,transcriber's ,note ,emphasized text denoted as ,italic and ,bold respectively4 ,cambridge ,natural ,science ,manuals4 ,geological ,series4 ,,the ,,principles ,,of ,,stratigraphical ,,geology ,london3 ,c4 ,j4 ,,clay ,,and ,,sons1 ,,cambridge ,,university ,,press ,,warehouse1 ,,ave ,,maria ,,lane4 ,,and ,h4 ,k4 ,,lewis1 #acf1 ,,gower ,,street1 ,w4,c4 ,illustration ,leipzig3 ,f4 ,a4 ,,brockhaus4 ,new ,york3 ,,the ,,macmillan ,,company4 ,bombay3 ,e4 ,,seymour ,,hale4 ,,the ,,principles ,,of ,,stratigraphical ,,geology ,,by ,j4 ,e4 ,,marr1 ,m4,a41 ,f4,r4,s4 ,,fellow ,,and ,,lecturer ,,of ,s4 ,,john',s ,,college1 ,,cambridge1 ,,and ,,university ,,lecturer ,,in ,,geology4 ,,cambridge3 ,,at ,,the ,,university ,,press4 #ahih ,all ,rights reserved4 ,cambridge3 ,,printed ,,by ,j4 ,c4 ,f4 ,,clay1 ,,at ,,the ,,university ,,press4 ,,preface4 ,the present work has been written in order that students may gain by its perusal some idea of the methods and scope of ,stratigraphical ,geology4 ,i believe that this idea can be obtained most satisfactorily1 if a large number of the details connected with the study of the stratified rocks are omitted1 and ,i have accordingly given very brief accounts of the strata of the different ,systems4 ,the work is intended for use in conjunction with any book which treats of the strata of the ,geological ,column at considerable length2 some of these books are mentioned on pages #abd1 #abe4 ,j4 ,e4 ,m4 ,cambridge1 ,november1 #ahih4 ,,contents4 ,,page ,,chapter ,i4 ,introduction #a ,,chapter ,,ii4 ,account of the growth and progress of stratigraphical geology #f ,,chapter ,,iii4 ,nature of the stratified rocks #ba ,,chapter ,,iv4 ,the law of superposition #ca ,,chapter ,v4 ,the test of included organisms #dj ,,chapter ,,vi4 ,methods of classification of the strata #eh ,,chapter ,,vii4 ,simulation of structures #gb ,,chapter ,,viii4 ,geological maps and sections #hd ,,chapter ,,ix4 ,evidences of conditions under which strata were formed #ig ,,chapter ,x4 ,evidences of conditions under which strata were formed1 continued #aaf ,,chapter ,,xi4 ,the classification of the stratified rocks #abe ,,chapter ,,xii4 ,the ,precambrian rocks #acb ,,chapter ,,xiii4 ,cycles of change in the ,british area #adi ,,chapter ,,xiv4 ,the ,cambrian system #aeb ,,chapter ,,xv4 ,the ,ordovician system #afd ,,chapter ,,xvi4 ,the ,silurian system and the changes which occurred in ,britain at the close of ,silurian times #agd ,,chapter ,,xvii4 ,the ,devonian system #ahc ,,chapter ,,xviii4 ,the ,carboniferous system #aib ,,chapter ,,xix4 ,the changes which occurred during the third continental period in ,britain2 and the foreign ,permo-,carboniferous rocks #bjb ,,chapter ,,xx4 ,the ,permian system #bji ,,chapter ,,xxi4 ,the ,triassic system #bah ,,chapter ,,xxii4 ,the ,jurassic system #bbf ,,chapter ,,xxiii4 ,the ,cretaceous system #bcf ,,chapter ,,xxiv4 ,the ,eocene rocks #bdd ,,chapter ,,xxv4 ,the ,oligocene and ,miocene periods #bea ,,chapter ,,xxvi4 ,the ,pliocene beds #bef ,,chapter ,,xxvii4 ,the ,pleistocene accumulations #bfj ,,chapter ,,xxviii4 ,the ,steppe period #bfg ,,chapter ,,xxix4 ,the ,forest period #bge ,,chapter ,,xxx4 ,remarks on various questions #bgh ,,addenda ,,et ,,corrigenda4 ,,tn3 ,corrections made6 p4 #ch1 line #ae from bottom3 for 'joining' read 'jointing' p4 #bjh1 line #f from bottom3 for ',dr' read ',messrs ,medlicott and' p4 #bad1 line #ae from bottom3 after ',permo-,carboniferous ,strata' insert 'through the ,permian' p4 #bag1 last line of footnote3 for ',dr' read ',messrs ,medlicott and' insert a second footnote3 ',for information concerning the ,permian volcanic rocks see ,sir ,a4 ,geikie's ,ancient ,volcanoes of ,great ,britain4' p4 #bce1 insert a footnote3 ',a good account of the ,british ,jurassic rocks will be found in ,mr ,h4 ,b4 ,woodward's ,memoir on ,the ,jurassic ,rocks of ,britain4 ,mem4 ,geol4 ,survey1 #ahic--4' p4 #bej1 top line3 for ',gardiner' read ',gardner' ,,chapter ,i4 ,,introduction4 ,it is the aim of the ,stratigraphical ,geologist to record the events which have occurred during the existence of the earth in the order in which they have taken place4 ,he tries to restore the physical geography of each period of the past1 and in this way to write a connected history of the earth4 ,his methods are in a general way similar to those of the ethnologist1 the archologist1 and the historian1 and he is confronted with difficulties resembling those which attend the researches of the students of human history4 ,foremost amongst these difficulties is that due to the imperfection of the geological record1 but similar difficulty is felt by those who pursue the study of other uncertain sciences1 and whilst this imperfection is very patent to the geologist1 it is perhaps unduly exaggerated by those who have only a general knowledge of the principles and aims of geology4 ,the history of the earth1 like other histories1 is a connected one1 in which one period is linked on to the next4 ,this was not always supposed to be the case2 the catastrophic geologist of bygone times believed that after each great geological period a convulsion of nature left the earth's crust as a tabula rasa on which a new set of records was engraved1 having no connexion with those which had been destroyed4 ,careful study of the records of the rocks has proved that the conclusions of the catastrophists were erroneous1 and that the events of one period produce their impression upon the history of the next4 ,every event which occurs1 however insignificant1 introduces a new complication into the conditions of the earth1 and accordingly those conditions are never quite the same4 ,although the changes were no doubt very slow1 so that the same general conditions may be traced as existent during two successive periods1 minor complications occurred in the inorganic and organic worlds1 and we never get an exact recurrence of events4 ,vegetable deposits may now be in process of accumulation which in ages to come may be converted into coal1 but the general conditions which were prevalent during that ,carboniferous period when most of our workable coal was deposited do not now exist1 and will never exist again4 ,the changes which have taken place and which are taking place show an advance from the simple to the more complex1 and the stratigraphical geologist is confronted with a problem to which the key is development1 and it is his task to trace the development of the earth from the primitive state to the complex condition in which we find it at the present day4 ,our general ignorance of the events of the earliest periods of the history of the earth will be emphasised in the sequel1 and it will be found that the complexity which marks the inorganic and organic conditions which existed during the deposition of the earliest rocks of which we have detailed knowledge points to the lapse of enormous periods of time subsequent to the formation of the earth1 and previous to the deposition of those rocks4 ,the imperfection of the record is most pronounced for that long period of time1 but in this respect the geologist is in the same condition as the student of human history1 for the relics of the early stone age prove that man in that age had attained a fairly high state of civilisation1 and the gap which separates palolithic man from the first of our race is relatively speaking as great as that which divides the ,cambrian period from the commencement of earth-history4 ,nevertheless1 human history is a science which has made gigantic strides towards the solution of many problems connected with the development of man and civilisation1 and similarly geology has advanced some way in its task of elucidating the history of our globe4 ,the task of the stratigraphical geologist is two-fold4 ,in the first place1 he must establish the order of succession of the strata1 for a correct chronology is of paramount importance to the student of earth-lore4 ,the precautions which must be taken in making out the order of deposition of the rocks of any area1 and correlating those of one area with those of another will be considered in the body of the work4 ,when this task is completed1 there yet remains the careful examination of all the information supplied by a study of the rocks of the crust1 in order to ascertain the actual conditions which existed during the deposition of any stratum or group of strata4 ,in practice1 it is generally very difficult to separate these two departments of the labour of the stratigraphical geologist1 and the two kinds of work are often done to a large extent simultaneously1 or sometimes alternately4 ,frequently the general succession of the deposits comprising an important group is ascertained1 and at the same time observations made concerning the physical characters of the deposits and the nature of their included organisms1 which are sufficient to afford some insight into the general history of the period when these deposits were laid down2 a more detailed classification of the same set of deposits may be subsequently made1 and as the result of this1 more minute observations as to the variations in the physical and biological conditions of the period are possible1 which permit us to write a much more concise history of the period4 ,so great has been the tendency to carry on work in a more and more detailed manner1 that it is very difficult if not impossible to tell when any approach to finality is reached in the study of a group of strata in any area4 ,roughly speaking1 we may state that our knowledge of a group of strata is obtained by three processes1 or rather modifications of one process4 ,the general order of succession is established by the pioneer1 frequently as the result of work carried on through one or two seasons4 ,subsequently to this1 a more minute subdivision of the rocks is possible as the result of labours conducted by one or more workers who are enabled to avail themselves of the work of the pioneer1 and our knowledge of the rocks is largely increased thereby4 ,but the minuti1 often of prime importance1 are supplied by workers who must spend a large portion of their time in the area where the work lies1 and it is only in districts where work of this character has been performed1 that our knowledge of the strata approaches completion4 ,the strata of the ,arctic regions1 for example1 have in many places been examined by pioneers1 but a great deal remains to be done in those regions2 the main subdivisions only have been defined in many cases1 and our information concerning the physical history of ,arctic regions in past times is comparatively meagre4 ,to come nearer home--a few miles north of ,cambridge lies the little patch of ,corallian rock at ,upware2 it has been frequently visited1 and a large suite of organic remains extracted from it1 but no one has devoted the time to the collection of remains from this deposit which has been devoted to that of some other formations presently to be mentioned1 and accordingly our knowledge of the fauna of that deposit is far from complete4 ,contrast with this the information we possess of the little seam known as the ,cambridge ,greensand1 from which organic remains have been sedulously collected during the extensive operations which have been carried on for the extraction of the phosphatic nodules which occur in the seam4 ,the suite of relics of the organisms of that period is accordingly far more perfect than in the case of many other beds1 and indeed the large and varied collection of relics of the vertebrata of the period which furnish much information of value to the palontologist would not have been gathered together1 had not this seam been so carefully worked1 and an important paragraph in the chapter bearing on the history of this period would have remained unknown to us4 ,again1 two little patches of limestone of the same age1 one in central ,england and the other in the island of ,gothland1 have been the objects of sedulous inquiry by local observers1 and we find again that our knowledge of the physical history of the period1 as regards these two regions1 is exceptionally perfect4 ,special stress is laid upon this point1 for in these days1 when every county possesses its learned societies whose members are desirous of advancing in every possible way the progress of science1 it is well to insist upon the importance of this detailed work which can only be done by those who have a large amount of time to devote to the rigorous examination of the rocks of a limited area4 ,,chapter ,,ii4 ,,account ,,of ,,the ,,growth ,,and ,,progress ,,of ,,stratigraphical ,,geology4 ,the history of the growth of a science is not always treated as an essential part of our knowledge of that science1 and many text-books barely allude to the past progress of the science with which they deal4 ,the importance of a review of past progress has1 however1 attracted the attention of many geologists1 and ,sir ,charles ,lyell1 in his ,principles of ,geology1 gave prominence to an historical sketch of the rise and progress of the science4 ,historical studies of this nature have more than an academic value2 the very errors made by men in past times are useful as warnings to prevent those of the present day from going astray2 the lines along which a science has progressed in the past may often be used as guides to indicate how work is to be conducted in the future2 but perhaps the greatest lesson which is taught by a careful consideration of the rise and progress of a study is one which has a moral value1 for he who pays attention to the growth of his science in past times1 gains a reverence for the old masters1 and at the same time learns that a slavish regard for authority is a dangerous thing4 ,this is a lesson which is of the utmost importance to the student who wishes to advance his science1 and will prevent him from paying too little attention to the work of those who have gone before him1 whilst it will enable him to perceive that as great men have fallen into error through not having sufficient data at their disposal1 he need not be unduly troubled should he find that conclusions which he has lawfully attained after consideration of evidence unknown to his predecessors clash with those which they adopted4 ,want of this historic knowledge has no doubt caused many workers to waste their time on work which has already been performed1 but it has also led others to withhold important conclusions from their fellow-workers because they were supposed to be heterodox4 ,in an uncertain science like geology one of the great difficulties is to keep an even balance between contempt and undue respect for authority1 and assuredly a scientific study of the past history of a science will do much to enable a student to attain this end4 ,it will be useful1 therefore1 at this point to give a brief account of the rise and progress of the study of stratigraphical geology1 so far as that can be done without entering into technical details1 at the same time recommending the student to survey the progress of this branch of our science for himself1 after he has mastered the principles of the subject1 and such details as are the property of all who have studied the science from the various text-books written for advanced students4 ,william ,smith1 the ',father of ,english ,geology1' is rightly regarded as the founder of stratigraphical geology on a true scientific basis1 but like all great discoverers1 his work was foreshadowed by others1 though so dimly1 that this does not and cannot detract from his fame4 ,it is desirable1 however1 to begin our historical review at a time somewhat further back than that at which ,smith gave to the world his epoch-making map and memoirs4 ,before the eighteenth century1 stratigraphical geology cannot be said to have existed as a branch of science--the way had not been prepared for it4 ,data had been accumulated which would have been invaluable if at the disposal of open-minded philosophers1 but with few exceptions prejudice prevented the truth from becoming known4 ,there were two great stumbling-blocks to the establishment of a definite system of stratigraphical geology by the writers of the ,middle ,ages1 firstly1 the contention that fossils were not the relics of organisms1 and1 secondly1 when it was conceded that they represented portions of organisms which had once existed1 the assertion that they had reached their present positions out of reach of the sea during the ,noachian ,deluge4 ,for full details concerning the mischievous effects of these tenets upon the science the reader is referred to the luminous sketch of the growth of geology in the first four chapters of ,sir ,charles ,lyell's ,principles of ,geology4 ,the disposition of rocks in strata1 and the occurrence of different fossils in different strata1 was known to ,woodward when he published his ,essay toward a ,natural ,history of the ,earth in #afie1 and the valuable collections made by ,woodward and now deposited in the ,woodwardian ,museum at ,cambridge1 show how fully he appreciated the importance of these facts1 though he formed very erroneous conclusions from them1 owing to the manner in which he drew upon his imagination when facts failed him1 maintaining that fossils were deposited in the strata according to their gravity1 the heaviest sinking first1 and the lightest last1 during the time of the universal deluge4 ,the following extracts from ,part ,,ii4 of ,woodward's book1 show the position in which our knowledge of the strata stood at the end of the seventeenth century3 ,the ,matter1 subsiding 4441 formed the ,strata of ,stone1 of ,marble1 of ,cole1 of ,earth1 and the rest2 of which ,strata1 lying one upon another1 the ,terrestrial ,globe1 or at least as much of it as is ever displayed to view1 doth mainly consist4444 ,the ,shells of those ,cockles1 ,escalops1 ,perewinkles1 and the rest1 which have a greater degree of ,gravity1 were enclosed and lodged in the ,strata of ,stone1 ,marble1 and the heavier kinds of ,terrestrial ,matter3 the lighter ,shells not sinking down till afterwards1 and so falling amongst the lighter ,matter1 such as ,chalk1 and the like 444 accordingly we now find the lighter kinds of ,shells1 such as those of the ,echini1 and the like1 very plentifully in ,chalk4444 ,humane ,bodies1 the ,bodies of ,quadrupeds1 and other ,land-,animals1 of ,birds1 of ,fishes1 both of the ,cartilaginous1 the ,squamose1 and ,crustaceous kinds2 the ,bones1 ,teeth1 ,horns1 and other parts of ,beasts1 and of ,fishes3 the ,shells of ,land-,snails3 and the ,shells of those ,river and ,sea ,shell-,fish that were lighter than ,chalk c4 ,trees1 ,shrubs1 and all other ,vegetables1 and the ,seeds of them3 and that peculiar ,terrestrial ,matter whereof these consist1 and out of which they are all formed1 444 were not precipitated till the last1 and so lay above all the former1 constituting the supreme or outmost ,stratum of the ,globe4444 ,the said ,strata1 whether of ,stone1 of ,chalk1 of ,cole1 of ,earth1 or whatever other ,matter they consisted of1 lying thus each upon other1 were all originally parallel3 444 they were plain1 eaven1 and regular4444 ,after some time the ,strata were broken1 on all sides of the ,globe3 444 they were dislocated1 and their ,situation varied1 being elevated in some places1 and depressed in others 444 the ,agent1 or force1 which effected this ,disruption and ,dislocation of the ,strata1 was seated within the ,earth4 ,woodward's writings no doubt exercised a direct influence on the growth of our subject1 but the indirect effects of his munificent bequest to the ,university of ,cambridge and his foundation of the ,chair of ,geology in that ,university were even greater1 for as will be pointed out in its proper place1 two of the occupants of that chair played a considerable part in raising stratigraphical geology to the position which it now occupies4 ,the discoveries which were made after the publication of ,woodward's book and before the appearance of the map and writings of ,william ,smith are given in the memoir of the latter author1 written by his nephew1 who formerly occupied the ,chair of ,geology at ,oxford#a4 ,it would appear that the fact that the strata1 considered as definitely extended masses1 were arranged one upon another in a certain settled order or series was first published by ,john ,strachey in the ,philosophical ,transactions for #agai and #agbe4 ,in a section he represents1 in their true order1 chalk1 oolites1 lias1 red marls and coal1 and the metalliferous rocks of ,somersetshire1 but confines his attention to the rocks of a limited district4 ,footnote #a3 ,memoirs of ,william ,smith1 ,,ll4,d4 ,by ,j4 ,phillips1 ,f4,r4,s41 ,f4,g4,s4 #ahdd4 ,the ,rev4 ,john ,michell published in the ,philosophical ,transactions for #agfj an ,essay on the ,cause and ,phnomena of ,earthquakes1 but ,prof4 ,phillips gives proofs that ,michell1 who in #agfb became ,woodwardian ,professor1 had before #aghh discovered 7what he never published7 the first approximate succession of the ,mesozoic rocks1 in the district extending from ,yorkshire to the country about ,cambridge4 ,michell's account was discovered written by ,smeaton on the back of a letter dated #aghh4 ,the following is the succession as quoted in ,phillips' memoir 7p4 #acf73 ,yards of thickness4 ,chalk #abj ,golt #ej ,sand of ,bedfordshire #aj to #bj ,northamptonshire lime and ,portland lime1 lying in several strata #ajj ,lyas strata #gh to #ajj ,sand of ,newark about #cj ,red ,clay of ,tuxford1 and several #ajj ,sherwood ,forest pebbles and gravel #ej unequal ,very fine white sand uncertain ,roche ,abbey and ,brotherton limes #ajj ,coal strata of ,yorkshire -- ,the order of succession of the ,cretaceous1 ,jurassic1 ,triassic and ,permian beds will be readily recognised as indicated in this section1 though the discovery of the detailed succession of the ,jurassic rocks was reserved for ,smith4 ,in the year #aggh1 ,john ,whitehurst published ,an ,inquiry into the ,original ,state and ,formation of the ,earth1 containing an ,appendix in which the general succession of the strata of ,derbyshire is noted4 ,the main points of interest are that the author clearly recognised the 'toad-stones' of ,derbyshire as igneous rocks1 as much a lava as that which flows from ,hecla1 ,vesuvius1 or tna1 though he believed that they were intrusive and not contemporaneous1 and he also foreshadows the distinction between the solid strata and the superficial deposits1--we may conclude1 he says1 that all beds of sand and gravel are assemblages of adventitious bodies and not original strata3 therefore wherever sand or gravel form the surface of the earth1 they conceal the original strata from our observation1 and deprive us of the advantages of judging1 whether coal or limestone are contained in the lower regions of the earth1 and more especially in flat countries where the strata do not basset4 ,werner1 who was born in #agej1 exercised more influence by his teaching than by his writings4 ,his ideas of stratigraphical geology were somewhat vitiated by his theoretical views concerning the deposition of sediment from a universal ocean1 in a definite order1 beginning with granite1 followed by gneiss1 schists1 serpentines1 porphyries and traps1 and lastly ordinary sediments4 ,he recognised and taught that these rocks had a definite order in which the remains of living bodies are successively accumulated1 in an order not less determinate than that of the rocks which contain them#b4 ,the limited value of ,werner's stratigraphical teaching is accounted for by ,lyell1 who remarks that ,werner had not travelled to distant countries2 he had merely explored a small portion of ,germany1 and conceived and persuaded others to believe that the whole surface of our planet1 and all the mountain-chains in the world1 were made after the model of his own province1 and the author of the ,principles justly calls attention to the great importance of travel to the geologist4 ,those who cannot travel extensively should at any rate pay special attention to the works published upon districts other than their own1 and even at the present time1 the writings of some ,british workers are apt to be marked by some of that 'insularity' which our neighbours regard as a national characteristic4 ,footnote #b3 ,cuvier's ,eloge4 ,it is now time to turn directly to the work of ,william ,smith1 who1 of all men1 exercised the most profound influence upon the study of stratigraphical geology and may indeed be regarded as the true founder of that branch of the science4 ,the memoir of his life which was before mentioned is all too short to illustrate the methods of work which he followed1 but in it we can trace his success to three things3--firstly1 his 'eye for a country1' to use a phrase which is thoroughly understood by practical geologists1 though it is hard to explain to others1 inasmuch as it epitomises a number of qualifications of which the most important are1 a ready recognition of the main geological features from some coign of vantage1 an intuitive perception of what to note and what to neglect1 and the power of storing up acquired information in the mind rather than the note-book1 so that one may use it almost unconsciously for future work2 secondly1 ability to draw conclusions from his observations1 and thirdly1 and perhaps most important of all in its ultimate results1 a facility for checking these conclusions by means of further observations1 and dropping those which were clearly erroneous1 whilst extracting the truth from those which contained a germ of truth mixed with error4 ,besides writers referred to above some foreign writers1 in particular ,scilla and ,rouelle1 appear to have made very just comparisons of the natural associations of fossil shells1 corals1 c4 in the earth1 with the groups of similar objects as they are found in the sea1 and thus to have produced new proofs of the organic origin of these fossil bodies2 but they give no sign of any knowledge of the limitation of particular tribes of organic remains to particular strata1 of the successive existence of different groups of organization1 on successive beds of the antient sea4 ,mr ,smith's claim to this happy and fertile induction is clear and unquestionable#c4 ,we get a clue to the manner in which he arrived at his view in the following passage#d3--;,accustomed to view the surfaces of the several strata which are met with near ,bath uncovered in large breadths at once1 ,mr ,smith saw with the distinctness of certainty1 that 'each stratum had been in succession the bed of the sea'2 finding in several of these strata abundance of the exuviae of marine animals1 he concluded that these animals had lived and died during the period of time which elapsed between the formation of the stratum below and the stratum above1 at or near the places where now they are imbedded2 and observing that in the successively-deposited strata the organic remains were of different forms and structures--,gryphites in the lias1 ,trigoni in the inferior oolite1 hooked oysters in the fuller's earth1--and finding these facts repeated in other districts1 he inferred that each of the separate periods occupied in the formation of the strata was accompanied by a peculiar series of the forms of organic life1 that these forms characterized those periods1 and that the different strata could be identified in different localities and otherwise doubtful cases by peculiar imbedded organic remains#e4 ,footnote #c3 ,memoir of ,william ,smith1 p4 #adb4 ,footnote #d3 ,ibid4 p4 #ada4 ,footnote #e3 ,the work of ,smith which directly bears upon the establishment of the law of identification of strata by included organisms is published in two treatises1 entitled3-- 7i7 ,strata identified by ,organized ,fossils1 #dto4 7intended to comprise seven parts1 of which four only were published71 commenced in #ahaf4 7ii7 ,a ,stratigraphical ,system of ,organized ,fossils1 compiled from the original ,geological ,collection deposited in the ,british ,museum4 #dto4 #ahag4 ,william ,smith seems to have recognised intuitively the truth of a law which was but dimly understood before his time1--the law of superposition1 which may be thus stated3 of any two strata1 the one which was originally the lower1 is the older4 ,this may appear self-evident but it was certainly not so4 ,as the result of this recognition he established the second great stratigraphical law1 with which his name will ever be linked1 that strata are identifiable by their included organisms4 ,before ,smith's time1 geological maps were lithological rather than stratigraphical1 they represented the different kinds of rocks seen upon the surface without regard to their age2 since ,smith revolutionised geology1 the maps of a country composed largely of stratified rocks are essentially stratigraphical1 but partly no doubt on account of adherence to old custom1 partly on economic grounds1 the majority of our stratigraphical maps are lithological rather than palontological1 that is the subdivisions of the strata represented upon the map are chosen rather on account of lithological peculiarities than because of the variations in their enclosed organisms4 ,it is hardly likely that ,government surveys will be allowed to publish palontological maps1 which will be almost exclusively of theoretical interest1 and it remains for zealous private individuals to accomplish the production of such maps4 ,when they are produced1 a comparison of stratigraphical maps founded on lithological and palontological considerations will furnish results of extreme scientific interest4 ,turning now from ,smith's contributions to the science as a whole1 we may now consider what he did for ,british geology4 ,his geological map was published in #ahae and was described as follows3--,a ,geological ,map of ,england and ,wales1 with part of ,scotland2 exhibiting the ,collieries1 ,mines1 and ,canals1 the ,marshes and ,fen ,lands originally overflowed by the ,sea1 and the varieties of ,soil1 according to the variations of the ,substrata2 illustrated by the most descriptive ,names of ,places and of ,local ,districts2 showing also the ,rivers1 ,sites of ,parks1 and principal ,seats of the ,nobility and ,gentry1 and the opposite ,coast of ,france4 ,by ,william ,smith1 ,mineral ,surveyor4 ,the map was originally on the scale of five miles to an inch4 ,in #ahai a reduced map was published1 and in later years a series of county maps4 ,he also published several geological sections1 including one 7in #ahai7 showing the strata from ,london to ,snowdon4 ,the student should compare ,smith's map of the strata with one published in modern times in order to see how accurate was ,smith's delineation of the outcrop of the later deposits of our island4 ,the following table1 taken from ,phillips' memoir1 p4 #adf1 is also of interest as showing the development of ,smith's work and the completeness of his classification in his later years1 and as illustrating how much we are indebted to ,smith for our present nomenclature1 so much so that as ,prof4 ,sedgwick remarked when presenting the first ,wollaston ,medal of the ,geological ,society to ,smith1 ,if in the pride of our present strength1 we were disposed to forget our origin1 our very speech would bewray us3 for we use the language which he taught us in the infancy of our science4 ,if we1 by our united efforts1 are chiselling the ornaments and slowly raising up the pinnacles of one of the temples of nature1 it was he who gave the plan1 and laid the foundations1 and erected a portion of the solid walls by the unassisted labour of his hands4#f ,footnote #f3 ,the reader may consult an interesting paper by ,professor ,judd1 on ,william ,smith's ,manuscript ,maps1 ,geological ,magazine1 ,decade ,,iv4 vol4 ,,iv4 7#ahig7 p4 #dci4 ,comparative ,view of the ,names and ,succession of the ,strata4 ---------------------------------------- ------------------------------- ,improved table drawn up ,table drawn up ,table accompanying the in #ahae and #ahaf after in #agii4 map1 drawn up in #ahab4 the first copies of the map had been issued4 ---------------------------------------- ------------------------------- ,london ,clay #a ,london ,clay ,clay or ,brick-earth #b ,sand #c ,crag ,sand or light loam #d ,sand #a ,chalk ,chalk #e ,chalk ,upper ,lower #b ,sand ,green ,sand #f ,green ,sand ,blue ,marl #g ,brick ,earth ,purbeck ,stone1 ,kentish #h ,sand ,rag and ,limestone #i ,portland ,rock of the vales #aj ,sand of ,pickering and #aa ,oaktree ,clay ,aylesbury1 #ab ,coral ,rag and ,pisolite ,iron ,sand and ,carstone #ac ,sand #c ,clay ,dark ,blue ,shale #ad ,clunch ,clay and ,shale #ae ,kelloway's ,stone ,cornbrash #af ,cornbrash #d ,sand and ,stone #ag ,sand and ,sandstone #e ,clay #f ,forest ,marble ,forest ,marble ,rock #ah ,forest ,marble #ai ,clay over ,upper ,oolite #g ,freestone ,great ,oolite ,rock #bj ,upper ,oolite #h ,blue ,clay #i ,yellow ,clay #aj ,fuller's ,earth #ba ,fuller's ,earth and ,rock #aa ,bastard ditto and ,sundries #ab ,freestone ,under ,oolite #bb ,under ,oolite #ac ,sand #bc ,sand #bd ,marlstone #ad ,marl ,blue ,blue ,marl #be ,blue ,marl #ae ,blue ,lias ,blue ,lias #bf ,blue ,lias #af ,white ,lias ,white ,lias #bg ,white ,lias #ag ,marlstone1 ,indigo and ,black ,marls #ah ,red ,ground ,red ,marl and ,gypsum #bh ,red ,marl #ai ,millstone ,magnesian ,limestone #bi ,redland ,limestone ,soft ,sandstone #bj ,pennant ,street #ba ,grays ,coal ,districts #cj ,coal ,measures #bb ,cliff #bc ,coal ,derbyshire ,limestone #ca ,mountain ,limestone ,red and ,dunstone #cb ,red ,rhab and ,dunstone ,killas or ,slate #cc ,killas ,granite1 ,sienite and #cd ,granite1 ,sienite and ,gneiss ,gneiss ---------------------------------------- ------------------------------- ,the above table contains a very complete classification of the ,british ,mesozoic rocks1 one of the ,tertiary strata which is less complete1 and a preliminary division of the ,palozoic rocks into ,permian 7,redland ,limestone71 ,carboniferous 7,coal ,measures and ,mountain ,limestone71 ,devonian 7,red ,rhab and ,dunstone7 and ,lower ,palozoic 7,killas74 ,since ,smith's time the main work which has been done in classification is a fuller elucidation of the sequence of the ,tertiary and ,palozoic ,rocks1 and this we may now consider4 ,the ,mesozoic rocks are developed in ,britain under circumstances which render the application of the test of superposition comparatively simple1 for the various subdivisions crop out on the surface over long distances1 and the stratification is not greatly disturbed4 ,with the ,tertiary and ,palozoic ,rocks it is otherwise1 for some members of the former are found in isolated patches1 whilst the latter have usually been much disturbed after their formation4 ,commencing with the ,tertiary deposits we may note that the first deposits of this class1 of which the characters were accurately determined1 were those occurring in the neighbourhood of ,paris1 described in #ahaj by ,,mm4 ,cuvier and ,brongniart4444 ,strata were soon afterwards brought to light in the vicinity of ,london1 and in ,hampshire1 which although dissimilar in mineral composition were justly inferred by ,mr ,t4 ,webster to be of the same age as those of ,paris1 because the greater number of fossil shells were specifically identical#g4 ,it is to ,lyell that we owe the establishment of a satisfactory classification of the ,tertiary deposits which is the basis of later classifications4 ,recognising the difficulty of applying the ordinary test of superposition to deposits so scattered as are those of ,tertiary age in north-west ,europe1 he in #ahcj1 assisted by ,g4 ,p4 ,deshayes1 proposed a classification based on the percentage of recent mollusca in the various deposits4 ,it may be noted1 that although this method was sufficient for the purpose1 it has been practically superseded1 as the result of increase of our knowledge of the ,tertiary faunas1 by the more general method of identifying the various divisions by their actual fossils without reference to the number of living forms contained amongst them4 ,the further study of the ,british ,tertiary rocks was largely carried on by ,joseph ,prestwich1 formerly ,professor of ,geology in the ,university of ,oxford4 ,footnote #g3 ,lyell1 ,students' ,elements of ,geology4 #bnd ,edition1 p4 #aah4 ,amongst the ,palozoic rocks1 it has been seen that the ,permian1 ,carboniferous and some of the ,devonian beds were recognised as distinct by ,smith1 though a large number of deposits now known to belong to the last named were thrown in with other rocks as 'killas4' ,the ,devonian system was established and the name given to it in #ahch by ,sedgwick and ,murchison1 largely owing to the palontological researches of ,lonsdale4 ,an attempt was subsequently made to abolish the system1 but the detailed palontological studies of ,r4 ,etheridge finally placed it upon a secure basis4 ,the establishment of the ,devonian system cleared the way for the right understanding of the ,lower ,palozoic rocks1 which ,sedgwick and ,murchison had commenced to study before the actual establishment of the ,devonian system1 and to these workers belongs the credit of practically completing what was begun by ,william ,smith1 namely1 the establishment of the ,geological ,sequence of the ,british strata4 ,the controversy which unfortunately marked the early years of the study of the ,british ,lower ,palozoic ,rocks is well-nigh forgotten1 and in the future the names of ,sedgwick and ,murchison will be handed down together1 in the manner which is most fitting4 ,our account of the growth of ,british ,stratigraphical ,geology is not yet complete4 ,in #ahed1 ,sir ,william ,logan applied the term ,laurentian to a group of rocks discovered in ,canada1 which occurred beneath the ,lower ,palozoic ,rocks4 ,murchison shortly afterwards claimed certain rocks in ,n4,w4 ,scotland as being of generally similar age1 and since then a number of geologists1 most of whom are still living1 have proved the occurrence of several large subdivisions of rocks in ,britain1 each of which is of pre-,palozoic age4 ,the above is a brief description of the growth of our knowledge of the order of succession of the strata which is the foundation of ,stratigraphical ,geology4 ,a sketch of the manner in which the knowledge which has been obtained has been applied to the elucidation of the earth's history of different times would require far more space than can be devoted to it in a work like the present1 but some idea of it may be gained from a study of the later chapters of the book4 ,it will suffice here to remark1 that to ,godwin-,austen we owe the foundation of what may be termed the physical branch of ,palo-physiography1 which is concerned with the restoration of the physical conditions of past ages1 while ,cuvier and ,darwin have exerted the most influence on the study of ,stratigraphical ,palontology4 ,,chapter ,,iii4 ,,nature ,,of ,,the ,,stratified ,,rocks4 ,the present constituents of the earth which are accessible for direct study are divisible into three parts4 ,the inner portion1 consisting of rocks1 is known as the lithosphere2 outside this1 with portions of the lithosphere projecting through into the outermost part1 is the hydrosphere1 comprising the ocean1 lakes1 rivers1 and all masses of water which rest upon the lithosphere in a liquid condition4 ,the outermost envelope1 which is continuous and unbroken is the atmosphere1 in a gaseous condition4 ,it is well known that some of the constituents of any one of these parts may be abstracted from it1 and become a component of either of the others2 thus the atmosphere abstracts aqueous vapour from the hydrosphere1 and the lithosphere takes up water from the hydrosphere1 and carbonic anhydride from the atmosphere4 ,the nebular hypothesis of ,kant and ,laplace necessitates the former existence of the present solid portions of the lithosphere in a molten condition1 and accordingly the first formed solid covering of the lithosphere1 if this hypothesis be true1 must have been formed from molten material1 or in the language of ,geology1 it was an igneous rock4 ,consequently1 the earliest sedimentary rock was necessarily derived directly from an igneous rock1 with possible addition of material from the early hydrosphere and atmosphere1 and all subsequently formed sedimentary rocks have therefore been derived from igneous rocks 7with the additions above stated7 either directly1 or indirectly through the breaking up of other sedimentary rocks which were themselves derived directly or indirectly from igneous rocks4 ,the observations of geologists show that this supposition that the materials of sediments have been directly or indirectly obtained for the most part from once-molten rocks is in accordance with the observed facts1 and so far their observations testify to the truth of the nebular hypothesis4 ,this being the case1 the study of the petrology of the igneous rocks is necessary1 in order to arrive at a true understanding of the composition of the sedimentary ones4 ,the igneous rocks are largely composed of four groups of minerals1 viz4--quartz1 felspars1 ferro-magnesian minerals1 and ores4 ,of these the quartz 7composed of silica7 yields particles of silica for the formation of sedimentary rocks2 the felspars1 which are double silicates of alumina and an alkali or alkaline earth1 being prone to decomposition furnish silicate of alumina and compounds of soda1 potash1 lime1 c4 ,the ferro-magnesian minerals 7such as augite1 hornblende and mica7 may undergo a certain amount of decomposition1 and yield compounds of iron1 lime1 c4 ,we may also have fragments of any of these minerals1 and of the ore group in an unaltered condition4 ,the composition of a sedimentary rock which has undergone no alteration after its formation will therefore depend upon the character of the rock from which it was derived1 the chemical changes which take place in the materials which compose it1 before they enter into its mass1 and the mechanical sorting which they undergo prior to their deposition4 ,in the above passage the terms igneous rock and sedimentary rock have been used1 and it is necessary to give some account of the sense in which they were used4 ,an igneous rock is one which has been consolidated from a state of fusion4 ,it is not necessary to discuss here the exact significance of the word fusion1 and whether certain rocks which are included in the igneous division were formed rather from solution at high temperature than from actual fusion4 ,this point is of importance to the petrologist1 but to the student of stratigraphical geology the term igneous rock may be used in its most comprehensive sense4 ,these igneous rocks were consolidated either upon the surface of the lithosphere or in its interior4 ,the other great group of rocks is one to which it is difficult to apply a satisfactory name4 ,they have been termed by different writers1 sedimentary1 stratified1 derivative1 aqueous1 and clastic1 but no one of these terms is strictly accurate4 ,the term sedimentary implies that they have settled down1 at the bottom of a sheet of water for instance4 ,it can hardly be maintained that limestones formed by organic agency1 like the limestones of coral reefs1 are sedimentary in the strict sense of the term1 and an accumulation like surface-soil can only be called a sediment by straining the term4 ,stratified rocks are those which are formed in strata or layers1 but many of the rocks which we are considering do not show layers on a small scale1 and igneous rocks 7such as lava-flows7 are also found in layers1 though such layers are not true strata in the sense in which the term is used by geologists2 the term stratified is perhaps the least open to objection of any of those named above4 ,derivative implies that the fragments have been derived from some pre-existing rock1 but as there are many ways in which fragments of one rock may be derived from another1 the term is too comprehensive4 ,aqueous rocks should be formed in water1 and most of the class of rocks which we are considering have been so formed1 but others such as sand-dunes and surface-soil have not4 7,the term ,aerial or olian has been suggested to include these rocks which are thus separated from the ,aqueous rocks proper2 the objection to this is that the origin of these rocks is closely connected with that of the true ,aqueous rocks1 and moreover the group is too small to be raised to the dignity of a separate subdivision47 ,lastly1 the name clastic has been given1 because the rocks so called are formed by the breaking up of pre-existing rocks4 ,there are two objections to this name4 ,in the first place1 some rocks included under the head clastic are formed by solution of material and its consolidation from a state of solution by chemical or organic agency1 though we may perhaps speak of rocks being broken up by chemical as well as by mechanical action4 ,the most important objection is that many clastic rocks are formed by the breaking up of rocks subsequently to their formation1 and it has been proposed that rocks of this nature should be termed cataclastic1 while those which are formed by the breaking up of pre-existing rocks upon the earth's surface should be termed epiclastic2 another group formed of materials broken up within the earth1 and accumulated upon its surface as the result of ejection of fragmental material from volcanic vents being termed pyroclastic4 ,this classification is scientific1 and under special circumstances is extremely useful1 but the older terms have been used so generally1 and with this explanation their use is so unobjectionable1 that they may be retained1 and the term stratified will be generally used to indicate all rocks which are not of igneous origin or formed as mineral veins in the earth's interior4 ,the division of rocks into three great groups1 the ,igneous1 ,stratified and ,metamorphic 7the latter name being applied to those rocks which have undergone considerable alteration since their formation71 is objectionable1 since we have metamorphic igneous rocks as well as metamorphic stratified ones4 ,the most convenient classification is as follows3-- ,a4 ,igneous #a4 ,unaltered4 #b4 ,metamorphic4 ,b4 ,stratified #a4 ,unaltered4 #b4 ,metamorphic4 ,it must be distinctly understood that all geological phenomena must be taken into account by the stratigraphical geologist4 ,the upheaval of strata1 the production of jointing and cleavage in them1 their intrusion by igneous material1 their metamorphism1 give indications of former physical conditions equally with the lithological characters of the strata1 and their fossil contents4 ,nevertheless it is not proposed to give a full account of the various phenomena displayed by rocks2 the student is referred to ,text-books of ,general ,geology for this information4 ,it will be as well here1 however1 to point out in a few words the exact