,a4,d4 #djj4 ,there is only one region in central ,asia where the population appears to have been less in classical times than now1 and that is the high basin of ,kashmir4 ,huntington points out that this basin is at present near the upward limit of agriculture1 and any fall of temperature and increase of snowfall would drive out the inhabitants4 ,but local legends point to such a period in the remote past1 corresponding to the period of increased habitability of the central ,asian deserts2 at its close there were extensive migrations from ,turkestan into ,kashmir4 ,passing to ,america1 we come to interesting evidence of a very different class--,i refer to the 8big trees0 7,sequoia7 of ,california4 ,since these trees live in a semi-arid climate1 the amount of rainfall is the chief factor in their growth1 which finds an expression in the breadth of the annual rings measured on the stump of the tree when it is cut down4 ,the method of utilizing the data was due to ,a4 ,e4 ,douglass4 ,a careful comparison was first made between the measurements of rings and the rainfall measured at neighbouring stations1 and a formula was developed by which the rainfall of each year could be reconstructed from the tree-growth with a high degree of accuracy4 ,in extrapolating to find the rainfall for earlier years before rainfall measurements began1 various corrections had to be applied1 for instance trees grow more rapidly when young than when they are old1 while trees which are likely to live to a great age grow more slowly at first than trees which die younger4 ,these methods were applied to nearly two thousand 8big trees10 some of which were found to be four thousand years old1 but it is pointed out that the corrections eliminate any progressive variation of climate which may have occurred1 so that the results show only 8cycles0 of greater or lesser length4 ,summing up1 ,huntington says3 8,judging from what we have seen of the rainfall of to-day and its relation to the growth of the ,sequoias1 high portions of their curve 7of growth7 seem to indicate periods when the winters were longer than now1 when storms began earlier in the fall and lasted later into the spring1 and when mid-winter was characterized by the great development of a cold continental high-pressure area1 which pushed the storms of the prevailing zone of westerly winds far down into sub-tropical regions and thus caused sub-tropical conditions to invade what is now the zone of equatorial rains40 ,neglecting later favourable periods1 which are relatively short and unimportant1 it is found that these conditions prevailed very markedly between #abjj ,b4,c4 and ,a4,d4 #bjj1 with maxima about #aaej ,b4,c41 #gjj ,b4,c41 and from #dej ,b4,c4 to #bej ,b4,c4 ,thus over the greater part of the temperate regions of the northern hemisphere we have evidence of an important rainy period between the extreme limits of #ahjj ,b4,c4 and ,a4,d4 #djj or #ejj4 ,this period was best developed from #abjj ,b4,c4 to ,a4,d4 #bjj1 and reached its maximum about #djj ,b4,c4 ,it constitutes a remarkable wave of climatic variation1 which is hitherto without adequate explanation4 ,a somewhat similar1 though less intense1 wave which occurred about ,a4,d4 #abjj-acjj1 and which is described in the following chapter1 was associated by ,wolf to a great outburst of sunspots which took place about ,a4,d4 #abjj4 ,it is well known that sunspots are an index of solar activity1 the sun's radiation being greater at times of spot maximum than at times of spot minimum4 ,greater solar radiation increases the evaporation over the oceans1 so that the air becomes more humid4 ,this moist air is carried by atmospheric currents over the land1 where the moisture is condensed into clouds and greatly increases the rainfall4 ,at the same time the cloud canopy shuts off some of the direct heat of the sun1 and we have the curious paradox that at times of sunspot maximum1 or greatest solar radiation1 the temperature of the earth's surface is lowest4 ,the connexion outlined above is1 however1 extremely problematical for temperate regions4 ,since the absolute sunspot maximum at ,a4,d4 #abjj is also very doubtful1 it will be realized that the evidence for the sunspot hypothesis of the medival rainfall maximum is extremely slender4 ,furthermore1 since we know nothing whatever about the solar activity during the classical rainfall maximum1 we are still less in a position to extend the sunspot hypothesis to that period also4 ,the interesting theory recently put forward by ,o4 ,pettersson1 already alluded to1 provides a plausible alternative explanation of the severe stormy climate of the ,peat-bog period1 which reached a maximum near #djj ,b4,c4 ,without going into details this theory is that the strength of the tides depends on the relative positions of the sun and moon1 and the tides are greatest when these act in conjunction1 and also when they are nearest to the earth4 ,this fluctuation of strength passes through various cyclic variations with periods of nine years1 about ninety years and about #ahjj years1 though the lengths of the periods are not constant4 ,the latter cycle is most important to our purposes2 according to ,pettersson's calculations the fluctuations of the 8tide-generating force0 were as follow3 ,maxima #cejj ,b4,c4 #bajj ,b4,c4 #cej ,b4,c4 ,a4,d4 #adcd ,minima #bhjj ,b4,c4 #abjj ,b4,c4 ,a4,d4 #ecj4 ,increased range of the tides means increased circulation in the waters of the oceans1 especially an increased interchange between the warm ,north ,atlantic and the cold ,arctic waters4 ,it also means than an unusual amount of ice is brought down from high into low latitudes4 ,wide local variations of temperature of the surface waters of the oceans cause increased cyclonic activity1 and hence we may expect a generally increased storminess at times of maximum 8tide-generating force10 and the reverse at times of minimum4 ,for the last maximum 7,a4,d4 #adcd7 ,pettersson is able to adduce a good deal of historical evidence of increased storminess in north-west ,europe and bad ice-conditions near ,iceland and ,greenland1 while ,huntington has found an increase of rainfall shown by the big trees of ,california4 ,the next preceding maximum1 that of #cfj ,b4,c41 marks the culminating point of the ,peat-bog phase4 ,the ,norse sagas and the ,germanic myths point to a severe climate about #fej ,b4,c41 which destroyed an early civilization4 ,this was the 8,twilight of the ,gods10 when frost and snow ruled the world for generations4 ,the period was the ,early ,iron ,age1 when civilization deteriorated greatly in north-west ,europe4 ,of the maximum of #bajj ,b4,c4 there is no trace4 ,it is possible that the great ,atlantic submergence of