significance of the existence of strata in the lithosphere4 ,the formation of strata and their subsequent destruction to supply material for fresh strata are due to three great classes of changes4 ,beginning with a portion of lithosphere composed of rock1 it is found that rock is broken up by agents of denudation1 as wind1 rain1 frost1 rivers and sea4 ,these agents perform their function mainly upon the portion of the lithosphere which projects through the hydrosphere to form land1 and the land is the main area of denudation4 ,the materials furnished by denudation are carried away1 and owing to gravitation1 naturally proceed from a higher to a lower level1 often resting on the way1 but if nothing else occurs1 ultimately finding their way to the sea1 where they are deposited as strata4 ,the sea is the principal area for the reception of this material1 and it is there accordingly that the bulk of stratified rock is formed4 ,if nothing else occurred1 in time the whole of the land would be destroyed1 and the wreckage of the land deposited beneath the sea as stratified rock4 ,as it is there is a third class of change1 underground change1 causing movements of the earth's crust 7to use a term which can hardly be defined in few words but which is generally understood71 and as the result of the relative uplift of portions of the earth's crust1 the stratified rocks formed beneath the oceans are raised above its level1 giving rise to new masses of land1 which are once more ready for destruction by the agents of denudation4 ,this cycle of change 7all parts of which are ever proceeding simultaneously7 is one of the utmost importance to the stratigraphical geologist4 ,stratification is the rock-structure of prime importance in stratigraphical geology1 and a few words must here be devoted to its consideration1 leaving further details to be dealt with hereafter4 ,the surface of the ocean-floor is1 when viewed on a large scale1 so level1 that it may be considered practically horizontal1 and accordingly in most places the materials which are laid down on the ocean-floor give rise to accumulations which at all times have a general horizontal surface 7when the ocean-slopes depart markedly from horizontality the deposits tend to abut against these slopes rather than to lie with their upper surfaces parallel to their original angle74 ,a practically horizontal surface of this character may give rise to a plane of stratification 7or bedding-plane7 in more than one way4 ,a pause may occur during which there is a cessation of the supply of material1 so that the material which has already been accumulated has sufficient time to become partially consolidated before the deposition of fresh material upon it4 ,in this way a want of coherence between the two masses is produced1 along the plane of junction1 which after consolidation of the deposits causes an actual divisional plane along which the two deposits may be separated4 ,this is a plane of stratification4 ,the pause may be produced in various ways1 sometimes between successive high tides1 at others as the result of physical changes which may have taken ages to happen4 ,again1 after material of one kind has been deposited1 say sand1 some other substance such as clay may be accumulated on its upper surface1 giving rise to a plane of stratification between two deposits of different lithological characters4 ,if this occurs alone1 there may be actual coherence between the two strata1 so that it is erroneous to speak of a plane of stratification as if it were always one along which one deposit could be readily split from the other1 though as a general though by no means universal rule1 change from one kind of deposit to another is also marked by want of coherence between the two4 ,the material between two planes of stratification forms a stratum or bed1 though if the deposit be very thin it is known as a lamina1 and the planes are spoken of as planes of lamination 7no hard and fast line can be drawn between strata and lamin2 several of the latter usually occur in the space of an inch74 ,a stratum will have its upper and lower surface apparently parallel1 though not really so1 for no stratum extends universally round the earth1 and many of them disappear at no great distance when traced in any direction4 ,parts of one stratum may be composed of different materials from other parts when traced laterally1 thus one stratum may be found composed essentially of sand in one place1 of mud in another1 and of a mixture of the two in an intervening locality4 ,whatever be the composition of a stratum it dies out eventually1 owing to the coming together of the upper and lower bounding planes of stratification4 ,the stratum is thickest at some spot1 from that spot it becomes thinner in all directions1 until it disappears at last by the coalescence of the bounding-planes4 ,this is spoken of as thinning-out4 ,strata1 then1 consist of lenticular masses of rock1 separated from the underlying and overlying strata by planes of stratification4 ,the shape of the lenticle may vary immensely1 the thickness bearing no definite relationship to the horizontal extent4 ,some strata1 many feet in thickness1 may thin out and disappear completely in the course of a few yards1 whilst others an inch or two in thickness may be traced horizontally for many miles4 ,we often find thin strata of coal and limestone1 extending for great distances1 strata of mud thinning out more rapidly1 and sandstones still more rapidly1 but no universal rule connecting rapidity of thinning-out with composition of the strata can be laid down4 ,having seen what a stratum is1 it now remains to speak of the composition of the stratified rocks4 ,they have been classified according to their composition1 and according to their origin4 ,according to composition they have been divided into3 ,arenaceous rocks1 composed essentially of grains of sand4 ,argillaceous rocks1 composed essentially of particles of mud4 ,calcareous rocks1 composed essentially of particles of carbonate of lime4 ,carbonaceous rocks1 composed largely of hydrocarbon compounds4 ,siliceous rocks1 composed essentially of silica not in the form of grains2 whilst according to their origin they have been separated into3-- ,mechanically-formed rocks1 composed of fragments derived from other rocks by mechanical fracture4 ,chemically-formed rocks1 composed of particles which have been chemically deposited from a state of solution4 ,organically-formed rocks1 composed of materials which have been derived from a state of solution or from the gaseous condition by the agency of organisms4 ,whichever classification be adopted 7and each is useful for special purposes71 it must be noted that no hard and fast line can be drawn between one division and another4 ,a rock may be partly arenaceous and partly calcareous1 composed of a mixture of sand and lime1 and the same rock may similarly be partly mechanically and partly organically formed1 the sand being due to mechanical fracture1 and the lime to the agency of organisms1 and so with the other divisions4 ,as many of the changes which have occurred in past times have been concerned in destruction and obliteration1 whilst deposition is the cause of preservation1 the study of deposits is peculiarly adapted for testing the truth of the grand principle of geology that the changes which have taken place in past times are generally speaking similar in kind and in intensity of action to those which are in progress at the present day1 and a study of the modern deposits is specially important as throwing light upon the characters of those which have been formed in past times4 ,it will be abundantly shown in the sequel that the deposits of the strata are in general comparable in all essential respects with those which are being formed at present1 and accordingly they give most valuable indications as to the nature of the physical and other conditions under which they were laid down4 ,the desert sand1 the precipitate of the inland sea1 the reef-limestone and many another deposit can thus be detected by an examination of their lithological characters1 combined with consideration of other kinds of evidence4 ,the petrology of the sedimentary rocks is still in its infancy1 though much has already been done1 but it offers a wide field of inquiry to the field-geologist and worker with the microscope#h4 ,footnote #h3 ,the student will do well to consult ,the ,challenger ,report by ,messrs ,murray and ,renard 7#ahia71 for information concerning many modern sediments1 and ,harker's ,petrology for ,students ,section ,d1 for general information on the ,petrology of the ,stratified ,rocks4 ,,chapter ,,iv4 ,,the ,,law ,,of ,,superposition4 ,in a previous chapter this law was given as follows3 ,of any two strata1 the one which was originally the lower is the older2 the general truth of the law depends upon the fact that except under very exceptional circumstances the strata are deposited upon the surface of the lithosphere1 and not beneath it4 ,there are occasions where strata may be deposited beneath the lithosphere1 but as a general rule the geologist will not be misled by such occurrences4 ,in caverns1 accumulations often occur which are newer than the strata over the cavern roof1 and so long as caverns are formed in ordinary sedimentary rocks1 no great difficulty will result from this exception to the law of superposition4 ,when caverns occur beneath masses of land ice1 the order of superposition may be misleading4 ,a deposit may be formed on the surface of the ice1 and subsequently to this a newer deposit may be laid down in a sub-glacial or englacial cavern2 upon the melting of the ice the newer deposit would be found with the older one resting upon its surface4 ,apart from these exceptional cases1 the law as stated holds good1 but the reader will notice the insertion of the word 'originally' which requires some comment4 ,a geologist speaks of one bed lying upon another not only when the beds are horizontal1 but when they are inclined at any angle1 until they become vertical1 so that until beds have been turned through an angle of #ij by earth-movement the test of superposition is applicable1 but when they have been turned more than #ij1 the stratum which was originally lower rests upon that which was originally above it1 and in the case of these inverted strata1 the test of superposition is no longer applicable4 ,it was formerly supposed that cases of inversion were comparatively rare and local1 and that the test of superposition could therefore be generally applied with confidence1 but it is now known that though this is generally true of such strata as have been subjected only to those widespread1 fairly uniform movements which are spoken of as epeirogenic or continent-forming1 where the radius of each curve is very long1 inversion is a frequent accompaniment of the more local orogenic or mountain-forming movements1 where the radius of a curve is short4 ,though orogenic movements are limited as compared with those of epeirogenic character1 they often affect large tracts of country1 in which case the apparent order of succession of the strata need not be the true one1 and examples of inversion may be frequent#i4 ,footnote #i3 ,for a discussion of the principles of mountain-building see ,heim1 ,a41 ,untersuchungen ber den ,mechanismus der ,gebirgsbildung1 and ,lapworth1 ,c4 ,the ,secret of the ,highlands1 ,geological ,magazine1 ,decade ,,ii4 vol4 x4 pp4 #abj1 #aic1 #ccg4 ,it is not easy to lay down any definite rules for detecting inverted strata1 where the top of an inverted arch is swept off by denudation or the bottom of an inverted trough concealed beneath the surface1 beyond stating that if an easily recognised set of beds is obviously repeated in inverse order1 inversion must have occurred1 though even then it may not be clear which side of the fold shows the beds in original and which in inverted sequence4 ,suggestions are frequently made that ripple-marks and worm-tracks may be utilised in order to discover inversion1 for the well-formed ripple-marks will appear convex on the upper surface of a bed which is not inverted1 and we may note concave casts of these ripple-marks on the under surface of the overlying bed1 whilst worm-tracks will appear concave on the upper surface1 and their casts convex on the lower surface of the succeeding bed under similar conditions4 ,in the case of inversion the occurrences will be the exact opposite to these4 ,unfortunately ripple-marks and worm-tracks may1 as will appear in the sequel1 be simulated by structures produced in quite a different way1 and unless the observer is certain that he is confronted with true ripple-marks and worm-tracks he may be seriously misled4 ,the geologist must take into account all the evidence at his disposal1 when he is dealing with cases of possible inversion1 but oftentimes he will after due consideration of all the phenomena be left in doubt unless he is able to supplement his observations on the succession of the strata by evidence derived from the included fossils4 ,the test of superposition is most apt to be misleading when the strata have been affected by the faults known as reversed faults or thrust-planes4 ,reference to text-books will show that a fold consists of two parts1 the arch and the trough1 and that the two are connected by a common-1 middle-1 or partition-limb4 ,in the case of an inverted fold1 an ,s-shaped or sigmoidal structure is the result 7,fig4 #a ,a74 ,illustration3 ,fig4 #a4 ,a4 ,a sigmoidal fold1 showing a bed xx in an overfold with arch 7a71 trough 7t7 and common limb c4 ,b4 ,a similar bed xx affected by a thrust-plane tt which replaces the common limb4 ,here the portions of any bed 7xx7 which occur in the arch or trough are in normal position1 and have not been moved round through an angle of #ij1 whilst the portion which occurs in the common limb c has been moved round through an angle greater than #ij and is inverted1 so that its former upper surface now faces downwards4 ,in ,fig4 #a ,b the common limb is replaced by a reversed fault1 or thrust-plane1 and the inverted portion of the bed seen in the common limb is therefore absent4 ,an observer1 applying the test of superposition1 might suppose that the position of the bed x on the left-hand side of the figure was a different bed from the portion which is seen on the right-hand side1 instead of belonging to the same bed1 and in this way1 if a number of parallel thrust-planes affected one bed or a set of beds1 he might be led to infer the occurrence of a great thickness of strata where there was in reality a slight thickness1 or even one bed only repeated again and again by faulting4 ,it is quite certain that exaggerated estimates of the thickness of deposits have frequently been made owing to the non-recognition of the occurrence of repetition as a consequence of the existence of thrust-planes4 ,where thrust-planes are suspected1 it is well to look for some of the following features3 7a7 ,the strata of a country affected by thrust-planes often crop out as lenticular masses1 thinning out rapidly in the direction of the strike#aj4 ,this is true of beds thrown into sharp folds whether or not inverted1 but the lenticles will be wider in a direction at right angles to that of the strike as compared with their length when inversion has not occurred4 ,it is also true of beds which were originally deposited as lenticles1 such as many massive sandstones1 and as almost any kind of deposit may be formed originally as a lenticle1 the test by itself is by no means sufficient as a proof of thrusting1 though it is suggestive4 ,footnote #aj3 ,for definitions of the terms dip1 strike1 outcrop and allied expressions1 the reader is referred to a ,text-,book of ,geology4 7b7 ,the surfaces of the strata are often affected by the striations known as slickensides1 and the joint-faces of gently inclined beds are also frequently marked by slickensides which often run in a nearly horizontal direction4 7c7 ,a parallel structure presenting the appearances characteristic of the mechanically-formed features of a foliated rock is often developed1 and one or more of certain accompanying phenomena will probably be found1 which will be noticed more fully in a later chapter4 7d7 ,extension or stretching of the rocks will have been frequently produced1 causing rupture1 and the resulting fissures are usually filled with mineral-veins1 though this occurrence is by no means characteristic of rocks which have been affected by thrust-planes4 7e7 ,chemical changes may have occurred which have resulted in the reconstitution of some of the rock-constituents1 which may crystallise where pressure is least1 thus we often find rocks which have undergone movements of the type we are considering marked by the existence of sericitic films upon the surfaces4 ,another reservation must be made when considering the law of superposition4 ,the test is only applicable for limited areas4 ,suppose we find a deposit of clay a resting upon another deposit of limestone b in the south of ,england1 and can prove that the apparent succession is the true one1 that is1 that there has been no inversion2 it is clear that the test of superposition is applicable in that area4 ,now1 we may be able to trace the two deposits continuously across the country1 one as a clay1 the other as a limestone2 so that when we reach the north of ,england we find the clay a still reposing upon the limestone b4 ,the test of superposition is applicable in that area also1 the clay of the northern area being newer than the limestone of the same region4 ,but1 for reasons which will ultimately appear1 it by no means follows that the clay of the north is newer than the limestone of the south1 although the two deposits are continuously traceable with the same lithological characters2 it may have been formed simultaneously with the limestone of the south1 or even before it4 ,something more1 therefore1 than the test of superposition is necessary in order to make out the relative ages of continuous deposits in a wide region1 and this is still truer in the case of deposits which are discontinuous1 whether separated from one another by the sea1 or by outcrops of older or newer rocks4 ,a few words of warning may be added with reference to the detection of bedding-planes4 ,a bedding-plane is one which separates two beds1 and its existence is determined during the deposition of the beds4 ,many other planes are formed in rocks subsequently to their deposition1 and it is not always easy to distinguish these from true bedding-planes4 ,that even experienced observers may be led astray is shown by the fact that1 of recent years1 it has been proved that great masses of rock have been claimed as of sedimentary origin1 and their apparent order of succession noted1 which are in truth naught but irregular masses of intrusive igneous rocks affected by divisional planes which simulate bedding1 produced in the rocks subsequently to their consolidation4 ,joints1 faults1 and cleavage-planes may all at times simulate planes of bedding1 and it is frequently very difficult to distinguish them in the limited exposures with which a geologist has oftentimes to deal4 ,it is easier to make suggestions for distinguishing bedding-planes from other planes which simulate them1 than to apply the suggestions in practice1 and the student of field geology will find that experience is the only guide1 though after years of experience he may be confronted with cases where the evidence is insufficient to convince him that he is dealing with planes of stratification and not with some other structure4 ,from what has been remarked1 it will be inferred that the test of superposition though of prime importance to the geologist is frequently insufficient to enable him to ascertain the true order of succession of the strata1 and he is compelled to supplement this test by some other4 ,there are several useful physical tests which may frequently be applied4 ,thus1 if a rock a contains fragments of another rock b1 under such circumstances as to show that the fragments of b were included in a during its deposition1 it is clear that b is older than a4 ,here again1 it will be found from what appears in a later chapter that the student is confronted with difficulties when actually examining rocks1 for fragmental rocks of cataclastic origin1 where the fragments have been formed as the result of fracture produced by earth-movements subsequently to the deposition of the rock1 simulate epiclastic rocks in which the fragments were introduced during the accumulation of the deposits to so surprising a degree as sometimes to baffle the most experienced observer4 ,not only are the fragments of these cataclastic rocks broken up1 but they may be further rounded so as to imitate in a remarkable manner the water-worn pebbles of an epiclastic conglomerate4 ,again1 an older series of rocks may have had structures impressed upon them as the result of changes subsequent to their formation1 and before the formation of a newer set which the latter therefore do not exhibit4 ,jointing1 cleavage1 and various metamorphic phenomena may thus be exhibited by the older rocks1 but great care is required in applying this test1 especially with a limited thickness of rocks1 as one set may not exhibit the structures not because they were not in existence when the structures were developed1 but because their nature is such that they were incapable of receiving or retaining the structures4 ,for instance a mass of grit which is older than a mass of clay-slate may not be cleaved1 because1 although subjected to the pressure which produced the cleavage1 it was of a nature not adapted to the development of cleavage structure4 ,on the whole1 application of tests dependent upon physical features of rocks1 does not often supplement to any great extent the information supplied by ascertaining the order of superposition1 and in all cases1 where possible1 every other kind of information should be supplemented1 by that which is acquired after examination of the included organisms of the strata4 ,,chapter ,v4 ,,the ,,test ,,of ,,included ,,organisms4 ,the second great law of the ,stratigraphical ,geologist is that fossiliferous strata are identifiable by their included organisms1 in other words1 that we can tell the geological age of deposits by examination of the fossils contained in them1 though the determination of age must be given in more general terms in some cases than in others4 ,considerable misconception has arisen concerning the value of fossils as indices of age1 and it is necessary therefore to discuss the significance of the law of identification of strata by their included organisms at some length4 ,the comparison between fossils and medals has frequently been made and fossils have well been styled the ,medals of ,creation2 and the significance of fossils as guides to the age of deposits may perhaps be made clearer if we pursue this comparison some way4 ,in the first place there is clear indication of a gradual increase in the complexity of organisation of the fossils as one passes from the earlier to the later rocks1 and accordingly the general facies of a fauna is likely to furnish a clue to the age of the rocks in which it is found1 even though every species or even genus represented in the fauna was previously unknown to science4 ,so an antiquary versed in the evolution of art or metallurgy1 might detect the general age of a medal with whose image and superscription he was not acquainted4 ,he would know that a medal struck in iron was formed subsequently to the bronze age1 or that one formed of palladium appertained to the present century4 ,but quite apart from any theoretical knowledge1 an antiquary would find as the result of accumulated experience that certain medals are characteristic of certain periods2 he would learn that the denarius is characteristic of a different period from that indicated by the coin of the ,victorian era1 even though he had no knowledge of the technicalities of numismatics4 ,the same is the case with the geologist4 ,he may not be influenced by any knowledge of the evolution of faunas and floras1 but actual work amongst the rocks will show him that the trilobite is not found with the belemnite or the ichthyosaur with the elephant1 save under exceptional circumstances1 which only prove the rule1 as for instance when worn bones of ichthyosaurs are washed from their proper strata into gravels with elephant-bones4 ,it must be distinctly understood that the determination of fossils as characteristic of different periods is solely made as the result of experience4 ,no priori reasoning may give one indication of the actual range in time of a species or genus2 no one can say why ,discina has a long range in time1 whilst that of the closely related ,trematis is very limited4 ,this being the case1 the greater the mass of evidence which is accumulated as to the range of a fossil1 the greater will be the value of that fossil as a clue to the age of the deposit in which it is found4 ,this is so important1 that it requires more than mere notice4 ,if a fossil is found in abundance in a group of strata ,b in any one area1 and is not found in an underlying group ,a or overlying group ,c in that area after prolonged search1 we may confidently speak of the fossil as characteristic of the strata ,b in that area1 though without further work1 the value of the fossil as a clue to age in other areas would be unproved4 ,it may nevertheless happen1 that after more prolonged search in ,a or ,c1 in the original area a few specimens of the fossil which has been spoken of as characteristic of ,b may be found in one or other of them1 in small quantity4 ,the value of the fossil as one characteristic of ,b will be slightly diminished1 though only slightly1 as it is not likely to turn up in numbers in the strata ,a or ,c after the prolonged search4 ,should the fossil be found also to be characteristic of the strata ,b in areas other than the original one1 it becomes of more than local value1 and if1 after much study it is found to characterise the same strata over wide areas1 the cumulative evidence now obtained will render the fossil peculiarly important to the stratigraphical geologist4 ,the detection of characteristic fossils is not quite so simple as might be supposed from the above remarks1 for examination of the position of one fossil will not prove the contemporaneity of beds in different places1 to prove this1 all the evidence at our disposal must be considered1 for reasons which will be presently pointed out4 ,as the result of accumulated knowledge1 we can now compile lists of characteristic fossils of the major subdivisions of the strata1 which are of world-wide utility and as our knowledge increases1 we are enabled to subdivide the strata into minor divisions of more than local value4 ,what is a fossil8 ,before discussing the value of fossils as aids to the stratigraphical geologist1 it may be well to make a few observations as to what constitutes a fossil4 ,it is difficult to give any concise definition1 and as is often the case in geology1 an explanatory paragraph is of more value than a mere definition4 ,the term fossil was originally applied to anything dug up from the rocks of the earth's crust1 and was used with reference to inorganic objects as well as organic remains1 for instance minerals were spoken of as fossils4 ,it is now applied essentially though not exclusively to relics of former organisms1 though one still reads of fossil rain-drops1 fossil sun-cracks1 and so on4 ,furthermore1 the relics need not necessarily be parts of the organism1 the track of a worm or a bird's nest if embedded in the strata would be termed a fossil4 ,it is generally agreed that no sharp line can be drawn between recent and fossil organic remains which is based upon the degree of mineralisation 7or as it was sometimes termed petrifaction7 of the relics1 for many true fossils have not undergone mineralisation1 subsequent to their entombment4 ,it has been suggested that the name fossil should be applied to organic remains which have been entombed by some process other than human agency1 but this restriction is undesirable4 ,the stone-implement of the river gravels is as genuine a fossil as the ammonite extracted from the chalk1 and the human relics of very recent date may give information of a character quite similar to that supplied by other remains1 for instance1 the occurrence of moa-bones in ,new ,zealand in accumulations below those containing biscuit-tins and jam-pots has been used as a geological argument pointing to the extinction of the moa before the arrival of ,europeans in ,new ,zealand4 ,the biscuit-tin here serves all the purposes of a fossil1 and there is no valid reason why it should not be spoken of as such4 ,this statement brings one to consider another method which has been adopted in order to separate fossil organisms from recent ones1 namely the time-test4 ,this again is inapplicable1 for no line can be drawn between the shell which was buried in yesterday's tidal deposit and that which has lain in the strata through geological ages1 and each may be equally useful to the geologist4 ,whilst1 then1 we can give no definition of fossil which is likely to meet with general acceptance1 the term can be so used1 as not to give rise to any doubts as to its meaning1 and it is generally applicable to any organic relics which have been embedded in any deposit or accumulation by any agent human or otherwise4 ,mode of occurrence of fossils4 ,it will not be out of place to say a few words as to the way in which fossils are found in strata1 as beds are often inferred to be unfossiliferous1 because of ignorance of methods which should be pursued in searching for organic relics4 ,it is unnecessary to dilate upon the actual modes of preservation of organisms1 which is treated of fully in other works4 ,in the first place1 it is rash to assert that any deposit is unfossiliferous because no fossils have been found in it1 even after prolonged search4 ,the ,llanberis slates had been eagerly searched for fossils for many years without result1 but that the search was not exhaustive was proved by the discovery of trilobites in them some years ago4 ,seekers after fossils are rather prone to confine their attention to strata which are already known to be fossiliferous than to pay much attention to those which have hitherto yielded no organic remains4 ,some kinds of deposits are more often fossiliferous than others4 ,limestones which are frequently largely of organic origin1 are often rich in remains1 and muddy deposits more frequently furnish fossils than those of a purely sandy nature4 ,the difference in the yield is not necessarily due to the original inclusion of more remains in one rock than in another1 but is often caused by the obliteration of former relics owing to changes which have taken place in the rocks subsequently to their deposition4 ,no sedimentary rock must be regarded as unfossiliferous1 however unfitted it appears for the preservation of fossils4 ,the writer has seen fossils1 not only in coarse conglomerates1 rocks which frequently contain no traces of organisms1 but in deposits composed largely of specular iron ore1 and even in intrusive igneous rocks1 though in the latter case1 the inclusion of fossils was due to circumstances which cannot have occurred with frequency4 ,in sandy strata1 the substance of the fossils has often been completely removed1 leaving hollow casts1 which may be almost or quite unrecognisable4 ,in these circumstances1 much information may be obtained by taking impressions of the casts in modelling wax or some other material4 ,the importance of this process may be judged from the results it yielded to ,mr ,clement ,reid in the case of the fossils of the ,pliocene deposits occurring in pipe-like hollows in the ,cretaceous rocks of ,kent and the discovery of the remarkable reptiles described by ,mr ,e4 ,t4 ,newton from the ,triassic sandstones of ,elgin4 ,in argillaceous rocks which have been affected by the processes producing cleavage1 the fossils may be distorted beyond recognition or owing to the difficulty of breaking the rocks along the original planes of deposition1 may remain invisible4 ,under such circumstances1 small nodules of sandy or calcareous nature may sometimes be found included in the argillaceous deposits and may perhaps yield fossils4 ,oftentimes1 also1 where the argillaceous rock is in close proximity to a harder rock1 such as massive grit1 the argillaceous rock in close contiguity to the hard rock may escape the impress of cleavage-structure1 and fossils may be readily extracted from rocks in this position when not obtainable from other parts of the deposit4 ,it was under these circumstances that the trilobites alluded to above were obtained from the ,llanberis slates4 ,the fossils of calcareous rocks are often very obvious1 but difficult to extract1 as they break across when the rock is fractured4 ,they are frequently obtainable in a perfect condition when the rock is weathered4 ,occasionally they may be extracted from certain argillaceous limestones if the limestone be heated to redness1 and suddenly plunged into cold water4 ,fossils are often found in a state which enables them to be readily extracted when a limestone is coarsely crystalline1 though they cannot be extracted in a perfect condition when the same limestone is in a different state4 ,many microzoa1 which are invisible in rocks1 even when viewed through a lens1 may be found in microscopic sections of calcareous and silicious rocks1 and plant structures may be detected under similar circumstances in the case of carbonaceous rocks4 ,various special methods of extracting fossils from rocks have been described by different writers1 many of which are very complex1 and require much time4 ,the mechanical action of the sand-blast and the solvent action of various acids as hydrochloric and hydrofluosilicic have been found of use upon different occasions#aa4 ,the various processes which have been utilised in order to extract and develop fossils can1 however1 be best learned by information obtainable from curators of palontological collections1 and by actual experience1 and there is yet much information to be acquired as to the manner of extracting fossils from various kinds of rocks4 ,footnote #aa3 ,for information concerning use of acids see especially ,wiman1 ,c4 ,ueber die ,graptoliten1 ,bull4 ,geol4 ,inst41 ,upsala1 ,no4 #d1 vol4 ,,ii4 ,part ,,ii4 ,relative value of fossils to the ,stratigraphical ,geologist4 ,it has been hinted above that no general rule as to the relative value of fossils as guides to the age of strata can be laid down1 and that the ascertainment of their relative value is largely the result of actual experience4 ,it may be noted1 however1 that organisms which possess hard parts are naturally more important to the geologist than those which do not1 as few traces of the latter are preserved in the fossil state1 and even when preserved are usually too obscure to be of much practical use4 ,of the organisms which do possess hard parts1 different groups have been utilised to a different degree1 and one group will be more or less important than another1 according to the use to which it is applied4 ,groups of organisms which have a long range in time are naturally useful for the identification of large subdivisions of the strata1 whilst those which have had a shorter range are valuable when separating minor subdivisions4 ,again1 as the bulk of the sedimentary deposits has been formed beneath the waters of the ocean1 relics of marine organisms are naturally more useful than those of freshwater ones4 ,other things being equal1 the more easily the organism is recognisable1 and the more abundant are its remains1 the greater its value to the stratigraphical geologist1 and as the remains of invertebrates are usually found in greater quantities and in more readily recognisable condition than those of the vertebrates1 they have been used more extensively as indices of age4 ,of the invertebrates1 the mollusca are often very abundant1 their remains are adapted for preservation1 and their characteristics have been extensively studied1 and accordingly they have been and are of great use to the geologist4 ,of other groups1 the graptolites1 corals1 echinids1 brachiopods1 and trilobites have been very largely utilised4 ,the ,lower ,palozoic strata have been divided into numerous groups1 each characterised by definite forms of graptolites1 and a similar use has been made of the ammonites in the case of the ,mesozoic rocks4 ,it is not to be inferred that these groups of organisms are naturally more useful than other groups1 on account of the extent to which they have been used2 we can merely state that they have been proved to be useful as the result of prolonged study2 when other groups have received equal attention1 they may well be found to be equally useful for the purposes which we have in view4 ,contemporaneity and ,homotaxis4 ,from what has been already stated1 it will be recognised that the ages of the various fossiliferous rocks of the geological column#ab in any one area can be identified with greater or less degree of certainty by reference to their included organisms1 the various subdivisions being marked by the possession of characteristic fossils1 and it will be naturally and rightly inferred that the greater the number of characteristic fossils of any one deposit1 the more certain is the identification of that deposit4 ,in practice1 geologists are wont to ascertain the age of the strata after consideration of all the fossils found therein1 some of which may be actually characteristic whilst many may come up from the strata below1 or pass into those above4 ,having ascertained the order of succession and fossil contents of the strata in various regions1 it is the task of the geologist to compare the strata of these two regions1 and this task is fraught with considerable difficulty4 ,much controversy has arisen as to the degree of accuracy with which strata of remote regions can be correlated1 and the subject is one which requires full consideration4 ,footnote #ab3 ,although the rocks do not always lie on one another in regular succession1 it is often convenient to speak of them as though they did1 and as though a column of strata could be carved out in any region consisting of horizontal bands of deposit one above another4 ,we speak of such an ideal arrangement as constituting a 'geological column4' ,suppose that a series of strata which we will call ,a1 ,b1 and ,c is found in any one area1 each member of which contains characteristic fossils which enable it to be recognised in that area1 and we will further suppose that in another area a series of strata ,a1 ,b1 and ,c is discovered1 of which ,a has the fauna of ,a in the former area1 and similarly ,b the fauna of ,b1 and ,c that of ,c4 ,it cannot be assumed that the stratum ,a is therefore contemporaneous with ,a1 ,b with ,b1 and ,c with ,c1 but on the other hand1 it must not be assumed that they are not contemporaneous4 ,this is a statement which requires some comment4 ,it has been urged that if the deposits ,a and ,a in different localities contain the same fauna1 this is a proof that the two are not contemporaneous1 for some time must have elapsed in order to allow of the migration of the organisms from one area to another1 it being justifiably assumed that they did not originate simultaneously in the two areas4 ,but everything depends on the time taken for migration as compared with the period of existence of the fauna4 ,if the former was extremely short as compared with the latter it may be practically ignored1 for we might then speak of the strata as contemporaneous1 just as a historian would rightly speak of events in the same way which occurred upon the same afternoon1 though one might have happened an hour before the other4 ,let us then glance at the evidence which we have at our disposal1 which bears upon this matter4 ,the objection to identification of strata with similar faunas as contemporaneous was urged by ,whewell1 ,herbert ,spencer1 and ,huxley1 and the latter suggested the term ,homotaxis or similarity of arrangement as applicable to groups of strata in different areas1 in which a similar succession of faunas was traceable1 maintaining that though not contemporaneous the strata might be spoken of as homotaxial4 ,huxley went so far as to assert that for anything that geology or palontology are able to show to the contrary1 a ,devonian fauna and flora in the ,british ,islands may have been contemporaneous with ,silurian life in ,north ,america1 and with a ,carboniferous fauna and flora in ,africa#ac1 a statement which few if any living geologists will endorse4 ,if the statement be true1 and the fauna which we speak of as ,devonian1 when present be always found 7as it is7 above that which we in ,britain know as ,silurian and below that which we term ,carboniferous1 the faunas must have originated independently in the three centres1 and disappeared before the appearance of the next fauna1 or having originated at the same centre1 each must have migrated in the same direction1 spread over the world1 and become extinct as it reached the point or line from which it started4 ,suppose for instance a fauna ,a originates at the meridian of ,greenwich1 migrates eastward1 and dies out again when it once more reaches ,greenwich1 that ,b and ,c do the same1 at a later period1 then the fauna ,b will always be found above ,a and ,c above ,b1 but if ,b did not become extinct when it reached the ,greenwich meridian1 it would continue its eastward course1 and ,c having in the meantime started on its first round1 the fossils of the fauna ,b would be found both above and below those of ,c4 ,it will be shown below that cases of recurrence do occur1 but nowhere do we find a ,silurian fauna above a ,devonian one1 or a ,devonian one above one belonging to the ,carboniferous1 nor is the fauna of a great group of rocks found in one region above the fauna of another group1 and in another region below the same4 ,and this is true not only of the faunas of one major division1 such as those of the ,silurian and ,carboniferous periods1 but also of the faunas of many minor subdivisions into which the large ones are separated1 for instance we do not find the ,llandovery fauna of the ,silurian period which in ,britain is found below the ,wenlock fauna embedded elsewhere in strata above the ,wenlock4 ,i have simplified the statement by assuming that the faunas are identical in the different localities1 and exactly similar throughout the whole thickness of the containing strata1 which is naturally not the case1 but the additional complexity does not conceal the truth of what has been stated4 ,in the absence of actual inversion of well-marked faunas1 only one explanation is possible1 namely1 that the time for migration of forms is so short as compared with the entire period during which the forms existed1 that it may be practically ignored1 and the strata containing similar faunas may be therefore spoken of truthfully as contemporaneous and not merely homotaxial#ad4 ,footnote #ac3 ,huxley1 ,t4 ,h4 ,geological ,contemporaneity and ,persistent ,types of ,life1 being the ,anniversary ,address to the ,geological ,society for #ahfb2 reprinted in ,lay ,sermons1 ,addresses and ,reviews4 ,footnote #ad3 ,for fuller discussion of this matter see a paper by the ,author ',on ,homotaxis1' ,proc4 ,camb4 ,phil4 ,soc41 vol4 ,,vi4 ,part ,,ii4 p4 #gd4 ,apparent anomalies in the distribution of fossils4 ,there are several occurrences which have tended to augment the distrust frequently felt concerning the value of fossils as indices of the age of the beds in which they occur1 which may be here considered4 ,though the greater number of fossil remains belonged to organisms which lived during the time of accumulation of the deposits in which they are now embedded1 this is by no means universally the case1 and the occurrence of remani fossils1 which have been derived from deposits more ancient than the ones in which they are now found is far from being a rare event4 ,the existence of remains of this nature in the superficial drifts and river-gravels of our own country has long been recognised1 and no one would suppose that the ,grypha and other shells furnished by these gravels had lived contemporaneously with the species of ,corbicula1 ,unio and other molluscs which are part of the true fauna of the gravels4 ,in this case the water-worn nature of the remains is a good index to their origin1 but in other cases1 it is by no means an infallible guide1 for we sometimes find on the one hand that remains of organisms proper to the deposits in which they occur are water-worn1 whilst on the other the relics of remani fossils are not4 ,the now well-known gault fossils of the ,cambridge ,greensand at the base of the chalk were not always recognised as having been derived from older beds1 and there are certain fossils found in nodules in the ,cretaceous rocks of ,lincolnshire1 which still form a subject for difference of opinion1 for while some writers maintain that they belong to the deposits in which they are now found1 others suppose that the nodules have been washed out of earlier beds4 ,occasionally we find forms which occurring in a set of beds ,a in an area1 are absent from the overlying beds ,b1 and appear again in the succeeding deposits ,c4 ,such cases of recurrence are by no means rare1 though many supposed instances of recurrence have been recorded as the result of stratigraphical or palontological errors4 ,the best examples have been noted by ,barrande among the ,lower ,palozoic deposits of ,bohemia4 ,the stage ,d of ,bohemia consists of five 'bandes' or subdivisions1 the lowest 7d #a71 central 7d #c7 and uppermost 7d #e7 divisions are mainly argillaceous1 whilst the second 7d #b7 and fourth 7d #d7 are essentially arenaceous4 ,some of the forms found in d #a1 d #c and d #e have not been found in d #b and d #d4 ,the best-known example is the trilobite glina rediviva4 ,it is clear that this and other forms did not become extinct during the deposition of the strata of d #b and d #d1 though they may have disappeared temporarily from the ,bohemian area1 or else lingered on in such diminished numbers that their remains have not been discovered4 ,the range of the organism is in fact right through the deposits of the stage ,d1 and the discontinuity of distribution is not a real anomaly2 it may be compared to some extent with cases of discontinuous distribution in space4 ,it is needless to remark that the whole fauna does not disappear for a time and then reappear1 but only a few out of the many forms which compose it4 ,the comparative rarity of examples of recurrence after long intervals