the ,maritime phase is connected with the tidal maximum of #cejj ,b4,c41 but the phenomena were on a scale so much greater than those of the more recent maxima that this can hardly have been the sole cause4 ,the minima should have been characterized by periods of relatively quiet stable climate with little ice near ,iceland and ,greenland4 ,that the last minimum1 in ,a4,d4 #ecj1 was such a period there is considerable evidence in the high level reached by civilization at that period in ,scandinavia and by the revival in ,ireland4 ,again1 about #abjj ,b4,c41 in the early part of the ,peat-bog phase1 there is evidence of considerable traffic by sea between ,scandinavia and ,ireland4 ,the ,irish ,museum has lately discovered a hoard of gold objects dated about #ajjj ,b4,c41 in which the designs show a ,scandinavian origin4 ,the minimum of #bhjj ,b4,c41 which occurred in the ,forest phase1 may have contributed to the dry climate of that period1 but otherwise has left no trace4 ,although at first sight the effect which ,pettersson sets out to explain seems out of all proportion to the smallness of his cause1 the coincidences after #bjjj ,b4,c4 are extremely interesting1 and suggest that after the land and sea distribution reached its present form the astronomical cause adduced by ,pettersson was possibly effective1 but before that date the astronomical cause1 if it existed1 was masked by the much greater climatic variations due to changes in the land and sea distribution4 ,the opinion has frequently been expressed that the 8,classical0 and 8,medival0 rainfall maxima were phenomena similar to the ,glacial period1 but less intensive4 ,this view is often carried to its logical conclusion1 that the thirty-five-year cycle1 the eleven-year1 and still smaller cycles of climate1 are also part of the same series1 and that the ,glacial period and1 let us say1 the three-year periodicity of rainfall are therefore due to variations of the same agent1 in this case the sun4 ,this logical extension of the theory is1 however1 completely untenable4 ,the eleven-year periodicity is admittedly connected with variations in the solar activity1 but there are other cycles which are completely independent of such variations1 such as1 for instance1 the annual variation undergone by all meteorological elements1 which depends entirely on the inclination of the earth's axis4 ,there is a well-marked #d4h year period in the amount of ice off ,iceland1 the half-cycle of which is exactly equal to the distance travelled by the water taking part in the ,north ,atlantic circulation1 divided by the velocity with which it travels4 ,there is1 therefore1 no a priori reason for assuming that the cause of the ,glacial period was identical with the cause of the ,classical and ,medival rainfall maxima4 ,further1 in the latter case1 the chief phenomenon was the increase of rainfall2 the decrease of temperature was merely incidental1 but in the ,glacial period the outstanding feature was a great lowering of temperature in the polar and temperate regions1 and in this case it was the increase of rainfall which was incidental4 ,,bibliography ,lewis1 ,f4 ,j4 8,the history of the ,scottish peat-mosses and their relation to the ,glacial period40 ,edinburgh1 ,scot4 ,geogr4 ,mag41 #bb1 #aiaf1 p4 #bda4 ,brooks1 ,c4 ,e4 ,p4 8,the correlation of the ,quaternary deposits of ,great ,britain with those of the ,continent of ,europe40 ,ann4 ,rep4 ,smithsonian ,inst41 #aiag1 p4 #bgg4 ,huntington1 ,ellsworth4 8,the pulse of ,asia40 ,boston and ,new ,york1 #aijg4 ----4 8,the climatic factor as illustrated in arid ,america40 ,washington1 ,carnegie ,institution1 #aiad4 ----4 8,world power and evolution40 ,new ,haven1 #aiai1 pp4 #ahf-bjg4 ,pettersson1 ,o4 8,climatic variations in historic and prehistoric time40 ,svenska ,hydrogr4-,biol4 ,komm4 ,skrifter1 ,heft #e4 ,,chapter ,,xvii ,,the ,,climatic ,,fluctuations ,,since ,a4,d4 #ejj ,the question of climatic changes during the historic period has been the subject of much discussion1 and several great meteorologists and geographers have endeavoured to prove that at least since about #ejj ,b4,c4 there has been no appreciable variation4 ,it is admitted that there have been shiftings of the centres of population and civilization1 first from ,egypt and ,mesopotamia to the ,mediterranean regions1 and later to northern and western ,europe1 but these have been attributed chiefly to political causes1 and especially to the rise of ,islam and the rule of the 8accursed ,turk40 ,recently1 however1 there has arisen a class of evidence which cannot be explained away on political grounds1 and which appears to have decided the battle in favour of the supporters of change2 ,i refer to the evidence of the trees1 explained in the preceding chapter4 ,the conclusions derived from the big trees of ,california have fallen admirably into line with archological work in central ,america1 in central ,asia and other regions1 and have shown that the larger variations even of comparatively recent times have been very extensive1 if not world-wide1 in their development4 ,let us consider first the evidence of the trees4 ,these indicate that after the moist period ending about ,a4,d4 #djj1 described in the preceding chapter1 the rainfall was generally light until about ,a4,d4 #ajjj1 when it showed a sharp rise1 probably to the level attained in ,a4,d4 #a4 7,the correction for age renders an exact comparison between periods a thousand years apart difficult47 ,this period of abundant rainfall lasted some fifty years1 followed by a gradual decline to a brief minimum1 shortly before ,a4,d4 #abjj4 ,about #acjj occurred another rapid rise1 reaching a maximum before #acej2 the period of heavy rain continued a short while after #adjj1 when a decline set in1 reaching a minimum at #aejj1 after which the rainfall recovered somewhat1 and subsequently maintained approximately its present level1 with a slight maximum about #afjj to #afde4 ,in the desert of ,arizona1 in regions at present too dry for agriculture1 there are abundant ruins1 which are attributed by ,huntington to three periods3 7a7 ,pueblo ruins1 dating back to just before the coming of the ,spaniards 7i4e4 about ,a4,d4 #afjj71 and indicating merely an increase of population at the present centres4 7b7 ,ruins of an older civilization1 termed by ,huntington the ,pajaritan1 during which numerous inhabitants lived in places where at present no crops can be raised4 8,these people1 as appears from their pottery1 their skulls and their methods of agriculture1 belong to a different civilization from that of the modern ,pueblos who inhabited ,gran ,quivera at the time of the coming of the ,spaniards4 ,they had evidently disappeared long before that date1 as is evident from the present ruins of their villages1 and from the absence of any hint of their existence in the early annals of the country0 7,geogr4 ,journal1 #dj1 #aiab1 p4 #cif74 ,the largest ruins of this type invariably lie near the main lines of drainage4 ,they consist of villages with houses of several storeys4 ,but digging down beneath these ruins we find 7c7 traces of an older occupation1 and ruins of a primitive type are also found on the plateaus remote from any except small valleys4 8,they are usually small1 and are greatly ruined1 and seem to belong to a time long anterior to the main large ruins40 ,huntington terms this type the ,hohokam2 unfortunately this and the ,pajaritan occupations cannot be accurately dated1 but it is reasonable to connect them with the rainfall maxima shown by the trees1 about the time of ,christ1 and in ,a4,d4 #ajjj to ,a4,d4 #acjj4 ,a similar succession has been found in the neighbourhood of ,mexico ,city4 ,the earliest trace of occupation is a crude 8mountain pottery10 in ordinary river sand and gravel4 ,these deposits are succeeded by finer sand with better pottery known as the 8,san ,juan0 type1 above which comes a culture layer with the remains of houses4 ,this is covered by a bed of 8tepetate10 a white calcareous deposit frequently found in dry regions where much water evaporates4 ,the gravels suggest the occasional heavy rains of arid countries4 ,the ,san ,juan pottery extends throughout the 8tepetate10 which probably corresponds to the dry period of ,a4,d4 #djj-ajjj in ,california4 ,historical records in ,mexico date back to the coming of the ,aztecs in ,a4,d4 #acbe4 ,they show that in #acbe and again in #addf the level of the lake of ,mexico was high1 but towards the end of the fifteenth century the water was much lower4 ,in #aebj it was high again2 in #afjj it was low1 but high from #afbi to #afcd4 ,from #afge to #agee was a long dry period4 ,on the whole the climate from #cjj to #fjj years ago seems to have been moister than that of to-day4 ,still further south in the ,peninsula of ,yucatan recent explorations have yielded results of extreme interest4 ,yucatan lies within the tropical rain-belt1 and is covered by almost impenetrable forests4 ,the climate is enervating and unhealthy1 and the present inhabitants are greatly lacking in vigour4 ,in the forest1 however1 have been found the ruins of ninety-two towns1 some of them of great size1 and all remarkable for the beauty as well as the solidity of their architecture4 ,these ruins belong to the great ,mayan civilization4 ,mayan history has been briefly summarized by ,huntington as follows3 8,first we have a long period of active development1 during which the calendar was evolved and the arts of architecture and sculpture were gradually developed4444 ,this time of marked growth must have preceded the ,christian era4 ,then comes 444 the building of the great cities of ,copan1 ,quirigua1 ,tikal and others4 ,these first great cities were in the southern part of the ,maya area1 on the borders of ,honduras or in eastern ,guatemala4 ,they lasted perhaps three or four centuries2 then quickly declined4 ,so far as we have any evidence1 civilization never revived in this southern area1 for the structures of the great period have not been rebuilt by later inhabitants4 ,towards the end of the period of greatness the centre of ,mayan culture moved northward4444 ,the great period1 according to ,bowditch1 lasted from #ajj ,b4,c4 to ,a4,d4 #cej 444 then came a time of very low civilization1 lasting for centuries4444 ,a revival ensued about ,a4,d4 #ijj or ,a4,d4 #ajjj1 and architecture once more reached a high pitch1 but 444 only in northern ,yucatan2 all the rest of the country seems to have remained in darkness4 ,moreover1 this medival revival was relatively shortlived4 ,since that time the condition of the ,mayas has fluctuated more or less1 but on the whole there has been a decline40 ,now at the present day the densest and most progressive population in ,yucatan is found in the driest part of the country1 where the forest gives place to jungle4 ,if the line of separation between jungle and forest were moved southward #cjj miles1 the former would include all the districts where ruins are now found4 ,we see from the above summary that the prosperous periods of ,mayan history were just those periods which in ,california were moist2 in ,yucatan they must have been dry4 ,huntington's explanation is the theory of the 8shifting of climatic belts02 during the rainy period in ,california the temperate storm-tracks were shifted further southward4 ,at the same time the sub-tropical high-pressure belt1 which at present lies over the ,west ,indies1 was also shifted southwards1 and this brought a dry cool winter to ,yucatan1 with an increased contrast of seasons1 and consequently a more invigorating climate4 ,in ,asia1 ,huntington and other explorers have found similar traces of past variations of climate1 a fascinating account of which is given in 8,the ,pulse of ,asia40 ,space will not permit of a summary in detail1 but the following general conclusions may be quoted3#f 8,if we omit the ,volga and the ,european portions of the ,caspian drainage area1 the limits 7of the six basins considered7 lie over sixteen hundred miles apart from north to south and over three thousand from east to west4 ,all this great area seems to have been subject to the same great waves of climatic change4 8,in the ancient days when the ,oxus ,river entered the ,scythian ,gulf of the expanded ,caspian ,sea1 and ,lake ,gyoljuk discharged permanently to the ,tigris1 the lake of ,seyistan had not been converted into dry land by the giants4 ,kashmir was so cold and snowy that agriculture was impossible4444 ,in the ,lop basin the rivers were full of water2 ,lop-,nor was the 8,great ,salt ,lake02 the desert was comparatively small and the zone of vegetation extensive2 and on all sides there was a density of population and a degree of prosperity far beyond those of to-day4 ,and in the ,turfan basin the same was probably true4 8,a great change took place throughout the six basins during the early centuries of the ,christian era4 ,the lakes of ,gyoljuk1 ,seyistan1 the ,caspian1 ,lop-,nor and presumably ,turfan were greatly reduced in size4 ,in the case of the first three1 parts of the old lake-beds were used as sites for villages4 ,except in ,kashmir1 the change of climate appears to have brought disaster4444 8,again there came a change 7about ,a4,d4 #gjj74 ,the process of desiccation gave place to a slight but important tendency toward increased rainfall and lower temperature4 ,kashmir became colder and more snowy1 and hence more isolated2 the rivers of ,lop