is an indication that the palontological record as it is termed is not so imperfect as some suppose1 for if our knowledge of fossils were very imperfect1 we should expect cases of apparent recurrence to be common1 as the result of the non-detection of fossils in the intermediate beds4 ,one of the most marked cases of apparent recurrence known some years ago was the reappearance of a genus of trilobite ,ampyx in ,ludlow rocks1 found in the ,bala rocks1 but not in the ,llandovery or ,wenlock strata4 ,it has since been discovered in ,llandovery beds1 and its eventual discovery in beds of ,wenlock age may be regarded as certain4 ,a supposed case of recurrence which would have been remarkable1 that of the disappearance of ,phillipsia in ,ordovician rocks1 its entire absence in those of ,silurian age1 and its reappearance in the ,devonian1 has broken down1 for the supposed ,ordovician form has been shown to belong to an entirely different group of trilobites from that containing the genus ,phillipsia1 and it has been therefore renamed ,phillipsinella4 ,many apparent anomalies of distribution have been explained as due to migration1 but it is doubtful whether any one of these supposed anomalies is actual and not due to errors in determining the position of the beds or the nature of their included fossils4 ,some of the supposed anomalies have already been shown to be due to error1 and the others will almost certainly be cleared up4 ,in speaking of anomalies of distribution1 the geologist can only be guided by experience as to what constitutes an anomaly4 ,for instance the existence of a complete fauna in any one place in the beds of a system above that to which it is elsewhere confined would be regarded as anomalous and as probably due to error1 whilst the reappearance of several forms in beds of a system higher than that in which they had hitherto been found1 could hardly be considered as an anomaly4 ,a geologist would suspect the statement that after the disappearance of an ,ordovician fauna in an area and its replacement by a ,silurian fauna1 the ,ordovician fauna reappeared for a time1 but would not regard the statement that a ,cenomanian fauna partly reappeared in the ,chalk ,rock with surprise4 ,the existence of a ,silurian fauna in ,ordovician times was maintained by ,barrande in the case of the ,bohemian basin4 ,lenticular patches of ,silurian rocks having the lithological characters of the ,silurian strata are found in the ,ordovician beds of that region1 and they contain fossils specifically identical with those of the ,silurian rocks4 ,barrande explained this appearance as due to the existence of a fauna in other regions resembling the ,silurian fauna of ,bohemia1 during the ,ordovician period1 when the normal ,ordovician fauna of ,bohemia inhabited that area4 ,he supposed that in parts of the basin1 when favourable conditions arose1 colonies of the foreign fauna settled for a time1 but did not get a permanent footing in the basin until the commencement of ,silurian times4 ,the theory of colonies has now been rejected for the ,bohemian area1 and the phenomena shown to be due to repetition of strata by folding and faulting1 but it is a theory which is again and again advocated in order to explain apparently anomalous phenomena in other areas1 and these apparent anomalies which are so explained1 must be regarded with grave suspicion4 ,the various complexities alluded to in the foregoing pages increase the difficulty experienced by the geologist in correlating strata in different areas by their included organisms1 but no one of them disproves the possibility of making these correlations1 which can be carried on to a greater or less extent according to the nature of the faunas4 ,a good deal of misconception has arisen concerning the geographical distribution of former faunas1 owing to the tendency to compare them exclusively with the littoral faunas of the present day4 ,these littoral faunas have a comparatively limited geographical distribution1 the forms of one marine province often differing considerably from those of an adjoining one1 and still more widely from one which is remote1 so that anyone confronted with the relics of faunas from the existing ,australian and ,european seas1 would find no indications furnished by identity of species that the faunas were contemporaneous4 ,recent researches have shown1 however1 that the creatures whose remains are deposited at some distance from the coast-line have a much stronger resemblance to one another than the littoral organisms have1 if the fauna of two distant areas be compared4 ,it is still a moot point which will be discussed in a later chapter1 how far the deep-sea deposits of modern times are represented amongst the strata of the geological column by deposits of similar origin4 ,but it is certain that many of the ancient strata are not littoral deposits1 and it will be found that it is by comparison of the faunas of the deeper-water deposits that the geologist correlates the strata of remote regions3 where shallow water deposits are formed1 the faunas differ markedly in different regions1 and these shallow-water forms can only be correlated owing to their occurrence between deeper-water strata4 ,thus if strata ,a1 ,b and ,c be found in one area1 and the fauna of ,a and ,c are deep-water forms1 those of ,b being shallow-water forms1 and in another area beds ,a contain the same fauna as ,a1 and ,c the same fauna as ,c whilst the fauna of ,b is different from that of ,b1 we can nevertheless correlate the strata ,b and ,b 7if they be conformable with the underlying and overlying beds71 because of the identity of age of the associated beds in the two areas4 ,it will possibly be found that the strata ,a and ,c can be further subdivided into ,a#a1 ,a#b1 444 c4 ,c#a1 ,c#b1 444 by the existence of minor faunas1 which are comparable in the two cases1 but such subdivisions may not be established in the case of the beds ,b and ,b4 ,to take actual examples3--,the ,llandovery beds of ,dumfriesshire can be subdivided into several minor divisions each of which can be recognised in the ,lake ,district of ,england1 and to a large extent in ,scandinavia and elsewhere1 for the deposits in these areas are of deep-water character1 and the sub-faunas of the subdivisions are similar in the different areas1 but the ,llandovery rocks of the ,welsh borderland are shallow-water deposits1 with a different fauna from that of the deep-water deposits of this age1 and can only be stated to be contemporaneous with the ,llandovery rocks elsewhere1 because the deeper-water faunas of the underlying ,bala rocks and overlying ,wenlock rocks of the ,welsh borders are respectively similar to those of the ,bala and ,wenlock rocks of the other regions4 ,the shallow-water ,llandoveries of the ,welsh borders have only been separated into two divisions1 upper and lower1 and have not been split up into a number of subdivisions1 each characterised by a sub-fauna1 and each comparable with one of the subdivisions of ,dumfriesshire1 ,lakeland and the other regions where the deep-water facies is found4 ,it will be seen that though the principle of ,william ,smith that strata can be recognised by their included organisms has been extended since his time1 and shown to apply to far smaller subdivisions of the strata than was suspected1 the method of application is the same1 and is more or less successful according to the amount of evidence which is accumulated in support of it4 ,,chapter ,,vi4 ,,methods ,,of ,,classification ,,of ,,the ,,strata4 ,earth-history like human history is the record of an unbroken chain of events4 ,the agents which have produced geological phenomena have been in operation since the earth came into existence4 ,accordingly a perfect earth-history would be written as a continuous narrative1 just as would a complete history of the human race4 ,the historian of man finds it not only convenient but necessary to divide the epoch of which he is writing into periods of time1 and so does the geologist1 and in each case the division is necessarily more or less arbitrary4 ,it is true that in writing the history or geology of a country1 marked events stand out which form a convenient means of making divisions1 but the marked events occurring in one country are not likely to take place simultaneously with those of another country1 and consequently a classification of this character is only locally applicable4 ,the classification which is at present used by geologists was originally founded upon definite principles1 and although our principles of classification have1 as will appear1 been somewhat altered subsequently1 it has been found more convenient to modify the original classification than to adopt a new one in its entirety4 ,the largest divisions into which the strata of the geological column were separated were instituted because of the supposed extinction of faunas1 and sudden or rapid replacement by other faunas of an entirely different character4 ,this supposed rapid extinction and replacement is now known to have been only apparent and due to observation in restricted areas1 and it is doubtful whether the three great divisions founded upon them are not rather mischievous than useful1 as tending to disseminate wrong notions4 ,moreover there is considerable diversity of opinion as to the terms to be adopted4 ,the rocks were formerly divided into ,primary1 ,secondary1 and ,tertiary4 ,owing chiefly to the use of the term ,primary in another sense1 the alternative titles ,palozoic1 ,mesozoic and ,cainozoic 7or ,cnozoic7 were suggested1 and though the term ,primary has been definitely abandoned in favour of ,palozoic1 the words ,secondary and ,tertiary are used extensively as synonyms of ,mesozoic and ,cainozoic4 ,it was soon perceived that the period of time included in the ,palozoic age was much longer than the combined periods of ,secondary and ,tertiary ages1 and it was proposed to group the latter under one title ,neozoic1 whilst another suggestion was to split the ,palozoic age into an earlier ,proterozoic and later ,deuterozoic division4 ,the interest excited by the advent of man is probably the cause of the attempt to establish a ,quaternary division1 which some hold to be a minor subdivision of the ,tertiary1 whilst others would separate it altogether4 ,the terms ,palozoic1 ,mesozoic 7or ,secondary7 and ,cainozoic 7or ,tertiary7 are now used so generally that any attempt to abolish them would be doomed to failure1 but it must be remembered that they are purely arbitrary expressions1 and the other terms which are not in general use1 might be dropped with advantage4 ,the other subdivisions have been used somewhat loosely1 and although an attempt has been made by the ,international ,geological ,congress to restrict certain names to subdivisions of varying degrees of value1 it will probably be found best to allow of a certain elasticity in the use of terms1 merely agreeing that they shall be used as nearly as possible with the signification assigned to them by the ,congress4 ,according to this classification1 and apart from the division into ,palozoic1 ,mesozoic and ,cainozoic1 the strata of the geological column are grouped into ,systems1 which are subdivided into ,series1 and the series are further split up into ,stages4 ,a number of chronological terms were also suggested1 of equivalent importance1 thus the beds of a system would be deposited during a ,period1 those of a series during an ,epoch1 and those of a stage during an ,age#ae4 ,footnote #ae3 ,the chronological words have been used so loosely that it is doubtful whether any good will come of trying to restrict their use1 and ,sir ,a4 ,geikie has pointed out the confusion which would arise if the term group be employed for the largest divisions 7,palozoic1 c474 ,the terms ,system1 ,series and ,stage may well be employed in the senses suggested by the ,congress4 ,the rocks of the ,geological ,column were originally divided into systems1 owing to the occurrence of marked physical and palontological breaks between the rocks of two adjacent systems1 except in cases where a complete change occurred locally in the lithological characters of the rocks of two systems which were in juxtaposition3 it is necessary to consider for awhile the nature of these breaks4 ,the most apparent physical break is where the rocks of one set of deposits rest unconformably upon the rocks of another one1 indicating that the older set has been uplifted and to some extent eroded before the deposition of the strata of the newer set4 ,this uplift and erosion signifies a change from oceanic to continental conditions in the area in which unconformity is found on a large scale1 and accordingly a long period of time would elapse during which the continental surface would not receive deposits1 so that the highest rocks of the underlying system would be considerably older than the lowest rocks of the one which succeeds it4 ,such a break may be obviously utilised for purposes of classification1 but as some areas of the earth's surface must have been occupied by the waters of the ocean when other regions formed land1 deposit in some areas must constantly have occurred simultaneously with denudation in others1 and any classification founded upon the existence of unconformities will therefore have a purely local value4 ,another1 and less apparent physical break1 which will also be locally applicable1 may be due to the depression of an area to so great a depth that little or no deposit was formed upon the ocean floor there during the period of great depression2 but as a break of this character is difficult to detect1 the existence of unconformities has alone been practically utilised as a means of separating strata into systems owing to marked physical change1 except in the cases where the lithological character of the strata completely changes1 as between the ,triassic and ,jurassic rocks of ,england4 ,illustration3 ,fig4 #b4 ,palontological breaks or breaks in the succession of organisms are in many cases1 the result of physical breaks1 and accordingly it is often possible to separate one set of strata from another by the existence of a combined physical and palontological break between them4 ,it is by no means necessary however that a physical break should be accompanied by a break in succession of the organisms1 and the latter may also occur without the former4 ,it was once maintained that a palontological break was due to the complete and sudden extinction of a fauna and its entire replacement by a new one1 but this is far from true1 and accordingly the breaks differ in degree4 ,study of the strata shows that when the succession is not to any extent interrupted1 the species do not appear simultaneously1 but come in at different horizons1 and they disappear in the same way4 ,in ,figure #b let ,a represent a set of conformable strata ab 444 k1 and suppose the vertical lines represent the ranges of the various species found in these strata4 ,it will be seen that of #bg species whose range is shown only #b pass through the whole thickness1 so that the fauna of k is very different from the fauna of a1 nevertheless the fauna of each stratum is closely similar to that of the underlying as well as to that of the overlying stratum1 and though most of the species of k are different from those of a1 this need not be the case with the genera4 ,the fauna of the set of strata would contain every species whose range is represented1 and for convenience' sake it might be said to be composed of sub-faunas1 one of which occurs in each division ab 4441 but the separation into sub-faunas would be artificial and merely for convenience' sake1 for there is no break between any two sub-faunas4 ,turning now to ,b 7,fig4 #b71 an attempt is made there to show what happens when there has been a physical break1 resulting in the denudation of the strata ghik1 and the deposition of another set op 444 unconformably upon those deposits of the earlier set which have not been denuded4 ,as the result of this we note1 first1 that the relics of organisms which existed in the area during the deposition of ghik1 and were entombed in those strata1 are destroyed by the processes of denudation1 and a large number of organisms which lived long after the deposition of f1 and disappeared not simultaneously but at different times during the period when denudation was in operation1 seem to become extinct simultaneously at the top of f1 though1 if we could visit an area which was receiving sediment during the period of denudation1 we should find them dying out in the rocks of that region at different levels4 ,furthermore1 whilst denudation is going on1 a longer or shorter period of time elapses1 during which the upheaved area receives no deposit1 and accordingly no organisms which lived during that period are preserved in the upheaved area4 ,during this time a set of deposits lmn may have been laid down elsewhere1 and besides the gradual disappearance of some of the organisms of ab 444 k1 there will have been a gradual appearance of new species4 ,when the upheaved area is once more submerged1 a new set of deposits op 444 is accumulated in it1 and the species which gradually appeared in adjoining regions will now migrate to it1 and will seem to come in simultaneously at the bottom of o2 accordingly we may find that there is not a single species which passes through from f to o and the palontological break in this area is complete1 though it is clear that it only implies local change1 and that we may and indeed must find intermediate forms in other regions which fill up the gap4 ,as an illustration of the local character of a palontological break we may cite the case of the ,carboniferous and ,permian systems of ,britain4 ,these rocks are separated from one another in our area by a physical and palontological break1 but in parts of ,india1 and other places1 we find a group of rocks now known as the ,permo-,carboniferous rocks which contain a fauna intermediate in character between those of the ,permian and ,carboniferous systems1 and a study of this fauna shows that the hiatus which exists locally is filled by the species contained in the ,permo-,carboniferous rocks4 ,a palontological break may1 like a physical one1 result from depression of the ocean-floor to so great a depth1 that no organisms are preserved there during the period of great depression1 and the remarks made concerning a depression of this nature when speaking of physical breaks will apply here also4 ,a local palontological break may result owing to physical changes without the production of an unconformity in the area1 or its submergence to a great depth1 or if an unconformity is found1 the break may be more marked owing to other physical changes4 ,the difference between the ,upper and ,lower ,carboniferous faunas is very marked in ,england1 where the ,upper ,carboniferous beds were deposited under physical conditions different from those of the ,lower ,carboniferous1 and accordingly the corals1 crinoids and other open-water animals which flourished in ,lower ,carboniferous times are rare or altogether absent in the higher rocks4 ,where the change of conditions did not occur to a great extent as in parts of ,spain and ,north ,america1 the similarity between the two faunas is much more pronounced4 ,again1 there is an unconformity between the ,cretaceous and ,eocene beds of ,england1 which is accompanied by a palontological break1 but this break is more pronounced owing to difference of physical conditions1 for we find abundance of gastropods in the lower ,tertiary beds1 and a rarity of these shells at the top of the chalk of ,england1 though where physical conditions were favourable for the growth of gastropods1 their shells are found in the higher strata of chalk age1 and the palontological break is not so apparent4 ,a palontological break may occur also as the result of climatic change1 though actual instances of this occurrence are much more difficult to detect owing to the general absence of any evidence of climatic change other than that supplied by the organisms themselves4 ,still1 when no physical break exists1 and the lithological characters of a group of sediments remain constant throughout1 indicating the prevalence of similar physical conditions through the period of deposition of the sediments1 if the fauna suddenly changes1 there must have been cause for the change1 and in the absence of any other cause which is likely to produce the change1 alteration of the character of the climate may be suspected4 ,it follows from the observations which have been made1 that although the rocks of the ,geological ,column may be divided into systems owing to the existence of physical and palontological breaks1 and this classification may be and has been applied generally1 the line of demarcation between the rocks of two systems will be a purely conventional one1 where there is no break1 and1 to avoid confusion1 that line when once drawn should be adopted by everyone1 unless good cause can be shown for its abandonment4 ,the subdivision of systems into series has been conducted in a manner generally similar to that in which large masses of strata have been grouped into systems1 with the exception that actual breaks need not occur4 ,the subdivision was usually made on account of marked differences in the lithological characters or fossil contents of the rocks of the various series1 and frequently the lithological characters as well as the fossil contents are dissimilar2 taking the rocks of the ,silurian system of the typical ,silurian area as an example1 we find the ,llandovery rocks largely arenaceous1 the ,wenlock rocks largely calcareo-argillaceous1 and the ,ludlow rocks argillaceo-arenaceous1 whilst the fauna of the ,wenlock rocks differs from that of the ,llandovery rocks below and also from that of the ,ludlow rocks above4 ,the ,llandovery1 ,wenlock and ,ludlow therefore constitute three series of the ,silurian system1 but the lines of demarcation between these series are nevertheless conventional1 for it has been suggested that a more natural division1 as far as the ,british rocks are concerned1 could be made by drawing a line1 not as at present at the base of the ,ludlow1 but in the middle of that series as now defined1 and uniting the ,lower ,ludlow beds with the ,wenlock strata to form a single series4 ,the same process as that adopted in the case of series has been essentially pursued in subdividing these into stages4 ,each stage is usually different from that above and below in its lithological characters1 fossil contents1 or both1 though the difference is usually less in degree than that which has been utilised for the demarcation of series4 ,a stage is often1 though not always1 composed of deposits of one kind of sediment1 and is furthermore frequently characterised by the possession of one or1 it may be1 two1 three or more characteristic fossils4 ,thus the ,wenlock series is divided in the typical area into ,woolhope limestone1 ,wenlock shale1 and ,wenlock limestone1 and the very names given to these stages indicate that each is largely composed of one kind of material4 ,their fossils are also to some extent different1 though the difference between them is not likely to be of so marked a nature as that which exists between the faunas of separate series4 ,it will be seen that the system differs from the series and the series from the stage in degree rather than in kind1 and no hard line can be drawn between divisions of different degrees of magnitude4 ,it follows therefore that frequently a mass of sediment which one author will consider sufficiently important to constitute a system will be defined by another as a series1 and similarly a series of one writer may become a stage of another4 ,the student of ,stratigraphical ,geology will find the expression 'fossil zone' occurring over and over again in geological literature1 and as the term has been used somewhat vaguely by many writers and is apt to be misunderstood1 it will be useful to notice the expression at some length4 ,strictly speaking the term zone 7a belt or girdle71 when applied to distribution of fossils1 should refer to the belt of strata through which a fossil or group of fossils ranges4 ,generally speaking1 the expression is used in connexion with one fossil2 thus we speak of the zone of ,coenograptus gracilis1 the zone of ,cidaris florigemma and the zone of ,belemnites jaculum1 though sometimes it is used with reference to more than one species1 as the zone of ,micrasters and the ,olenellus zone4 ,the term has been used not of a belt of strata but of a group of organisms#af1 and zones defined as assemblages of organic remains of which one abundant and characteristic form is chosen as an index1 but if it be agreed that the term should be applied to strata and not to organisms this might be modified and the definition run3--',zones are belts of strata1 each of which is characterised by an assemblage of organic remains of which one abundant and characteristic form is chosen as an index4' ,footnote #af3 ,see ,h4 ,b4 ,woodward1 ,on ,geological ,zones1 ,proc4 ,geol4 ,assoc41 vol4 ,,xii4 ,part #g1 p4 #bie1 and vol4 ,,xii4 ,part #h1 p4 #cac4 ,it has been objected that the subdivision of strata into zones has been pushed too far1 but this is merely because in the establishment of zones1 workers find it easier to work out the successive zones where the strata are thin and presumably deposited with extreme slowness1 than where they are much thicker and have been rapidly accumulated1 and accordingly1 as the subdivision of strata into zones is a recent event1 geological literature contains many more references to thin zones than to those of great thickness4 ,where an abundant and characteristic form 7which is chosen as an index7 of an assemblage of organic remains ranges through a great thickness of deposit1 there is no objection to speaking of the whole as a zone1 and it cannot be divided4 ,to give some idea of the variations in the thickness of strata through which these abundant and characteristic forms will range1 ,i append a list of the zones of graptolites which have been established amongst the ,silurian rocks of ,english ,lakeland and the thickness of each 7which in the case of the thicker deposits is naturally only approximate73-- ,thickness4 ,zone of ,feet4 ,inches4 ,monograptus leintwardinensis #ejjj #j ,monograptus bohemicus #ejjj #j ,monograptus ,nilssoni #ajjj #j ,cyrtograptus ,murchisoni #ajjj #j ,monograptus crispus #bb #j ,monograptus turriculatus #fj #j ,rastutes maximus #be #j ,monograptus spinigerus #c #j ,monograptus ,clingani #c #j ,monograptus convolutus #g #f ,monograptus argenteus #j #h ,monograptus fimbriatus #g #f ,dimorphograptus confertus #be #j ,diplograptus acuminatus #b #f ,it must not be supposed that each of the subdivisions in the above list is of equal importance1 and has occupied approximately the same length of time for its formation1 but a study of the strata proves by various kinds of evidence that the deposits in which the characteristic forms range through a small thickness of rock were on the whole deposited much more slowly than where the range is continuous through a great thickness of deposit4 ,the geological systems1 as originally founded1 were not very accurately separated from one another except locally4 ,a comprehensive view of the characters of a system was taken1 and accordingly the lines of demarcation between the same systems adopted by workers in different countries were by no means necessarily at or near the same geological horizon4 ,as the result of more recent work1 the establishment of fossil zones has been growing apace1 and though many of these are seen to have only local significance1 it is found as the result of experience that many of them are widely spread and occur in the same order in different localities2 accordingly the remarks that have been made concerning the contemporaneity of strata apply to these zones also4 ,after a study of this kind1 a much more accurate comparison of strata is possible1 and correlation of strata can be carried on to a much greater extent than when the systems were only roughly subdivided by reference to breaks1 differences of lithological character1 and general comparison of the faunas2 accordingly whilst largely retaining the old names1 the old method of classification is being partly superseded1 and the included faunas alone are utilised to establish accurate correlations of the strata in various parts of the world4 ,how far this correlation can be carried on remains to be seen1 for the work though well advanced has by no means reached completion1 and predictions as to the ultimate issue are useless without the experience by means of which only the work can be done4 ,the difference between the methods of classification is well shown by an examination of the old and new divisions of the chalk4 ,it was formerly roughly divided mainly by lithological characters into ,chalk ,marl1 ,lower ,chalk without flints1 ,middle ,chalk with few flints and ,upper ,chalk with many flints1 but no two observers would probably agree as to where the deposit with few flints ceased and that with many commenced4 ,the chalk is now separated on palontological grounds into ,cenomanian1 ,turonian1 ,senonian and ,danian1 and the superiority of the new method to the old is practically shown by the abandonment of the old classification except for very rough purposes1 and the general acceptance of the new one4 ,many other examples might be given1 but this one will suffice4 ,in the case of some of the systems1 the ,carboniferous for example1 the old classification founded upon lithological characters is largely extant1 and it has been inferred therefore that no accurate subdivisions of the ,carboniferous rocks can be made by reference to the faunas1 owing to the rapidity with which the deposits were accumulated4 ,it is by no means certain because the work has not been done that it cannot be done1 and the experience obtained from a study of other strata in which subdivisions have been established by reference to the fauna would lead one to suppose that the non-establishment of subdivisions of the ,carboniferous strata is due to our want of knowledge rather than to their non-existence4 ,the establishment of a classification on palontological lines by no means does away with the necessity for local classifications on a lithological basis1 and it has already been remarked that important results will follow from a comparison of the classifications of sediments founded on the two lines1 results which have hitherto largely escaped our attention owing to the existence of a cumbrous classification attained by the application sometimes of one method1 at other times of the alternative one4 ,,chapter ,,vii4 ,,simulation ,,of ,,structures4 ,although it is easy to give an account of the structures which are of importance to the student of the stratified rocks1 actual observation of these structures is frequently attended with difficulties owing to the close imitation of one structure by another1 and the past history of the science shows that erroneous conclusions have been reached again and again on account of the incorrect interpretation of structures4 ,simulation of organisms has frequently been the cause of error4 ,inorganic substances take on the form of organisms with various degrees of closeness4 ,the dendritic markings produced by efflorescences of oxide of manganese are familiar to all1 and as the name implies1 they simulate1 to some extent1 plant remains4 ,more complex chemical changes have resulted in the production of rock-masses in which1 not the outward form alone but1 the internal structure of organisms is reproduced with more or less approach to fidelity1 as the rocks which contain the supposed organisms described as ,eozoon bohemicum1 ,e4 bavaricum1 and1 we may add1 ,e4 canadense4 ,mechanical changes in rocks subsequent to their formation may also cause the simulation of organisms by inorganic substances4 ,prof4 ,sollas has given reasons for considering the structure described as ,oldhamia to be inorganic1 and in the ,carboniferous ,sandstones of ,little ,haven1 ,pembrokeshire1 every stage in the formation of tubular bodies resembling worm-tubes1 as the result of complex folding of the strata1 may be observed1 whilst in other cases we find imitation of worm-tracks1 as has been observed before4 ,it is when one inorganic structure is simulated by another that the stratigraphical geologist is most likely to be led astray1 and accordingly it is worth noting some cases where this has occurred1 as a warning1 for it must not be supposed that the cases here noted are the only ones which are likely to occur4 ,it has been seen that the existence of bedding-planes is of prime importance to the geologist1 and their detection is a matter of supreme moment4 ,under ordinary circumstances there is no great difficulty in distinguishing bedding-planes from other planes1 but the importance of discovering them is often greatest when the difficulty is most pronounced4 ,in rocks which have undergone no great amount of disturbance the planes of stratification are often marked by their regular parallelism1 the separation of layers having different lithological characters by these planes1 the arrangement of the longer axes of pebbles parallel to them1 and the occurrence of fossils and also of rain-prints1 ripple-marks and other structures produced during deposition1 upon the surfaces of the strata1 but none of these appearances is necessarily conclusive1 especially in areas where the rocks have been subjected to orogenic movements4 ,in regularly-jointed rocks1 jointing may well be mistaken for bedding1 and there is often great difficulty in discriminating between bedding and cleavage1 especially when the exposures of rock are of small extent4 ,fossils may be dragged out along planes at an angle to the true bedding1 pebbles will be compressed by cleavage so that their longer axes do not remain parallel to the bedding-planes but now lie parallel to the superinduced planes of cleavage1 and a structure closely resembling 'ripple-mark' may be produced on planes other than those of original bedding1 as the result of puckering4 ,the alternation of rocks having different lithological characters may also be misleading4 ,intrusion of dykes along cleavage-planes1 followed by decomposition of the dyke-rock causing it to resemble a sediment1 and formation of mineral veins along the same planes1 may give rise to an apparent succession of rocks of different lithological characters which could easily mislead an observer and cause him to mistake the cleavage-planes for planes of stratification4 ,in rocks which have undergone great lateral pressure1 the beds of different lithological character may be folded in such a way as to give very erroneous ideas of the true dip of the rock on a large scale4 ,in ,fig4 #c the dip of the rocks in a small exposure might appear to be in the direction indicated by the unfeathered arrow1 whilst the true dip of the strata as a whole1 leaving the minor foldings out of account1 is in the direction of the feathered arrow1 at the inclination represented by the dotted line4 ,the minor folds in a case like that represented may extend upwards for scores or even hundreds of feet1 so that an error as to the direction and amount of dip may be made1 even if the observer faces a cliff of considerable height4 ,illustration3 ,fig4 #c4 ,false-bedding on a large scale may be a cause of error4 ,in the ,penrith ,sandstone of ,cumberland1 the planes of deposition are often found dipping in one direction in a large quarry1 but inspection of a wider area shows that this is not the true dip of the beds as a whole1 but merely a local dip due to deposition on a slope1 and any one attempting to calculate the total thickness of the beds by reference to these divisional planes might be seriously led astray4 ,a reference to ,fig4 #d will explain this4 ,the lines ,,aa1 ,,bb are the true bedding-planes cut across in the section1 whilst the lines sloping to the right from xx are only lines of false-bedding on a large scale4 ,an exaggerated estimate of the thickness of the deposit would be made by measuring the thickness of each of these stratula from ,a to ,a and adding these thicknesses together1 whereas the actual thickness of the middle bed is the distance between ,a and ,b or ,a and ,b4 ,illustration3 ,fig4 #d4 ,when rocks have been affected by thrust-planes1 the simulation of bedding may be carried out to a very full extent4 ,not only do the major thrust-planes resemble bedding-planes but the minor thrusts produce an appearance of divisional planes separating stratula or lamin1 and a close approximation to false-bedding is the result4 ,to this structure ,prof4 ,bonney has given the name 'pseudo-stromatism#ag4' ,it may be developed in rocks of all kinds1 whether possessing original planes of stratification or not1 and as a result of its existence the geologist may be seriously misled1 not merely by mistaking the direction of the strata1 but also the nature of the rock1 for we may find it produced in an unstratified glacial till1 and in a massive igneous rock1 and in each case the resulting rock will resemble a sedimentary deposit1 and of course the observer may be confirmed in his erroneous opinion by the formation of apparent fossils1 ripple-marks or other objects which he might expect to discover in sediments4 ,as illustrative examples1 reference may be made to a number of schistose rocks1 in which the planes of discontinuity 7which are in truth planes of foliation7 have been taken for bedding-planes and the rocks claimed as sedimentary though they are in reality igneous2 for instance many of the rocks of the ,laurentian of ,canada1 of the ,hebridean of the ,north ,west ,highlands1 and some of the ancient rocks of ,anglesey4 ,footnote #ag3 ,bonney1 ,t4 ,g41 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlii4 ,proc4 p4 #fe4 ,a foliated structure may1 as is now well known1 be simulated by a structure developed in a rock prior to its consolidation4 ,the similarity of flow structure of some lavas to the foliated structure of a schist was long ago pointed out by ,darwin and ,scrope1 and recent work has proved that parallel structure due to differential movement prior to consolidation may be developed in plutonic rocks1 as shown by ,lieut4-,general ,mc,mahon in the ,himalayan granites1 and by ,lawson amongst the plutonic rocks of the ,rainy ,lake ,region2 and as the foliated structure may be mistaken for original stratification the same may occur1 and has occurred1 when dealing with this flow-structure4 ,this is not the place to discuss the truth of the old theory of progressive metamorphism1 in which it was maintained that a gradual passage could be traced between ordinary sediments and plutonic rocks1 but it may be pointed out that much of the evidence which was relied upon to prove the theory was fallacious and due to the confusion of the parallel structure set up in plutonic rocks prior to1 or subsequent to1 consolidation1 with original stratification4 ,recent study of metamorphic rocks has proved that the parallel structures developed in the rocks of an area which has undergone metamorphism may be produced by three distinct processes2 they may be original planes of deposition1 or formed in a solid rock subsequently to its formation1 or in an igneous rock before its consolidation1 and although it is sometimes possible to separate the structures produced by these processes1 this is not always the case#ah4 ,when a plutonic rock contains large phenocrysts and an eye-structure is developed in it1 it may simulate a conglomerate1 the rounded phenocrysts being taken for pebbles#ai4 ,still closer simulation of an epiclastic conglomerate may be produced in other ways and will be referred to immediately4 ,footnote #ah3 ,it must be noticed that the rock in which parallel structure is produced before consolidation1 if it undergoes no further change1 though often associated with metamorphic rocks1 is not itself metamorphic4 ,the term gneiss applied to these rocks is a misnomer1 unless the term be used even more vaguely than it is at present4 ,footnote #ai3 ,see ,lehmann1 ,untersuchungen ber die ,entstehung der ,altkrystallinischen ,schiefergesteine mit besonderer ,bezugnahme auf das ,schsische ,granulitgebirge1 ,plate ,,xi4 fig4 #a4 ,we have already seen that the existence of unconformities has been utilised in the demarcation of large divisions of strata in various regions1 and whether they be utilised in this manner or not1 their detection is a matter of importance to the stratigraphical geologist1 as they afford information concerning the occurrence of great physical changes during their production4 ,these unconformities may also be closely simulated by structures produced in very different manner4 ,the occurrence of an unconformity implies the denudation of one set of beds before the deposition of another set upon them1 and accordingly the denuded edges of the lower set will somewhere abut against the lower surface of the lowest deposit or deposits of the overlying set#bj4 ,the existence of an unconformity may often be detected in section1 but when the unconformity is upon a large scale this may not be possible1 but it will be discovered by mapping the strata and will be apparent on a map owing to the deposits of the lower set of beds abutting against the others4 ,this is well seen where the ,permian rocks of ,durham1 ,yorkshire1 and ,nottinghamshire rest upon different members of the underlying ,carboniferous series1 and will be noticed on any good geological map of ,england4 ,but a similar effect may be caused by a fault1 so that mere inspection of a map or even of the strata in the field and discovery of one set of beds ending off against another does not prove unconformity4 ,when the fault is a normal one1 with low hade 7that is1 having a fissure approaching the vertical position71 the outcrop of the fault-fissure will approximate to a straight line if the fault has a straight course1 even if the ground be very uneven1 whereas1 if the plane of unconformity has not been tilted to a high angle from its original horizontal position1 it will crop out in a sinuous manner across uneven ground1 in a way similar to that of beds which are nearly horizontal1 so that though the general trend of the outcrop of the plane of unconformity may be fairly straight1 its deviation from a straight line will be frequent and marked1 as seen in the case of the ,permian unconformity above referred to4 ,but if the unconformable junction has been highly inclined its outcrop will resemble that of a normal fault1 or if the fault be a thrust-plane with high hade1 the outcrop of this will resemble that of an unconformable junction which has not been greatly tilted from its original horizontal position4 ,in these cases we require more evidence before we can decide whether we are dealing with an unconformable junction or a faulted one4 ,footnote #bj3 ,an unconformity may be simulated or an actual unconformity rendered apparently more important1 as the result of underground solution of the underlying strata subsequently to the deposition of the upper set upon them1 and any insoluble materials in the underlying strata may be left as an apparent pebble-bed at the base of the upper beds4 ,this is seen at the junction of the ,tertiary beds with the chalk near ,london4 ,subterranean water has dissolved the upper part of the chalk1 increasing the unconformity which naturally exists between chalk and ,tertiary beds1 and the insoluble flint of the dissolved chalk is left as a layer of 'green-coated flint' at the base of the ,tertiary deposits4 ,the lowest deposits of the newer set of strata lying above an unconformity have probably been laid down in water near the shore-line4 ,as the unconformity1 if large1 implies elevation above the sea-level1 the deposits first formed after this elevation has ceased1 and depression commenced1 will necessarily be littoral in character and possibly of beach-formation1 and accordingly we often find that an unconformity is marked by the existence of an epiclastic conglomerate immediately above the plane of unconformity and1 although this need not be continuous1 it is usually found somewhere along the line of junction4 ,the conglomeratic base of the ,lowest ,carboniferous strata when they repose upon the upturned edges of the ,lower ,palozoic rocks of the dales of ,west ,yorkshire is well known1 and may be cited as an example4 ,the association of conglomerates with unconformities is indeed so frequent that its possible occurrence will always be suspected and sought by the geologist4 ,unfortunately the result of recent observation is to show that along thrust-planes of which the outcrop simulates those of unconformable junctions1 the difficulty of discrimination may be increased by the existence of cataclastic rocks which bear a close resemblance to epiclastic conglomerates1 and which may be and have been styled conglomerates4 ,it is well known that fragments of the adjoining rocks are knocked into a fault-fissure during the occurrence of the movements which cause the fault1 to constitute a fault-breccia1 and as the result of the abrasion of these fragments by chemical or mechanical agency1 the angular fragments may become rounded and converted into rounded pebble-like bodies1 when the rock is changed into a fault-conglomerate4 ,fig4 #e1 from a photograph kindly supplied by ,prof4 ,w4 ,w4 ,watts1 shows a stage in the formation of a conglomerate of this nature from a fault-breccia2 the fragment on the right remains angular1 whilst those on the left have become much more rounded4 ,the illustration is from a case described by ,mr ,lamplugh occurring in the slaty rocks of the ,isle of ,man1 and ,mr ,lamplugh's paper#ba furnishes the reader with references to other examples of the production of similar rocks4 ,no general rule can be laid down for distinguishing the true from the apparent unconformity1 for the attendant phenomena will differ in each case2 but if a fault-conglomerate should be suspected1 the observer should try to ascertain whether fragments of a newer rock are imbedded in an older one1 which sometimes occurs2 he should note the existence of extensive slickensiding along the plane of junction and along planes of faulting1 though the existence of these1 implying as it does the occurrence of differential movement along the plane1 does not prove that the movement was necessarily great1 or that it did not take place along a plane of original unconformity2 above all1 he should look for structures such as mylonitic structure1 pseudo-stromatism1 development of new minerals1 crushing out and stretching of fossils and fragments and1 in short1 for any structure which is familiar to him as a result of orogenic movements4 ,footnote #ba3 ,lamplugh1 ,g4 ,w41 ,on the ,crush-,conglomerates of the ,isle of ,man1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,li4 p4 #efc4 ,illustration3 ,fig4 #e4 ,the effects of thrusting not only give rise to appearances suggestive of unconformity1 but naturally also to a simulation of overlap4 ,the thrust-planes are often parallel to original bedding-planes for some distance1 but must cut across them sooner or later1 producing lenticular masses which might be supposed to be due to the thinning out of beds as the result of cessation of deposition in a lateral direction4 ,attention has already been directed to the deceptive appearance of great thickness of strata which is due to repetition of one stratum or set of strata by a series of thrust-planes1 so that there is no actual inversion of any part of a bed4 ,when masses of limestone are affected in this way1 the thrust-planes may become sealed up1 as the result of chemical change1 and a compact irregular mass of limestone devoid of any definite divisional planes may be the consequence1 and beds of grit sometimes exhibit the same feature to some extent4 ,enough has been said to show that simulation of one structure by another has frequently occurred in rocks in so marked a degree as to render mistakes easy2 and that these examples of 'mimicry' in the inorganic world are particularly frequent in rocks which have been subjected to great orogenic movements4 ,the student will do well to acquaint himself with the macroscopic and microscopic structures which may be taken as characteristic of the rocks which have been thus affected1 some of which can usually be detected with ease1 and when he discovers them he may suspect that many phenomena which appear explicable in one way were in reality produced in a different one1 for it is frequently very true of a region in which the rocks have been violently squeezed1 stretched and broken that 'things are not what they seem4' ,,chapter ,,viii4 ,,geological ,,maps ,,and ,,sections4 ,the writer does not propose to give an account of the intricacies of geological mapping1 for their right consideration requires a separate treatise#bb2 all he desires is to call attention to some of the uses of geological maps as a means of conveying information4 ,a geological map may be looked upon as an attempt to express as far as possible in two dimensions phenomena which possess three dimensions2 this can be done to some extent on the actual surface of the map1 by conventional signs1 still more fully1 by supplementing the map with sections2 but best of all by a geological model1 which is cut across in various directions in order to show the underground structure as well as that of the surface4 ,footnote #bb3 ,the student is recommended to consult in particular1 ,appendix ,i4 ,on ,geological ,surveying in ,the ,student's ,manual of ,geology1 by ,j4 ,b4 ,jukes 7,third ,edition1 ,edited by ,a4 ,geikie71 p4 #gdg1 and ,outlines of ,field ,geology1 by ,sir ,a4 ,geikie 7,macmillan and ,co474 ,the ordinary geological map is one which shows the outcrop of the strata1 subdivided according to age1 as they would be seen upon the surface of the earth after stripping off the superficial accumulations1 and it is to be feared that the term 'geological map' is associated in the minds of most students with a map of this character and of no other4 ,nevertheless1 a great many most important observations other than those connected with the order of succession of the strata are capable of representation upon a geological map1 and the possession of a large number of maps of any area upon the geology of which a person is engaged--each map to be used for recording observations of a particular kind--will save much writing in note-books and1 what is of more importance1 will allow him to compare observations which have been made at different times at a glance1 instead of causing him to search through a series of note-books4 ,still1 however well furnished with maps1 the geologist will find a note-book essential#bc4 ,footnote #bc3 ,as a result of some experience1 the writer recommends every student to acquire some skill in the use of the pencil1 and if to such a degree that he can combine artistic effect with accuracy1 so much the better4 ,an acquaintance with photography is invaluable3 often the possession of a camera would enable a section to be recorded1 which is otherwise lost to science4 ,the earliest geological maps represented the variations in the surface soils1 or at most the general lithological characters of the rocks which by their decay furnished the materials for the soils4 ,we have seen that the first chronological map was due to ,william ,smith1 and most subsequent ,english geological maps have been based upon his map of the strata of ,england and ,wales4 ,the order of succession of the strata is represented in these maps to some extent by the use of arrows to indicate the direction of dip of the strata1 though this is not an unerring guide where strata are reversed1 and accordingly the addition of a legend at the side of the map may be looked upon as essential to the correct understanding of the map itself4 ,the legend is usually in the form of a section of a column1 the strata being arranged in right order1 the oldest at the base and the newest at the summit1 the colours by which the strata are indicated being similar to those placed upon the map4 ,other information besides the mere order of succession of the strata may appear in the legend2 thus their relative and actual thicknesses can be indicated if the column is drawn to some definite scale1 and a brief description of the lithological characters of the rocks may well be appended to the side of the column4 ,on the actual maps it is customary to exhibit the outcrop of the junctions of all igneous rocks as well as of the sedimentary ones3 the nature of the metamorphism which sedimentary rocks have undergone at the contact with igneous ones may be and often is indicated by suitable signs2 the position of faults is shown1 and often also that of metalliferous veins1 the nature of the ore in the latter being further indicated in some suitable manner1 as by giving the recognised symbol for the metal2 and in many maps an attempt is made to show the variations in dip and strike of the cleavage-planes4 ,the ,geological ,survey of the ,united ,kingdom publishes two sets of maps1 one showing the 'solid geology' and the other the 'superficial geology4' ,it is easier to understand these terms than to define them1 for in ,britain there is a sharp line between the two everywhere except near ,cromer4 ,the maps showing the superficial geology represent gravels1 glacial drifts and other incoherent accumulations of geologically recent origin1 which to a greater or less extent mask the strata below which are usually composed of more or less solidified material4 ,the maps showing the solid geology display the outcrops of these strata1 though it is usual to insert alluvium upon these maps1 as it is often impossible to trace the junction-lines of the strata below it4 ,attention has already been directed to the fact that these maps of solid geology1 though chronological1 that is1 having the strata represented according to age1 are founded largely upon lithological differences1 rather than upon included organisms2 and it has been stated that for theoretical purposes two sets of chronological maps1 one founded upon lithological differences1 the other upon difference of fossil organisms1 would be extremely valuable4 ,other phenomena are often best represented upon separate maps1 for if all observations are crowded upon one map the result will be very confusing4 ,special glacial maps showing the contour of the country1 with the portions between the contour lines coloured differently according to altitude1 say the country between sea-level and #ejj feet light green1 that between #ejj and #ajjj dark green1 that between #ajjj and #aejj light brown and so on1 exhibiting the direction of all observed glacial striae1 the distribution of boulders so far as it is possible1 and any other glacial phenomena which can be noted upon the map1 will be valuable to the student of glaciation#bd4 ,footnote #bd3 ,for examples see ,tiddeman1 ,r4 ,h41 ,evidence for the ,ice-,sheet in ,north ,lancashire and the adjacent parts of ,yorkshire and ,westmorland1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxviii4 pl4 ,,xxx41 and ,goodchild1 ,j4 ,g41 ,glacial ,phenomena of the ,eden ,valley c41 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxi4 pl4 ,,ii42 and for a map of distribution of boulders1 ,ward1 ,j4 ,c41 ,geology of the ,northern ,part of the ,english ,lake ,district 7,mem4 ,geol4 ,survey71 pl4 ,,iv4 ,various structural features may be well displayed on separate maps4 ,the trend of the axes of folds will be useful1 and may be accompanied by other information of cognate character#be2 maps of the distribution of joint planes may be given in combination with those showing the folding of the strata if it be desired to exhibit the relationship between these2 or with the physical features of the country1 if the dependence of physical features upon joint structure be under consideration#bf4 ,much information concerning cleavage may be acquired from a map showing anticlinal and synclinal axes of cleavage#bg1 or the actual strike of the cleavage over different parts of a map may be represented1 and its relationship to the geological structure of the district exhibited#bh4 ,footnote #be3 ,see ,bertrand1 ,m41 ,sur le ,raccordement des ,bassins ,houillers du nord de la ,france et du sud de l',angleterre1 ,annales des ,mines1 ,jan4 #ahic1 ,plate #a4 ,footnote #bf3 ,see ,daubre1 ,a41 tudes ,synthtiques de ,gologie ,exprimentale1 #are ,partie1 ,plates ,,iii4-,,vi41 for an example of the latter1 which is also interesting as showing the utility of a map on transparent paper super-posed on another1 when illustrating the connexion between two sets of structures4 ,footnote #bg3 ,ward1 ,j4 ,c41 ,geology of the ,northern ,part of the ,english ,lake ,district1 ,plate ,,ix4 ,footnote #bh3 ,harker1 ,alfred1 ,the ,bala ,volcanic ,series of ,caernarvonshire 7,sedgwick ,essay for #ahhh71 ,fig4 #e4 ,maps exhibiting changes in physical geography appertain to the geologist as well as to the geographer4 ,the position of ancient beaches1 former lakes1 representation of the changes in the courses of rivers and kindred phenomena may be shown upon maps1 and will prove useful#bi4 ,footnote #bi3 ,for examples of maps of this kind1 see ,kjerulf1 ,th41 ,die ,geologie des sdlichen und mittleren ,norwegen4 ,a perusal of the maps to which reference has been made above will give the student some notion of the extent to which maps may be utilised to represent geological structures1 and may suggest other methods by which they may be utilised4 ,a geological section is usually drawn in order to exhibit the lie of the rocks1 as it would be seen if a vertical cutting were made in that part of the earth's crust which is under consideration4 ,the character of the section will depend upon circumstances4 ,the ,geological ,survey of ,great ,britain issues two kinds of sections which are usually spoken of as vertical sections and horizontal sections1 though each is in truth a vertical section2 but whereas in the former the horizontal distance represented is small as compared with the thickness of the strata1 in the latter the rocks of a considerable horizontal extent of country are exhibited in the section1 and the section is not carried down to a great depth below the earth's surface4 ,there is no essential difference between the two kinds of section1 and often sections are drawn which cannot be definitely classed as belonging to either kind1 but in extreme cases the vertical section is a representation of the order of succession as it would appear if the rocks were horizontal1 no matter how disturbed they may be in reality2 whereas the horizontal section represents the strata as they actually occur1 with all the folds and faults by which they are affected4 ,the accompanying figure 7,fig4 #f7 represents a horizontal section on the left side of the figure with a vertical section of the same rocks on the right side4 ,illustration3 ,fig4 #f4 ,vertical sections are extremely useful when it is desirable to compare variations in the strata over wide extents of country3 this can be done by drawing a series of columns of the strata1 each showing in vertical section the lithological characters and thicknesses of the strata in one place1 whilst the relationship between the strata of two different places may be indicated by joining the beds of the same age by dotted lines as shown in ,fig4 #gcj4 ,illustration3 ,fig4 #g4 ,footnote #cj3 ,it is useful to adopt conventional symbols for the representation of strata of different lithological characters1 and so far as possible to adhere to the same kind of symbol for any one kind of deposit4 ,those which are generally in use1 are rough pictorial representations of the characters of the deposits1 as shown in ,fig4 #g4 ,the conglomerate is indicated by circular marks representing cross-sections of the pebbles1 a breccia by triangular marks signifying that the fragments are angular and not rounded2 a sandstone is indicated by dots to represent the grains of sand2 a mud1 clay or shale by continuous or broken horizontal lines1 which reproduce the appearance of the planes of lamination so frequent in beds of this composition2 a limestone is usually marked by the use of regular horizontal lines illustrating the pronounced bedding1 with vertical lines at intervals to represent the regular jointing which occurs in so many limestones3 the nature of the bedding may be further shown by drawing the lines comparatively far apart when the limestone is a thick-bedded one1 nearer together when it is thin-bedded4 ,igneous rocks are represented by crosses or irregular ,v-shaped marks1 illustrating the absence of stratification and presence of joints4 ,volcanic ashes are sometimes represented by dots1 at other times by signs somewhat similar to those which are used for true igneous rocks4 ,sedimentary rocks which are composed of more than one kind of material may be further shown by a combination of two symbols1 thus the existence of a sandy clay may be shown by means of a combination of horizontal lines and dots1 and so with other combinations4 ,the practical geologist should become accustomed to the use of these symbols in his note-book2 if used1 they will save much writing4 ,these symbols are used in some of the later illustrations to this book4 ,the horizontal section is one which is in constant use by the practical geologist3 the results of the first traverse of a district may be jotted down in his note-book in the form of a horizontal section 7with accompanying notes71 and the written memoir on the geology of any district composed largely of stratified rocks will almost certainly require illustration by means of these sections4 ,perhaps nothing more clearly marks the careful observer than the nature of the sections which he makes1 and geological literature is too frequently marred by the publication of slovenly sections4 ,a badly drawn section not only offends the eye1 it may and frequently does convey inaccurate information4 ,illustration3 ,fig4 #h4 ,in the above figure 7,fig4 #h7 taken from ,sir ,henry de la ,beche's ,sections and ,views ,illustrative of ,geological ,phnomena1 ,plate ,,ii41 the lower drawing represents a section drawn to true scale1 while that above shows one which is exaggerated4 ,the student who saw this would infer that the uppermost beds on the left side of the upper section rested unconformably upon the dotted beds beneath1 and once abutted against them in that portion of the figure where the beds have been removed by denudation in the deep valley1 whereas an examination of the section drawn to true scale shows that the unconformity does not exist 7although there is one at the base of the deposits marked by dots71 and that there is room for the higher deposits to pass above those marked by dots at the place where the former have been removed by denudation4 ,whenever possible1 horizontal sections should be drawn to true scale1 the vertical heights being on the same scale as the horizontal distances4 ,sections which are so drawn represent the nature of the surface of the country as well as the relationship of the strata1 and often illustrate in a marked degree the influence which the character of the strata has exerted upon the nature of the superficial features of a country4 ,if it be impossible to draw a section in which the elevations and horizontal distances are represented upon a true scale1 the former ought to be drawn on a scale which is a multiple of the latter2 thus the vertical heights may be shown on #b1 #c1 or #d or more times the scale chosen for the horizontal distances2 when this is done1 it will often be necessary to show the strata with an exaggerated dip1 and accordingly the exaggerated section loses some of its value1 though if vertical and horizontal scales bear some definite proportion it will still be more valuable than a rough diagram which is not drawn to any scale4 ,section-drawing cannot be satisfactorily accomplished without some practice1 and the student is strongly advised to acquire the art of drawing good sections2 the writer can assert as the result of considerable experience in the conduct of examinations of all kinds1 that slovenly sections are the rule in candidates' papers1 and good sections very rarely appear4 ,study of the six-inch maps and horizontal sections 7drawn on the same scale7 of the ,geological ,survey of the ,united ,kingdom will enable the student to familiarise himself with admirable sections1 and it should be his aim to produce sections like these4 ,he is recommended to take some of these six-inch maps which show contour-lines as well as the disposition of the strata1 and to draw sections on the scale of six inches to the mile1 vertical and horizontal1 exhibiting the proper outline of the ground and the arrangement of the strata1 and afterwards to compare them with the published sections4 ,the sections should be drawn as far as possible at right angles to the general strike of the strata4 ,some datum-line is taken for the base of the section 7say sea-level7 and offsets drawn vertically from this where the section crosses a contour-line or recorded height4 ,the height is marked on these offsets2 thus if a recorded height of #bgjj feet 7just over half a mile7 occurred on the line of section a height of somewhat over three inches is marked on the offset1 and so with the other points where the section crosses contours or recorded heights4 ,by joining these points on the offsets1 giving the connecting lines curves similar to those which are likely to occur in nature1 the general character of the surface of the ground is represented4 ,the geology of the district is next shown4 ,wherever a dip is marked on the map1 the direction and amount of dip is shown by a short line on the section1 and where dips are not actually seen along the line of section1 the dips which are nearest to that line on the map must be considered1 and marked on the section4 ,the lines of junction between the various deposits shown by different colours upon the map are inserted on the section as short lines1 the inclination being judged by study of the nearest dips2 faults and igneous rocks must be marked off1 and any indication of the hade of the fault or the slope of the edges of the igneous rock which the map affords will be taken into account4 ,the section will then appear somewhat as shown in the following figure3 ,illustration3 ,fig4 #i4 and sufficient indication of the trend of the rocks will be obtained to shew that they form portions of curves which may then be filled in as shown in ,fig4 #aj and the section will be complete4 ,illustration3 ,fig4 #aj4 ,it will be noticed that the small dyke of igneous rock on the right of the main dyke is joined to it lower down1 though no indication of this is given along the line of section2 but the requisite information for this and evidence of the existence of the small dyke proceeding from the left-hand side of the main one may be obtained by the study of the rocks in a valley on one side or other of the line of section4 ,after the student has become conversant with the nature of geological maps and sections1 and has read ,sir ,a4 ,geikie's ,outlines of ,field ,geology1 he should on no account omit to learn something of the art of making geological maps1 by going into the field and attempting to produce a map1 for the art of geological surveying does not come naturally to any one1 and some acquaintance with the methods of surveying is a necessity to everyone who wishes to make original geological observations1 though all cannot expect to afford the time and acquire the skill necessary for the production of maps vying with the detailed maps of the ,government ,survey4 ,before actually attempting to draw lines on a map on his own account1 he will do well to tramp over a portion of a district with the published geological map in his hands1 selecting a country which is not characterised by great intricacy of geological structure1 and he can then attempt to represent the geology of another portion of the same district without consulting the published map4 ,of all the districts of ,britain with which he is acquainted the writer believes that the basin of the river ,ribble1 in the neighbourhood of the town of ,settle in the ,west ,riding of ,yorkshire1 is best adapted for studying field geology in the way suggested above1 for the main geological features are marked by extreme simplicity1 and the exposures are good1 whilst the presence of an important fault-system and of a great unconformity relieve the area from monotony4 ,anyone who stands on the summit of ,ingleborough or ,penyghent will grasp the main features of a portion of the district without any difficulty1 for it lies beneath his feet like a geological model1 and when the student has mastered and mapped in the leading features1 he can find bits of country with geology of varying degrees of complexity amongst the ,lower ,palozoic rocks of the valleys which run down to ,ingleton1 ,clapham1 ,austwick and ,settle4 ,the biologist is supplied with laboratories at home and abroad1 where he may study his science under the best conditions4 ,would that some munificent person would found1 in a district like that referred to above1 a geological station where ,cambridge students would have the means of acquiring a knowledge of field-geology under conditions more favourable than those presented by the flats around the sluggish ,cam6 ,,chapter ,,ix4 ,,evidences ,,of ,,conditions ,,under ,,which ,,strata ,,were ,,formed4 ,the establishment of the order of succession of the strata1 and the correlation of strata of different areas merely pave the way for the geologist4 ,to write the history of the earth during various geological ages1 he has to ascertain the physical and climatic conditions which prevailed during the successive geological periods1 and to study the various problems connected with the life of each period4 ,in the present chapter an attempt will be made to illustrate the methods which have been pursued in order to write to the fullest degree which is compatible with our present knowledge1 the earth-history of various ages of the past4 ,in making this attempt1 the physical and climatic conditions may be first considered1 and their consideration followed by that of the changes in the faunas1 though it will frequently be necessary to refer to one set of conditions as illustrative of the other4 ,it will be assumed here that the great principle of geology1 that the modern changes of the earth and its inhabitants are illustrative of past changes1 is rigidly true4 ,reference will be made to this principle in a later chapter1 but it is sufficient to state here that the study of the sediments which have been deposited from the commencement of ,lower ,palozoic times to the times in which we now live bear the marks of having been formed under physical conditions1 which1 in the main1 are similar in kind to those which prevail upon some part of the surface of the lithosphere at the present day4 ,one of the most important inferences of the stratigrapher relates to the existence of marine or terrestrial conditions over an area at any particular time1 and we may1 in the first place1 consider the evidence which supplies us with a clue to this subject4 ,it has been previously stated that the ocean is essentially the theatre of deposition1 the land that of destruction1 and accordingly1 the presence of deposit as a general rule indicates the evidence of marine conditions during the formation of those deposits1 though this is not universally the case4 ,again1 as denudation is practically confined to the land areas1 and the shallow-waters at their margins1 unconformity on a large scale gives evidence of the existence of terrestrial conditions in the area in which it is developed1 during its production4 ,accordingly a mass of deposit separated from deposits above and below by marked unconformities shows the alternation of terrestrial conditions 7during which the unconformity was produced7 and marine conditions 7during which the deposits were laid down74 ,the deposits formed after an unconformity has been developed will naturally be of shallow-water character1 as will also be those of the period immediately preceding the incoming of conditions which will cause the occurrence of another unconformity1 and between these two shallow-water periods will occur a period when deeper-water conditions probably prevailed4 ,we can therefore not only divide the history of any particular area into a series of chapters1 of which every two successive ones will describe a continental period and a marine one1 but each marine period may be divided into three phases--a shallow-water phase at the commencement1 an intermediate deeper-water phase1 and a shallow-water phase at the end4 ,these phases are frequently complicated by the occurrence of a host of minor changes1 but on eliminating these1 the effects of the three great phases are shown by study of the nature of the strata1 and their recognition does much to simplify the detailed study of the stratigraphical geology of various parts of the earth's surface4 ,in discriminating between terrestrial conditions and marine ones1 the existence of unconformities is of great importance in marking terrestrial conditions and is often the only available evidence1 for no accumulations or deposits formed on the land may be preserved to testify to the terrestrial conditions#ca4 ,when terrestrial deposits and accumulations do occur1 they are extremely important1 and it is necessary to allude to the points wherein they differ from marine deposits4 ,footnote #ca3 ,the term terrestrial is used above in opposition to marine1 to include the conditions prevalent above sea-level4 ,the term continental would be better if it did not exclude insular conditions4 ,accordingly deposits formed in rivers1 and fresh-water and salt-water lakes are spoken of as terrestrial4 ,apart from organic contents1 the mechanically formed deposits of rivers and lakes resemble in general characters the shallow-water deposits of the ocean1 though they are usually less widely distributed4 ,it is the accumulations which have actually been formed as olian rocks1 or those which have been laid down as chemical precipitates in salt-lakes which1 by study of lithological characters1 furnish the most convincing evidence of their terrestrial origin4 ,many olian accumulations may be looked upon as soils1 if the term soil be used in a special sense to refer to the accumulations which are produced as the result of the excess of disintegration over transportation in an area1 whilst others are due to transport which has not been sufficiently effective to carry the material to the sea4 ,when the weathered material accumulates above the weathered rock1 it depends chiefly upon climate whether the disintegrated rock becomes mingled with much decayed organic matter forming humus4 ,if this organic matter exists in quantity1 the probability is that the accumulation is a terrestrial one1 though this is by no means necessarily the case1 for under exceptional circumstances a good deal of humus may be deposited in the sea1 as beneath the mangrove-swamps which line the coasts of some regions1 and to go further back1 in the case of the ,cromer ,forest series of ,pliocene times1 or some coals1 such as the ,wigan ,cannel ,coal of the ,carboniferous strata4 ,in addition to the work of water1 which affects both land and sea-deposits1 the land is especially characterised by the operations of wind and frost upon it1 for these produce results which may frequently serve to differentiate a land-accumulation from a deposit laid down beneath sea-level4 ,the effect of wind in rounding the grains of sand which are blown by it is well-known1 and samples of the 'millet-seed' sands of desert regions are preserved in most museums4 ,the greater rounding which characterises wind-borne as compared with water-borne sand grains is due1 in great measure1 to the greater friction between the grains when carried by the air than when swept along by the water4 ,under favourable circumstances water-worn grains may become rounded1 especially when agitated by gentle currents sweeping over a shoal#cb2 but a large mass of sand1 in which most of the grains have undergone much rounding so as to give rise to 'millet-seed' sand1 will nevertheless be probably formed by wind-action except where a marine deposit is formed of material largely derived from an earlier olian one4 ,the effect of frost is to split rocks into fragments which are more or less angular before they are subjected to water-action4 ,the broken fragments are prone to collect on slopes as screes1 and as any scree-material falling into the sea is likely to become rounded except under conditions which rarely prevail1 the existence of much scree-material in a rock suggests its terrestrial origin4 ,glaciers gave rise to terrestrial moraines1 which may occasionally be identified as land-accumulations by mere inspection of their physical characters1 but all geologists are aware of the difficulties with which they are confronted when they attempt to discriminate between terrestrial and marine glacial deposits4 ,footnote #cb3 ,cf4 ,hunt1 ,a4 ,r41 ,the ,evidence of the ,skerries ,shoal on the wearing of ,fine ,sands by ,waves1 ,trans4 ,devon4 ,assoc41 #ahhg1 vol4 ,,xix4 p4 #dih4 ,the existence of much material amongst the stratified rocks which has been precipitated from a state of solution is an indication of the terrestrial origin of the rocks1 which were laid down on the floors of the inland seas1 separated more or less completely from the open ocean2 for the waters of the ocean are capable of retaining in solution all of the material which is brought down to them1 and accordingly precipitates of carbonate of lime1 rock-salt1 gypsum and other compounds formed from solution1 are only formed on a large scale in inland lakes1 though they may be formed to some extent when the water of a lagoon is only slightly connected with that of the open ocean1 and the evaporation is great1 for instance in the lagoons of coral reefs4 ,certain physical features often mark the deposits of chemical origin1 cubical or hopper-crystals of rock-salt may be dissolved1 and the hollow afterwards filled with mud1 so that the rock surfaces are sometimes marked with pseudomorphs of mud after rock-salt4 ,sun-cracks and rain-prints impressed on the rock are not actual indications of terrestrial origin of the rocks on which they are found1 for the shallow-water muds of an estuary may be deposited in the sea and yet exposed to the action of the air at low tide1 but they mark very shallow-water deposits which have been exposed to the atmosphere immediately after their formation if not during the time they were formed1 and they frequently occur amongst the deposits of inland lakes4 ,it will be observed that the characters of the terrestrial accumulations serve to distinguish them to some extent from the marine ones1 but they also enable one to detect to some degree the actual conditions under which the accumulation was produced1 whether on the mountain-slope1 or in the plain1 the desert or the fen1 the river-bank or the lake-floor4 ,the conditions of formation of the marine deposits may be distinguished within certain limits with ease1 by examination of their physical characters1 for the near-shore deposits will generally be coarser and contain more mechanically-transported material than the sediments which accumulate at a greater distance from the shore1 though it is not safe to infer that deposits are formed away from the shore on account of the absence of mechanically-transported sediments4 ,in districts where the mechanically-transported material is rapidly deposited1 organic deposits of great purity may form close to the coast-line2 for instance1 when the rivers of a country end in fjords1 the mechanical sediments are deposited in the fjords1 and the sea around the coast is free from this sediment1 and there the organisms can build up deposits of great purity2 and a similar thing may happen when the rivers on one side of a country have short courses1 and do not carry down much sediment1 which occurs when the watershed is near the coast4 ,on the one hand1 clay may be formed in considerable purity near the coast1 where the supply of mud is so great that the organisms existing there can do little in the way of contribution to the mass of the deposit1 or it may be formed on the other hand in great depths of the ocean1 where the supply of sediment is extremely small1 but where all the organic tests become dissolved2 as the characters of the deep sea clays are mainly negative1 a geologist examining the rocks of the geological column would have much difficulty in distinguishing a deep-water clay from a shallow-water one by its lithological characters only4 ,in cases of difficulty1 information of importance is likely to be furnished by examination of the relative thickness of equivalent deposits in adjoining areas1 for if we find a mass of clay a few feet thick in one region represented by hundreds of feet of clay and limestone in another1 the former mass probably accumulated slowly and at some distance from the land2 again1 the uniformity of lithological characters of a deposit over a very wide area is a possible indication of its formation away from land1 but this is not a safe guide1 for reasons which will eventually appear1 unless it can be shown that the deposit is everywhere of the same age4 ,a clue to climatic conditions is frequently furnished by the physical characters of accumulations1 especially terrestrial ones4 ,the accumulations containing a large percentage of hydrocarbons have probably been formed under fairly temperate and moist climatic conditions1 whilst the existence of millet-seed sandstones associated with chemical deposits points to desert conditions and inland lakes1 requiring a dry climate and probably a warm one4 ,glaciated surfaces and glacial deposits of course indicate a low temperature4 ,some geologists profess that occasionally they can even determine the direction of the prevailing winds during past periods1 by examination of the character of ripple-marks1 rain-pits and other features1 though it is doubtful whether much reliance can be placed upon these obscure indications4 ,useful as is the physical evidence supplied by deposits1 as an index to the conditions under which they were formed1 it is usually only supplementary to the evidence derived from a study of the fossils4 ,fossils when present in the rocks1 usually supply considerable information concerning the prevalent conditions during the deposition of the rocks4 ,by them we can not only separate marine from terrestrial deposits1 but also freshwater deposits from olian accumulations2 each kind of deposit will generally contain the remains of organisms which existed under the conditions prevalent in the area of formation of the rock1 though it is of course a frequent thing for a terrestrial creature or plant to be washed into a freshwater area or into the sea4 ,in an olian deposit1 the invertebrate remains may be those of any air-breathing forms1 as insects1 galley-worms1 spiders1 scorpions and molluscs4 ,the land-molluscs are all univalve4 ,of vertebrates1 we may find the bones and teeth of amphibians1 reptiles1 birds and mammals4 ,occasionally freshwater or even marine forms may be found in an olian deposit1 but they will be exceptional4 ,marine shells are often blown amongst the sand-grains of the coastal dunes1 and seagulls and other birds frequently carry marine organisms far inland4 ,the creatures frequenting fresh water differ from those of the land and of the sea4 ,the most abundant vertebrate remains will be those of fishes1 and of the invertebrates we find mollusca preponderate4 ,the variety of molluscs is not so great as in the case of marine faunas4 ,the bivalves always possess two muscular scars on each valve 7except adult ,mulleria72 whilst many marine shells as the oyster have only one muscular scar on each valve4 7,see ,fig4 #aa47 ,illustration3 ,fig4 #aa4 ,a4 ,monomyary shell with one scar4 ,b4 ,dimyary shell with two scars4 ,these scars mark the attachment of the adductor muscles1 for drawing the valves together1 and the shells with only one impression on each valve are called monomyary1 those with two impressions dimyary4 ,the discovery of monomyary shells indicates with tolerable certainty the marine character of the deposit in which they are found1 though their absence cannot be taken as proof of freshwater origin4 ,the beaks or umbones of the bivalves are often corroded in freshwater deposits1 as may be seen by examining shells of the common freshwater mussel4 ,all univalve shells of land and freshwater species1 with the exception of ,melanopsis and ,achatina1 which has a slight indentation1 have entire mouths2 and this circumstance may often serve as a convenient rule for distinguishing freshwater from marine strata2 since if any univalves occur of which the mouths are not entire1 we may presume that the formation is marine#cc4 ,footnote #cc3 ,lyell's ,students' ,elements of ,geology1 ,second ,edition 7#ahgd71 ,chap4 ,,iii4 ,a good account of the differences between freshwater and marine organisms1 from which some of the facts here cited are extracted1 will be there found4 ,illustration3 ,fig4 #ab4 ,a4 ,holostomatous shell4 ,b4 ,siphonostomatous shell4 ,in ,fig4 #ab ,a shows a freshwater shell 7,vivipara7 with entire mouth1 whilst ,b exhibits the shell of a marine gastropod 7,pleurotoma7 with a notched mouth4 ,the entire-mouthed shells are called holostomatous whilst those which are notched1 the notch being often prolonged into a canal1 are termed siphonostomatous4 ,many groups of invertebrates are seldom or never found in fresh water4 ,of exclusively or nearly exclusively marine creatures we may name the foraminifera1 radiolaria1 sponges with a hard framework1 most hydrozoa which secrete hard parts1 corals1 echinoderms1 cirripedes1 king-crabs1 locust-shrimps1 most polyzoa1 brachiopods1 pteropods1 heteropods1 and cephalopods4 ,of extinct groups1 the graptolites and trilobites seem to have been entirely confined to the sea4 ,in the modern and comparatively modern deposits1 the forms frequently belong to existing genera1 and we get fairly conclusive evidence of the conditions of deposit by determination of the genera4 ,the terrestrial 7including freshwater7 molluscs have mostly a long range in time4 ,we find pulmoniferous gastropods of living genera in the ,carboniferous period1 one 7,dendropupa7 belongs to a subgenus of the modern land-shell ,pupa1 the other 7,zonites7 to a subgenus of the snail group ,helix4 ,many freshwater molluscs as ,unio1 ,cyclas1 and ,physa are found amongst the secondary rocks1 and give a clue to the origin of the deposits which contain them4 ,many extinct genera are closely allied to modern genera1 and their mode of existence may be assumed with fair certainty4 ,with all these guides1 we may sometimes be left in doubt as to the conditions of deposit when organisms are few in number2 thus1 it is yet a matter for discussion whether the ,old ,red ,sandstone and many of the deposits of the ,coal ,measures of ,britain were of freshwater or marine origin4 ,in considering the possibility of fossils having been carried from land to water or vice versa1 it will be remembered that generally speaking they are more readily transferred from a higher to a lower level1 so we are more likely to find remains of land-animals and plants in fresh water or the sea1 and relics of freshwater animals and plants in the sea1 than of marine or freshwater animals and plants in land1 or marine organisms in fresh water4 ,river-gravels and lacustrine deposits are especially prone to contain a considerable intermixture of land-forms with those proper to the station4 ,fossils supply much information concerning the depth and distance from land at which the deposits were laid down4 ,when portions of the ocean-water have been separated to form inland lakes1 the water becomes saltier than that of the open ocean1 if the evaporation is greater than the supply of fresh water1 and the life of the inland sea undergoes change under the unfavourable conditions set up4 ,many forms disappear altogether1 and those which survive tend to become stunted1 and the shells of many of the mollusca are abnormally thin2 the fauna of an inland sea though it may have abundance of individuals is apt to be characterised by paucity of species4 ,turning now to the faunas of the open oceans1 it is found that in addition to latitude1 the distribution of organisms is affected by depth1 and by the nature of the sea-floor1 and accordingly we find different organisms in different areas2 and in examining the same area the organisms inhabiting different depths are not all the same1 and at the same depth some kinds of animals have different stations from those of others1 one creature being confined to a sandy floor1 another to a muddy one1 and so on#cd4 ,the oceans have been divided into #ah provinces1 each of which is more or less characterised by the possession of peculiar forms which are termed endemic1 in contrast to the sporadic forms which are widely distributed4 ,in any area which is margined by a coast line1 the molluscs are distributed in zones which were formerly classed as follows3--the littoral zone between tide marks1 the laminarian zone from low water to fifteen fathoms1 the coralline zone between fifteen and fifty fathoms1 and the deep-sea coral zone from fifty fathoms to one hundred fathoms or more2 this last depth was once supposed to mark the limit of the downward extension of marine life1 but as the result of modern deep-sea soundings we know that organisms extend to a much greater depth1 and the deep-sea fauna1 owing to uniformity of conditions over wide areas1 contains fewer endemic forms in proportion to the sporadic ones than the shallow-water#ce4 ,the deep-sea deposits entomb the remains of these deep-sea organisms and also of numerous pelagic organisms which live upon the surface of the ocean1 whose remains sink to the ocean-floor after death4 ,amongst the deposits of the deeper parts of the ocean1 we find many which are almost exclusively composed of the tests of foraminifera1 radiolaria and pteropods1 the spicules of sponges1 and the frustules of diatoms2 and accordingly the existence of foraminiferal1 pteropodan1 radiolarian1 and diatomaceous oozes1 amongst the strata of the geological column1 has been taken by some as indicating the prevalence of deep-sea conditions during the formation of those deposits3 as the purity of a calcareous ooze depends upon the absence of mechanical sediment1 or volcanic dust1 and as the component organisms of these oozes are pelagic forms which live near the continents as well as in the open oceans1 the presence of calcareous oozes implies the existence of a clear sea during their deposition but not necessarily of a deep one1 for if the sea-area be far away from land masses1 or if the sediment be strained off in fjords1 calcareous oozes may be formed in shallow water4 ,the existence of pure radiolarian or diatomaceous deposits is better evidence of deep water1 for if they were formed in shallow water we should expect an intermixture of calcareous tests1 whereas these are dissolved whilst sinking into the extreme depths of the ocean4 ,as the deep-sea creatures are under very different conditions from those of shallower waters1 we might expect marked structural differences between the deep and shallow-water creatures3 one such difference has been emphasized1 namely the occurrence of animals which are blind or have enormously developed eyes in the great depths of the sea1 where the only light is due to phosphorescent organisms4 ,this is well seen in the case of many recent crustacea1 and has been noted by ,suess in the case of the trilobites of some beds which he accordingly infers to be of deep-water origin1 and it is interesting to find that these creatures are found in deposits which give independent evidence of an open-water origin4 ,the glin of the ,ordovician strata are frequently furnished with enormous eyes1 and they are often accompanied by blind trilobites1 and in ,bohemia the blind and large-eyed forms are sometimes different species of the same genus1 for instance ,illnus#cf4 ,footnote #cd3 ,for an account of the distribution of one group of organisms see ,woodward1 ,s4 ,p41 ,a ,manual of the ,mollusca1 from which many of the following observations are taken4 ,footnote #ce3 ,for an account of the deep-sea fauna1 see ,hickson1 ,s4 ,j41 ,the ,fauna of the ,deep ,sea1 #ahid4 ,footnote #cf3 ,suess1 ,e41 ,das ,antlitz der ,erde1 #b;er4 ,bd41 p4 #bff4 ,as one would naturally expect1 the actual depth at which deposits were formed can generally be calculated with a greater degree of certainty amongst the newer rocks than amongst the older ones4 ,in the case of the ,pliocene ,crags1 the depth in fathoms may be confidently given4 ,in the ,cretaceous rocks attempts have been made to give numerical estimates of the depths at which different accumulations were formed1 but some differences of opinion have arisen in the case of these rocks4 ,in the ,palozoic rocks1 only a rough idea of the general depth can usually be obtained1 and no attempt to calculate the depth in fathoms is likely to be even approximately correct in the present state of our knowledge4 ,the comminution of fossils has sometimes been taken as an indication of shallower