and ,turfan gained greater volume2 and the lakes of ,lop1 the ,caspian and ,turfan expanded once more4 ,the habitability of the arid regions began to increase2 migrations came to an end2 and central ,asia was prosperous for a time4 ,finally 7about #acej7 a latest and slightest change took place in the other direction1 and we seem to-day to be in the midst of an epoch of comparative equilibrium1 with no marked tendency towards climatic change in either direction40 ,there was1 however1 a period of comparatively high water in the ,caspian in the early part of the seventeenth century4 ,in ,europe the evidence for climatic changes during historical times is more difficult to follow1 since variations of rainfall leave fewer traces in a moist than in an arid or semi-arid country4 ,a certain amount of material is given by ,brckner in his 8,klimaschwankungen40 ,he finds that there was a great advance of the ,alpine glaciers from #aeie to #afaj1 while two ,italian lakes without outlet1 the ,lago di ,fucina and ,lake ,trasimeno1 attained a high level about the same time4 ,other evidence for western ,europe is derived from the date of the wine-harvest and from the records of severe winters4 ,like the growth-curves of the big trees1 they need a secular correction to alter the general slope of the curve1 especially in the case of severe winters1 but the larger irregularities probably correspond to real variations of climate4 ,i have added in column #d the numbers of winters with sea-ice on some part of the ,danish coast1 as tabulated from the records compiled by ,captain ,c4 ,i4 ,h4 ,speerschneider4 ,the results are in general agreement with column #c1 particularly as showing that the period #adja-ej was relatively mild2 but the first half of the seventeenth century is less instead of greater than its two neighbours in this column4 ,the figures for the wine-harvest refer to the average for the period #ahaf-hj2 - indicates that the harvest was so many days earlier than normal1 corresponding to a high summer temperature 7,may to ,august74 ,the table shows that cold winters were especially numerous in the first half of the twelfth century and again in the thirteenth4 ,the end of the fifteenth century was marked by hot summers and mild winters1 or a warmer climate2 the beginning of the seventeenth century by cold 7presumably snowy7 winters and cool summers4 ,thus the periods of increased rainfall in the arid regions of ,asia and ,america were marked by a colder climate in the rainy regions of western ,europe4 ---------------------------------------- ------------ #a4 #b4 #c4 #d4 #e4 ,period1 ,date of ,no4 ,winters with #ej years ,wine of ,severe,ice on ,danish ,remarks4 about4 ,harvest4 ,winters4 coast4 ---------------------------------------- ------------ #hbe #d #hge #g #ibe #e #ige #f #ajbe #f #ajge #aj #aabe #ae ,cold winters #aage #aj #abbe #ac #abge #ac ,cold winters #acbe #ac #g #acge #aa #d #adbe #e #ac #g #adge #a #g #b ,warm #aebe #b4i #aj #e #aege #b4b #ad #ad #afbe #d4a #ag #aa ,cold #afge #b4g #ae #ad #agbe #j4a #aj #e #agge -#j4b -- #bb #ahbe -#j4i -- #ba ---------------------------------------- ------------ ,the date of the break up of the ,river ,dwina at ,mitau was recorded intermittently from #aecj to #agji1 and regularly since that date1 and the figures have been discussed by ,rykatchef4 ,recasting them in our unit of fifty years we find the mean dates to be3 ---------------------------------------- ---------------------- #aeea-afjj #afja-ej #afea-agjj #agja-ej #agea-ahjj #ahja-ej ,march #bi ,march #cj ,march #e ,march #bf ,march #bf ,march #bh ---------------------------------------- ---------------------- ,this again points to a cold period about the beginning of the seventeenth century4 ,the climate of ,iceland and ,greenland in the ,middle ,ages has been the subject of much controversy1 the view that there were extensive changes during that period being warmly upheld by one party and as warmly combated by the other party4 ,the case for climatic change has been well set out by ,o4 ,pettersson#g4 ,the ,roman authors 7,pliny1 ,solinus1 etc47 wrote that there was a frozen sea about ,thule 7,iceland71 but a party of monks who visited the island about ,a4,d4 #gie during the months of ,february to ,august1 in which the ice is normally most abundant in ,icelandic waters1 found the coast free1 though they met with a frozen sea a day's journey to the northward4 ,in the ninth century the ,norsemen visited ,iceland regularly1 and at times sailed round it1 apparently without interference from ice4 ,the early settlers practised agriculture with some success4 ,in the thirteenth century1 however1 the reports of ice off ,iceland became frequent--apparently the conditions were worse than those of the present day1 and much more so than in the eighth and ninth centuries4 ,according to ,rabot1 it appears from ancient records that considerable areas cultivated in the tenth century are now covered with ice4 ,the first spread of the glaciers took place in the first half of the fourteenth century4 ,in the fifteenth and sixteenth centuries the climate of ,iceland ameliorated somewhat1 but in the seventeenth there was a readvance1 which destroyed several farms about #afdj or #afej4 ,since then there has been a slight retreat4 ,the ice-conditions of ,greenland are closely related to those of ,iceland1 and the records of the ,norse colonization of ,greenland bear out the conclusions drawn from the latter island4 ,up to the close of the twelfth century ice is hardly ever mentioned in the accounts of voyages1 though it is now a great hindrance4 ,eric1 the pioneer explorer of ,west ,greenland1 spent three successive winters on the islands in ,juliaanehaab ,bay 7latitude #fj #de ,n471 and explored the country during the summer2 8this cannot be explained otherwise than by assuming that the ,polar ice did not reach ,cape ,farewell and the west coast of ,greenland in those days40 ,in the thirteenth century ice is first specifically mentioned as a danger to navigation1 and at the end of the fourteenth century the old ,norse sailing route was on account of ice definitely abandoned in favour of one further south4 ,shortly afterwards the ,norse colonies were wiped out by a southward migration of the ,eskimos4 ,even in ,norway itself the fourteenth century was a time of dearth1 short harvests and political troubles1 when corn had to be imported from ,germany instead of being exported to ,iceland as in former years4 ,it should be noted that ,pettersson's conclusions are considered invalid by ,h4 ,h4 ,hildebrandsson#h on the ground of the incompleteness of the records4 ,for the southern hemisphere our records are naturally much rarer and of less antiquity than for the northern hemisphere1 and until the tree-rings are investigated we cannot carry our study back beyond the sixteenth century4 ,from some researches into the municipal archives of ,santiago de ,chile1 latitude #cc ,s41 published by ,b4 ,v4 ,mackenna in #ahgg1 we can infer1 however1 that the general course of variation since #aebj was similar to that of corresponding regions in ,north ,america4 ,santiago lies in a semi-arid region where a temporary shortage of water is severely felt1 the average annual rainfall being only #cfd mm4 7#ad4c inches74 ,the early travellers1 however1 make no specific mention of drought1 and in #aedj ,pedro de ,valdivia crossed the desert of ,atacama with a column of troops and cattle without inconvenience--a feat which would be difficult nowadays4 ,in #aedd there were heavy rains and great floods in ,june4 ,the next record is for the year #afji1 recording another heavy flood on the ,mapocho1 which was repeated nine years later in #afah4 ,the first recorded drought occurred in the years #afcg to #afdj2 there was another flood in #afdg1 after which came a series of severe droughts interrupted by occasional floods1 which lasted until the close of the eighteenth century4 ,the first half of the nineteenth century was again comparatively rainy4 ,the records thus indicate a wet period centred about #afjj1 followed by a dry period during the eighteenth century1 exactly parallel to the records from the ,united ,states and ,europe4 ,,bibliography ,huntington1 ,e4 8,the climatic factor as illustrated in arid ,america40 ,washington1 ,carnegie ,institution1 #aiad4 ----4 8,the fluctuating climate of ,north ,america40 ,geogr4 ,j4 #dj1 #aiab1 pp4 #bfd1 #cib4 ----4 8,the pulse of ,asia40 ,boston and ,new ,york1 #aijg4 ----4 8,world power and evolution40 ,new ,haven1 #aiai4 ,pettersson1 ,o4 8,climatic fluctuations in historic and prehistoric time40 ,svenska ,hydrogr4-,biol4 ,komm4 ,skrifter1 ,h4 #e4 ,rabot1 ,ch4 8,essai de chronologie des variations glaciaires40 ,bull4 gogr4 historique et descriptive1 ,no4 #b1 #aijb4 ,brckner1 ,e4 8,klimaschwankungen seit #agjj0 444 ,vienna1 #ahij4 ,hildebrandsson1 ,h4 ,h4 8,sur le prtendu changement du climat europen en temps historique40 ,upsala1 ,nova ,actae ,regiae ,soc4 ,sci4 7#d71 ,vol4 #d1 ,no4 #e1 #aiae4 ,brooks1 ,c4 ,e4 ,p4 8,an historical notice of the variations of climate in ,chile40 ,washington1 ,dept4 ,agric41 ,u4,s4 ,weather ,bureau1 ,monthly ,weather ,rev4 #dg1 #aiai1 p4 #fcg4 ,,chapter ,,xviii ,,climatic ,,fluctuations ,,and ,,the ,,evolution ,,of ,,man ,the origin of man from an ape-like ancestor#i is generally admitted1 but owing to the incompleteness of the palontological record we are still in ignorance as to the circumstances1 while the place is generally put vaguely as somewhere in ,asia1 and the time as the late ,tertiary 7,prof4 ,elliot ,smith places it near the ,siwalik hills in the ,miocene74 ,for this early period we are reduced to speculation1 in which we may reasonably utilize the facts which we have gained about climatic variation4 ,the chief problem to be explained is why man's arboreal ancestor left the safe shelter and easy food supply of his primval forest and ventured forth into the plains4 ,an article by ,professor ,j4 ,barrell1#aj of ,yale ,university1 gives a plausible account of the change1 putting it down to necessity1 and not to choice4 ,his theory is that the human ancestor lived in the forests spread over ,asia1 then a vast well-watered plain1 during the middle-,tertiary period4 ,then the gradual uplifting of the ,himalayas and other mountain ranges caused a decrease in the rainfall of central ,asia1 so that ultimately the forests were unable to thrive1 and gradually gave place to steppe conditions4 ,the change was slow enough to give the less specialized inhabitants of the forest time to change their habits and evolve into forms suitable to a terrestrial life1 and the chief of the animals which took advantage of this period of grace was the pre-human4 ,forced to live on the ground1 with a diminishing food supply1 only the most progressive individuals were able to survive1 and evolution was rapid4 ,the changing type was saved from being submerged in the great mass of the original type in the forests which continued to exist further south by the impassable wall of mountains4 ,major ,cherry#aa considers that there is sufficient evidence to prove that a portion of this evolution took place on the seashore1 an environment which would have been much more favourable to a small ape-like animal than the open steppe would have been4 ,it is quite likely that the earliest migrations1 such as that which carried ,pithecanthropus to ,java1 took place along the shore4 ,but after a time1 when increasing brainpower and the use of primitive stone implements enabled man to take the offensive against the larger animals1 the centre of activity changed to the steppes4 ,a familiar view of the early development of man was advocated by ,w4 ,d4 ,mathew1#ab who writes3 8,in view of the data obtainable from historical record1 from tradition1 from the present geographical distribution of higher and lower races of men1 from the physical and physiological adaptation of all and especially of the higher races1 it seems fair to conclude that the centre of dispersal of mankind in prehistoric times was central ,asia1 north of the great ,himalayan ranges1 and that when by progressive aridity that region became desert it was transferred to the regions bordering it to the east1 south and west4 ,we may further assume that the environment in which man primarily evolved was not a moist tropical climate1 but a temperate and more or less arid one1 progressively cold and dry during the course of his evolution4 ,in this region and under these conditions1 the race first attained a dominance which enabled it to spread out in successive waves of migration to the most remote parts of the earth40 ,we do not know anything of the migrations of the ,eolithic and earlier ,palolithic races1 except that they spread rapidly over a considerable portion of the earth4 ,both migration and evolution1 especially mental evolution1 must have been accelerated by the great changes of climate which were taking place4 ,in the ,mindel-,riss interglacial period we know of two types1 the ,piltdown man 7,eoanthropus dawsoni7 and the ,heidelberg man 7,homo heidelbergensis71 the latter a true man1 though probably not on the direct line of evolution of ,homo sapiens4 ,the stress of the succeeding second ,glacial period was too great for ,eoanthropus1 which appears to have died out1 but ,homo1 probably an ,asiatic or ,african type similar to ,h4 ,heidelbergensis1 survived4 ,the next form1 associated with ,mousterian implements1 is ,neanderthal man 7,h4 neanderthalensis71 who closely resembled modern man1 and all the remains of races which lived subsequently to the last glaciation are those of modern man 7,h4 sapiens71 including the magnificent ,cro-,magnards and the negroid ,grimaldi race4 ,thus each glaciation has been marked by a step upwards in the scale of humanity2 does this mean that the coming of the super-man is contingent on another glacial epoch8 ,,bibliography ,barrell1 ,j4 8,probable relations of climatic change to the origin of the ,tertiary ,ape-man40 ,scientific ,monthly1 ,new ,york1 #d1 #aiag1 p4 #af4 ,mathew1 ,w4 ,d4 8,climate and evolution40 ,annals ,new ,york ,acad4 ,sci41 #bd1 #aiae1 p4 #bab4 ,london1 ,british ,museum4 8,a guide to the fossil remains of man44440 ,london1 #aiah4 ,,chapter ,,xix ,,climate ,,and ,,history ,it is a remarkable fact in human history that civilization began in regions which are at present inhabited chiefly by backward races1 and the centres of progress have shifted from one country to another with the passage of time4 ,many accidental factors--position on trade-routes1 possession of special mineral advantages1 and so on1 have undoubtedly played a part in this1 but it will not be difficult to show that climatic fluctuations have also had their share4 ,a brilliant study of ,ellsworth ,huntington#ac has shown that there are certain optimum conditions of climate which are most suitable for efficient work4 ,these conditions1 which were determined by an analysis of the output of work in ,american factories1 were then found to be just those which prevail in the most progressive regions of the globe1 which are located in the temperate storm-belts1 and it is shown in certain instances that fluctuations in the position of this storm-belt coincided with fluctuations in the centres of civilization4 ,a few additional examples of this may be given4 ,the beginnings of civilization may reasonably be placed with the transition from the ,palolithic to the ,neolithic type1 a transition which involved much more than just the polishing of stone weapons4 ,it involved also the beginnings of agriculture1 crude pottery1 and later1 the domestication of animals4 ,one of the earliest ,neolithic cities known is probably that of ,anau1 near ,askabad in ,transcaspia1 excavated by ,pumpelly in #aijd4 ,from the thickness of the accumulated debris the date of first settlement is placed at or before #hjjj ,b4,c41 i4e4 #aj1jjj years ago1 or during the period which in ,europe is assigned to the concluding stages of the ,wurm glaciation4 ,pumpelly's time-estimates are based on careful comparison with accumulations in ,merv and other cities4 ,at present the mean annual rainfall in that part of ,turkestan is below ten inches a year1 and the country is practically desert1 and is entirely unfitted for agriculture4 ,but with the remains of the ice-sheet still over ,scandinavia and depressions following a more southerly course along the ,mediterranean basin and into southern ,asia1 the rainfall was considerably heavier1 and the climate in general was more suited to a progressive race4 ,at the outset we find this ,neolithic race living in rectangular houses built of uniform sun-dried bricks2 they were skilful potters1 cultivating cereals1 but at first without domestic animals4 ,the beginning of ,neolithic civilization in ,crete is placed by ,evans at about #abjjj ,b4,c41 while on the basis of excavations by de ,morgan at ,susa in ,persia1 ,montelius places the origin of ,neolithic culture in this part of ,asia as early as about #ahjjj ,b4,c4 ,at ,susa the deposits are #acj feet thick1 and of these the upper #dj feet cover a period of #fjjj years4 ,thus we see that what may be considered as the great step from savagery to civilization took place while the present centres of progress in ,europe and ,america were still in the ,ice ,age4 ,at this time the climate of southern ,asia must have resembled the present climate of north-west ,europe in heavier rainfall and the day-to-day fluctuations of weather--in fact1 the districts where civilization began probably had at that time the most stimulating climate in the northern hemisphere4 ,with the vanishing of the ice-sheets and the setting in of the mild climate of the ,maritime phase the ,neolithic culture spread rapidly to ,europe1 and by #bjjj ,b4,c4 even the ,baltic regions were well inhabited1 and it is probable that the ,aryan race was developing in the ,russian steppes4 ,about this time ,anau was abandoned owing to increasing aridity4 ,with the coming of the ,bronze ,age in western ,europe1 about #ahjj ,b4,c41 however1 the climate again became colder and rainier1 corresponding to the ,peat-bog phase or 8,classical0 rainfall maximum1 the deterioration culminating in the ,early ,iron ,age4 ,this period was marked by a great southward spread of the ,aryan peoples1 and ushered in the ,heroic ,age of ,greece4 ,the races of the ,mediterranean1 as we have seen1 continued to thrive throughout this rainy period1 and their power did not diminish until its close1 about ,a4,d4 #djj4 ,this downfall was accelerated if not caused by the pressure of nomad peoples driven out of ,asia by the increasing drought4 ,these ,asiatic migrations included the great marches of the ,tartar hordes and1 aided by religious enthusiasm1 the conquests of the ,moslems4 ,the early ,middle ,ages1 after the downfall of ,rome1 appear to have been characterized by a dry warm climate4 ,this was the age of the ,vikings1 when the ,norse races rose to dominance in western ,europe1 finally invading and occupying large areas of ,france and ,britain1 and even extending their power to ,sicily4 ,with the increasing cold and wet of the 8,medival0 rainfall maximum came a final burst of ,norse migration1 which left the homeland poor and scantily populated1 and the centre of activity and progress lay once again with the ,mediterranean peoples1 and especially with ,italy and ,spain4 ,the ,tartar invasions ceased1 and against the increasing power of ,europe the ,moslem wave broke and receded4 ,at the close of this rainy period political dominance again moved north4 ,from that time the fluctuations of climate have been of minor importance1 and correspondingly there have been no great shiftings of political power from latitude to latitude4 ,,bibliography4 ,tyler1 ,j4 ,m4 8,the ,new ,stone ,age in ,northern ,europe40 ,london1 #aiba4 ,huntington1 ,ellsworth1 8,world ,power and ,evolution40 ,new ,haven1 #aiai4 ,haddon1 ,a4 ,c41 8,the wanderings of peoples40 ,cambridge ,university ,press1 #aiai4 ,,appendix ,,the ,,factors ,,of ,,temperature ,to calculate the probable temperature of ,january or ,july at any point1 the following procedure