water origin of the deposits which contain them1 but although the hard parts of organisms in a broken condition have frequently been shattered by the action of the waves1 they may also be broken at great depths by predaceous creatures1 and in many instances the fracture is the result of earth-movements occurring subsequently to the formation of the deposits4 ,turning now to the difference in organisms which results from difference of station1 it will be sufficient to give a quotation from ,woodward's ,manual of the ,mollusca as an illustration3--,in ,europe the characteristic genera of rocky shores are ,littorina1 ,patella1 and ,purpura2 of sandy beaches1 ,cardium1 ,tellina1 ,solen2 gravelly shores1 ,mytilus2 and on muddy shores1 ,lutraria and ,pullastra4 ,on rocky coasts are also found many species of ,haliotis1 ,siphonaria1 ,fissurella1 and ,trochus2 they occur at various levels1 some only at the high-water line1 others in a middle zone1 or at the verge of low-water4 ,cypra and ,conus shelter under coral-blocks1 and ,cerithium1 ,terebra1 ,natica and ,pyramidella bury in sand at low-water1 but may be found by tracing the marks of their long burrows 7,macgillivray7#cg4 ,footnote #cg3 ,woodward1 ,s4 ,p41 ,a ,manual of the ,mollusca1 p4 #aea4 ,the geologist will naturally select sporadic forms rather than endemic ones in comparing the strata of different areas1 but how far differences in faunas are the result of existence at different times1 and how far they are due to difference of conditions affecting contemporaneous organisms can only be discovered as the result of accurate observation4 ,the main points to be regarded when comparing the successive faunas of different regions have been noticed in this and the preceding chapters1 and it has been shown that as the evidence is cumulative1 it requires the collection of a large number of facts obtained by observation of the strata before accurate inferences can be drawn4 ,the indications of climatic conditions furnished by organisms require some consideration4 ,in the comparatively recent deposits it is not difficult to get some notion of the prevalent climatic conditions when the fossils belong to forms closely related to modern genera4 ,the existence of the arctic birch and arctic willow1 and of shells belonging to species now living north of the ,british ,isles1 in deposits of comparatively recent date in ,britain would afford convincing evidence of the occurrence of colder climatic conditions than those which are now prevalent in the area1 even if the evidence were not confirmed as it is1 by physical proof of glaciation in deposits of the same age4 ,nevertheless1 even in these recent beds1 we have a useful warning1 by finding species of elephant and rhinoceros associated with northern forms like the lemming1 glutton1 and musk-ox4 ,we know that the species of elephant and rhinoceros 7the mammoth and woolly rhinoceros7 were provided with thick coverings which would enable them to resist the severity of an arctic climate1 but had not these coverings been found1 we might have been puzzled by the association of forms whose nearest allies are sub-tropical with others of arctic character4 ,as we go back in time and deal with earlier deposits1 the ascertainment of the climatic conditions becomes more difficult1 as the fossils mostly belong to extinct species1 genera or even families4 ,in these circumstances1 it is very dangerous to draw conclusions as to climatic conditions from examination of a few forms1 but when we find that plants and animals1 terrestrial and marine forms1 vertebrates and invertebrates alike point to the same conclusion1 as in the ,london ,clay1 where all the fossils belong to forms allied to those now living under sub-tropical conditions1 the state of the climate may be inferred with considerable certainty#ch4 ,the character of the fossils must be taken into account rather than their size4 ,there was a tendency amongst geologists to believe that large organisms probably indicate warm conditions4 ,recent researches in arctic seas have dispelled this belief4 ,marine alg of enormous size are found in the cold seas1 and the size of creatures1 abundance of individuals and variety of forms in the arctic faunas of some regions is very noteworthy4 ,in the ,kara ,sea1 for instance1 a variety of creatures were dredged up during the voyage of the ,vega1 and ,baron ,nordenskjld makes the following pertinent remarks about them3 ,for the science of our time1 which so often places the origin of a northern form in the south1 and vice versa1 as the foundation of very wide theoretical conclusions1 a knowledge of the types which can live by turns in nearly fresh water of a temperature of #aj1 and in water cooled down to -#bg and of nearly the same salinity as that of the ,mediterranean1 must have a certain interest4 ,the most remarkable were1 according to ,dr ,stuxberg1 the following3 a species of ,mysis1 ,diastylis ,rathkei ,kr41 ,idothea entomon ,lin41 ,idothea ,sabinei ,kr41 two species of ,lysianassida1 ,pontoporeia setosa ,stbrg41 ,halimedon brevicalcar ,gos1 an ,annelid1 a ,molgula1 ,yoldia intermedia ,m4 ,sars1 ,yoldia 787 arctica ,gray1 and a ,solecurtus#ci4 ,the temperatures were taken by a centigrade thermometer4 ,again we read of the results of dredging off ,cape ,chelyuskin4 ,the yield of the trawling was extraordinarily abundant2 large asterids1 crinoids1 sponges1 holothuria1 a gigantic sea-spider 7,pycnogonid71 masses of worms1 crustacea1 etc4 ,it was the most abundant yield that the trawl-net at any one time brought up during the whole of our voyage round the coast of ,asia1 and this from the sea off the northern extremity of that continent#dj4 ,footnote #ch3 ,for a discussion as to the value of plants as indices of climate see ,seward1 ,a4 ,c41 ,sedgwick ,essay for #ahib4 ,footnote #ci3 ,nordenskjld1 ,a4 ,e41 ,the ,voyage of the ,vega1 ,vol4 ,i4 ,chap4 ,,iv4 ,footnote #dj3 ,ibid4 ,chap4 ,,vii4 ,amongst the marine invertebrates reef-building corals and mollusca perhaps furnish the best evidence of climatic conditions4 ,the coral-reefs of the ,jurassic rocks with large gastropods and lamellibranchs clustered around them have been appealed to in proof of the existence of sub-tropical conditions during their formation2 further back in time we find evidence of climate furnished by the fossils of the ,silurian rocks of the ,isle of ,gothland in the ,baltic ,sea4 ,of these1 ,lindstrm writes ,the fauna had a tropical character4 ,in consideration of the great numbers of ,pleurotomariae1 ,trochi1 ,turbinidae and the large ,pteropods the assumption of a tropical character of the fauna may seem justifiable#da4 ,footnote #da3 ,lindstrm1 ,g41 ,on the ,silurian ,gastropoda and ,pteropoda of ,gotland1 ,stockholm1 #ahhd1 p4 #cc4 ,structure may give some indication of climate even though the organism is not allied to living species4 ,the bark of trees in arctic regions is often thicker than in more temperate regions1 and the leaves of arctic plants often have special characters to enable them to resist the long periods during which they are deprived of water1 though the fact that desert-plants frequently shew similar modifications deprives this test of any particular value except as a means of corroborating conclusions reached from other evidence#db4 ,the shells of arctic mollusca may become stunted1 but this is not by any means universal1 and the same result may be brought about by other abnormal conditions1 as for instance the increase of salt in a water area by evaporation4 ,footnote #db3 ,for an account of the modifications of the leaves of arctic plants1 see ,warming1 ,eug41 ,om ,grnlands ,vegetation1 ,meddelelser om ,grnland1 #abth part1 p4 #aje4 ,on the whole1 an examination of the evidence available for ascertaining the character of climate by reference to included organisms1 shews that inferences may be drawn within certain limits1 but that the task is a difficult one not unaccompanied by danger1 and every kind of available evidence derived from a study of physical phenomena and the included organisms should be utilised before any conclusion is drawn4 ,the likelihood of accurate inference is increased by comparing the faunas of various areas2 should they seem to indicate a progressive lowering of climate when passing from lower to higher latitudes1 it is probable that the indication is correct4 ,the student is referred to a paper by the late ,professor ,neumayr for an account of the existence of climatic zones during the ,mesozoic ,period#dc4 ,footnote #dc3 ,neumayr1 ,m41 ,ueber klimatische ,zonen whrend der ,jura- und ,kreidezeit1 ,denkschrift4 der ,math4-,naturwissensch4 ,classe der k4 ,akad4 der ,wissenschaften1 ,bd4 ,,xlvii4 ,vienna1 #ahhc4 ,,chapter ,x4 ,,evidences ,,of ,,conditions ,,under ,,which ,,strata ,,were ,,formed1 ,,continued4 ,in the preceding chapter1 attention was drawn to the indications as to conditions of deposition furnished by the sediments of any one locality1 and only passing reference was made to variation in the nature of the sediments and their organic contents1 when the deposits are traced laterally from place to place2 some attention must now be paid to this matter4 ,it is sometimes inferred that1 whereas similarity of organisms is a dangerous guide in correlating the strata of two areas1 accurate correlations may be made1 if the deposits can be traced continuously through the intervening interval2 no doubt the task is simplified when this can be done1 but the continuity of deposit of one particular composition is no more proof of contemporaneity than the occurrence of the same fossils continuously through the interval1 imbedded in strata of different character1 indeed probably not so much so4 ,the existence of widespread masses of conglomerate1 which are not found as linear strips1 but which extend in all directions1 is in itself an indication of this2 the ,oldhaven pebble bed for instance1 in the ,tertiary rocks of the ,london basin1 is very widely distributed4 ,we cannot suppose that coastal conditions prevailed far away from the shore-line1 and accordingly when a conglomerate occurs in a widespread sheet1 and not in a linear strip1 this is indicative that the deposit has not been formed continuously but that strip has been added to strip along an advancing or receding shore line1 and if this happens with conglomerates1 it must occur also in the case of other deposits4 ,illustration3 ,fig4 #ac4 ,in fig4 #acdd let ,a represent a shore line of a continent which is undergoing gradual elevation4 ,a deposit of pebbles a will be formed against the coast1 one of sand b further away1 then one of mud c and lastly limestone d1 may be formed in the open sea away from land4 ,naturally there may be intermingling of two kinds of deposit at the junctions1 but for the sake of simplicity this may be disregarded4 ,during the accumulation of the deposits a1 b1 c1 d1 certain sporadic forms may be distributed throughout all the deposits1 and some of them may become extinct before the deposition of these beds is completed1 if the process is carried out on a large scale2 we may speak of the characteristic fossils of this period as fauna ,i4 ,as the result of elevation or of mere silting up of the sea-margin1 or of both combined1 the next mass of pebble-deposit will be laid down further away from the original shore1 for the shore line will now be at ,a and not at ,a1 and it will partly overlap the mass of sand b2 the sand b#a will also be deposited somewhat further out and partly overlap the mud c1 and similarly the mud c#a will partly overlie the limestone d4 ,during the formation of a#a1 b#a1 c#a1 d#a1 other sporadic forms belonging to a fauna ,,ii may replace those of the first fauna4 ,in the same way a#b1 b#b1 c#b1 d#b will be deposited1 and in the meantime a new fauna ,,iii may arise and replace ,,ii4 ,so the process will go on until we finally have a group of deposits lying one over the other1 consisting of a basal accumulation of limestone1 succeeded by mud1 sandstone and pebble-beds in succession4 ,each of these will be continuous1 though the inner part of the pebble-deposit was formed long before the outer part of the limestone1 which is nevertheless beneath a mass of pebble-deposit continuous with that formed first1 and the various deposits will be separated by fairly horizontal planes x1 y1 z1 which might be regarded as bedding planes1 but which are not so1 strictly speaking4 ,the true bedding planes will occur at a slight angle to these planes of separation1 for the structure resembles false bedding on a gigantic scale1 but of course1 the lines separating two masses of similar deposit will be practically horizontal and parallel to the planes of demarcation of two distinct kinds of material4 ,the lines separating two faunas would1 under the conditions postulated1 run approximately parallel to the planes of separation of adjoining deposits of the same lithological character but would pass from conglomerate1 through sandstone1 mud and limestone1 as indicated by the lines #a1 #b1 #c1 444 and the deposits between adjoining lines would be contemporaneous#de4 ,in nature1 complications will arise1 owing to the gradual appearance and disappearance of forms1 and the existence of endemic species in contemporaneous deposits formed in different stations and having different lithological characters4 ,footnote #dd3 ,the writer gratefully acknowledges his indebtedness to ,prof4 ,lapworth for some of his views concerning deposition of strata4 ,footnote #de3 ,the lines #a1 #b1 #c 444 are incorrectly drawn in the figure4 ,line #a should be drawn so as to separate a1 b1 c1 d from a#a1 b#a1 c#a1 d#a1 line #b to separate a#a1 b#a1 c#a1 d#a from a#b1 b#b1 c#b1 d#b1 and so with the others4 ,if elevation ceased and were succeeded by depression1 the exact opposite would occur1 and the pebble beds would be overlain by sandstones1 these by muds1 and lastly limestones would appear4 ,it follows that during a marine phase occurring between two unconformities we should have a ,v-shaped accumulation of deposits with the apex pointing to the part of the shore line which was last submerged before the commencement of elevation1 as shewn in fig4 #ad1 though the beds of the apex will in most cases be denuded during the re-emergence4 ,illustration3 ,fig4 #ad4 ,indications of the non-coincidence of the planes separating faunas and those which separate deposits of one lithological character from those of another have already been detected1 for instance the 'greensand' condition of the ,cretaceous period occurs in some places during the existence of one fauna1 and in others during that of another1 though the planes have not been traced continuously4 ,mr ,lamplugh has furnished another example amongst the ,cretaceous rocks of ,yorkshire and ,lincolnshire1 but as has already been observed1 a great deal remains to be done in this direction1 and geologists are much in want of two sets of stratigraphical maps1 in one of which the lines are drawn with reference to the differences of lithological character1 whilst in the other they separate different faunas4 ,the student will notice the normal recurrence of deposits in definite order2 conglomerate succeeded by sandstone1 mud and limestone1 in a sinking area1 and limestone succeeded by mud1 sandstone and conglomerate in a rising area4 ,naturally many instances of departure from this rule are seen1 owing to local conditions1 but on a large scale1 it is very frequently noted1 and recognition of this will enable the student to remember the variations in the lithological characters of the deposits more easily1 than if he simply acquired them from a text-book without taking heed as to their significance4 ,upon the variations in the lithological characters of deposits and of their faunas1 when the beds are traced laterally depends very largely the successful ascertainment of the existence of former coast-lines1 the restoration of which constitutes an important part1 of ,palo-physiography1 concerning which some observations may here be made#df4 ,if a set of deposits having different lithological characters can be proved to be contemporaneous1 the coarser detrital accumulations will point to the approach to a coast-line1 and the actual position of the coast during the period of accumulation of the deposits may be very accurately fixed4 ,the pebble-beds at the base of the ,cambrian rocks of ,llanberis indicate the existence of a coast-line in that position during the accumulation of those pebble-beds4 ,similar pebble-beds occur at ,st ,david's1 at the base of the ,cambrian1 but it is impossible in the case of these rapidly accumulated sediments to say that two deposited so far away from one another were actually contemporaneous1 and therefore although we might draw a line through ,llanberis and ,st ,david's to indicate the old coast-line of the period1 it does not follow that the actual beach existed simultaneously at the positions indicated4 ,the palo-physiographer1 however1 attempts to restore the physical conditions of greater thicknesses of deposit2 for instance1 the distribution of land and sea during ,lower ,carboniferous times over the area now occupied by the ,british ,isles is often taken to illustrate the methods of restoration of ancient features1 and all admit that the lithological and palontological characters of the rocks indicate a shallowing of the ,carboniferous sea when passing northwards towards ,scotland4 ,for conveying an idea of the restorations to the student1 it is almost imperative to portray the distribution of land and sea upon a map1 and this can only be done by drawing definite lines4 ,it must be distinctly understood that these lines are necessarily only an approximation to the actual position of the ancient shore-lines1 which must have shifted again and again during the long period occupied by the accumulation of the ,lower ,carboniferous strata1 so that a true idea of the positions of the ,lower ,carboniferous shore-lines could only be obtained by placing on a series of maps the successive shore-lines of different parts of the ,lower ,carboniferous period1 and taking a composite photograph of these1 which would appear as a wide belt of shaded portion of the map with no definite boundaries4 ,the utmost that the maker of palo-physiographical maps can expect to indicate1 when dealing with considerable thicknesses of strata1 is an approximation to the mean position of the shore-lines of the period when these strata were deposited4 ,this is extremely valuable in enabling the student to understand the significance of the variations in the characters of the strata and their organic contents1 if he distinctly recognises the generalised nature of the map4 ,examination of any two palo-physiographical maps of the same period by different authors will shew wide divergences in the details1 but a general resemblance of the main features4 ,the reader will do well to consult ,prof4 ,hull's restoration of the physical features of ,old ,red ,sandstone and ,lower ,carboniferous ,times on ,plate ,,vi4 of his ,contributions to the ,physical ,history of the ,british ,isles1 and compare it with the map drawn by ,prof4 ,green 7,coal3 its ,history and ,uses1 by ,profs4 ,green1 ,miall1 ,thorpe1 ,rcker1 and ,marshall1 ,fig4 #c1 p4 #ch71 which will be found to bear out this statement4 ,footnote #df3 ,on this subject1 the student may consult ,prof4 ,e4 ,hull's ,contributions to the ,physical ,history of the ,british ,isles4 ,valuable as the published maps of palo-physiography are as an aid to the student in understanding the significance of the variations of characters amongst the sediments1 he will do well to supplement them by maps which he fills in for himself4 ,he is recommended to procure a number of outline maps of ,england1 or of the ,british ,isles1 and when studying in detail the characters of the ,british sedimentary rocks formed during the various periods1 to place a blank map by his side when beginning the study of each period or important portion of a period4 ,on this map he should jot down the geographical distribution of the different kinds of sediments1 using the conventional signs indicated at p4 #ij3 thus1 in the case of the ,lower ,carboniferous rocks he would place the conventional sign for limestone in ,derbyshire1 a combination of those for limestone and shale in ,yorkshire1 and would add to these the sandstone sign in ,northumberland4 ,he should also note the general character of the fossils1 using abbreviations for such terms as fresh-water fossils1 shallow-sea fossils1 deep-water fossils4 ,after reading the account of the group of rocks in a comprehensive text-book1 and inserting his notes on the map1 he should proceed to insert the probable position of the coast-lines4 ,he should also take notes of any indications of contemporaneous volcanic action1 though these might well be inserted on a separate map4 ,if this course be pursued1 the student will not only have the significance of the variations amongst the strata impressed upon his mind1 but he will have a means of obtaining at a glance the distribution of sediments and faunas of different kinds in the ,british area during the principal geological periods4 ,on another set of maps he may indicate the axes of the orogenic movements which have occurred at different times1 and when his various maps are completed1 he will have the materials for the construction of a general account of the various geological processes which have been concerned with the building of the ,british area4 ,when an area like ,britain has been studied1 the student may proceed to construction of maps of wider regions1 and he will find that in doing this1 new sets of facts must be taken into consideration1 as for instance the occurrence of different faunas on opposite sides of once-existing continental masses1 and the problems connected with the present distribution of the faunas and floras4 ,for an instance of the importance of the former distribution of life the reader may consult the twelfth section of the first part of ,professor ,suess' ,das ,antlitz der ,erde1 whilst a good account of the value of recent geographical distribution of organisms in supplying a clue to former distribution of land and sea will be found in ,mr ,a4 ,r4 ,wallace's ,island ,life1 ,chapter xxii4 ,should the method suggested above be adopted1 the student is likely to acquire a much more coherent idea of the significance of the facts of stratigraphical geology than can be obtained by a mere perusal of the accounts of the strata given in those portions of the various text-books which are devoted to a consideration of the stratigraphical branch of the science4 ,,chapter ,,xi4 ,,the ,,classification ,,of ,,the ,,stratified ,,rocks4 ,in the succeeding chapters1 a general account of the characters of the ,geological ,deposits of different periods will be given1 for the purposes of illustrating the principles to the consideration of which the earlier chapters have been devoted4 ,it is not proposed to enter into a description of numberless details1 which would only confuse the student who wished to grasp the main principles1 for many facts have been recorded which it is necessary to notice in a comprehensive text-book treating of stratigraphical geology1 though their full significance is not yet grasped4 ,the writer1 while noting the main characters of the various subdivisions of the different stratigraphical systems1 will assume that this work is used in conjunction with some recognised text-book4 ,the stratigraphical portion of ,sir ,a4 ,geikie's ,class ,book of ,geology gives an admirable general account of the ,british ,strata1 while the larger text-book by the same author has a condensed though very full account of the rocks of the stratigraphical column in all parts of the world1 and this is supplemented by numerous references to the original works wherein further descriptions may be found4 ,the ,english edition of ,prof4 ,e4 ,kayser's ,text-,book of ,comparative ,geology1 edited by ,p4 ,lake1 is also well adapted to the wants of the student1 and an excellent account of the strata is given in ,mr ,a4 ,j4 ,jukes-,browne's ,handbook of ,historical ,geology1 which may be read with the same author's ,building of the ,british ,isles4 ,the reader who refers to different text-books will be struck with the variations of nomenclature even amongst the larger stratigraphical divisions1 for two authors seldom subdivide the geological column into the same number of rock-systems4 ,the following classification will be here adopted3-- ,groups4 ,systems4 ,recent ,pleistocene ,cainozoic or ,pliocene ,tertiary ,miocene ,oligocene ,eocene ,cretaceous ,mesozoic or ,jurassic ,secondary ,triassic ,permian ,permo-,carboniferous ,carboniferous ,palozoic ,devonian ,silurian ,ordovician ,cambrian4 ,precambrian4 ,a few remarks may be given as to the reason for adopting this classification4 ,it is not for a moment suggested that the ,systems have the same value1 if the time taken for their accumulation be alone considered4 ,the beds classified as ,recent1 for example1 were probably accumulated during a lapse of time far shorter than that occupied for the deposit of some of the series or even stages of a system like the ,silurian1 but the recent rocks acquire a special significance from the fact that we are living in the period1 and the ,cainozoic rocks as a whole are capable of greater subdivision than the earlier groups1 on account of the greater ease with which they can be studied1 owing to the small amount of disturbance which they have usually undergone when compared with that which has affected older rocks1 and the closer resemblance of their faunas and floras to those of existing times4 ,with reference to the groups1 the writer has already commented upon the use of the terms ,palozoic1 ,mesozoic and ,cainozoic2 below the lowest ,palozoic rocks 7those of the ,cambrian system7 lie a group of rocks which have been variously spoken of as ,azoic1 ,eozoic1 and ,archan4 ,there is an objection to the use of any one of these words in this sense2 the objection in the case of the first two is that the term is theoretical and probably incorrect1 whilst the word ,archan1 otherwise suitable1 has also been used in a more restricted sense4 ,in these circumstances the term ,precambrian will be used when referring to any rocks which were formed below ,palozoic times1 though no doubt when this obscure group of rocks is more thoroughly understood a satisfactory classification will be applied to it4 ,taking the other groups into account1 the lower systems of the ,palozoic group will be found to vary greatly according to the views of different writers2 some make only one system1 the ,silurian1 others two1 the ,cambrian and ,silurian4 ,the three systems are here adopted1 not only because the one1 ,silurian1 is too unwieldy on account of its size and requires subdivision 7and the ,cambrian and ,silurian however defined1 will be found to be of very unequal importance1 whereas the three systems adopted are of fairly equal value71 but especially because when the term ,ordovician is used1 the significance of the other terms ,cambrian and ,silurian is at once understood4 ,an attempt has been made to shew that the ,devonian system is non-existent1 but the result of modern research is to shew that the rocks placed in this system are worthy of the distinction1 both from their importance and from the distinctness of the fauna from those of the underlying and overlying systems4 ,the ,permo-,carboniferous system is adopted1 because an important group of deposits has recently been brought to light which were not represented either in the ,permian or ,carboniferous system as originally defined4 ,some authors have advocated the union of the ,permian and ,triassic systems into one system placed at the base of the ,mesozoic group4 ,this is unnecessary1 and would depart from the classification originally proposed1 which is to be deprecated1 unless there is any strong reason for it4 ,the ,mesozoic systems are classified according to the method generally adopted4 ,were a fresh classification to be proposed1 a portion of the ,cretaceous system might be included with the ,jurassic rocks1 but it is better to adhere to the old classification4 ,the divisions of the ,cainozoic rocks are hardly systems in the sense in which the term is used in the case of the older rocks1 but the reason for using these smaller subdivisions has already been mentioned4 ,the addition of the ,oligocene to the original divisions suggested by ,lyell has been found useful1 and the term will be used in this work4 ,the reasons for the adoption of the particular minor subdivisions 7series and stages7 in the following chapters will frequently appear when the rocks of the various systems are described1 and need not be further alluded to in this place4 ,although most geologists describe the stratified rocks in ascending sequence beginning with the oldest1 and proceeding towards the newest1 others1 and notably ,lyell1 adopted the opposite method and commenced with an account of the newest beds4 ,the argument generally used for the latter method is that it is easier to work from the study of the known to that of the less known1 and as the faunas of the newest rocks are most like the existing faunas1 the student would more readily follow a description of the rocks in the order which is opposite to that in which they were deposited4 ,in practice1 the study of the sediments in their proper order1 that is1 in the order of deposit1 will not be found to task the student to any great extent1 especially if1 as is very desirable1 he has studied the main facts and principles of ,palontology before commencing the study of the rock-systems in detail4 ,there is one reason for beginning with the study of the older sediments which outweighs any reasons which can be advanced against it1 namely that the events of any period produce their effect not only upon the strata of that period1 but also on those of succeeding periods4 ,the task of the stratigraphical geologist is really to learn the evolution of the earth1 in its changes from the simple to the more complex conditions1 and it is quite obvious that it is unnatural to attempt any study of evolution by working backward4 ,for this reason the study of the sediments will be here made in the order which is usually adopted1 by passing from the older to the newer1 and from the simple to the more complex4 ,the ,british strata will be mainly considered1 though references will frequently be made to their foreign equivalents1 and a fuller account of the latter will be added when the ,british strata are abnormal1 as are those of ,triassic times1 and also when a period is not represented amongst the strata of the ,british ,isles1 as for instance1 the ,permo-,carboniferous and ,miocene periods4 ,the student is recommended to refer constantly to good geological maps of the ,british ,isles1 of ,europe1 and of the world4 ,of maps of the ,british ,isles1 mention may be made of ,sir ,a4 ,ramsay's geological map of ,england1 ,sir ,a4 ,geikie's map of ,scotland1 and his map of the ,british ,isles1 ,j4 ,g4 ,goodchild's map of ,england and ,wales1 a map of ,europe by ,w4 ,topley and one of the world reduced from that by ,j4 ,marcou1 accompanying the first and second volumes of the late ,sir ,j4 ,prestwich's ,geology4 ,for special purposes more detailed maps will be studied1 including the one-inch maps of ,h4 ,m4 ,geological ,survey1 and the index map on a smaller scale4 ,lastly1 for an account of ,british ,geology1 reference must be made to ,h4 ,b4 ,woodward's ,geology of ,england and ,wales1 where the ,british formations are described in order1 and to ,w4 ,j4 ,harrison's ,geology of the ,counties of ,england and ,wales1 where the stratigraphical geology of the country is given under the head of the different counties1 which are taken in alphabetical order4 ,in concluding this chapter1 it is hardly necessary to say that every opportunity of studying the characters of the deposits and their fossils in the field should be eagerly seized1 and that much information may be acquired even on a railway journey1 especially as to the influence which the deposits exert upon the scenery of a region#dg4 ,footnote #dg3 ,in the first edition of ,h4 ,b4 ,woodward's ,geology of ,england and ,wales1 an account of the geology of the main lines of ,english railways is given1 which is omitted in the later edition4 ,it is well worth consulting by those who take a long journey1 and it will be found useful to take a geological map with one on the journey so as to discover when one is passing from one formation to another4 ,,chapter ,,xii4 ,,the ,,precambrian ,,rocks4 ,study of a geological map of the world will shew that extensive regions1 such as parts of ,scandinavia1 many tracts of ,central ,europe1 a large area in ,canada1 and a considerable portion of ,brazil and the adjoining countries are occupied by crystalline schists1 which underlie the oldest known sedimentary strata in those places4 ,these crystalline schists form the floor upon which the sediments constituting the bulk of the geological column rest1 and it is necessary that we should know something of the character of this floor4 ,other rocks which can be definitely proved to be of ,precambrian age are often found associated with the crystalline schists1 and these associated rocks have often undergone more or less alteration subsequently to their formation4 ,the difference between the coarser types of crystalline schists and these associated rocks is sometimes so marked that geologists have necessarily paid attention to it1 and separated the two groups of rocks2 the term ,archan has been used by some geologists to include the crystalline schists1 and ,eparchan for the associated rocks of known ,precambrian age1 but though this separation may sometimes be effected1 there are cases when it is impossible to draw any sharp line of demarcation between ',archan' and ',eparchan' types4 ,in the present state of our knowledge1 a chronological classification of the ,precambrian rocks when applied to wide and distant regions is destined to break down1 and it will be convenient if we consider at some length the features of the ,precambrian rocks of a particular region1 and apply the knowledge thus gained to a study of ,precambrian rocks of other areas1 and to a consideration of our knowledge of the ,precambrian rocks as a whole4 ,in doing so1 the term 'crystalline schists' will be used somewhat vaguely with reference to a complex of schistose rocks of which the mode of origin cannot be fully determined4 ,we may take our own country as a region where a good development of the ,precambrian rocks occurs4 ,a few explanatory remarks concerning the mode of detection of ,precambrian rocks may not be amiss4 ,if any true organisms have been hitherto discovered amongst the rocks formed before ,cambrian times they are valueless as a means of correlating rocks1 and accordingly lithological characters only are available in attempting to correlate the rocks of one area with those of another4 ,those who have read the preceding chapters will have gathered that comparisons founded on similarity of lithological character are not so valuable as those made after careful scrutiny of the fossils of strata1 but they are by no means valueless1 and when the rocks of two areas which are not far distant from one another present close lithological resemblances1 their general contemporaneity may be inferred with some degree of certainty4 ,it is only when we get the lowest ,cambrian strata overlying earlier rocks that we have absolute proof of the ,precambrian age of the latter1 and it is necessary1 therefore1 that we should have some definite lower limit to the rocks of the ,cambrian system4 ,it is now generally agreed that that limit shall be drawn at the base of a group of rocks containing what is known as the ,olenellus-fauna1 which will be considered at greater length in the next chapter1 and it will be well1 if the term ,cambrian be not in future applied to any rocks beneath the ones containing the relics of this fauna1 for otherwise there is danger of the indefinite downward extension of the ,cambrian system4 ,we need not be surprised to find great thicknesses of rock below the rocks containing the ,olenellus-fauna1 and passing upwards with complete conformity into those rocks2 nevertheless1 if it can be shewn that the ,olenellus-fauna had not appeared during the deposition of the underlying group1 the rocks of that group should be termed ,precambrian4 ,a case of this nature has not yet been detected in our area1 and all the rocks which have been proved to be ,precambrian in ,britain are separated from the overlying ,cambrian rocks by a physical break1 though that break is not necessarily very large1 and in some districts is probably of little importance4 ,hitherto the ,olenellus-fauna has been detected in ,ross1 ,warwickshire1 ,shropshire1 ,worcestershire and probably in ,pembrokeshire1 and the rocks underlying the ,olenellus-beds in those counties can be proved to be ,precambrian 7i4e4 if the ,olenellus-age of the ,pembrokeshire rocks be ultimately established1 and the researches of ,dr ,hicks tend to prove that it will almost certainly be done74 ,it will be convenient if we take the instances where the age of the rocks can be proved with certainty or with a considerable degree of probability first1 and then consider the examples of rocks which are found below ,cambrian strata1 though these have not hitherto yielded the ,olenellus-fauna1 concluding with a notice of rocks which have been claimed to be of ,precambrian age on account of their lithological characters1 though they are not now seen to be immediately succeeded by strata appertaining to the ,cambrian system4 ,commencing with the region where we have the greatest development of the known ,precambrian rocks1 namely ,ross1 ,sutherland and the ,hebrides1 we may explain the general relationship of the rocks by means of a generalised section 7fig4 #ae74 ,illustration3 ,fig4 #ae4 ,the lowest rocks a are crystalline schists1 they are succeeded by a set of arenaceous rocks b known as the ,torridonian beds1 which rest unconformably upon the upturned edges of the crystalline schists1 whilst the ,cambrian rocks1 c1 rest with another unconformity sometimes upon the partly denuded ,torridonian beds1 or where the latter have been completely removed1 as on the right side of the figure1 directly upon the crystalline schists1 thus presenting an example of unconformable overlap4 ,the occurrence of the ,olenellus-fauna in the basement beds of the ,cambrian system near ,loch ,maree1 proves the ,precambrian age of the ,torridonian strata1 whilst the unconformable junction between the latter and the crystalline schists indicates that we are here dealing with two distinct sets of ,precambrian rocks1 one of ,eparchan and the other of ,archan type4 ,the crystalline schists consist of rocks of very varied lithological characters1 some with gneissose1 and others with schistose structure1 and they vary in degree of acidity from ultrabasic rocks to those of acid composition4 ,most of them exhibit parallel structures1 which in many cases can be shewn to have been impressed on the rocks subsequently to their consolidation1 though this need not have occurred and probably did not occur with some of them1 especially the granitoid gneisses4 ,the researches of the members of ,h4 ,m4 ,geological ,survey have shewn that many of these rocks were originally intrusive igneous rocks1 though it is not yet known into what rocks those which were first consolidated were injected1 and the origin of the bulk of the schists still remains to be elucidated4 ,subsequently to their consolidation and before the deposition of the earliest ,torridonian rocks they were subjected to more than one set of earth-movements1 which folded them and impressed a series of parallel structures upon many of them2 and accordingly we find that the pebbles of the crystalline schists which are found amongst the basal conglomerates of the ,torridonian rocks consist of fragments which had undergone the alteration caused by these earth-movements before they were denuded from their parent-rocks#dh4 ,footnote #dh3 ,for an account of these rocks1 their characters1 and the effects of earth movement upon them1 the reader should consult a ,report on the ,recent ,work of the ,geological ,survey in the ,north-,west ,highlands of ,scotland3 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xliv4 p4 #cgh4 ,the ,torridonian system is composed of rocks which are largely of arenaceous character1 the most prominent beds being formed of red sandstones1 and the bulk of the fragments in them have clearly been derived by denudation from the crystalline schists1 many of the beds being composed of arkose1 where the quartz is mixed with a large proportion of felspar and often of ferro-magnesian minerals4 ,the deposits are clearly sedimentary1 and are as little altered as many strata of much more recent origin1 only possessing structures produced by metamorphic action under exceptional circumstances4 ,the detailed researches of the geological surveyors prove that the rocks of this system have a much greater thickness and are of more varied lithological characters than was previously supposed4 ,the total thickness of the strata is over #aj1jjj feet1 and the sandstones are associated with deposits of a muddy character1 and with occasional bands of limestone2 in these circumstances the discovery of fossils would excite no surprise1 and in #ahia ,sir ,a4 ,geikie announced the detection of traces of annelids and some more obscure remains of other organisms in these strata1 which have not yet been described#di4 ,these ,torridonian strata furnish us with the most satisfactory group of ,precambrian sediments yet detected in ,britain#ej4 ,footnote #di3 ,an account of the subdivisions and lithological characters of the rocks of the ,torridonian ,system will be found in the ,annual ,report of the ,geological ,survey of the ,united ,kingdom for #ahic4 ,footnote #ej3 ,it has been recently maintained that some of the ,torridonian rocks are of olian origin4 ,in the south-east ,highlands is a great mass of crystalline schists of a less gneissose character than that of the north-west1 to which ,sir ,a4 ,geikie has applied the name ,dalradian4 ,many of these schists will be found by examination of the geological map of ,scotland to be separable into divisions1 which by means of their lithological characters can be traced long distances across the country1 and they present all the characters of sedimentary rocks1 though they are associated with intrusive igneous rocks1 and have undergone great metamorphic changes since their formation4 ,cambrian rocks have not yet been discovered immediately above them1 though they are clearly older than ,ordovician times1 but the existence of rocks associated with them along their north-west borders1 which in lithological characters closely resemble some of the rocks of the crystalline schists of the north-west ,highlands1 indicates the probability of their general ,precambrian age4 ,in some instances1 the extreme types of metamorphism which they exhibit are the result of the kind of action usually termed pyrometamorphic as has been shewn by ,mr ,g4 ,barrow#ea4 ,footnote #ea3 ,barrow1 ,g4 ,on an ,intrusion of ,muscovite-biotite gneiss in the ,s4,e4 ,highlands of ,scotland1 and its accompanying metamorphism4 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlix4 p4 #ccj4 ,in ,england and ,wales the rocks which have been shewn or inferred to be ,precambrian1 when not intrusive1 are largely of volcanic origin4 ,the most satisfactory example of the occurrence of the ,olenellus-fauna is that of the ,cambrian ,comley sandstone of ,shropshire1 which rests unconformably upon a set of rocks termed by ,dr ,callaway the ,uriconian rocks2 the latter are essentially volcanic1 and strongly resemble ,precambrian rocks of other ,british areas4 ,there is also strong reason to suppose that the sediments to which the name ,longmyndian has been applied1 which have been described by the ,rev4 ,j4 ,f4 ,blake1 are of ,precambrian age1 for1 as ,professor ,lapworth has pointed out1 the three great subdivisions of the ,cambrian system are present in the area under consideration1 and the rocks of each are entirely different from those of the adjoining ,longmynd area4 ,in ,shropshire therefore we meet with one set of volcanic rocks1 and another set consisting of sedimentary rocks1 of which the former is certainly1 the latter almost certainly of ,precambrian age1 and as the ,longmyndian rocks are in a comparatively unaltered condition1 consisting of normal sediments1 we may well expect the discovery of fossils in them also#eb4 ,the ,olenellus-fauna has been found near ,nuneaton in ,warwickshire in beds which unconformably succeed volcanic rocks1 the ,caldecote series of ,prof4 ,lapworth1 and the latter are therefore of ,precambrian age#ec4 ,a few fossils belonging to the ,olenellus-fauna have occurred in the oldest ,cambrian rocks of the ,malvern district1 and these rocks rest unconformably upon those of an old ridge which is therefore composed of ,precambrian rocks4 ,the rocks of this ridge are largely of intrusive igneous origin1 though parallel structures have been impressed upon them as the result of subsequent deformation1 but some of the rocks are almost certainly of contemporaneous volcanic origin#ed4 ,in the ,wrekin ridge1 igneous and pyroclastic rocks are found succeeded unconformably by ,cambrian rocks which resemble those of the ,malvern and ,nuneaton districts1 and probably belong to the period of existence of the ,olenellus-fauna1 and these igneous and pyroclastic rocks are presumably of ,precambrian age1 and the contemporaneous rocks constitute ,dr ,callaway's typical ,uriconian group4 ,volcanic ashes and breccias are accompanied by devitrified pitchstones and intruded granitic rocks1 which may or may not be all of the same general age#ee4 ,the rocks which have been claimed as ,precambrian in ,pembrokeshire and in ,caernarvonshire have the same general characters as those of the ,wrekin ridge4 ,pyroclastic rocks underlie the oldest ,cambrian rocks1 with discordance between the two1 and associated with these pyroclastic rocks are quartz felsites which according to some are of contemporaneous nature whilst others maintain their intrusive origin4 ,in each county granites are found which are now generally recognised to be intrusive1 though there seems to be no doubt as to their being of the same general age as the rocks with which they are associated1 and therefore presumably ,precambrian4 ,the ,pembrokeshire rocks are marked by the occurrence of a certain amount of metamorphism1 probably of more than one kind1 which has converted pyroclastic volcanic rocks into sericitic-schists and quartz-felsites into hlleflintas#ef4 ,the term ,pebidian given by ,dr ,hicks to the contemporaneous volcanic fragmental rocks should be retained1 and if these rocks be eventually shewn to be contemporaneous with similar volcanic rocks of other districts1 may be applied generally1 as it has priority over other terms as ,uriconian and ,caldecote series4 ,the term ,dimetian was applied to rocks known to be intrusive1 and must be dropped as a chronological term1 whilst the existence of an ,arvonian system separate from the ,pebidian system is not fully proved4 ,footnote #eb3 ,the reader may consult a paper by ,prof4 ,lapworth ,on ,olenellus ,callavei and its geological relationships1 ,geol4 ,mag4 ,dec ,,iii4 vol4 ,,viii4 p4 #ebi1 for information concerning the relationship of the ,olenellus beds of ,shropshire to the more ancient rocks2 the ,uriconian rocks are described by ,dr ,callaway in a series of papers1 especially in the ,quarterly ,journal of the ,geological ,society1 vol4 ,,xxxv4 p4 #fdc1 vol4 ,,xxxviii4 p4 #aai1 vol4 ,,xlii4 p4 #dha and vol4 ,,xlvii4 p4 #aji1 whilst the lithological characters of the ,longmyndian rocks are described by the ,rev4 ,j4 ,f4 ,blake 7,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlvi4 p4 #chf74 ,footnote #ec3 ,see ,lapworth1 ,c41 ,on the sequence and systematic position of the ,cambrian rocks of ,nuneaton1 ,geol4 ,mag4 ,dec ,,iii4 vol4 ,,iii4 p4 #cai2 and ,waller1 ,t4 ,h41 ,preliminary ,note on the ,volcanic and ,associated ,rocks of the neighbourhood of ,nuneaton1 ibid4 p4 #cbb4 ,footnote #ed3 ,for details concerning the rocks of the ,malvern ,hills see papers by ,callaway in the ,quarterly ,journal of the ,geological ,society1 vol4 ,,xxxvi4 p4 #ecf1 ,,xliii4 p4 #ebe1 ,,xlv4 p4 #dge1 and ,,xlix4 p4 #cih1 and a paper by ,prof4 ,a4 ,h4 ,green1 ibid4 vol4 ,,lvi4 p4 #a4 ,footnote #ee3 ,callaway1 ,c41 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxv4 p4 #fdc4 ,footnote #ef3 ,the ,pembrokeshire area is of interest as the probable existence of ,precambrian rocks in ,britain was first indicated on good evidence in this county4 ,the general structure of the district is fairly simple1 consisting of ,cambrian rocks beneath which ,precambrian rocks are exposed in at least two ridges of which the northerly and more important one runs through ,st ,davids4 ,the rocks of the ,st ,davids ridge consist of a binary granite 7granitoidite71 felsites1 and volcanic ashes and breccias of intermediate composition4 ,much diversity of opinion has existed1 and to some extent still exists as to questions of detail1 and a very extensive literature has been devoted to these rocks4 ,amongst the numerous papers which treat of them1 the student may consult the following3--,hicks1 ,h41 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxiii4 p4 #bbi1 ,,xxxiv4 p4 #adg1 ,,xxxv4 p4 #bhe1 ,,xl4 p4 #ejg1 ,,xlii4 p4 #cea1 ,geikie1 ,a41 ibid4 vol4 ,,xxxiv4 p4 #bfa1 ,blake1 ,j4 ,f41 ibid4 vol4 ,,xl4 p4 #bid1 and ,morgan1 ,c4 ,ll41 ibid4 vol4 ,,xlvi4 p4 #bda4 ,much of the matter contained in these papers is controversial1 and need not be fully read by those who merely wish to obtain a general account of the rocks of the district4 ,in ,caernarvonshire two ridges are found1 the one running from ,bangor to ,caernarvon1 and the other through ,llanberis lake4 ,the rocks of these are generally similar to those of ,st ,davids1 and as the lowest ,cambrian rocks of the area closely resemble those of ,st ,davids1 the ,precambrian age of the rocks of these ridges is rendered highly probable1 though until the discovery of the ,olenellus-fauna in the area1 it cannot be regarded as proved#eg4 ,footnote #eg3 ,these rocks are described by ,t4 ,mc,k4 ,hughes1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxiv4 p4 #acg1 and ,,xxxv4 p4 #fhb2 by ,prof4 ,t4 ,g4 ,bonney1 ibid4 vol4 ,,xxxiv4 p4 #add2 and by ,dr ,hicks1 ibid4 vol4 ,,xxxv4 p4 #bie4 ,the actual position of the similar rocks of ,anglesey has not been so clearly fixed1 as the rocks associated with them are of ,ordovician age1 but their resemblance to the rocks of the adjoining regions renders their ,precambrian age highly probable4 ,it is interesting to find in association with the rocks which resemble those of ,caernarvonshire1 others which ,sir ,a4 ,geikie recognises as quite similar to some existing amongst the crystalline schists of the north-west ,highlands of ,scotland1 and when these ancient rocks of ,anglesey have been mapped in detail1 they will probably be found to present greater variety than is afforded by any ,precambrian rocks of ,great ,britain occurring ,s4 of the ,scotch border#eh4 ,footnote #eh3 ,papers upon the old rocks of ,anglesey will be found in many volumes of the ,quarterly ,journal of the ,geological ,society2 see especially ,hicks1 vol4 ,,xxxv4 p4 #bie1 ,callaway1 vol4 ,,xxxvi4 p4 #ecf1 ,,xxxvii4 p4 #baj1 and ,blake1 ,,xliv4 p4 #dfc4 ,of rocks whose age is more uncertain1 but which are probably of ,precambrian age1 those of ,charnwood ,forest in ,leicestershire may first be noticed4 ,they are largely of pyroclastic origin1 and from their likeness to similar rocks of proved ,precambrian age1 they are very probably of this age1 as suggested by ,messrs ,hill and ,bonney#ei4 ,a group of crystalline schists is found in the south of ,cornwall1 especially near the ,lizard1 and similar rocks are found in the ,channel ,isles4 ,as their relationship to newer rocks is not clear1 little can be said about them1 which has not already been noticed in mentioning the crystalline schists of other regions#fj4 ,footnote #ei3 ,hill and ,bonney1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxiii4 p4 #ged1 ,,xxxiv4 p4 #aii and ,,xlvii4 p4 #gh2 see also ,watts1 ,w4 ,w41 ,rep4 ,brit4 ,assoc4 for #ahif1 p4 #gie4 ,footnote #fj3 ,for an account of the ,volcanic ,history of ,britain in ,precambrian times1 see ,sir ,a4 ,geikie1 ,presidential ,address to the ,geological ,society1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlvii4 p4 #fc4 ,the ,precambrian rocks of the ,european continent consist largely of crystalline schists which in their general aspects recall those of the north-west ,highlands of ,scotland4 ,important masses are found in ,bavaria1 ,bohemia1 ,france1 ,spain1 ,scandinavia and ,russia4 ,the ,scandinavian and ,russian rocks of ,archan type are in places succeeded by the ,olenellus-bearing beds of the ,cambrian rocks1 and rocks of ,eparchan character are not extensively developed1 though certain ,norwegian rocks may be the equivalents of the ,torridonian rocks of ,scotland1 and other rocks of this type are found in places in ,sweden4 ,in ,bohemia and in ,brittany ,precambrian strata of ,eparchan type have been discovered1 and this type probably occurs elsewhere in ,europe4 ,the ,north ,american rocks require some notice1 for it was in ,canada that the existence of ,precambrian rocks was first recognised1 and the term ,laurentian1 originally applied to an ,archan type of ,precambrian rocks in ,canada1 was subsequently adopted in speaking of many ,precambrian rocks elsewhere1 though it is now wisely restricted to the type of rock in the original area to which the name was first given4 ,these ,laurentian rocks acquired a special1 interest on account of the occurrence in their limestones of a supposed reef-building foraminifer1 ,eozoon canadense1 but detailed study of its structure and mode of occurrence has convinced most geologists that the structure is inorganic4 ,the ,laurentian rocks of the typical ,laurentide region are largely crystalline schists associated with massive crystalline rocks4 ,the attempt to separate them chronologically into a ,lower and ,upper division was premature1 as shewn by the fact that many of them1 upon detailed study1 prove to be intrusive igneous rocks4 ,in the neighbourhood of ,lake ,huron1 a set of sedimentary rocks overlying the ,archan rocks is of ,eparchan type1 consisting to a great extent of volcanic rocks1 clay-slates and schists with intrusive igneous rocks2 it has been termed the ,huronian ,system1 and this term has also been extensively applied to other ,eparchan types found elsewhere1 but should be restricted to the rocks of the ,huron district4 ,a number of other rocks of ,eparchan type have been discovered in various parts of ,north ,america1 and have been grouped together under the title of ,algonkian1 a name proposed for them by ,dr ,c4 ,d4 ,walcott1 and an attempt has been made to arrange them in chronological order1 though in the absence of fossils1 the rocks of different districts can only be so arranged by reference to lithological characters2 nevertheless a detailed study of the ,eparchan and some of the more finely crystalline schistose rocks points to the existence of a number of divisions of sedimentary rocks of ,precambrian age1 some of which may attain to the dignity of forming separate systems#fa4 ,by far the most instructive development of ,american ,precambrian rocks has been found in the ,rainy ,lake region of ,canada1 and it is the subject of a special memoir by ,dr ,a4 ,c4 ,lawson#fb4 ,the ,archan rocks of the region are divided into a lower ,laurentian and an upper division1 which is further subdivided into the ,coutchiching series below and the ,keewatin series above1 though the rocks of the ,keewatin series are largely of ,eparchan character4 ,the ,laurentian rocks of this region resemble those of the ,laurentide area1 and consist of highly crystalline schistose and gneissose rocks associated with compact rocks4 ,the ,coutchiching series consists of mica schists and grey laminated gneisses1 which appear to have been of sedimentary origin1 altered by subsequent metamorphic action1 while the ,keewatin series1 which reposes sometimes upon the rocks of the ,coutchiching series 7when the junction is an unconformable one71 sometimes upon the ,laurentian rocks1 is formed of pyroclastic rocks and lava flows with intercalated sedimentary rocks2 some of the ,keewatin rocks are highly metamorphosed but others have undergone little or no metamorphic change4 ,the most important point in connexion with these rocks of the ,rainy ,lake ,region has reference to the relationship between the ,laurentian rocks and those of the ,coutchiching and ,keewatin series4 ,lawson demonstrates the igneous nature of the ,laurentian rocks1 and brings forward evidence of various kinds that they were formed by the fusion of the basement or floor upon which the formations of the upper division of the ,archan were originally deposited4 ,with the fusion of this floor it seems probable that portions of the superincumbent strata1 which once formed integral parts of either the ,coutchiching series or the ,keewatin1 have also been absorbed into the general magma1 and reappeared on crystallization as ,laurentian gneiss4 ,this fusion1 however1 only extended up to a certain uneven surface1 which surface constitutes the demarcation between the present upper and lower ,archan4 ,above this surface1 or upper limit of fusion1 the formation of the ,coutchiching and ,keewatin series retained their stratiform or bedded disposition1 and rested as a crust of hard and brittle rocks upon the magma1 subject to its metamorphosing influences#fc4 ,footnote #fa3 ,a large number of classifications have been proposed for the ,archan rocks of ,america2 the most plausible one is given in ,sir ,a4 ,geikie's ,text ,book of ,geology1 ,third ,edition1 p4 #gaf4 ,footnote #fb3 ,lawson1 ,a4 ,c41 ,report on the ,geology of the ,rainy ,lake ,region4 ,montreal1 #ahhh4 ,footnote #fc3 ,lawson1 op4 cit4 p4 #aci4 ,we may now pass briefly in review the evidence which has been so far obtained as to the mode of formation of the various ,precambrian rocks4 ,the existence of a very varied fauna amongst the earliest ,cambrian strata has been commented upon by many geologists1 and according to accepted explanations of the origin of that fauna1 an enormous period of time elapsed before the deposition of the earliest ,cambrian strata4 ,during portions of that long period1 the undoubtedly clastic rocks of ,eparchan type were deposited1 and probably many others which are now so altered by metamorphism1 like some of the ,coutchiching rocks of ,canada1 that their original clastic origin can only be inferred and not directly proved4 ,volcanic activity was very rife during the deposition of some of these ,eparchan rocks1 though perhaps not more so than during the formation of some of the ,lower ,palozoic ,rocks4 ,all attempts to prove the occurrence of organisms in ,precambrian strata have hitherto failed1 for no undoubted fossil has been described which is unhesitatingly accepted as of ,precambrian age1 notwithstanding the many asserted occurrences of such fossils4 ,that fossils will eventually be discovered is more than probable1 and their non-detection at the present time is in no way very surprising1 when we remember the long time that elapsed after the existence of stratified rocks below the ,upper ,palozoic rocks had been recognised1 before definite faunas were discovered in them4 ,the determination of the ,precambrian age of stratified rocks is recent1 and now that this determination has been made1 the search for fossils will be more eager1 and is likely to be rewarded by their discovery4 ,furthermore1 experience shows that when fossils are discovered in rocks of unknown age1 there is a tendency to refer those rocks to some known period1 and consequently we may actually possess ,precambrian fossils1 out of beds which have been erroneously referred to the ,cambrian or a later period4 ,another important question is that of the metamorphism of a large number of ,precambrian rocks1 and here again recent research tends to show that the metamorphism is not of a kind different from that which occurred after the end of ,precambrian times2 the discovery of crystalline schists in ,norway1 ,kirkcudbrightshire and ,westmorland amongst ,lower ,palozoic rocks1 which resemble those of ,archan masses in all respects except in the extent of area which they cover1 shows that similar processes to those which occurred in ,precambrian times went on during later periods1 though perhaps not on so large a scale4 ,the great extent of these metamorphic rocks of ,precambrian age can hardly be due in any great degree to the longer time during which they have been subjected to metamorphic influence1 for there is evidence that much of the change took place in ,precambrian times1 far more than has occurred since1 and it is a significant fact that these old rocks are more extensively penetrated by intrusive igneous masses than those of later periods2 here again we find that much of the intrusion actually occurred in ,precambrian times4 ,the greater extent of intrusion and metamorphism amongst these ,precambrian rocks than amongst later sediments indicates some differences of conditions in the case of ,precambrian and later times4 ,if besides intrusion1 actual fusion of floors of ,precambrian rocks occurred1 we may well suppose that the earlier records of the rocks are for ever lost to us1 the earliest sediments having been fused1 but that the history of life upon our earth is to be revealed to us first in so late a stage as that of ,cambrian times is highly improbable1 and we may look forward with confidence to laying bare the records of the rocks composing the geological column some way below the ,cambrian portion of the column4 ,upon this foundation of igneous rock1 sediment and volcanic material1 formed in ,precambrian times1 whose history we have only begun to study1 was laid down the great mass of sediment which the geologist has more completely studied1 where abundant traces of life are preserved1 and concerning whose history we can gain a greater insight than is permitted us in the case of the old ,foundation ,stones4 ,,chapter ,,xiii4 ,,cycles ,,of ,,change ,,in ,,the ,,british ,,area4 ,before studying in further detail the strata of the geological column1 it will be convenient to deal with the great physical changes which have occurred in the ,british area from ,precambrian times to the present day1 as this will clear the way for a right appreciation of the main variations in the characters and distribution of the strata4 ,at the end of ,precambrian times there was a general upheaval of the ,british area1 and this we may speak of as the ,first ,continental ,period4 ,it was followed by depression and extensive sedimentation1 proceeding more or less continuously though with local interruptions through ,lower ,palozoic times1 so that so far as ,britain is concerned we may speak of ,lower ,palozoic times as constituting the ,first ,marine ,period4 ,extensive upheaval gave rise to continental tracts and mountain chains1 and deposits of abnormal character 7as compared with ordinary marine deposits7 at the end of ,lower ,palozoic times2--the ,devonian period was one of elevation and denudation1 and we may therefore refer to it as the ,second ,continental ,period4 ,this was followed by depression and sedimentation in ,carboniferous times1 and these ,carboniferous times constitute the ,second ,marine ,period4 ,elevation gave rise to continental tracts and mountain chains at the end of ,carboniferous times1 and here again we find proofs of extensive denudation and the formation of abnormal deposits3--the ,permo-,triassic period is the ,third ,continental ,period4 ,depression set in during early ,jurassic times and continued throughout the ,mesozoic and the early part of ,tertiary times1 which form the ,third ,marine ,period4 ,disturbances culminating in ,miocene times once more produced terrestrial conditions4 ,in this1 the ,fourth ,continental ,period1 we are still living4 ,from what has been previously written it will be seen that each of the marine periods should be marked by an early and late shallow-water phase1 separated by an intervening marine phase1 and the importance of the phases will depend upon the length of time during which they existed1 and will differ markedly in different cases1 whilst the distinctness of the middle phase from the upper and lower1 will depend upon the magnitude of the maximum submergence4 ,during the first marine period submergence was comparatively rapid1 and the shallow-water phase only lasted through very early ,cambrian times in most regions1 whilst the deep-water phase1 complicated by many minor upheavals1 extended through the main part of ,cambrian1 ,ordovician and ,silurian times1 and was replaced by the later shallow-water phase at the end of ,silurian times4 ,the second marine period again was ushered in by rapid submergence1 so that the shallow-water phase was brief1 and the main mass of the ,lower ,carboniferous strata was deposited in deep water2 but1 unlike the first marine period1 the second was characterised by the occurrence of a long interval of time marking the later shallow-water phase1 during which the whole of the ,upper ,carboniferous strata were deposited4 ,the ,carboniferous ,marine ,period is the simplest of the three with which we have to deal1 as the local oscillations occurring on a fairly large scale for such movements were less frequent than was the case during the first and third marine periods4 ,the third marine period had a long shallow-water phase at the commencement1 with many minor oscillations1 causing great variation in the character of the deposits and frequent minor unconformities4 ,this shallow-water phase existed throughout ,jurassic and ,lower ,cretaceous times4 ,the deep-water phase existed during the deposition of the ,upper ,cretaceous deposits1 and was succeeded by the second shallow-water phase1 when the early ,tertiary strata were accumulated4 ,the difference between the elevations which accompanied the ,continental ,periods and those which have been alluded to as minor elevations is no doubt one of degree1 but in considering the ,british strata only no confusion is likely to arise on this account1 as the difference was here very great4 ,the events which occurred during the continental periods are of extreme importance to the geologist4 ,every great upheaval was accompanied by crumpling and stiffening of portions of the earth's crust1 and a definite trend was given to the strata as the result of these movements4 ,it is to the earth-movements of the four great continental periods that the present structure of the ,british ,isles is largely due1 and in any attempt to restore the physical history of our islands considerable attention must be paid to the changes which were produced in the stratified rocks during these periods of earth-movement4 ,,chapter ,,xiv4 ,,the ,,cambrian ,,system4 ,classification4 ,the rocks of the ,cambrian system when found reposing on ,precambrian rocks in ,britain are always separated from the latter by an unconformity4 ,the typical development of the rocks of the system1 as the name implies1 is in the hilly region of ,caernarvonshire and ,merionethshire in ,north ,wales1 and they are also well represented in ,south ,wales1 the border counties between ,england and ,wales1 and the ,north-,west ,highlands of ,scotland4 ,two distinct classifications of the ,cambrian rocks of ,britain are in use1 the original one founded on variations of lithological character1 whilst the second depends upon faunistic differences1 but the original lithological classification has been to some extent modified to make it locally correspond with the classification based upon palontological grounds4 ,the following table will shew the differences3-- ,lithological ,classification4 ,palontological ,classification4 ,tremadoc ,slate ,series#fd ,beds with ,intermediate ,fauna ,lingula ,flags ,series ,beds with ,olenus ,fauna ,menevian beds 7formerly included in ,lingula ,flags7 ,beds with ,paradoxides ,fauna ,formerly grouped ,solva beds together as ,harlech ,caerfai beds or ,llanberis beds ,beds with ,olenellus ,fauna ,footnote #fd3 ,in accordance with the custom usually observed in ,britain1 the ,tremadoc slates are placed in the ,cambrian system2 most continental geologists place them in the succeeding ,ordovician system4 ,the matter is not an important one1 as the fauna is an intermediate one between that of the ,lingula ,flags and that of the ,arenig series of the ,ordovician system1 and the beds are true beds of passage4 ,as the lithological classification is essentially ,british1 it will be as well to retain the ,tremadoc ,slates in the ,cambrian system4 ,the original lithological classification was essentially the result of ,prof4 ,sedgwick's work in ,north ,wales1 while the classification according to faunas is the outcome of the researches of ,dr ,hicks in ,south ,wales4 ,description of the ,strata4 ,the ,cambrian rocks of ,north ,wales occur in two complex anticlines1 separated by an intermediate syncline of ,ordovician strata occupying the ,snowdonian hills4 ,the southerly or ,harlech anticline forms a part of ,merionethshire to the east of ,harlech1 whilst the northern one is developed around ,bangor and ,llanberis4 ,the ,south ,welsh ,cambrian rocks are chiefly found on either side of the ,pembrokeshire axis of ,precambrian rocks which runs through ,st ,david's4 ,as the corresponding rocks of the two regions were deposited in bathymetrical zones of much the same depth1 it will be convenient to give a general account of the rocks of the two regions at the same time1 leaving the student to acquire information of the detailed variations in the larger text-books and in special memoirs#fe4 ,footnote #fe3 ,a general account of the ,cambrian1 ,ordovician and ,silurian rocks will be found in the ,sedgwick ,essay for #ahhc1 ,a ,classification of the ,cambrian and ,silurian ,rocks1 though the use of a cumbrous nomenclature therein will tend to confuse the reader4 ,for a detailed account of the ,cambrian rocks of ,north ,wales the reader is referred to the ,geological ,survey ,memoir1 ,the ,geology of ,north ,wales1 by ,sir ,a4 ,ramsay 7#bnd edition71 he may also consult ,belt1 ,t41 ,on the ,lingula ,flags or ,festiniog ,group of the ,dolgelly district1 ,geol4 ,mag41 ,dec ,i4 vol4 ,,iv4 pp4 #dic1 #ecf1 vol4 ,v4 p4 #e4 ,the geology of the ,cambrian rocks is described in a series of ,memoirs in the ,quarterly ,journal of the ,geological ,society by ,dr ,h4 ,hicks2 the following should be consulted3 ,harkness1 ,r4 and ,hicks1 ,h41 ,on the ,ancient ,rocks of the ,st ,david's ,promontory1 ,south ,wales1 and their ,fossil ,contents1 vol4 ,,xxvii4 p4 #chd2 ,hicks1 ,h41 ,on some ,undescribed ,fossils from the ,menevian ,group1 vol4 ,,xxviii4 p4 #agc2 and ,on the ,tremadoc ,rocks in the neighbourhood of ,st ,david's1 ,south ,wales1 and their ,fossil ,contents1 vol4 ,,xxix4 p4 #ci4 ,see also ,hicks1 ,the ,classification of the ,eozoic and ,lower ,palozoic ,rocks of the ,british ,isles1 ,popular ,science ,review1 ,new ,series1 vol4 ,v41 and ,hicks1 ,life-zones in the ,lower ,palozoic ,rocks1 ,geol4 ,mag4 ,dec ,,iv4 vol4 ,i4 pp4 #cfh1 #cii and #dda4 ,the strata of the ,caerfai and ,solva groups show the prevalence of the shallow-water phase almost uninterruptedly through the whole of the time occupied by their accumulation in the ,welsh areas4 ,they consist chiefly of basal conglomerates1 succeeded by alternations of grits and shales1 though the latter are often converted into slates1 owing to the subsequent production of cleavage4 ,the basal conglomerates of the ,caerfai beds are frequently marked by the existence of enormous pebbles1 composed of fragments of the rocks of the underlying ,precambrian groups1 and the possibility of the occurrence of glacial action during their accumulation as advocated by ,dr ,hicks must be taken into account4 ,above these beds are various coloured grits1 with alternations of muddy sediments often coloured red#ff4 ,the ,solva group consists of massive grits1 of various colours1 also with alternations of mud1 which have prevalent purple and green hues4 ,the great thickness of the strata of the ,caerfai and ,solva ,series1 which sometimes exceeds #aj1jjj feet1 must also be noted4 ,footnote #ff3 ,in giving this description the red 7,glyn7 slates of ,north ,wales are treated as belonging to the ,caerfai series1 though this correlation depends on lithological characters only at present4 ,the ,menevian beds consist essentially of very fine1 well laminated black and grey muds1 which are of a texture favourable for the production of a somewhat regular jointing1 causing the rock to break into small rectangular blocks4 ,they are thin1 not exceeding #fjj feet in thickness1 and indicate the incoming of the general deep-water phase of the ,lower ,palozoic epoch4 ,the ,lingula ,flags mark a local return to shallower water conditions1 especially in the central portion4 ,the total thickness is over #c1jjj feet1 of which the lower stage 7locally the ,maentwrog series7 is over #ejj feet1 and consists of blackish muds1 the middle 7,festiniog stage#fg7 is about #b1jjj feet thick1 and is composed chiefly of shallower water gritty flags1 whilst the upper 7,dolgelly7 stage is of about the same thickness as the lower stage and has similar lithological characters4 ,footnote #fg3 ,the term ,festiniog has been used for the whole ,lingula ,flag series as well as for the middle stage4 ,it will be well to use it with reference to the stage only4 ,the ,tremadoc ,slates are about #a1jjj feet thick4 ,they are divided into a lower and upper stage1 of about equal thickness1 and are essentially composed of iron-stained slates1 with a considerable admixture of calcareous matter in some parts of ,south ,wales1 when they furnish the nearest approach to a limestone which has been found amongst the ,welsh ,cambrian strata4 ,they were probably formed in a fairly deep sea4 ,much pyroclastic rock and some lava flows are intercalated amongst the ,welsh ,cambrian sediments4 ,tuffs are formed in the lower beds of ,st ,david's1 and lavas and ashes have been found amongst the ,lingula ,flags and ,tremadoc ,slates of ,north ,wales1 while the ,lingula ,flags of ,south ,wales have furnished several bands of ash to the north of ,haverfordwest4 ,much of the material of the grits and muds may be derived from volcanic rocks1 though how far this is so cannot be stated in the absence of information obtained by detailed petrological examination of the rocks4 ,the various isolated outcrops of ,cambrian strata amongst the counties of the ,welsh borders and adjoining ,midland counties indicate a great thinning of the ,cambrian rocks in this direction4 ,the probable equivalents of the ,caerfai rocks occur at ,nuneaton1 ,comley1 and on the flanks of the ,wrekin and ,malvern hills4 ,the thin basal conglomerates are succeeded by quartzites1 and sometimes red calcareous sandstones 7,comley sandstone74 ,these rocks are succeeded by thin arenaceous and calcareous beds which represent either the ,solva or ,menevian beds of ,wales4 ,the ,lingula ,flags are represented by the ,malvern ,shales of the ,malvern area and the ,stockingford ,shales of ,nuneaton1 whilst the ,tremadoc ,slates have as their equivalents the ,shineton ,shales4 ,the exact thicknesses of these deposits do not seem to have been recorded1 but ,prof4 ,lapworth observes that in central ,shropshire the ,comley and ,shineton groups which 444 have a collective thickness of perhaps less than #c1jjj feet1 we have apparently a condensed epitome of the entire ,cambrian system as at present generally defined4 ,the ,cambrian rocks of the ,north-west ,highlands consist of a thin conglomerate succeeded by grits and flags with shaley beds1 and above these a mass of limestone1 which may represent some of the ,ordovician deposits as well as those of ,cambrian age4 ,pending a complete description of the faunas of these rocks1 it is sufficient to state that the only fauna which has hitherto been described in detail indicates the existence of ,lowest ,cambrian rocks4 ,further remarks will be made on this head when describing the character of the ,cambrian faunas4 ,the ,cambrian rocks of the ,north-west ,highlands are also very thin as compared with those of ,wales1 so that the ,highland and ,welsh borderland regions appear to have existed as a deeper sea area than that which is indicated by the ,cambrian rocks of ,wales1 an inference which is to some extent borne out by study of the ,cambrian rocks of extra-,british areas1 to which we may now turn4 ,the principal ,european developments of ,cambrian rock are found in ,scandinavia1 ,russia1 ,bohemia and ,spain1 and of these the ,scandinavian one is by far the most fully developed1 as there is a complete sequence in the rocks of that peninsula4 ,they occur both in ,norway and ,sweden1 but the ,swedish exposures are the most interesting in most respects1 especially those of ,westrogothia and ,scania4 ,the rocks are of no great thickness1 and consist essentially of black carbonaceous shales1 with inconstant bands of impure black limestone composed almost entirely of the remains of trilobites or more rarely of brachiopods4 ,these ,alum ,shales1 as they are termed1 rest unconformably upon ,precambrian rocks1 and have arenaceous and conglomeratic deposits at the base4 ,in ,russia the rocks are still further attenuated1 and have not yielded the relics of so many faunas as have been found in the ,scandinavian ,cambrian rocks4 ,the ,bohemian development is incomplete1 owing apparently to an unconformity at the base of the overlying ,ordovician rocks1 while the ,spanish deposits which seem fairly thick and composed largely of mechanical sediments have not been worked out in very great detail4 ,the ,american development of ,cambrian rocks resembles the ,european one in many striking particulars1 and as in the case of ,europe1 there are lateral variations in the lithological characters of the rocks1 though in the opposite direction1 the shallow-water deposits occurring on the east coast1 and the deep-water deposits further west4 ,the general distribution of the different types of ,cambrian strata in ,europe and ,north ,america has been accounted for on the supposition that in ,cambrian times a tract of land lay over much of the present site of the ,north ,atlantic ,ocean1 and that the detritus of that land formed the shallow-water accumulations of ,wales and the east of ,canada1 whilst further away from it were deposited the open-sea accumulations of ,scandinavia and ,russia on one side and of the more westerly regions of ,north ,america on the other1 as indicated in ,fig4 #af4 ,illustration3 ,fig4 #af4 ,p4 ,precambrian ,rocks4 ,a4 ,land4 ,x1 ,x4 ,sea level4 ,,bb4 ,shore deposits4 ,,cc4 ,deep-water deposits4 ,,dd4 ,abyssal deposits4 ,the ,cambrian ,faunas4 ,the ,cambrian ,period has been termed the age of trilobites1 for they are the dominant forms of the time1 but they are associated with many other forms of invertebrata2 indeed all the great groups of this division are represented in the earliest ,cambrian fauna4 ,dr ,c4 ,d4 ,walcott records representatives of ,spongiae1 ,hydrozoa1 ,echinodermata1 ,annelida1 ,brachiopoda1 ,lamellibranchiata1 ,gastropoda1 ,pteropoda1 ,crustacea and ,trilobita as occurring in the ,olenellus beds of ,north ,america and other groups are represented in the rocks of this age in the ,old ,world4 ,the ,cambrian trilobites as a whole are of more generalised types than those of the later systems which furnish their remains1 as indicated especially by the looseness of the body1 and the large number of body rings in many of the genera1 while the tail or pygidium was small and formed of only a few coalesced segments1 as pointed out by ,barrande4 ,in the later trilobites the test is more compact1 there are on the whole fewer body rings1 as more of these have become fused into a tail which is therefore larger than that of the average tail of the ,cambrian trilobite4 ,taking the faunas in order1 the oldest or ,olenellus fauna has furnished a great variety of forms in the ,north-west ,highlands of ,scotland1 ,shropshire1 ,scandinavia1 ,esthonia1 ,sardinia1 ,canada1 and ,newfoundland1 whilst representative species of the fauna have been recorded also from ,worcestershire1 ,warwickshire1 ,pembrokeshire1 ,india1 ,china1 and ,australia4 ,the dominant form is the trilobite of the genus or group ,olenellus1 which contains a great variety of species referable to three or four divisions which have been ranked as separate genera by some writers4 ,associated with ,olenellus are trilobites belonging to other genera1 which are found in higher deposits1 though there represented by different species4 ,brachiopods are fairly abundant1 especially those provided with a horny shell2 of these1 the genus ,kutorgina is widely distributed4 ,the zoological relationships of several of the fossils of this horizon are as yet doubtful4 ,the ,archocyathin show affinities with certain corals2 a number of tests1 included in the genus ,hyolithes and its allies are doubtfully referred to the ,pteropods1 and the position of the genus ,volborthella is uncertain4 ,special attention is directed to these doubtful relationships1 as it is possible that a number of 'generalised forms' of organisms occur in these strata#fh4 ,footnote #fh3 ,for an account of the ,olenellus fauna see ,walcott1 ,c4 ,d41 ,the ,fauna of the ,lower ,cambrian or ,olenellus ,zone1 ,tenth ,annual ,report of the ,director of the ,united ,states ,geological ,survey1 ,washington1 #ahij4 ,it is possible that some of the fossils mentioned in that report belong to strata above that containing ,olenellus4 ,it should be noticed here that faunas have been discovered which are possibly of earlier date than the ,olenellus fauna1 as they do not correspond with it1 or with those of newer strata4 ,one1 the ,neobolus fauna of the ,salt ,range of ,india1 occurs in beds below those with ,olenellus1 though it is not yet clear that ,olenellus will not be eventually discovered associated with it1 whilst the other1 the ,protolenus fauna of ,canada1 is of unknown age#fi4 ,footnote #fi3 ,for an account of the ,neobolus beds see ,noetling1 ,f41 ,on the ,cambrian ,formation of the ,eastern ,salt ,range1 ,records ,geol4 ,survey1 ,india1 vol4 ,,xxvii4 p4 #ga1 and for the ,protolenus fauna consult a paper by ,matthew1 ,g4 ,f41 ,the ,protolenus ,fauna1 ,trans4 ,new ,york ,acad4 of ,science1 #ahie1 vol4 ,,xiv4 p4 #aja4 ,the ,olenellus beds are succeeded by beds containing the ,paradoxides fauna1 which have been found in ,north and ,south ,wales1 ,shropshire1 ,scandinavia1 ,bohemia1 ,spain1 and ,north and ,south ,america4 ,olenellus and its allies became extinct 7or else so scarce that no relics of them have been discovered in the ,paradoxides beds7 before the commencement of the deposition of the strata containing the ,paradoxides fauna1 and few genera pass from the beds with the one fauna to that containing the other4 ,the ,paradoxides fauna existed for a considerable period1 and the beds have been divided into a series of zones characterised by different species of ,paradoxides1 thus ,dr ,hicks records the following zones in ,pembrokeshire#gj3-- ,zone of ,paradoxides ,davidis ,menevian4 ,hicksii ,aurora ,solvensis ,solva4 ,harknessi ,footnote #gj3 ,the order here as elsewhere is ascending1 i4e4 the newest deposit is placed at the top4 ,dr ,tullberg divides the ,paradoxides beds of ,scania into thirteen zones1 though only a few of these are characterised by definite species of ,paradoxides4 ,the ,olenellus beds have not yet been divided into zones1 though this will probably be the outcome of further study#ga4 ,footnote #ga3 ,the ,paradoxides fauna is described in the following works3 ,britain1 ,hicks1 ,h4 and ,salter ,j4 ,w41 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxiv4 p4 #eaj1 ,,xxv4 p4 #ea1 ,,xxvii4 p4 #agc1 and ,hicks1 ,h4 and ,harkness1 ,r41 ibid4 vol4 ,,xxvii4 p4 #chd2 ,scandinavia1 ,angelin1 ,n4 ,p41 ,palontologia ,scandinavica2 ,brgger1 ,w4 ,c41 ,nyt ,magazin for ,naturvidenskaberne1 vol4 ,,xxiv41 ,linnarsson1 ,g41 ,sveriges ,geologiska ,underskning1 ,ser4 ,c4 ,no4 #ce2 ,bohemia1 ,barrande1 ,j41 ,systme ,silurien du centre de la ,bohme2 ,spain1 ,prado1 ,c4 de1 ,sur l'existence de la faune ,primordiale dans la chane ,cantabrique suivie de la description des ,fossiles par ,,mm4 de ,verneuil et ,barrande1 ,bull4 ,soc4 ,geol4 ,france1 #b ,series1 vol4 ,,xvii4 p4 #eaf2 ,america1 ,walcott1 ,c4 ,d41 ,bull4 ,u4 ,s4 ,geol4 ,survey3 ,the ,cambrian ,faunas of ,north ,america1 and ,matthew1 ,g4 ,f41 ,trans4 ,roy4 ,soc4 ,canada1 #ahhb and succeeding years4 ,the strata with ,paradoxides are succeeded by those with the ,olenus fauna1 characterised by the genus ,olenus and a large number of allied genera or sub-genera as some prefer to term them4 ,the genus ,olenus 7sensu stricto7 is very abundant in the lower part of the series1 whilst the allied forms are more abundant in the upper beds4 ,the genus ,paradoxides and its associates disappeared before the deposition of these strata containing ,olenus and its allies1 and indeed the complete change in the character of the faunas in ,europe is very remarkable4 ,the ,olenus fauna has been found in ,north ,wales1 ,pembrokeshire1 ,warwickshire1 ,worcestershire1 and abroad in ,scandinavia and ,canada4 ,it is interesting to note among the fossils of the ,olenus beds the occurrence of a graptolite which is associated with ,olenus in ,scandinavia2 this is the earliest recorded appearance of a group which is destined to play so important a role amongst the fossils of the succeeding system#gb4 ,the following zones have been detected by ,dr ,s4 ,a4 ,tullberg amongst the ,olenus beds of ,scania3-- ,zone of ,acerocare ecorne4 ,dictyograptus flabelliformis4 ,cyclognathus micropygus4 ,peltura scaraboides4 ,eurycare camuricorne4 ,parabolina spinulosa4 ,ceratopyge sp4 ,olenus 7proper74 ,leperditia4 ,agnostus pisiformis4 ,footnote #gb3 ,for descriptions of the ,olenus fauna consult the following3--,wales1 ,belt1 ,t41 ,geol4 ,mag4 ,dec4 ,i4 vol4 ,v4 p4 #e1 and ,salter1 ,j4 ,w41 ,decades ,geol4 ,survey1 ,decade ,,ii4 ,pl4 ,,ix4 and ,decade ,,xi4 ,pl4 ,,viii42 ,scandinavia1 ,angelin1 ,n4 ,p41 ,palontologia ,scandinavica1 and ,brgger1 ,w4 ,c41 ,die ,silurischen ,etagen #b und #c im ,kristianiagebiet und auf ,eker2 ,canada1 ,matthew1 ,g4 ,f41 ,illustrations of the ,fauna of the ,st ,john ,group1 ,no4 ,,vi41 ,trans4 ,roy4 ,soc4 ,canada1 #ahia4 ,the beds with ,dictyograptus flabelliformis form a wonderfully constant horizon at or near the top of the ,olenus beds4 ,they are found in ,north ,wales1 the ,border ,counties between ,wales and ,england1 ,france1 ,scandinavia1 ,russia and ,canada4 ,the passage fauna of the beds which are the equivalents of the ,tremadoc ,slates may be spoken of as the ,ceratopyge fauna1 for ,ceratopyge forficula1 a remarkable species of trilobite1 characterises it in ,scandinavia1 and will probably be found elsewhere4 ,ceratopyge beds have been found in ,north and ,south ,wales1 ,shropshire1 ,scandinavia1 ,bavaria and ,north ,america1 and in each case the fauna is intermediate in character between that of the ,cambrian and that of the ,ordovician system1 containing the loosely-formed trilobites of the former with the more compact ones of the latter4 ,the genus ,bryograptus1 a many-branched graptolite1 also appears to characterise this fauna#gc4 ,footnote #gc3 ,for accounts of the ,tremadoc ,slates ,fauna in ,england and ,wales see ,ramsay1 ,a4 ,c41 ,geology of ,north ,wales1 ,appendix2 ,hicks1 ,h41 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxix4 p4 #ci2 ,callaway1 ,c41 ibid4 vol4 ,,xxxiii4 p4 #feb1 whilst many of the foreign fossils are noticed in ,brgger's ,die ,silurischen ,etagen #b und #c and ,barrande's ,faune silurienne des ,environs de ,hof en ,bavire4 ,the faunas of the ,cambrian rocks have not been studied in sufficient detail1 with reference to the physical surroundings of the organisms1 to throw much light upon the conditions under which the strata were deposited1 though the evidence obtained from an examination of the lithological characters of the deposits is generally corroborated by study of the organic contents4 ,,chapter ,,xv4 ,,the ,,ordovician ,,system4 ,classification4 ,the ,ordovician strata were originally divided into series by ,sedgwick as follows3-- ,upper ,bala1 ,middle ,bala1 ,lower ,bala1 ,arenig4 ,the ,arenig series was at one time included by some writers with the ,lower ,bala under the name ,llandeilo1 but the word ,llandeilo is now used in the sense of ,sedgwick's ,lower ,bala4 ,the ,middle ,bala is often spoken of as ,caradoc1 but the terms ,bala and ,caradoc are sometimes used interchangeably4 ,as much confusion attaches to the use of the name ,bala without explanation1 the alternative titles have been largely adopted1 and as the series are well defined there is no objection to their use1 save that some expression is wanted equivalent to ,upper ,bala4 ,the local term ,ashgill shales was originally applied by ,mr ,w4 ,talbot ,aveline to beds of this age in ,lakeland1 and ,i have elsewhere suggested the use of this name for the whole series in that region2 its use may well be extended to the series which is developed in many parts of ,britain and the continent4 ,the terms which will be used here1 therefore1 for the different series of the ,ordovician system are the following3-- ,ashgill ,series 7 ,upper ,bala7 ,caradoc 7 ,middle 7 ,llandeilo 7 ,lower 7 ,arenig ,adopting a palontological classification1 we may speak of the ,arenig and ,llandeilo beds as those containing the ,asaphus fauna1 whilst the ,caradoc and ,ashgill beds possess the ,trinucleus fauna2 this is the terminology employed by ,angelin for the equivalent strata of ,sweden4 ,it must be noted that here the names applied are not those of absolutely characteristic genera1 as was the case with those adopted for naming the ,cambrian faunas1 for both ,asaphus and ,trinucleus range through the beds of the system2 but whereas ,asaphus is most abundant in the beds of the two lower series1 ,trinucleus occurs most frequently in those of the two upper series4 ,description of the strata4 ,the ,ordovician rocks are found over large tracts in ,north and ,south ,wales1 in the counties on the ,welsh border1 in ,lakeland and the outlying districts in the ,southern ,uplands of ,scotland1 and in detached areas in ,ireland4 ,there are three main types of deposit3--7i7 the volcanic type1 in which the ordinary sediments are associated with a large amount of contemporaneous volcanic matter1 7ii7 the black shale type1 with a fauna consisting largely of graptolites1 and 7iii7 the ordinary sedimentary type1 in which we find alternations of grits1 shales1 and more or less impure limestones4 ,we also find developments which are intermediate between any two or even all three of these types4 ,the first type is characteristically developed in ,caernarvonshire and ,merionethshire1 the second in the ,dumfriesshire ,uplands1 and the third in the ,girvan district of ,ayrshire4 ,the variation in the thickness of these three types of deposit is shown in the accompanying sections of the ,caernarvon1 ,merioneth1 ,moffat and ,girvan regions 7see ,fig4 #ag74 ,illustration3 ,fig4 #ag4 ,showing the variations in the characters of the ,ordovician deposits of the three principal types4 ,scale #a in4 #ajjj feet4 ,a ,arenig4 ,l ,llandeilo4 ,c ,caradoc4 ,the thickness of the ,arenig rocks of the ,scotch areas is unknown4 ,the ,north ,welsh area gives two different developments of the ,ordovician strata1 one of which is much less volcanic than the other4 ,in the ,merioneth-,caernarvon area1 two great masses of volcanic rock form the ,aran and ,arenig hills of ,merioneth and the ,snowdonian group of ,caernarvon4 ,the former are of ,arenig1 the latter of ,caradoc age4 ,the ,merionethshire volcanic rocks consist of a great thickness of lavas and ashes of intermediate composition 7anderites71 associated with sandy and muddy sediments of no great vertical depth4 ,the ,llandeilo beds of this area are chiefly of the nature of black shales1 while the ,caradoc series is represented by volcanic lavas and ashes of acid composition 7felsites7 with a few thin interbedded sediments4 ,a calcareous ash forming the summit of ,snowdon is of importance as being on the same horizon as a limestone 7the ,bala limestone7 found in the other ,north ,welsh area4 ,the ,ashgill series is not represented in ,snowdonia4 ,in the other ,north ,welsh tract1 around ,bala ,lake1 the volcanic matter is much less conspicuous4 ,the ,arenig rocks are not seen nearer than the ,arenig mountains which form the western boundary of this second tract4 ,the ,llandeilo beds consist of shaley deposits with a well-marked limestone1 the ,llandeilo limestone1 in the centre1 whilst the ,caradoc beds consist chiefly of muddy sediments with some thin ashes and a limestone1 the ,bala limestone1 at the top4 ,the ,ashgill series contains a basal limestone1 the ,rhiwlas limestone1 succeeded by shales1 and another thin limestone called the ,hirnant limestone