should be adopted3 ,draw a circle round the point of angular radius ten degrees 7i4e4 set the compass to cover ten degrees of latitude7 and divide this into two halves by a line passing from north to south through the centre4 ,by means of squared tracing paper1 or otherwise1 measure3 7a7 the amount of ice in the whole circle2 7b7 the amount of land in the western half2 7c7 the amount of land in the eastern half4 7a7 is expressed as a percentage of the area of the whole circle2 7b7 and 7c7 as percentages of the area of a semicircle4 ,the term 8ice0 includes ice-sheets such as that of ,greenland or ,antarctica1 and also frozen sea or sea closely covered by pack-ice2 the latter figure may vary in different months4 ,the temperature in ,january or ,july is then calculated from the following formula3 ,temperature basal temperature ice coeff4 x per cent4 of ice land west coeff4 x per cent4 of land to west land east coeff4 x per cent4 of land to east4 ,the basal temperatures and the appropriate coefficients are given in the following table4 ,in calculating the effect of a given slight change of land and sea distribution1 it is not necessary to employ the basal temperature4 ,instead the equation can be treated as a differential1 and the change of temperature due to the change of land and ice calculated from the figures in columns #c to #e4 ,the figures are given in degrees absolute1 #bgcj #cb ,f4 ,to convert differences to ,fahrenheit1 multiply by #ah4 ---------------------------------------- -------------- ,latitude4 ,basal ,temp4 ,ice ,coeff4 ,land1 ,land1 7,water ,zone74 ,west ,coeff4,east ,coeff4 ---------------------------------------- -------------- ,jan4 a4 #gj ,n4 #bih4h -#j4di -#j4dc -#j4bj #fj #bgg4d -#j4jg -#j4ca -#j4ja #ej #bgf4h -#j4ji -#j4bi #j4ji #dj #bhb4e -- -#j4ag #j4jd #cj #bhi4f -- -#j4jh #j4jc #bj #bid4b -- -#j4ja -#j4ja #aj #bih4f -- -#j4ja #j4jc #j #bii4c -- #j4ja #j4jj #aj ,s4 #bih4b -- #j4jd -#j4ja #bj #bif4b -- #j4jg #j4jj #cj #bic4e -- #j4jf #j4jc #dj #bhi4c -- #j4ji -#j4jc ,july4 #gj ,n4 #bgi4c -#j4af #j4jb #j4jb #fj #bhj4g -- -#j4ja #j4aa #ej #bhe4h -- #j4jd #j4jf #dj #bia4a -- #j4je #j4jg #cj #bif4h -- #j4jh -#j4ja #bj #big4f -- #j4jg #j4jb #aj #bih4h -- #j4jc -#j4ja #j #bih4f -- #j4jb -#j4ja #aj ,s4 #bif4i -- #j4jd -#j4jc #bj #bic4a -- #j4jb -#j4jb #cj #bhh4b -- -#j4ja -#j4ja #dj #bhd4j -- #j4jj -#j4jc ---------------------------------------- -------------- ,in the case of the calculation of the effect of comparatively slight and irregular changes in land and sea distribution in a limited area1 such as those of the ,littorina ,sea referred to on p4 #abh1 it may be found that a ten-degree circle is too wide an area to employ1 the changes from land to sea at one point being nullified by changes from sea to land at another more distant point4 ,in such a case a smaller unit such as a circle of five degrees radius can be employed4 ,as a rough approximation it may be said that the effect of the conversion of a square mile of land into sea1 or vice versa1 on the temperature of a neighbouring point is inversely proportional to its distance4 ,since the area of a five-degree circle is one-quarter that of a ten-degree circle1 while the average distance of the land composing it is one-half1 we have to divide our regression coefficients by two in order to fit the new data4 ,this method was applied to obtain the probable temperature distribution on the shores of the ,littorina ,sea at its maximum extension1 and gave results which agreed remarkably well with those calculated by geologists from the animal and plant life of the time4 ,see ,london ,q4 ,f4 ,r4 ,meteor4 ,soc41 #dc1 #aiag1 pp4 #afi-aga4 ,,index ,a4 ,acheulian1 #eb ,aciphylla1 #abe ,africa1 #ajc1 #acc1 #adb ,aftonian1 #hg ,,ahlmann1 #ea1 #fa ,alaska1 #dc1 #abd ,algonquin1 ,lake1 #abc ,alps1 dry period1 #abb glaciation1 #bi1 #eb1 #ef retreat stadia1 #aai ,altai ,mountains1 #gg ,anau1 ruins1 #afc ,ancylus1 #abj1 #abg ,,andersson1 #aah1 #aba ,andes1 #ih ,antarctica1 #aad1 #acc ,anticyclonic circulation1 #ee ,antipodes ,is41 #aab ,aral ,sea1 #hc ,argentine1 #ajj ,arizona1 #id1 #aej ,,arrhenius1 #ai ,artesian water 7,australia71 #aaj ,aryans1 #afd ,asia1 #gf1 #abe1 #aci1 #adc1 #aec ,astronomical theory1 #ag ,atlantic ,stage1 #abf ,atlas ,mountains1 #fi ,australia1 #aji1 #abe1 #aee ,b4 ,balearic ,is41 #gj ,balkans1 #fi ,baltic ,interstadial1 #fd ,banded clays1 #di1 #ic ,baraba steppes1 #aba ,barkans1 #fe ,,barrell1 #aei ,,beddard1 #aae ,belfast1 #acj ,biloculina1 #acc ,,blytt1 #abg ,bonneville1 ,lake1 #ic ,brazil1 #aja ,british ,isles1 #eg1 #fb1 #fd1 #acf ,,br,,gger1 #abi ,bronze ,age1 #ach ,,br,,ckner1 #di1 #eg1 #aed ,buenos ,aires1 sand-dunes1 #abe ,bhlstadium1 #aai ,c4 ,calabrian1 #fh ,cambrian1 #cc ,campbell ,is41 #ajb ,canada1 post-glacial1 #acb ,cape ,colony1 raised beaches1 #acc ,carbon dioxide1 #ai ,carboniferous1 #cd ,caspian1 #hc1 #adc1 #aec ,,chamberlin1 #ai ,champlain ,stage1 #abc ,chellean1 #ea ,,cherry1 #afj ,chile1 rainfall fluctuations1 #aeg ,china1 #ha1 #aci ,chronology1 #dh1 #ib ,,chudeau1 #ajf ,classical ,rainfall ,maximum1 #adj ,climatic ,record1 #acb ,,coleman1 #ib ,colorado1 #id ,continentality1 #be ,continental ,phase1 #abj ,continents1 movement of1 #ba ,cordilleran glaciation1 #hg ,corsica1 #fi ,,craig1 #gb ,cretaceous1 #cg ,crete1 ,neolithic1 #afc ,,croll1 #ah ,cro-,magnards1 #afa ,cyrenaica1 desiccation1 #adb ,d4 ,daun-stadium1 #aai ,,david1 #aaj ,dead ice1 #acb ,denmark1 continental phase1 #abb ,depressions1 path of1 #dg1 #fj1 #ga1 #abb1 #aci ,devonian1 #cd ,diluvium1 #dh ,don ,valley1 #ia ,,douglass1 #adc ,drakensberg ,mountains1 #ajc ,drought in ,forest ,period1 #aci ,drumkelin ,bog1 #acg ,dunes1 fossil1 #fe ,frisian1 #adj ,e4 ,early ,iron ,age1 #ada ,earth's ,orbit1 eccentricity of1 #ah ,earthworms1 #aae ,east ,anglia1 #dg1 #eg ,eccentricity of ,earth's ,orbit1 #ah ,ecuador1 #ii ,egypt1 #gb ,eoanthropus1 #afa ,eocene glaciation1 #cg ,etosha ,pan1 #ajg ,europe1 #di1 #ee1 #aah1 #abg1 #acf1 #aed ,,evans1 #afc ,evolution of ,man1 #aee ,f4 ,,fairgrieve1 #ach ,falkland ,is41 #ig ,fennoscandian ,pause1 #aai ,finiglacial1 #aah ,finland1 post-glacial1 #abj1 #abh ,florida1 #ie ,forest bed1 #dg1 #ea period1 #abb1 #acf ,forests1 submerged1 #acg ,formby and ,leasowe ,beds1 #acj ,fossil ice1 #ei1 #gh ,franz ,josef ,land1 #acj ,,frech1 #bj ,,freydenberg1 #ajf ,frisian dunes1 #adj ,fucino1 ,lago di1 #aed ,fucus in ,spitzbergen1 #acj ,g4 ,gable ,island1 #ih ,galaxiid1 #aae ,,geer1 ,g4 ,,de1 #di1 #ic1 #aah ,,geikie1 ,j41 #ea1 #ha ,geographical theory1 #bb ,geological formations1 #ca rhythms1 #ch ,,gibbon1 #adj ,gibraltar1 #fi1 #gj ,gila conglomerate1 #ie ,glacial anticyclone1 #ee stages1 #dh ,globigerina1 #acc ,glossopteris1 #ce ,gondwanaland1 #cd1 #ce ,gotiglacial1 #aah ,graham ,land1 glaciation1 #aad ,great ,basin1 ,america1 #hi1 #ic1 #abd ,great ,lakes1 history1 #abc ,great ,salt ,lake1 #ic ,greece1 ,heroic ,age1 #afd ,greenland1 #aca1 #aef ,,gregory1 #ajd ,grimaldi ,race1 #afa ,gschnitz ,stadium1 #aai ,gunz ,glaciation1 #ef ,gunz-,mindel ,interglacial1 #ej1 #ea1 #ef ,h4 ,haplochitonid1 #aae ,hazel1 post-glacial extension1 #abb ,,hedley1 #aaf ,heidelberg ,man1 #afa ,height and temperature1 #bf ,,hildebrandsson1 #aeg ,himalayas1 #ha ,,hobley1 #aje1 #ajg ,hohokam1 #aej ,,hume1 #gb ,,humphreys1 #bj ,,huntington1 #ada1 #add1 #aej1 #aec1 #afb ,i4 ,ice on ,danish coasts1 #aee ,iceland1 #abe1 #aef ,illinoian glaciation1 #ij ,ingo ,is41 forests1 #abb ,iowan ,glaciation1 #ij ,ireland1 glaciation1 #eg1 #fb1 #fd ,heroic ,age1 #ach ,iroquois1 ,lake1 #abc ,isohalines1 #abg ,j4 ,japan1 #ha ,jurassic1 #cg ,k4 ,kalahari1 #ajg ,kamchatka1 #hj ,kansan1 #hh ,karst flora1 #aba ,kashmir1 #adc1 #aec ,keewatin1 #hh1 #ia ,,keidel1 #ii ,kenya1 #ajc ,kilimanjaro1 #ajc ,kioga1 ,lake1 #ajd ,kitchen-midden1 #abe ,kosciusko1 #aji ,,kreichgauer1 #bj ,,kupffer1 #aba ,l4 ,labradorean ,glaciation1 #hg1 #hi1 #ij ,lahontan1 ,lake1 #ic ,lena ,valley1 #gh ,,leverett1 #ia1 #ib ,limestone ,agglomerate1 #gj ,littorina1 #abh ,loess1 #eb1 #hc1 #ia1 #aab ,lofoten ,islands1 #fa ,lop-,nor1 #hc1 #aec ,m4 ,,mackenna1 #aeg ,maglemose culture1 #abe ,malta1 #fi ,mammoths1 frozen1 #gi ,marsupials1 #aae ,,mathew1 #afj ,maumee1 ,lake1 #abc ,maya ruins1 #aea ,medival ,rainfall ,maximum1 #afd ,medicine ,bow ,range1 #id ,mediterranean1 #fh1 #adb ,mesopotamia1 ,empires1 #aci ,mexico1 culture1 #aea ,,meyer1 #ii ,micmac ,stage1 #abd ,mindelian ,glaciation1 #di1 #fi ,mindel-,riss ,interglacial1 #ej ,miocene1 #dd ,mombasa1 #aje ,mono ,basin1 #id ,,montelius1 #afc ,mousterian ,man1 #fc ,,munthe1 #aah ,,murgoci1 #ff ,murman coast1 #acj ,n4 ,najas1 #abi ,neanderthal ,man1 #afa ,,negro1 #adb ,neolithic1 #abb1 #aca1 #acf1 #afc migration1 #abe1 #afc ,neudeckian1 #ea ,,neuhauss1 #aaa ,newfoundland1 #hg1 #ij ,new ,guinea1 #aaa ,new ,siberian ,islands1 #gh ,new ,south ,wales1 #abe ,new ,zealand1 #aaa1 #abe1 #acc ,ngami1 ,lake1 #ajg ,niagara1 #ic1 #acb ,nile1 #gb1 #aai ,,nordenskjold1 #aag ,nordic ,race1 #abe ,norfolkian1 #ea ,north ,america1 #hf1 #abb1 #acb1 #ada1 #adi ,north ,sea1 #ef1 #fa ,norway1 #ea1 #ee1 #abi ,o4 ,obliquity of ,ecliptic1 #af1 #abj ,old ,red ,sandstone1 #cd ,optimum of ,climate1 #abg ,ordovician1 #cc ,p4 ,pajaritan1 #aej ,palmyra1 #adb ,pamirs1 #gg ,pampean1 #ajj1 #abe ,patagonia1 post-glacial1 #acc ,patom ,highlands1 #gh ,peat-bog ,period1 #adj ,,penck1 #di1 #ea ,pendulation ,theory1 #bj ,peorian1 #ia ,permian1 #ce ,persia1 #hd1 #adb ,peru1 #ii ,,pettersson1 #acd1 #ade ,piedmont ice-sheets1 #eg1 #aji ,piltdown ,man1 #afa ,pithecanthropus1 #afj ,pliocene1 #dg ,pluvial periods1 #ga1 #adj ,poles1 motion of1 #bj1 #dj ,pre-,cambrian ,glaciation1 #cc ,proterozoic ,glaciation1 #cb ,pueblo ruins1 #aej ,pulse of ,asia1 #aec ,,pumpelly1 #hd1 #afc ,pyrenees1 #eg ,q4 ,quaternary ,ice ,age1 #dg ,r4 ,ragunda1 ,lake1 #di moraines1 #aba ,,reid1 #ach ,retreat of the ,ice1 #di ,riss ,glaciation1 #di1 #fa ,riss-,wurm ,interglacial1 #ej1 #ec ,rixdorf1 #fb ,,rodgers1 #acc ,romania1 #ff ,ruwenzori1 #ajc ,s4 ,sagas1 #ada1 #adf ,sahara1 #gd1 #aje ,sangamon1 #ij ,scania1 #di ,,schmidt1 #ec ,scotland1 #eg1 #fa1 #fd ,scrobicularia ,zone1 #acj ,selsey1 #eh ,sequoia1 #adc ,shell-banks1 #dg1 #ef ,siberia1 #gh ,sicilian1 #gj ,sierra ,nevada1 #ic1 #id ,,sievers1 #ii ,silurian1 #cc ,skrumhede1 #fc ,slugs1 #aae ,,smith1 ,,elliott1 #aei ,solar radiation1 #ae ,south ,america1 #ig1 #abe1 #acb1 #aeg ,south ,georgia1 #ig ,south ,orkneys1 #aad ,,spitaler1 #ah ,spitzbergen1 #hj1 #acj ,stanovoi ,mountains1 #gi ,steppe climate1 #ec ,stone rivers1 #ih ,submerged forests1 #acg ,suess1 ,lake1 #ajd ,sunspots1 #ade ,susa1 ,neolithic1 #afc ,,sven ,,hedin1 #hd ,sweden1 #di1 #ef1 #aah ,syria1 #gb ,t4 ,tapes1 #abi ,tasmania1 #aji ,tchad1 #ajf ,tertiary1 #db1 #aaf ,thracia ,zone1 #aca ,tian-,shan ,mountains1 #gg ,tibet1 #hb ,tidal friction1 #ci ,tide-generating force1 #acd1 #ade ,tierra del ,fuego1 #ig1 #acc ,tillite1 #cb ,titicaca1 ,lake1 #aja ,toronto ,stage1 #ia ,trapa1 #abi ,trasimeno1 ,lake1 #aed ,tree-rings and rainfall1 #adc ,turbarian1 #adj ,triassic1 #cg ,,tyndall1 #ai ,u4 ,uinta ,mountains1 #id ,unio in ,niagara1 #acb ,ural ,mountains1 #eg ,v4 ,venezuela1 #ajj ,verkhoiansk ,mountains1 #gi ,victoria ,nyanza1 #ajd ,vikings1 #afd ,volcanic dust1 #af1 #bj ,,vollossovitsch1 #gi ,w4 ,wales1 #eg1 #fd ,warren1 ,lake1 #abc ,wasatch ,mountains1 #ic1 #id ,,wayland1 #ajd ,,wegener1 #bj1 #cd ,,wernert1 #ec ,white ,sea1 #acj ,wine harvest1 #aee ,winters1 severe1 #aee ,wisconsin ,glaciation1 #ia1 #ib ,,wolf1 #ade ,wurm ,glaciation1 #dh ,y4 ,yarmouth ,stage1 #hh ,yoldia ,sea1 #ej1 #abd ,yucatan1 #aea ,yukon1 #abd ,printed in ,great ,britain by ,jarrold ,sons1 ,ltd41 ,norwich4 ,,footnotes3 #a ,by this term we shall in future understand only that part of it which is responsible for thermal effects4 #b ,if the figure of the earth is adjusted to its speed of rotation before the development of ice-sheets1 the latter renders it too prolate1 and there will be a tendency for readjustment by the transference of mass towards the equator4 #c ,this has been the subject of much discussion recently4 ,for a summary see ,science ,progress1 #ag1 #aibb1 ,october1 p4 #bcc4 #d ,leverett1 ,f4 7see ,bibliography74 #e ,see reference to ,antevs in this connexion4 #f 8,the pulse of ,asia10 p4 #cef4 ,see also a new work by ,e4 ,huntington1 entitled3 8,climatic changes40 #g 8,climatic variations in historic and prehistoric time40 #h 8,sur le prtendu changement du climat europen en temps historique40 #i ,or lemur-like ancestor4 ,there is evidence to show that man's ancestor was a nocturnal animal1 whose food supply was governed by the phases of the moon4 #aj 8,scientific monthly10 ,new ,york1 #d1 #aiag1 pp4 #af-bf4 #aa 8,science progress10 #ae1 #aibj1 p4 #gd4 #ab 8,climate and evolution40 #ac 8,civilization and climate40 ,,transcriber',s ,,note ,obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources4 ,some hyphens in words have been silently removed1 some added1 when a predominant preference was found in the original book4 ,except for those changes noted below1 all misspellings in the text1 and inconsistent or archaic usage1 have been retained4 ,pg #fd3 #8powerful conviction' replaced by #8powerful convection4 ,pg #ig3 #8and ,tierra del ,fuega' replaced by #8and ,tierra del ,fuego'4 ,pg #ajc3 #8,drakenberge ,mountains' replaced by #8,drakensberg ,mountains'4 ,pg #aej3 #8modern ,pueblas who' replaced by #8modern ,pueblos who'4 ,pg #aff3 #8coffiecients are' replaced by #8coefficients are'4