at the summit4 ,in ,south ,wales the ,arenig beds#gd are chiefly composed of slates1 and are divisible into an upper and lower group4 ,the total thickness is about #bjjj feet4 ,the ,llandeilo beds contain three series3-- ,upper ,llandeilo ,slates #ajjj ,llandeilo ,limestone #bjj ,lower ,llandeilo ,slates #hjj4 ,footnote #gd3 ,a remarkable fauna1 fairly well represented in ,britain and exceedingly well developed on the continent1 exists in the ,uppermost ,arenig and ,lower ,llandeilo beds1 and it is well separated from the dominant ,arenig fauna below and ,llandeilo fauna above4 ,to the beds which contain it ,dr ,hicks has given the name ,llanvirn series4 ,the ,caradoc beds consist of black graptolitic shales of no great thickness1 succeeded by an impure limestone on the horizon of the ,bala limestone1 while the ,ashgill series like that of ,north ,wales is separated into upper and lower limestone stages with an intervening stage composed of shales4 ,the deposits of the ,welsh borderland are well developed in ,shropshire1 where there is practically a repetition of the ,caernarvon-,merioneth development1 with variations in detail4 ,the ,arenig and ,caradoc volcanic rocks are not so thick as those of the ,welsh district1 but are nevertheless of considerable importance#ge4 ,footnote #ge3 ,for information concerning these beds see ,lapworth1 ,c4 and ,watts1 ,w4 ,w41 ,the ,geology of ,south ,shropshire1 ,proc4 ,geol4 ,assoc41 vol4 ,,xiii4 p4 #big4 ,in the hilly region of ,cumberland1 ,westmorland1 and the adjoining parts of ,yorkshire the succession differs from that of any of the ,welsh regions1 for the great period of volcanicity was during the formation of the ,llandeilo rocks1 and there were merely sporadic outbursts in ,arenig and ,caradoc times4 ,the ,arenig rocks consist of black shales with interstratified beds of coarser sediment1 and some thin lavas and ashes of intermediate type4 ,the ,llandeilo series is represented by a very great thickness of volcanic rocks1 varying in composition from basic to acid lavas1 with associated pyroclastic rocks4 ,the rocks of the ,caradoc period largely consist of impure limestone with associated argillaceous rocks1 and contemporaneous volcanic rocks of acid character4 ,a marked unconformity is found locally in the centre of these4 ,the ,ashgill series consists of a basal limestone with shales above1 and there is evidence that volcanic activity had not become extinct during the deposition of the rocks of this series4 ,passing on to ,scotland1 the graptolitic type is admirably shown in the southern ,uplands of the neighbourhood of ,moffat1 ,dumfriesshire4 ,the base of the ,ordovician system has not been found1 but the lowest series seems to be represented by shales with a graptolite possibly of ,arenig age4 ,above this are volcanic beds succeeded by a group of black shales known as the ,moffat shales4 ,they are only about six hundred feet in thickness1 and yet represent much of the ,ordovician and part of the ,silurian strata as developed elsewhere4 ,the beds belonging to the ,ordovician system are divided into two series1 the ,glenkiln shales below and the ,hartfell shales above4 ,the former consist of intensely black muds with few fossils save graptolites1 and a deposit of chert at the base which is composed of radiolaria4 ,the graptolites of the black shales are ,upper ,llandeilo forms1 but the thin deposit of radiolarian chert may represent the rest of the ,llandeilo period and part of the ,arenig period also4 ,the ,hartfell shales are also usually black graptolite shales with lighter deposits nearly barren of organic remains2 they represent the ,caradoc and ,ashgill series and pass conformably into the deposits of ,silurian age#gf4 ,the ordinary sedimentary type of ,ordovician rocks is found in ,ayrshire1 though a few thin graptolitic seams are intercalated with the conglomerates and shelly sands1 clays and limestones of the region1 which is therefore peculiarly valuable as affording a means of comparison of the shelly type with the graptolitic type of ,ordovician deposits4 ,the ,arenig series consists of black shales with graptolites1 and these rocks are succeeded by a volcanic group which is probably of ,llandeilo age4 ,above these volcanic beds1 as in ,dumfriesshire1 we find three great divisions1 two of which are of ,ordovician1 the third of ,silurian age4 ,the ,ordovician divisions are respectively termed the ,barr series1 which is the equivalent of the ,glenkiln shales1 and the ,ardmillan series above1 equivalent to the ,hartfell shales#gg4 ,footnote #gf3 ,the ,moffat beds are described in a paper by ,prof4 ,lapworth entitled ,the ,moffat ,series in the ,quarterly ,journal of the ,geological ,society1 vol4 ,,xxxiv4 p4 #bci4 ,this paper1 which is a masterpiece of detailed work1 has furnished a clue to many problems4 ,few students will be able to follow the numerous details1 and for general information concerning the beds they are recommended to read another paper by the same author ,on the ,ballantrae ,rocks of ,south ,scotland1 ,geol4 ,mag4 ,dec4 ,,iii4 vol4 ,,vi4 p4 #bj4 ,an account of the radiolarian cherts by ,dr ,g4 ,j4 ,hinde will be found in the ,annals and ,magazine of ,natural ,history for ,july1 #ahij1 p4 #dj4 ,footnote #gg3 ,see ,lapworth1 ,c41 ,the ,girvan ,succession1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxviii4 p4 #ecg1 and also the paper on the ,ballantrae ,rocks referred to in the preceding footnote4 ,the latter paper should be carefully read by all students of the stratigraphy of the ,lower ,palozoic ,rocks4 ,it is interesting to find that in the north of ,ireland the rocks generally coincide in characters with those which are found along the same line of strike in ,great ,britain2 thus1 the ,girvan type appears in ,londonderry1 ,tyrone and ,fermanagh1 the ,moffat type in ,county ,down1 and the ,lake ,district type in the counties of ,dublin and ,kildare4 ,on the continent the volcanic material which plays so important a part in the constitution of the ,ordovician accumulations of ,britain is practically absent1 and the strata are largely composed of accumulations of shale and limestone with occasional coarser deposits4 ,in ,scandinavia1 the ,arenig beds consist of limestones with a few shales1 the ,llandeilo deposits are largely calcareous1 those of ,caradoc age are partly calcareous and towards the top usually argillaceous1 while the equivalents of the ,british ,ashgill series are calcareous at the base and argillaceous at the summit4 ,in ,russia the calcareous matter preponderates over the argillaceous material4 ,ordovician strata are also found in ,belgium1 ,france1 ,bohemia1 and other places1 and are largely composed of mechanical sediments of varying degrees of fineness mixed occasionally with some calcareous matter4 ,the variation in the characters of the ,ordovician strata of ,britain points to accumulation in a fairly deep sea1 usually at some distance from the land1 but dotted over with volcanoes which often rose above the water1 causing the addition of much volcanic material to the ordinary sediments1 and the existence of minor unconformities at different horizons along their flanks4 ,as these unconformities are not always associated with volcanic material it is obvious that uplifts must have occurred occasionally during the deposition of the rocks2 one important uplift is indicated by the occurrence of an unconformity in the ,arenig rocks of ,wales1 while another is seen amongst the ,caradoc rocks of the ,welsh borders4 ,on the whole1 however1 the period was one of slow subsidence1 the deposition of material generally keeping pace with this subsidence1 and accordingly there is a great uniformity of characters amongst the strata over wide areas4 ,the probable continuation through the ,ordovician period of the tract of land over the present site of the ,n4 ,atlantic ocean which as we have reason to suppose existed during ,cambrian times1 is indicated by similar changes of lithological character amongst the strata when traced from ,britain eastward to ,russia in both ,cambrian and ,ordovician times1 and the continuance of these conditions over the ,american area is also indicated by study of the variations amongst the ,american ,ordovician deposits4 ,the ,ordovician ,faunas4 ,the ,ordovician period has justly been termed the ,period of ,graptolites1 which are the dominant forms of the time1 and continue in abundance throughout the period4 ,the abundance of graptolites in black shales associated with few other organisms has often been noted4 ,it appears to be due to a large extent to the slow accumulation of the graptolitic deposits1 allowing an abundance of these creatures to be showered upon the ocean floor1 after death1 for the evidence derived from detailed examination of their structure points to their existence as floating organisms4 ,the tests of other creatures largely calcareous may well have been dissolved before reaching the sea-floor4 ,in support of the view that these black shales are abysmal deposits may be noted the singular persistence of their lithological characters over wide areas1 their replacement by much greater thicknesses of normal sediments along the ancient coast-lines1 the frequent occurrence together of blind trilobites with those having abnormally large eyes when these creatures are associated with graptolites in the black shales1 and lastly the interstratification of the black shales with radiolarian cherts similar to the modern abysmal radiolarian oozes4 ,if this be so1 we ought to find graptolites in marine deposits of all kinds1 and indeed they are found there1 though largely masked by the mass of sediment and the hosts of other included fossils1 so that their discovery is rendered much more difficult than when they occur in the black shales1--a state of things which is familiar in the case of other pelagic organisms as ,globigerin1 radiolaria1 and pteropods1 whose tests abound in the abysmal deposits and are comparatively rare in those of terrigenous origin#gh4 ,footnote #gh3 ,the importance of the graptolites as indices of the geological age will be seen by perusal of ,prof4 ,lapworth's paper ,on the ,geological ,distribution of the ,rhabdophora1 ,ann4 and ,mag4 ,nat4 ,hist41 ,ser4 #e1 vol4 ,,iii4 7#ahig74 ,the characters of the ,ordovician trilobites have already been noticed4 ,these organisms are abundant1 and occur in sediments of all kinds4 ,of other groups1 the significance of the radiolaria has been referred to above4 ,corals occasionally form reef-like masses of limestone as in the limestones of the ,caradoc epoch2 the echinoderms are well represented1 cystids being locally abundant2 of the crustacea1 many remains of tests of phyllocarida have been recorded2 the brachiopods are very abundant1 and of the mollusca1 lamellibranchs1 gastropods and cephalopods all occur with frequency though none of these groups is very prevalent4 ,certain forms have been referred to pteropods though with doubt1 and other shells seem to be referable to the heteropods4 ,the existence of vertebrates during ,ordovician times is not1 in the opinion of many geologists1 proved1 though remains of fishes have been recorded from the ,ordovician strata of ,north ,america2 but it is desirable that more evidence of this occurrence should be given#gi4 ,footnote #gi3 ,walcott1 ,c4 ,d41 ,preliminary ,notes on the ,discovery of a ,vertebrate ,fauna in ,silurian 7,ordovician7 ,strata1 ,bulletin ,geol4 ,soc4 ,america1 vol4 ,,iii4 p4 #aec4 ,the distribution of the ,ordovician faunas like that of the sediments points to the prevalence of open ocean conditions over wide areas during the period1 with occasional approaches to land1 which was often of a volcanic nature4 ,around this land clustered the ordinary invertebrates1 building up coral-reefs and shell-banks1 whilst away in the open oceans the graptolites floated1 almost alone1 and sank to the ocean floor after death4 ,,chapter ,,xvi4 ,,the ,,silurian ,,system ,,and ,,the ,,changes ,,which ,,occurred ,,in ,,britain ,,at ,,the ,,close ,,of ,,silurian ,,times4 ,classification4 ,the ,silurian system was originally divided by its founder1 ,sir ,r4 ,i4 ,murchison1 into three series1 as follows3-- ,ludlow ,series ,wenlock ,llandovery ,the term ,may ,hill1 proposed by ,sedgwick1 is sometimes used as synonymous with ,llandovery4 ,this classification omits a somewhat important set of beds intercalated between those of the ,llandovery and ,wenlock series known as the ,tarannon shales1 and in ,britain if we were to classify afresh1 it would be more convenient to include some of the beds formerly referred to the ,ludlow in the ,wenlock4 ,i shall1 however1 adopt the old and well-established classification1 adding the term ,tarannon to ,llandovery1 and speaking of the ,llandovery-,tarannon series4 ,the nature of the two classifications is shown in the following table3 ,old ,new ,palontological ,stages4 ,classification4 ,classification4 ,classification4 #a ,upper ,ludlow #b ,aymestry ,limestone ,ludlow ,downtonian #c ,lower ,ludlow ,fauna with #d ,wenlock ,limestone ,encrinurus #e ,wenlock ,shale ,wenlock ,salopian #f ,woolhope ,limestone #g ,tarannon ,shales ,fauna #h ,upper ,llandovery ,llandovery ,valentian with #i ,lower ,llandovery ,harpes ,illustration3 ,fig4 #ah4 ,l ,ludlow4 ,w ,wenlock4 ,ll-,t ,llandovery-,tarannon4 ,description of the strata4 ,lithologically the ,silurian deposits of ,britain form a continuation of those of the ,ordovician period1 with a local interruption due to the elevation of portions of ,wales and the ,welsh borders at the close of ,ordovician times4 ,elsewhere we find a predominance of shales passing into grits at the top of the system1 the change indicating the incoming of the shallow-water phase before the commencement of the second continental period4 ,particular stress is laid upon the predominant shaley character of the beds1 for1 on account of the richness and variety of the faunas of the calcareous rocks1 greater attention is naturally paid to them in geological works1 and the student may get a false idea of their relative importance4 ,an attempt is made below 7,fig4 #ah7 to give a general idea of the variations in lithological characters of the ,silurian rocks in different parts of ,britain4 ,the ,silurian strata are mostly found in the same localities as those which furnish exposures of the rocks of ,ordovician age4 ,the development in the typical ,silurian region of the ,welsh borders is characterised by the abundance of calcareous matter which is found there as compared with that which exists in the other ,british localities4 ,the ,llandovery strata are sandy1 often conglomeratic1 with a fair amount of calcareous matter in places4 ,the arenaceous nature is undoubtedly due to the proximity of land caused by local upheaval at the end of ,ordovician times1 and the ,upper ,llandovery rocks sometimes rest unconformably on the ,lower ones1 at other times on ,ordovician1 ,cambrian1 or even ,precambrian rocks4 ,the ,tarannon shales are light green shales with intercalated grits4 ,the ,wenlock series consists of a group of shales separating a lower1 very inconstant1 earthy limestone from an upper1 more constant1 thicker and purer limestone4 ,the latter1 the ,wenlock limestone1 is composed of fragments and perfect specimens of various fossils1 and the fragmentary nature of many of the shells indicates the occurrence of wave-action and probable formation in shallow water1 in some places against coral-reefs4 ,the ,lower ,ludlow beds consist of sandy shales2 they are separated from the ,upper ,ludlow beds by an impure limestone1 the ,aymestry limestone4 ,the ,upper ,ludlow beds consist mainly of grits and flags1 often coloured red towards the summit4 ,in ,north ,wales the ,llandovery beds occasionally present the shelly arenaceous types of deposit as near ,llangollen1 at other times as near ,conway1 ,corwen1 and in ,anglesey1 the graptolitic shale type4 ,they also rest unconformably upon the ,ordovician rocks in this area4 ,the ,tarannon shales resemble those of the border county4 ,the ,wenlock series consists essentially of shales1 while the ,ludlow development differs from that of the borders in its greater thickness and the absence of any calcareous band in the centre4 ,in ,central ,wales the graptolitic type of the ,llandovery-,tarannon series is found1 but the graptolite-bearing shales of the ,llandovery epoch are thin beds occurring between grits and flags no doubt deposited in shallow water1 and this division of the series is of very great thickness4 ,in ,south ,wales the ,silurian rocks are very similar to those of the ,welsh borders1 save that the calcareous deposits are fewer and thinner4 ,the ,lake ,district ,silurian strata generally resemble those of ,north ,wales4 ,the ,llandovery-,tarannon rocks are of the graptolite-shale type1 intercalated with fine grits in the case of the beds of ,tarannon age4 ,the ,wenlock beds consist of shales1 and the ,ludlow beds of gritty shales beneath1 and massive flags and grits at the summit4 ,these ,ludlow beds are here of great thickness 7certainly not less than #gjjj feet7 and were obviously accumulated for the most part in shallow water4 ,the ,llandovery-,tarannon rocks of ,southern ,scotland show the two types which prevailed in the ,moffat and ,girvan areas in later ,ordovician times4 ,the ,llandovery beds of ,moffat are known as the ,birkhill shales1 and are very thin4 ,the representatives of the ,tarannon shales1 however1 the ,gala beds1 consist mainly of grits1 and attain a great thickness4 ,in the ,girvan area1 the ,llandovery beds are of the shelly type4 ,here as at ,moffat and in the ,lake ,district there is perfect conformity between the beds of ,ordovician and those of ,silurian age1 and accordingly it is instructive to note the completeness of the palontological break1 especially in the ,moffat district4 ,the higher ,silurian beds of ,southern ,scotland present a general resemblance to those of ,north ,wales and the ,lake ,district#hj4 ,footnote #hj3 ,for descriptions of the ,silurian beds of the typical region see ,lapworth and ,watts1 ,proc4 ,geol4 ,assoc41 vol4 ,,xiii4 p4 #big1 those of ,wales are described by ,lake and ,groom1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlix4 p4 #dbf1 and ,lake1 ibid4 vol4 ,,li4 p4 #i4 ,a description of those of ,lakeland will be found in the ,memoir of the ,geological ,survey ,the ,geology of the ,country around ,kendal1 etc4 while the ,scotch ,rocks are described in ,lapworth's papers on ,moffat and ,girvan4 ,on the ,european continent we find indications of conditions similar to those which prevailed during the ,ordovician period2 the strata become much thinner and more calcareous in ,scandinavia1 and still thinner in the ,baltic provinces of ,russia1 where they consist very largely of calcareous matter4 ,in central ,europe the greater abundance of calcareous matter1 compared with that which is found in the ,ordovician strata of that region1 points to a change in physical conditions which became still more marked after ,silurian times4 ,in ,north ,america1 the succession is very similar to that of ,britain1 the calcareous development of the ,silurian rocks being found around ,niagara1 but towards the close of ,silurian times the shallow-water phase became marked in places by the deposition of chemical precipitates which indicate the separation of a portion of the late ,silurian ocean from the main mass during the period of formation of these abnormal deposits4 ,the conditions of ,silurian times1 until the advent of the shallow-water phase1 recall those of ,ordovician times and point to a wide expanse of ocean at some distance from the land1 though the earliest deposits become arenaceous where they were deposited against an old land surface formed by the elevation of the ,welsh ,ordovician rocks1 which were denuded to supply this material4 ,one marked difference existed between the physical conditions of our area during ,ordovician and ,silurian times1 for the volcanic activity which was rife during ,ordovician times almost ceased during ,silurian times1 except in the region now occupied by the extreme south-west of ,ireland1 and accordingly volcanic material does not appreciably contribute to the formation of the ,silurian deposits4 ,the shallowness of the sea-floor at times is marked by the occurrence of masses of reef-building corals in the limestones1 and these probably indicate the prevalence of a fairly warm climate1 an inference supported by the nature of the ,gastropod fauna of ,gothland1 as noticed in ,chap4 ,,ix4 ,the shallow-water phase commences fairly simultaneously over the whole area at the beginning of the deposition of the ,lower ,ludlow rocks1 and becomes more marked in the ,upper ,ludlow rocks1 being most noticeable at their extreme summit1 when a change occurred which will be considered at the conclusion of this chapter4 ,the ,silurian ,faunas#ha4 ,the ,silurian period has been termed the period of ,crinoids1 and this group of creatures certainly contained a great variety of very remarkable forms1 which are specially numerous in the ,wenlock ,limestone of the ,welsh borders1 ,gothland1 and ,north ,america1 but many of the rocks of the system display few traces of these organisms4 ,the trilobites and graptolites still contribute largely to the fauna1 the latter becoming very scarce at the summit of the system1 though a few specimens have been detected in the rocks of the succeeding system4 ,the trilobites belong to few genera though these are mostly more highly organised than those of the ,ordovician period4 ,the genus ,harpes has been taken as fairly characteristic of the lower part of the system in ,sweden1 and it occurs there abundantly in places in ,britain1 whilst ,encrinurus is more abundant in the upper series1 but both of these genera range from higher ,ordovician beds into the ,devonian4 ,mention has already been made of the corals4 ,brachiopods are very abundant1 and ,mollusca appear with considerable frequency4 ,the appearance of true insects is of importance1 cockroaches have been recorded from ,silurian rocks and a number of other insects have lately been recorded from ,canada#hb4 ,eurypterids occur in considerable abundance in the higher parts of the system1 as do also the remains of fish4 ,footnote #ha3 ,for an account of the ,silurian faunas the student may consult ,sir ,r4 ,i4 ,murchison's ,silurian ,system or the shorter ,siluria and ,lapworth's paper on the ,geological ,distribution of the ,rhabdophora4 ,footnote #hb3 ,see an article by ,dr ,g4 ,f4 ,matthew1 ,description of an extinct ,palozoic ,insect and a review of the ,fauna with which it occurs1 ,bulletin ,,xv4 of the ,natural ,history ,society of ,new ,brunswick4 ,the ,silurian ,rocks of the ,little ,river ,group of ,st ,john1 ,new ,brunswick1 have yielded species of land snails1 two doubtful saw-bugs1 several arachnids1 and myriopods1 two insects of the order ,thysanura 7,spring-tails71 and eight ,palodictyoptera4 ,the close of ,silurian times ushered in the second continental period in ,britain when a large part of our area and the adjoining areas to the north and north-east were uplifted to form land1 which in the case of our area was interpenetrated by watery tracts1 whose exact nature is still a subject of dispute4 ,accordingly the deposits which were formed during this period are local and in some cases abnormal1 but they will be considered in the next chapter4 ,simultaneously with the formation of these deposits1 uplift of the sea-floor converted wider and wider areas into land1 and this land underwent considerable denudation1 so that the tops of the anticlines were worn away4 ,the general trend of the anticlines was east-north-east and west-south-west1 and accordingly a series of mountain chains possessed that direction1 for the epeirogenic movements were accompanied by orogenic ones4 ,between the regions of uplifts were depressions in which sediments accumulated4 ,the principal axes of uplift in our area range through the ,north of ,scotland towards ,scandinavia1 across the ,southern ,scotch ,uplands to the ,north of ,ireland1 through the ,lake ,district and through ,wales4 ,as the result of lateral pressure1 a cleavage structure was impressed on many of the ,lower ,palozoic rocks1 the strike of the rocks extended in the direction of the ridges and depressions1 and the rocks as a whole became considerably compacted and hardened1 thus producing one of the most important portions of the framework of our island1 for although the ancient mountain chains were largely denuded during their elevation1 and their stumps were afterwards covered by later deposits1 upon the removal of these1 the ancient stumps were once more exposed as fairly rigid masses which do not yield greatly to denuding influences1 and accordingly stand out as the most important upland regions of ,britain at the present day4 ,it is interesting to notice1 as an illustration of the now well established fact that successive earth movements often occur in the same direction1 that the axes of the folds produced during this second continental 7,devonian7 period1 run parallel with the lines separating tracts of different lithological characters4 ,it has been seen that the ,ordovician and ,silurian rocks of the ,southern ,uplands continue into ,ireland1 and that the beds of similar characters run in belts having a general east-north-east and west-south-west trend1 which accordingly must have been the direction of the coast-line parallel to which they were deposited1 and as that coast-line was due to uplift1 the movement which produced it would naturally produce foldings with east-north-east and west-south-west trend4 ,this is one of many cases where the lines separating belts of rock having different lithological characters run parallel to axial lines of folds which have been produced in the rocks at a later period4 ,as the result of the existence of land over parts of north-west ,europe in ,devonian times1 it is comparatively rare to find a passage from normal ,silurian rocks into normal ,devonian ones2 there is often an unconformity above the ,silurian strata4 ,as we proceed southwards towards central ,europe1 where the epeirogenic and orogenic movements died out1 this is not the case1 and we get complete conformity between marine sediments of the ,silurian and ,devonian periods4 ,,chapter ,,xvii4 ,,the ,,devonian ,,system4 ,classification4 ,as a result of the movements which were briefly described in the last chapter1 two types of ,devonian deposit are found in the ,british ,isles1 and are called respectively the ,devon type and the ,old ,red ,sandstone type4 ,the latter rocks1 formerly divided into three divisions1 are now separated into two only1 the upper and lower ,old ,red ,sandstone1 and the exact relation of these to the different subdivisions of the rocks of ,devon type remains to be settled4 ,the ,devon type itself has given rise to much difference of opinion1 two local classifications have been applied1 one for the rocks of ,north ,devon and another for those of ,south ,devon4 ,the classification which has been most generally adopted is as follows3-- ,n4 ,devon4 ,s4 ,devon#hc4 ,pilton ,beds ,entomis ,slates ,upper ,devonian ,cuculla 7,marwood7 ,goniatite ,limestones 7,clymenian7 ,beds and ,slates ,pickwell ,down ,sandstone ,massive ,limestones ,middle ,devonian ,morte ,slates ,middle ,devonian 7,eifelian7 ,ilfracombe ,beds ,limestones ,ashprington ,volcanic ,series ,eifelian ,slates and ,shaly ,limestones ,lower ,devonian ,lower ,devonian ,hangman ,grits ,slates 7,coblenzian7 ,lynton ,slates ,lincombe and ,warberry ,foreland ,grits ,grits and ,meadfoot ,sands ,footnote #hc3 ,an account of the ,south ,devon rocks by ,mr ,ussher will be found in the ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlvi4 p4 #dhg2 from it the above classification of the rocks of ,s4 ,devon is taken4 ,the division into ,lower ,middle and ,upper ,devonian is generally adopted1 though the alternative titles given to these divisions are not always used with the same signification1 and the distribution of the different local stages given in the above classifications is usually adopted in the main1 though a detailed comparison of the ,devonian beds of ,north and ,south ,devon is still attended with difficulty4 ,more than once an attempt has been made to prove that the apparent succession of the ,north ,devon rocks1 which is that given in the above table1 is not the true one1 and of recent years ,dr ,hicks has obtained a number of fossils from the ,morte ,slates which had hitherto yielded none1 and he believes that these fossils indicate that the ,morte ,slates are on a lower horizon than the beds on which they rest4 ,whatever be the ultimate verdict1 we can1 at any rate1 say that the ,devonian ,question1 as it is termed1 is not settled#hd4 ,footnote #hd3 ,see ,hicks1 ,h41 ,on the ,morte ,slates and ,associated ,beds in ,north ,devon and ,west ,somerset1 ,quart4 ,journ4 ,geol4 ,soc41 vols4 ,,lii4 p4 #bed1 ,,liii4 p4 #dch4 ,description of the ,strata4 ,the general variations in the lithological characters of the deposits of ,devonian age will be seen from the accompanying figure which represents the deposits of ,britain as they occurred from north to south before they had been affected by subsequent earth-movements 7,fig4 #ai74 ,the conventional signs which are used are similar to those which have been used in other parts of this work1 and will save description of the section4 ,illustration3 ,fig4 #ai4 ,a4 ,lower ,palozoic and ,precambrian ,rocks4 ,n4,s4 ,north of ,scotland ,c4,v4 ,central valley of ditto ,old ,red ,sandstone ,type4 ,w4 ,wales ,n4,d4 ,north ,devon ,devon ,type4 ,s4,d4 ,south ,devon ,the ridges separate different deposits of ,devonian rocks1 which were possibly deposited in isolated areas1 though there was probably connexion between them at any rate at times4 ,the ,old ,red ,sandstone type consists to a large extent1 as the name implies1 of sandstones which are coloured red by a deposit of peroxide of iron around the sand grains4 ,they are separable into a lower and upper division with an unconformity often occurring between them4 ,the lower ,old ,red passes down in places into the ,silurian rocks with perfect conformity1 and the upper ,old ,red similarly passes up into the ,carboniferous strata4 ,the existence of pebble beds at different horizons is a noteworthy feature4 ,they are frequently found at or near the base of the two divisions4 ,the sandstones of the lower division are often accompanied by flagstones1 while the red sandstones of the upper division usually have deposits of yellow and brown sandstone intercalated between them4 ,inconstant beds of limestone1 known as cornstones1 are found in both divisions1 and ,prof4 ,sollas has shown that some of these1 at any rate1 are true mechanical deposits1 formed by the destruction of pre-existing strata of limestone and the deposition of the resulting fragments from a state of suspension4 ,in ,scotland a great thickness of volcanic material of various kinds is associated with the two divisions4 ,for the sake of simplicity this is omitted from ,fig4 #aihe4 ,it is not known how far normal sediments are associated with the ,old ,red ,sandstone type of deposit4 ,the existence of some in ,south ,wales is suggested by evidence supplied by the late ,mr ,j4 ,w4 ,salter4 ,footnote #he3 ,for an account of these and all other ,british volcanic rocks the reader is referred to ,sir ,a4 ,geikie's work on ,the ,ancient ,volcanoes of ,great ,britain4 ,macmillan and ,co41 #ahig4 ,the ,devon type1 as will be seen in the figure1 consists of rocks which are to a great extent of normal character4 ,we find in ,devonshire alternations of sandstones1 shales and limestones1 but even here1 red sandstones1 which are comparable with those of the ,old ,red type occur in diminished amount3 the ,foreland ,grits and ,pickwell ,down ,sandstones are both coloured red1 and are like the sandstones formed further north4 ,the recognition of this fact induces one to believe that the contrast between the two types of rock which are found at a short distance from one another on opposite sides of the ,bristol ,channel is not so marked as one is sometimes led to suppose4 ,the rocks of ,north ,devon differ from those of ,south ,devon chiefly owing to the amount of calcareous sediment found in the two areas1 for limestones occur in ,south ,devon to a great extent1 and in ,north ,devon there is a comparative poverty of this kind of sediment4 ,here1 again1 the apparent difference is possibly greater than the real one4 ,the ,north ,devon limestones have in places been stretched out after their formation and thus rendered thinner1 and the highly-cleaved limestones are occasionally mistaken for shales1 while in ,south ,devon there is evidence of thickening of the limestones by folding subsequently to their deposition4 ,allowing for these changes1 however1 there is still a marked diminution in the amount of coarse mechanical sediments and increase in the quantity of calcareous matter as one passes from ,north to ,south ,devon1 and this prepares one for the condition of things met with on parts of the continent1 where the mechanical sediments become finer and thinner on the whole as one travels southward1 until1 when we reach the ,bohemian area1 the ,devonian rocks are found to be largely composed of calcareous sediments4 ,it is interesting to find that in ,north ,america the two types of ,devonian strata recur1 and present characters generally similar to those which they possess upon this side of the ,atlantic4 ,passing now to a consideration of the conditions under which the ,devonian rocks were deposited1 we may examine the bearing of the character of the strata as a whole1 and then proceed to more detailed consideration of the nature and conditions of deposits of the two types4 ,the gradual increase in calcareous matter and dying out of mechanical sediments as one travels southward points to recession from land in that direction1 and we have already seen that the epeirogenic and orogenic movements of this continental period elevated the ,silurian sea-floor in the north1 and gave rise to a ,northern ,continent1 while oceanic conditions continued further ,south1 and allowed the accumulation of sediments lying conformably upon those of ,silurian age1 and giving indications of the prevalence of physical conditions during ,devonian times which were in the main similar to those of the preceding ,silurian period4 ,in the shallow waters adjoining the land of the ,northern ,continent the ,old ,red ,sandstones were laid down1 and the exact conditions under which they were accumulated is a matter of some interest4 ,the late ,sir ,andrew ,ramsay gave reasons for supposing that many red deposits were accumulated in the waters of inland lakes1 which underwent rapid evaporation1 and his views have been applied1 with much corroborative evidence by ,sir ,a4 ,geikie1 to account for the red sandstones of ,devonian age1 which he believes to have been accumulated in a series of inland lakes1 though others hold a different opinion1 and consider that the ,old ,red ,sandstone waters had a direct connexion with those of the open ocean2 the question is too intricate to be discussed at length here4 ,besides the difference of physical characters of the two types of strata1 the difference in the nature of their included organisms is significant4 ,the ordinary invertebrates1 as corals1 crinoids1 brachiopods and molluscs are extremely rare in the ,old ,red ,sandstone1 which contains remarkable remains of ,agnatha fishes and eurypterids1 and although these are also found associated with a true marine fauna in ,russia1 ,germany and ,bohemia1 the rarity or apparent absence of the ordinary marine invertebrates1 though only negative evidence1 which is proverbially dangerous1 must be regarded4 ,the ,north ,devon rocks are sediments which might well be accumulated on the shores of a continent1 while those of ,south ,devon1 with their abundant coral reefs1 and other organic limestones were no doubt deposited in a clearer sea1 at a greater distance from the land1 and the clear water deposits of ,germany and still more of ,bohemia1 were accumulated in the open ocean4 ,it is interesting to note in these ,bohemian deposits abundance of shells of a ,pteropod ,styliola which has been proved by ,prof4 ,h4 ,a4 ,nicholson to form masses of limestone in the ,devonian system of ,canada4 ,the modern distribution of the ,pteropoda suggests the open ocean character of the deposits which contain them even so far back as ,devonian times1 though one cannot conclude that these deposits are really analogous to the so-called ,pteropod ooze of modern seas which1 as a matter of fact1 is largely composed of foraminiferal tests with a considerable percentage of pteropod shells4 ,the ,devonian flora and faunas4 ,the plant remains in the ,lower ,palozoic rocks are few in number4 ,some undoubted terrestrial plants have been discovered1 but the prevalent flora of lower ,palozoic times1 so far as yet known1 was one consisting of ,alg4 ,in ,devonian times we begin to meet with a number of ,cryptogams of higher type1 allied to those which form the dominant flora of the succeeding period4 ,the fauna is in many ways remarkable4 ,the ,devonian period has been termed the period of ganoid fishes1 and the remarkable remains1 so graphically described by the late ,hugh ,miller1 are indeed peculiarly characteristic of ,devonian times1 but they are largely though by no means exclusively entombed in rocks of the ,old ,red ,sandstone type#hf4 ,the ,devon type of rock contains a great abundance and variety of the problematical group1 the ,stromatoporoids1 which contribute extensively to the formation of many of the limestones1 and although these organisms are not by any means confined to ,devonian strata1 their abundance and variety therein might lead one to speak of the period as that of ,stromatoporoids4 ,the remains of corals are very abundant in the limestones1 and1 as already stated1 frequently give rise to true reef-masses4 ,the graptolites1 as remarked in the previous chapter1 disappear in the rocks of the ,devonian period1 and as only one or two fragments have been found1 we may assert that the group was practically extinct at the end of ,silurian times1 though species of one genus1 ,monograptus1 lingered for a short time in greatly diminished quantity4 ,the trilobites which played so important a part amongst the faunas of ,lower ,palozoic times still occur fairly abundantly amongst the rocks of the ,devonian system1 and there is a very interesting point to be noticed in connexion with them4 ,they seem to have become practically extinct in the succeeding ,carboniferous period1 where few genera are found1 and the decadence of the group began in ,devonian times4 ,in these circumstances it is interesting to note the tendency displayed by the creatures to possess spiny coverings4 ,it is true that ,acidaspis1 the most spinose of all trilobites1 is abundant in ,ordovician and ,silurian strata1 and that other spinose trilobites are found there1 but the peculiarity of the ,devonian trilobites is1 that genera which were previously smooth1 or rarely possessing one or few spines1 are found represented by extremely spinose species in these beds1--the spines being developed from all parts of the test1 sometimes as a fringe to head or tail1 sometimes as prominent projections from glabella and neck segment1 and frequently in rows down the body segments4 ,besides ,acidaspis1 we find spinose species of ,phacops1 ,homalonotus1 ,cyphaspis1 ,bronteus and ,encrinurus in ,devonian strata1 and the occurrence of these forms is so frequent and world-wide1 that one might perhaps infer with confidence that an unknown fauna containing many spiny trilobites was of ,devonian age4 ,footnote #hf3 ,for an account of these see ,a4 ,s4 ,woodward's ,vertebrate ,palontology4 ,the abundance of ,eurypterids has been previously noted4 ,occurring as they do in ,silurian rocks1 they are far more abundant in those of ,devonian age1 and are found indifferently in sediments of ,old ,red and ,devon types4 ,of air breathers1 several insects have been found in the strata of different parts of the world4 ,the ordinary marine faunas are otherwise intermediate in character between those of the ,silurian and ,carboniferous periods1 but there are several characteristic ,devonian genera1 and no one who is acquainted with the peculiarity of the ,devonian fauna would deny to the ,devonian strata the right to rank as a separate system1 containing a fauna as well marked in its way as that of the ,silurian system below or that of the ,carboniferous above4 ,special stress is laid upon this point because it has been suggested that the ,devonian system should be abolished1 and its strata either divided between the ,silurian and ,carboniferous systems or referred exclusively to the latter system#hg4 ,footnote #hg3 ,the literature of the fauna of the ,devonian rocks is a rich one4 ,for an account of the ,devonian rocks of ,britain1 the reader may consult the ,monograph of the ,devonian ,fossils of the ,south of ,england by ,rev4 ,g4 ,f4 ,whidbourne1 which is now appearing in the series of ,monographs of the ,palontographical ,society1 and in the publications of the same ,society he will find a ,monograph of the ,eurypterids from the pen of ,dr ,henry ,woodward4 ,the richest ,devonian fauna is undoubtedly that of the ,bohemian area1 for the work of ,dr ,e4 ,kayser has conclusively proved that the stages ,f1 ,g and ,h of that basin1 formerly referred to the ,silurian1 are of ,devonian age1 and an excellent idea of the richness of the ,devonian fauna may be obtained by studying the descriptions of the fossils from those stages which have appeared and are appearing in ,barrande's classic work4 ,,chapter ,,xviii4 ,,the ,,carboniferous ,,system4 ,the ,classification4 ,the ,british rocks of the ,carboniferous system have been classified according to their lithological characters1 but as the classification has been altered from time to time1 we may use that which seems most acceptable to the majority of ,british geologists at the present day4 ,according to this1 the beds are grouped as below3-- ,ardwick ,stage ,upper ,carboniferous ,coal ,measures ,pennant ,stage ,gannister ,stage ,millstone ,grit ,lower ,carboniferous ,carboniferous 7,mountain7 ,limestone ,series4 ,the ,lower ,carboniferous beds have been further subdivided into3-- ,yoredale ,series or ,upper ,limestone ,shales1 ,mountain ,limestone1 ,lower ,limestone ,shales1 with ,sandstones and ,conglomerates1 but as these lithological types are found to be very variable when traced laterally for comparatively short distances1 it is found more satisfactory to use the terms in a purely lithological sense rather than with chronological significance4 ,the somewhat abnormal development of the higher portions of the ,carboniferous rocks of ,britain renders the local classification only partially applicable in other regions1 and as our knowledge progresses1 a palontological classification will probably be adopted4 ,this has already been done with the more purely open-water sediments of ,russia and ,eastern ,asia1 where the development of the beds is more normal4 ,there the rocks are classified as under3-- ,upper ,carboniferous or ,gshellian1 ,middle ,carboniferous or ,moscovian1 ,lower ,carboniferous1 and as this classification has already been found to be applicable over rather wide areas1 it is almost certain that1 as in the case of the rocks of other systems1 it will prove more serviceable than one which is mainly 7though not quite exclusively7 based upon vertical variation of lithological characters1 especially as the ,carboniferous rocks over large tracts in ,north ,america possess faunas which are similar to those which have been discovered in ,russia1 ,eastern ,asia and ,north ,africa4 ,description of the strata4 ,the variations in the lithological characters and fossil contents of the ,british ,carboniferous strata when traced from north to south have been so frequently described1 and utilised as a means of illustrating the indications as to local variations in physical conditions which are supplied by those strata1 that little need be said upon the subject4 ,the restoration of the physical geography of ,carboniferous times over the ,british area will be found in a chapter by the late ,professor ,green in the work upon ,coal by various professors at the ,yorkshire ,college of ,science and also in ,prof4 ,hull's ,physical ,history of the ,british ,isles4 ,some modifications must be made in these restorations as the result of recent research1 the principal being caused by discoveries amongst the ,carboniferous rocks of ,devonshire4 ,taking the strata in vertical succession1 we find evidence of the occurrence of a complete marine period 7the second great marine period7 between the second and third continental periods4 ,the first shallow-water phase over a great portion of the ,british ,isles is marked by thin terrigenous sediments1 indicating that the period was a brief one2 it was followed by the deep-water phase1 probably of some length1 lasting through the greater part of the remainder of ,lower ,carboniferous times2 while the concluding shallow-water phase was lengthy as compared with that of the beginning of the period1 and is marked by the accumulation of the great thickness of deposits belonging to the ,millstone ,grit and ,coal ,measures4 ,there is no doubt1 however1 that in some parts of the ,british area minor changes produced local terrestrial conditions during the period1 and accordingly we find that the deepest water deposits of the system in ,britain are succeeded by an unconformable junction with the sediments of the upper portion of the system4 ,the general change in the lithological characters of the beds of the ,lower ,carboniferous division when traced from south to north is shewn in the following diagram 7,fig4 #bj74 ,it will be seen that the land and open sea areas were in the respective positions which they occupied during ,devonian times1 but that as the result of greater submergence1 with which the accumulation of sediment did not keep pace1 the shallow-water marine deposits of ,devonian age are in ,devon replaced by open-sea deposits#hh1 while shallow-water marine deposits further north replace the anomalous deposits which were found there during the ,devonian period4 ,footnote #hh3 ,the ,radiolarian ,cherts of the ,lower ,carboniferous rocks of ,devon1 and the associated sediments1 together with the unconformity between these and the ,upper ,carboniferous beds are described by ,messrs ,hinde and ,fox1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,li4 p4 #fji4 ,illustration3 ,fig4 #bj4 a4 ,radiolarian cherts of ,devon4 b4 ,mountain limestone of ,central ,england4 c4 ,mechanical sediments of ,northern ,england4 d4 ,freshwater deposits of ,southern ,scotland4 ,o4,r4 ,older rocks4 ,owing to the accumulation of thick masses of sediment1 the ,lower ,carboniferous sea of the north of ,england appears to have been largely silted up1 and although the organic deposits of the south are so thin that they did not render the sea shallow in that region1 the general level of the ,lower ,carboniferous floor of the south was also uplifted1 and actually converted into land1 as the result of the upward movement which took place in ,devonshire and tracts of ,france2 and owing to silting up in the north1 and elevation in the south1 a general plane surface was produced over very extensive areas1 not only in ,britain but upon the ,continent1 upon which the peculiar deposits and accumulations of ,upper ,carboniferous times were laid down1 sometimes in shallow water1 sometimes upon the land1 and often under conditions which cannot at present be determined with accuracy4 ,that the deposits of the ,millstone ,grit and ,coal ,measure epochs were to a large extent laid down in water is admitted by all1 and in the case of many of the deposits of the ,millstone ,grit1 and some thin deposits of the ,coal ,measures1 it is equally clear that the water area was part of an expanse of ocean1 for we find marine fossils1 as corals1 crinoids1 and cephalopods1 in these beds4 ,associated with them in the ,coal ,measures are other beds in which the ordinary ,carboniferous genera of marine invertebrates are absent1 and their place is taken by shells which bear much resemblance to the modern fresh-water mussel1 and it has been maintained with good reason that as the ordinary marine forms are rarely or never mixed with those resembling recent fresh-water shells1 the latter are truly fresh-water#hi4 ,if this be so1 many of the mechanically formed sediments of the ,coal ,measures were of fresh-water origin1 laid down in shallow lagoon-like expanses1 probably shut off from the main ocean by a narrow portion of intervening land1 which was occasionally destroyed1 thus permitting incursions of salt-water when some of the ordinary marine invertebrates of the period obtained a temporary footing in the area4 ,footnote #hi3 ,for further information upon this subject the student should consult the ,introduction to a ,monograph on ,carbonicola1 ,anthracomya and ,naiadites 7the shells in question7 by ,dr ,wheelton ,hind1 being one of the ,monographs of the ,palontographical ,society4 ,there is not only a difference of opinion as to the mode of accumulation of many of the mechanical sediments of the ,coal ,measures1 but also as to that of the coal-seams which accompanied them4 ,two different theories have been put forward to account for these coal-seams1 which are usually spoken of as the drift theory and the growth-in-place theory4 ,according to the former1 in its extreme application1 coal is an aqueous deposit formed by the settlement of drifted masses of vegetation upon the floor of a water-tract1 while those who push the growth-in-place theory to its extreme limits maintain that coal is the result of growth of vegetation upon the actual site where the coal is now found4 ,much apparently conflicting evidence has been advanced by the advocates of the two hypotheses1 and special cases of coal-formation have been appealed to by each in support of their views2 thus the existence of coal composed largely of bodies which resemble the spores of modern lycopods1--objects of so resinous a nature that they float on the surface until they are decomposed1--is cited by the upholders of the growth-in-place theory1 while the supporters of the other hypothesis can point with equal force to the occurrence of the finely divided carbonaceous mud containing remains of fishes which gives rise to cannel coal in some places4 ,one of the main assertions in support of the growth-in-place theory was that of the supposed universality of 'underclays' or old surface soils beneath all coal-seams1 but though these are common1 they are far from universal4 ,it is impossible to do justice in small compass to this question of coal-formation1 but it may be pointed out that much of the difference of opinion can be understood if it be remembered that the term 'coal' is rather a popular term which has been admitted into scientific terminology1 and therefore used somewhat loosely1 than a strictly scientific term applied to a definite substance1 and accordingly1 just as at the present day we find carbonaceous substances growing in one place on land to form peat1 in other places on a tract sometimes dry and sometimes submerged1 to form the carbonaceous deposits of the cypress-swamps1 and once more accumulated beneath the shallows of a sea as a sediment to form the carbonaceous muds of the ocean margins where the mangroves grow1 so the diverse substances which are included under the general term coal may have accumulated in one place on land1 in another beneath water1 and in a third on an area alternately dry and submerged4 ,this is not a question of great importance2 the important point is that accumulations of vegetation on a fairly large scale are found at the present day on plains1 for even if they grow on mountain regions1 the deposits are readily denuded before they are covered up1 and also it must be noted that a moist climate is necessary for the growth of much vegetation4 ,the conclusion that the accumulations of coaly matter were formed on plains is borne out by their great horizontal extent as compared with their thickness1 and it is now generally agreed that the coal vegetation which is found in the normal coal-measures was essentially a swamp vegetation4 ,an attempt has been made to prove that an upland vegetation of very different character existed contemporaneously with it1 but reasons will be given in the sequel for concluding that this supposed upland ,carboniferous flora is everywhere of later date4 ,the later shallow-water phase of ,carboniferous times1 as already stated1 was unusually long1 it was also very widespread1 and appears to have been accompanied over wide areas by humid conditions during its continuance1 and accordingly the marsh conditions which existed during ,upper ,carboniferous times were probably on a larger scale than that of similar conditions before or after4 ,special stress is laid upon this fact1 as it is a good illustration of the view which seems to be gaining ground1 that every period possessed peculiar conditions never to be repeated1 which must have left their impress upon the character of the sediments4 ,though the conditions above described were widespread1 they were naturally not universal1 and accordingly in many parts of the world1 as previously stated1 we find true marine deposits of ,upper ,carboniferous times1 though even these were sometimes replaced during part of the epoch1 by conditions which were favourable for the formation of coal-seams in those places4 ,interruption in the continuance of a humid temperate climate over the regions of ,north-,west ,europe is also suggested by the discovery of deposits which are maintained to be of glacial origin amongst the ,coal ,measures of ,france#ij4 ,footnote #ij3 ,for an account of the numerous volcanic products see ,sir ,a4 ,geikie's work on ,the ,ancient ,volcanoes of ,great ,britain4 ,the ,floras and ,faunas4 ,the flora of the ,carboniferous rock is so noteworthy that the period has been termed the ,period of ,cryptogams2 the remains of ferns1 horsetails1 and clubmosses predominate1 and many of the forms reached a gigantic size4 ,though the floras of the various stages are marked by a general resemblance1 there are differences which enable the palobotanist to ascertain the stratigraphical position of the beds by reference to the included plant remains1 and a considerable number of successive floras have been described#ia4 ,the invertebrate fauna does not differ on the whole very greatly from that of ,devonian times1 though the trilobites are now becoming rare1 and the mollusca assume a more prominent position as compared with the brachiopods4 ,corals occur in abundance in the calcareous deposits of the period1 and frequently give rise to sheets of reef-formation1 but the foraminifera and crinoidea certainly play the principal part as limestone-producers1 and the influence of the latter in giving rise to great masses of limestone which are frequently used for ornamental purposes is too well known to need more than passing reference4 ,the air-breathers have also been detected in greater abundance1 though they are rare1 when we consider the comparatively favourable conditions for their preservation presented by the ,coal ,measure rocks4 ,myriopods1 arachnids1 insects and pulmoniferous gastropods have however been found with tolerable frequency4 ,the danger of arguing from imperfect data is well illustrated by the great addition to our knowledge of the insect-fauna of these times due to the exploration of the beds of one small coal-field1 that of ,commentry in ,france1 of which the insects have been described by ,m4 ,c4 ,brongniart4 ,the vertebrates are represented by a considerable variety of fishes1 and less abundant though tolerably numerous remains of ,amphibia1 which occur in the ,carboniferous rocks of the ,north of ,england1 ,ireland1 ,france1 ,north ,america and elsewhere4 ,footnote #ia3 ,consult ,kidston1 ,r41 ,on the ,various ,divisions of the ,carboniferous ,rocks as determined by their ,fossil ,flora1 ,proc4 ,roy4 ,phys4 ,soc4 ,edin41 vol4 ,,xii4 p4 #ahc4 ,the existence of definite zones of organisms in the case of the ,carboniferous rocks has been denied1 and it appears to be considered by some that the ,carboniferous rocks were accumulated so rapidly as compared with rocks of some other systems that the fauna remained very similar throughout4 ,it is very doubtful if this was so4 ,in the case of other systems1 the division into zones has only been accomplished by means of more detailed researches than those which have been conducted amongst the ,carboniferous rocks of ,britain3 again1 the occurrence of successive floras suggests that there may have been a similar succession amongst the faunas1 and finally we find that zonal division has been carried on to some extent amongst the ,carboniferous strata of other regions4 ,the following classification of the ,russian type of sediment may prove useful1 as an indication of the possibility of more detailed separation of our own beds3-- ,beds with ,spirifera fascigera1 ,spiriferina ,gshellian ,saranae1 c4 7with ,fusulina and ,beds with ,producta cora1 ,p4 uralica1 ,archimedipora7 ,camarophoria crumena1 c4 ,beds with ,syringopora parallela and ,spirifera striata4 ,moscovian ,stage of ,spirifera mosquensis4 ,stage of ,spirifera ,kleini4 ,coals1 ,sandstones and ,shales with ,noeggerathia ,lower ,carboniferous tenuistriata and ,producta gigantea4 ,stage of ,producta mesoloba4 ,the marine fauna of the ,upper ,carboniferous beds1 which is so poorly represented in ,britain1 but is well developed in ,spain1 ,russia1 ,asia and ,north ,america1 is largely characterised by the abundance of foraminifers of the genus ,fusulina and ,fusulinella and of bryozoa of the genus ,archimedipora4 ,it is very desirable that the truly marine fauna of the ,spirorbis limestone and other marine bands of the ,british ,coal ,measures should be carefully studied to see if they present any close relationship with that of the ,gshellian beds#ib4 ,footnote #ib3 ,a good idea of the general characters of the ,carboniferous fauna of ,britain will be obtained from an examination of ,professor ,phillips' ,geology of ,yorkshire1 ,part ,i41 and ,mr 7now ,sir ,f47 ,mc,coy's ,carboniferous ,fossils of ,ireland1 while the nature of the ,european fauna is well illustrated in ,prof4 de ,koninck's well-known work ,description des animaux fossiles qui se trouvent dans le terrain carbonifre de ,belgique4 ,for an account of the characters of the marine fauna of the ,upper ,carboniferous rocks the reader should consult the work on ,geology and ,palontology published by the ,geological ,survey of the ,state of ,illinois in #ahff4 ,,chapter ,,xix4 ,,the ,,changes ,,which ,,occurred ,,during ,,the ,,third ,,continental ,,period ,,in ,,britain2 ,,and ,,the ,,foreign ,,permo-,,carboniferous ,,rocks4 ,at the close of ,carboniferous times a marked change took place in the nature of the earth-movements4 ,the prevalent depression which occurred over the ,british and adjoining regions during ,carboniferous times was replaced by upward movement1 accompanied by orogenic folds1 which once more brought on continental conditions and developed a series of mountain ranges4 ,the change is marked even at the close of ,carboniferous times by the abnormal red sandstones of the uppermost part of the ,carboniferous system which are found around ,whitehaven in ,cumberland and ,rotherham in ,yorkshire1 as the ,whitehaven ,sandstone and ,rotherham ,red ,rock4 ,these movements continued through ,permian and ,triassic times1 and it is to them and to the climatic conditions of the periods1 that the anomalous nature of the ,permo-,triassic deposits is largely due1 as will be shewn in the succeeding chapters4 ,at present it is our purpose to call attention to the effect of these movements upon the sediments which had been deposited previously to their occurrence4 ,over the ,british area1 two different systems of orogenic movement can be detected1 producing folds of which the axes run approximately at right angles to one another4 ,one of these1 of which the ,pennine system is the best representative in ,britain1 caused the production of elevations having axes in a general north and south direction1 and we may therefore speak of it as the ,pennine system of movement1 while the other1 which gave rise to folds running in an east and west direction1 is well represented in the ,mendip ,hills1 and may be therefore termed the ,mendip system1 though it is more widely known as the ,hercynian system1 as1 on the ,continent1 the rocks which are greatly affected by it form the foundations of the region occupied by the ancient ,hercynian forest4 ,the effects of these systems were in the main similar2 they resulted in the uplift of parallel belts of country to form hill-ranges with intervening lowlands1 but when studied in detail the movements are seen to be of a different character4 ,the ,pennine system of movements was of a type which is familiar to the geologists as developed in the ,great ,basin ,region of the western territories of ,north ,america1 and produced what is spoken of as ,basin-,range structure4 ,the movements were of the nature of direct uplift1 causing fracture1 only accompanied by folding in a minor degree1 and accordingly the hills are composed of terraced scarps1 with one gently sloping side1 and one steep scarp-side1 the latter on the upthrow side of the fault1 as seen in fig4 #ba4 ,in the ,mendip system1 the folds were of the ,alpine type1 which is a familiar product of lateral pressure1 consisting essentially of overfolds1 though these are often complicated by reversed faults4 ,of the ,pennine system1 the ,pennine ,chain itself furnishes the most noteworthy example in ,britain1 but we have indications of other folds of this system1 such as that which runs from the ,lake ,district to the ,ayrshire coast1 which is partly concealed as the result of other movements1 and a still more marked one1 in the rocks of the ,malvern ,hills4 ,illustration3 ,fig4 #ba4 a a4 ,one stratum displaced by faults f f4 h4 ,hills4 ,the ,mendip system is well shewn in the ,mendip ,hills1 but the remains of a still more important anticline are seen in ,south ,devon and ,cornwall1 separated from the ,mendip ,hills by the great syncline of ,devon4 ,another parallel anticline runs from ,lancashire to ,yorkshire at right angles to the ,pennine ,chain and separates the coal-field of ,cumberland and that of ,northumberland and ,durham1 from those of ,south ,lancashire1 and ,yorkshire1 ,notts1 and ,derbyshire4 ,on the ,european continent the ,ural ,chain is the most important uplift of the system of which the ,pennine ,chain forms a minor representative1 while the ,hercynian system has caused the compression and stiffening of many of the ,carboniferous and earlier rocks which now rise to the surface in many parts of central ,europe4 ,the extensive continental area which was the result of these uplifts not only determined the formation of abnormal deposits1 but allowed the occurrence of a long period of time subsequently to the close of the ,carboniferous period1 of which few deposits now exposed in ,europe are representative1 and we must accordingly seek other regions in order to find typical representatives of this ,permo-,carboniferous period1 of which the strata developed in the ,salt ,range of ,india have been most carefully worked1 especially by ,dr ,waagen1 though marine sediments of the period are known elsewhere1 as in ,spitsbergen1 the ,ural ,mountains1 ,china and ,australasia2 and a group of somewhat anomalous sediments of this age in parts of ,india1 ,australia and ,south ,america is of peculiar interest1 on account of the insight as to the climatic conditions of the times which it affords4 ,the ,permo-,carboniferous ,rocks4 ,in the ,salt ,range of the ,north-,west of ,india an interesting series of sandstones alternating with limestones rests unconformably upon lower rocks4 ,the sandstones are known as the ,speckled ,sandstones1 while the limestones are termed the ,productus ,limestones4 ,the ,lower and ,middle ,speckled ,sandstones are succeeded by the ,lower ,productus ,limestone which is separated from the ,lower division of the ,middle ,productus ,limestone by the ,upper ,speckled ,sandstone2 these are all of the ,permo-,carboniferous period1 while the upper part of the ,middle ,productus ,limestone and the ,upper ,productus ,limestone belongs to the ,permian period4 ,the fossils1 largely invertebrates1 are intermediate in character between those of ,carboniferous and ,permian ages4 ,similar fossils are found in the marine ,permo-,carboniferous beds of the other areas which have been named above4 ,the ,lower ,speckled ,sandstone is of interest on account of the occurrence of boulder-beds within it1 and this division of the sandstone has been correlated with the lowest 7,talchir7 stage of the ,permo-,carboniferous strata of other parts of ,india1 while the other ,speckled ,sandstones and those divisions of ,productus ,limestone which are referred to the ,permo-,carboniferous are correlated with the higher divisions of other parts4 ,special mention is made of the ,talchir division1 on account of the occurrence therein of boulder beds which have long been known1 and whose glacial origin was inferred by ,dr ,w4 ,t4 ,blanford forty years ago4 ,the accumulations shew signs of having been deposited in water1 but the existence of large subangular1 sometimes striated boulders therein1 which must have come from distant sources1 and the occasional occurrence of striated rock surfaces on the strata upon which the ,talchir beds repose unconformably points to ice-action2 this would not be so very remarkable if it were an isolated case1 though sufficiently so1 from the comparative nearness of the region to the equator2 but researches conducted in different parts of the southern hemisphere have brought to light similar1 and sometimes even more striking evidences of glacial action in widely distinct regions#ic4 ,in ,australia they have been found in ,new ,south ,wales1 ,victoria1 ,south ,australia1 ,east ,australia and ,tasmania2 the ,dwyka boulder-conglomerates of ,south ,africa and certain deposits of similar character discovered by ,prof4 ,derby in ,southern ,brazil have been referred to the same period1 and their glacial origin has also been inferred4 ,this widespread distribution of deposits which are generally contemporaneous1 of which the glacial origin may now be taken as established1 is extremely remarkable1 and must be taken into careful consideration by those who put forward theories framed to account for former climatic changes4 ,footnote #ic3 ,the reader will find an excellent account of the ,permo-,carboniferous glacial deposits in a paper by ,prof4 ,edgworth ,david1 entitled ,evidences of ,glacial ,action in ,australia in ,permo-,carboniferous ,time 7,quart4 ,journ4 ,geol4 ,soc4 ,vol4 ,,lii4 p4 #bhi74 ,in this paper other glacial beds besides those of ,australia are noticed4 ,the ,flora and ,fauna4 ,the flora of the ,permo-,carboniferous beds has caused as much discussion as the question concerning the origin of the boulder-deposits4 ,in the southern hemisphere1 the ,permo-,carboniferous rocks of those countries which have yielded boulder-beds also contain remains of a flora which is now known as the ,glossopteris flora1 from the prevailing genus1 which is associated with other genera1 such as ,gangamopteris4 ,these fossils appear to be ferns1 though their modern allies have not been indicated with certainty2 associated with them are rare cycads and conifers4 ,the ,glossopteris flora is markedly contrasted with the ,coal-,measure flora of the northern hemisphere with its giant lycopods4 ,moreover ,glossopteris appears in the northern hemisphere in rocks of later date than the ,permo-,carboniferous period4 ,it has been suggested that the ,glossopteris flora originated in a continent in the southern hemisphere1 on which the boulder beds were also formed in isolated water areas1 and that some of the forms migrated northwards4 ,to this continent the name ,gondwanaland has been applied by ,prof4 ,suess1 from the ,gondwana series of the ,permo-,carboniferous rocks of ,india1 in which the ,glossopteris flora is found1 and it has also been maintained that the southern ,glossopteris flora was contemporaneous with the northern flora of ordinary ,coal-measure type1 though whether this was so to any extent remains to be proved1 for the beds containing the ,glossopteris flora are distinctly newer than any which have furnished a typical northern ,coal-measure flora4 ,in any case1 the change of floras between ,coal ,measure and ,permo-,carboniferous times is very marked1 and when taken in connexion with the widespread glacial deposits1 is one of the most striking phenomena displayed by the rocks of the stratified column#id4 ,footnote #id3 ,for an account of the ,glossopteris flora and its geological relations1 consult ,seward1 ,a4 ,c41 ,science ,progress1 ,january1 #ahig1 p4 #agh4 ,the fauna has already been noticed4 ,it consists of brachiopods1 some of which are of peculiar genera4 ,the general similarity of the faunas in regions so remote as ,spitsbergen1 the ,ural ,mountains1 ,india1 and ,new ,south ,wales1 indicates an extensive sea during the period4 ,it can hardly be supposed that the fauna of ,permo-,carboniferous times has been completely described1 for the fossils of one or two areas only have been made known to us with any degree of fulness1 and when the ,permo-,carboniferous and marine ,permian faunas are as well known as those of ,triassic times 7and the latter have only been fully described very recently7 there is no doubt that the important break which was at one time supposed to exist between ,palozoic and ,mesozoic faunas will be filled in satisfactorily#ie4 ,footnote #ie3 ,the ,permo-,carboniferous beds are described in ,messrs ,medlicott and ,blanford's ,geology of ,india1 second edition 7edited by ,mr ,r4 ,d4 ,oldham71 and figures of some of the important fossils given therein4 ,for fuller information the reader should refer to ,waagen's account of the ,salt ,range ,fossils and ,feistmantel's description of the plants in the ,memoirs of the ,geological ,survey of ,india4 ,,chapter ,,xx4 ,,the ,,permian ,,system4 ,classification4 ,it has already been observed that as the result of the ,pennine and ,mendip systems of earth-movement1 the ,carboniferous rocks of ,britain are succeeded by a marked unconformity1 and that the rocks of the succeeding ,permian and ,triassic systems of ,britain shew an abnormal development4 ,the principal areas where ,permian rocks are found are on either side of the ,pennine ,chain in the ,north of ,england1 but sporadic exposures of rocks of this age are found in some of the ,midland and ,southern counties4 ,the ,permian rocks have been well studied in ,germany1 and the ,german names are sometimes adopted in ,britain1 and the following comparison will prove useful3-- ,britain4 ,germany4 ,magnesian ,limestone ,magnesian ,limestone ,zechstein4 ,marl ,slate ,kupferschiefer ,lower ,permian ,sandstones ,rothliegende4 ,the term ,zechstein has been applied in a somewhat different sense by different writers1 but the one given in the table appears to find most favour4 ,in a region which was essentially continental1 considerable variations in the lithological characters of the rocks may be expected1 when the strata are traced laterally1 but we nevertheless find that the differences are not so great as was formerly supposed to be the case when certain red sandstones lying above recognised ,permian strata in the district on the west side of the ,pennine ,chain towards its northern extremity were also referred to the ,permian2 these sandstones 7the ,st ,bees ,sandstones7 are now generally admitted to be of ,triassic age1 and comparison between the rocks on opposite sides of the ,pennine ,chain is much simplified1 as seen below4 ,west side4 ,east side4 ,thin ,magnesian ,limestones and ,marls ,magnesian ,limestone ,hilton ,shales ,marl ,slate ,penrith ,sandstone and ,brockrams ,lower ,permian ,sandstones4 ,description of the ,strata4 ,on the east side of the ,pennine ,chain1 the ,lower ,permian sandstone is an inconstant deposit often consisting of yellow false-bedded arenaceous strata4 ,the ,marl ,slate is an argillaceous shale1 often containing bituminous matter1 and yielding several fish-remains and some plants2 it is usually only a few feet in thickness4 ,the ,magnesian ,limestone is typically developed in ,durham as a yellow or greyish limestone containing a variable percentage of carbonate of magnesia2 when traced southward1 it alters its characters1 becoming mixed with mechanical deposits1 and some chemical precipitates in places1 so that at ,mansfield it appears as a red sandstone with grains cemented by a mixture of carbonates of lime and magnesia2 and1 like the rest of the ,permian strata1 it has disappeared when we reach ,nottingham4 ,in addition to the southward thinning of the ,permian beds of this area1 there is some evidence of their disappearance in a westerly direction1 though1 as the present strike of the beds is nearly north and south1 the indications of this are less convincing4 ,on the east side of the ,pennine ,chain1 the main difference observable is the relative thickness of the major divisions4 ,the ,lower ,permian sandstones have thickened out considerably1 while the reputed representatives of the ,magnesian ,limestone are thin4 ,the ,penrith sandstone is of considerable interest4 ,it contains in places1 as near ,appleby1 thick deposits of breccia consisting of angular fragments chiefly composed of ,carboniferous ,limestone1 which in many cases have undergone subsequent dolomitisation1 embedded in a matrix of red sandstone4 ,this breccia is known as brockram4 ,many beds of the ,penrith sandstone are composed of crystalline grains of sand1 due to deposition of silica in crystalline continuity with the quartz of the original grain after the formation of the deposit2 of more significance1 for our present purpose1 is the presence of other accumulations of the sand1 in which the individual grains often approach the form of spheres1 thus resembling the 'millet-seed' sands of modern desert regions4 ,the ,hilton shales are grey sandy shales1 with plant remains1 and above them are variable deposits including thin magnesian limestones which have yielded no fossils4 ,the isolated ,permian deposits of the midland and southern counties of ,england consist of red marls and sandstones with occasional breccias1 and in the absence of fossils1 their exact position in the ,permian series is still unknown4 ,the ,german ,permian rocks resemble those of ,britain1 especially as seen in ,durham1 in many particulars1 and give indications of formation under physical and climatic conditions generally similar to those which were then prevalent in the ,british area4 ,at ,stassfurt1 in ,germany1 the less soluble constituents of ocean water are accompanied by a great variety of salts3--chlorides1 sulphates and borates2 and the very soluble salts of potassium and magnesium known as the ,abraum salts are found in abundance as well as the less soluble salts of sodium and calcium4 ,the occurrence of these very soluble salts is so infrequent on a large scale among the rocks of the ,geological ,column1 and the matter is one of so great theoretical import1 that it is necessary to take special note of their presence in the ,permian strata4 ,the frequent existence of chemical deposits in the ,permian ,rocks of ,n4,w4 ,europe1 the formation of red sandstones1 and the dolomitisation of limestone beds and fragments of pre-existing limestones point to inland seas of a ,caspian character1 while the evaporation necessary for the formation of the precipitates also indicates a fairly warm temperature4 ,the presence of millet-seed sands1 in very lenticular patches1 suggesting former sand-dunes1 and the occurrence in places of breccias 7like some parts of the brockram7 almost devoid of matrix1 piled up against pre-existing cliffs1 recalling screes of modern times1 give almost certain evidence of the occurrence of land tracts most probably of desert character1 during part of the period of accumulation of the materials of the ,permian rocks4 ,the fossil evidence supports this view1 and geologists are mostly agreed that the ,permian rocks of north-west ,europe were accumulated in an area of desert character1 occupied in part by inland seas1 though there is much difference of opinion as to the extent of these seas1 some geologists holding that a number of isolated sheets of water were necessary to produce the distribution and character of the accumulations4 ,it is still a vexed question with ,british geologists how far the ,pennine ridge stood up as land during the period1 but leaving this and other minor considerations out of account1 it may be noted that the similarity of deposits in the different areas1 whether we examine the order of succession1 the lithological characters or the included fossils1 suggests communication between the water tracts of different regions1 though this communication need not have been more than a series of straits1 or comparatively narrow belts of water#if4 ,footnote #if3 ,it should be mentioned that some writers have inferred the evidence of glacial conditions over parts of the ,british area1 on account of the resemblance of some of the ,permian breccias to recent glacial deposits4 ,the question is still sub judice4 ,it is not necessarily opposed to the existence of desert conditions1 if the mountains were sufficiently high1 for the ,wahsatch regions adjoining the ,basin ,region of ,n4 ,america have been glaciated4 ,the extensive development of ,permian and ,triassic rocks with terrestrial characters in the southern hemisphere also1 and the absence of newer deposits in many places1 suggests that the land areas of these times in that hemisphere have largely remained such ever since1 in which case1 the ,permo-,triassic series of movements produced a marked direct effect upon our present continental areas1 and at any rate produced an indirect one upon the ,british land tracts4 ,the presence of anomalous deposits of ,permian age over wide areas need not be surprising1 but it would be indeed remarkable if no ordinary marine type of ,permian rocks was known1 and the researches of recent years have proved that this type is extensively developed1 in ,eastern ,europe1 ,asia1 and ,north ,america1 where ,permian rocks consisting of limestones1 with a greater or less admixture of mechanical deposits1 occur in some abundance4 ,the studies of ,waagen and others in ,india have given us the farthest insight into the nature of these beds4 ,below is a general classification taken from ,waagen's work3-- ,salt ,range4 ,germany4 ,base of ,trias ,unfossiliferous ,shale and ,sandstone ,passage ,beds into ,trias ,top ,beds of ,upper ,productus ,limestone ,cephalopoda ,beds of ,upper ,gypsum ,beds ,productus ,limestone ,middle ,division of ,upper ,productus ,limestone ,zechstein 7in restricted sense7 ,lower ,division of ,upper ,productus ,limestone ,upper ,division of ,middle ,weissliegende and ,kupferschiefer ,productus ,limestone ,middle ,division of ,middle ,rothliegende4 ,productus ,limestone ,it will be seen that in the ,salt ,range there is a complete passage from the ,permo-,carboniferous strata through the ,permian into the ,trias1 and the detailed work which has been carried out by ,waagen and others amongst the rocks of the ,salt ,range must make this1 for the present at all events1 the type area for the marine development of the strata of ,permo-,carboniferous and ,permian ages4 ,the ,permian flora and fauna4 ,the ,permian flora presents some difficulties4 ,the flora of the ,zechstein consists largely of ferns and conifers1 but that of the ,rothliegende of ,germany has been compared with that of the ,carboniferous1 and if a true ,permian flora of the northern hemisphere has many forms of ,carboniferous affinities1 the presence of the ,glossopteris flora in ,permo-,carboniferous rocks of more southerly regions seems to imply its origin there and slow migration northwards4 ,it must be noted1 however1 that the ,rothliegende has been divided by some geologists into an upper and lower division1 of which the lower is actually referred to the ,carboniferous system4 ,all that can be now said is1 that our knowledge of the floras of ,permo-,carboniferous and ,permian times is still incomplete1 and that the difficulties will no doubt be cleared up as the result of further work4 ,the invertebrate fauna of the north-west ,european ,permian deposits is chiefly noticeable on account of the paucity of species1 though individuals are often abundant4 ,the shells are also sometimes stunted and occasionally distorted4 ,these characters bear out the supposition that the aqueous deposits were laid down in inland seas of ,caspian character and not in the open ocean4 ,polyzoa1 brachiopods1 and lamellibranchs predominate1 but other groups are found4 ,the vertebrates consist of forms of fish1 amphibia and reptiles1 and the ,permian rocks are the earliest strata in which the remains of true ,reptilia are known to occur with certainty4 ,the ,reptiles belong to the orders ,anomodontia 7,theromora7 and ,rhynchocephalia1 of which the former is exclusively ,permian and ,triassic1 while the latter is abundant in the strata of those periods1 but is represented at the present day by the genus ,sphenodon of ,new ,zealand4 ,the ,amphibia belong to the order ,labyrinthodontia which ranges from ,carboniferous to ,lower ,jurassic1 but the members of the order are most abundant in ,permian and ,triassic strata1 and these periods may be spoken of as the ,periods of ,labyrinthodonts4 ,a few words must be said of the fauna of the truly marine ,permian beds4 ,it is much richer than that of the abnormal deposits of north-western ,europe1 and its study is important as furnishing another link between ,palozoic and ,mesozoic life4 ,many ,palozoic genera pass up into the ,permian rocks1 and1 as will be ultimately seen1 several occur in those of the ,triassic system1 and one or two even in the basal ,jurassic strata1 though ,mesozoic forms predominate in the ,lower ,jurassic ,rocks1 and there is a fairly equal admixture of forms usually considered as ,palozoic and of those generally regarded as ,mesozoic in ,triassic rocks1 while the ,palozoic forms still predominate over the ,mesozoic in the ,permian strata4 ,along with these characteristic ,palozoic genera1 it is interesting to find representatives of more than one genus of the tribe of ,ammonites1 which is to take so prominent a place in the fauna of the ,mesozoic rocks1 amongst the true marine ,permian sediments of ,india and other areas4 ,the announcement of the contemporaneity of ammonites with fossils regarded as exclusively palozoic was received with considerable doubt1 but this contemporaneity is now clearly established1 and need not be regarded as in any way anomalous4 ,with the deposition of the ,permian rocks1 ,palozoic time comes to an end1 but as already remarked there is no marked and sudden change to characterise it4 ,had our classification been originally founded on study of the ,indian ,rocks instead of those of ,britain1 and similar terms adopted1 the line of demarcation between ,palozoic and ,mesozoic rocks would probably have been drawn below the ,permo-,carboniferous deposits1 and if it had been based on study of other areas1 perhaps elsewhere4 ,the palontological break is purely local1 and it is of the utmost importance that it should be recognised as such1 and that it should not be considered that division into ,palozoic and ,mesozoic implies some great and widespread change which occurred between the times covered by the deposits of each of these great divisions#ig4 ,footnote #ig3 ,the ,permian ,fossils of ,britain are described by ,professor ,king in the ,monographs of the ,palontographical ,society 7the ,brachiopods by ,dr ,davidson in the ,monographs of the same ,society74 ,for a general account of the marine type the student may consult the second edition of ,messrs ,medlicott and ,blanford's ,geology of ,india4 ,for information concerning the ,permian volcanic rocks see ,sir ,a4 ,geikie's ,ancient ,volcanoes of ,great ,britain4 ,,chapter ,,xxi4 ,,the ,,triassic ,,system4 ,classification4 ,the term ,triassic has been applied to these rocks on account of the threefold division into which those of ,germany naturally fall4 ,these three divisions are3-- ,keuper1 ,muschelkalk1 ,bunter2 but above the ,keuper beds we find a group of deposits of some importance1 which shew affinities with both ,triassic and ,jurassic rocks1 which may be looked upon as true passage beds1 though they are generally placed in the ,triassic ,system4 ,they are known as ,rhtic or locally in ,britain as ,penarth ,beds4 ,the ,muschelkalk is usually considered to be unrepresented in ,britain1 and accordingly the ,british deposits may be1 and are usually grouped as under3-- ,rhtic or ,penarth beds ,keuper ,keuper ,marls ,keuper ,sandstones ,muschelkalk absent ,upper ,red and ,mottled ,sandstones ,bunter ,bunter ,pebble ,beds ,lower ,red and ,mottled ,sandstones4 ,the threefold grouping has been applied more or less universally1 but when used outside the north-west ,european area1 it loses its significance1 as the conditions which enable one to differentiate the rocks of the three divisions were naturally only prevalent over a limited area4 ,description of the strata4 ,the ,british ,triassic rocks possess a certain sameness as regards their general characters1 consisting mainly of mechanical sediments coloured red by peroxide of iron1 with occasional chemical precipitates of rock-salt and gypsum4 ,they have a wider distribution over ,britain than have the ,permian rocks1 and the lithological characters of the different subdivisions do not as a rule vary to a remarkable degree when traced laterally4 ,the differences in detail in the characters of the various deposits are noteworthy1 and an explanation of the exact origin of some of these abnormal deposits which will satisfy everyone is not yet forthcoming4 ,leaving the details out of consideration for the moment1 and looking at the general aspect of the deposits1 the prevalence of conditions generally similar to those which existed over the ,british ,isles in the preceding ,permian period is decidedly indicated by the nature of the strata1 though the continental conditions appear to have been more widely established over our area1 as shewn by the general absence of any calcareous deposits resembling the ,magnesian ,limestone4 ,we find chemical precipitates1 millet-seed sandstones1 and scree-like breccias in the ,british ,triassic rocks as well as in those of ,permian age1 and the paucity of a marine invertebrate fauna in the ,triassic rocks of ,britain is even more apparent than in the ,permian strata4 ,it is only at the extreme close of the ,triassic period1 during the deposition of the rocks which are admitted on all hands to be of ,rhtic age1 that we note the incoming of those marine conditions over our area1 which prevailed so extensively1 with few local exceptions1 during the remainder of the ,mesozoic and the early part of ,tertiary times2 the ,rhtic beds1 in fact1 mark the commencement of the third marine period4 ,referring to the strata in further detail1 we may proceed to consider the character of the different subdivisions in the order of their formation1 commencing as usual with the oldest4 ,the ,bunter deposits rest in places upon those of ,permian age with an unconformity at the junction1 but as these unconformities occur frequently among the ,british ,triassic rocks1 it is doubtful whether this unconformity marks more than very local change of physical conditions4 ,the lower and upper divisions of the ,bunter sandstone consist of false-bedded red and variegated sandstones1 and there is no great difficulty in explaining their formation in desert areas with tracts of water1 but the great change which marks the appearance and disappearance of the middle division1 the ,bunter pebble beds1 requires some explanation1 for the contrast between the lithological characters of the rocks of this division and those of the rocks appertaining to the preceding and succeeding division is very marked4 ,the matrix differs1 but the main difference is the abundance of pebbles1 mostly of fairly uniform size1 well rounded1 and largely consisting of liver-coloured quartzite4 ,much difference of opinion exists as to the exact origin of these pebble beds1 and the source of the pebbles1 but without entering into this vexed question1 it may be remarked that the agency of rivers has been somewhat generally invoked to account for their transport1 and the conditions during their accumulation need not have been very different from those which are now found in northern ,india where the torrential rivers of the south side of the ,himalayan chains debouch upon the plain1 and spread an abundant deposit of well-worn pebbles over the finer silts which were previously laid down thereon4 ,the junction of the ,bunter and ,keuper beds requires a short notice4 ,it is usually if not always an unconformable one in ,britain1 and it is generally assumed that the absence of the ,muschelkalk of the ,continent is due to the presence of land undergoing denudation in ,britain during the time when the ,muschelkalk was elsewhere deposited1 though it is quite possible that the ,muschelkalk epoch is represented in ,britain not only by the time which elapsed when the unconformity was being impressed on the rocks1 but also during the true deposition of the upper part of the ,bunter beds1 or the lower part of the ,keuper1 or both4 ,the ,keuper sandstones and marls contain a great development of chemical deposits1 of millet-seed sands1 and of many other features pointing to desert conditions1 such as sun-cracks1 tracks of animals impressed upon a rapidly drying surface1 and pseudomorphs of mud after rock salt in the form of cubes and hopper-crystals2 furthermore we find the scree-like breccias at different horizons of the ,keuper beds where they abut against the old ,mendip ridge composed largely of mountain-limestone which furnished the fragments1 as was the case with the brockrams abutting against the ,pennine ridge4 ,it must be noted that the chemical precipitates of ,triassic age consist of the less soluble substances dissolved in ocean water1 namely1 gypsum and rock salt1 whilst the more deliquescent potash and magnesia salts are not represented in ,britain4 ,turning to these continental beds1 we get evidence of a general approach to open sea conditions as we pass away from ,britain in a south-easterly direction as roughly shewn in the following diagram 7fig4 #bb71 where ,b represents the ,bunter beds1 ,m the ,muschelkalk1 and ,k the ,keuper4 ,illustration3 ,fig4 #bb4 ,it will be seen that the mechanical sediments gradually die out and become replaced by calcareous material as one passes from ,britain towards ,switzerland2 the ,muschelkalk is very thin in the east of ,france and thickens out in ,germany1 while in ,switzerland ,keuper1 ,muschelkalk and ,bunter are alike largely represented by calcareous deposits1 and the mechanical deposits are chiefly argillaceous1 the only important sandstone being situated at the extreme base of the ,bunter series4 ,the marine development of the ,triassic system is naturally the one which is most widely spread1 though full appreciation of its importance has only taken place as the result of researches in distant climes of recent years4 ,it is found in southern ,europe1 in ,spitsbergen1 in considerable tracts of ,asia1 including ,india1 and along the ,pacific coast region of ,north ,america1 and everywhere possesses much the same characters4 ,it will be seen from the above remarks that the physical conditions which prevailed in the continental area of ,triassic times which is now partly occupied by the ,british ,isles are most closely represented by those of the desert regions of central ,asia1 hemmed in by the mountain ranges which intercept the vapour-laden winds of the oceans1 and cause them to precipitate the great bulk of their vapour on the seaward slopes of the mountains1 so that they blow over the deserts as dry winds1 causing the fall of any large amount of rain to be a rare though by no means unknown event in the desert regions4 ,flora and ,fauna of the ,period4 ,the ,triassic flora is essentially similar to that of the higher ,permian strata1 though many of the genera are different4 ,the invertebrate fauna of the ,british deposits is1 as might be expected1 very poor until the beds of the ,rhtic series are reached4 ,in the beds below the ,rhtics1 the principal invertebrate remains are the tests of the crustacean genus ,estheria1 though a few obscure lamellibranch shells have been recorded4 ,the vertebrate fauna is of great interest4 ,a number of fishes have been found1 the most remarkable of which is the genus ,ceratodus1 occurring in the ,rhtic beds of ,britain and lower ,triassic strata of foreign countries4 ,it is closely related to the ,barramunda of the ,queensland rivers belonging to the order ,dipnoi4 ,as in the ,permian strata1 abundance of ,labyrinthodont amphibians have been discovered1 and the reptiles belong to the orders ,anomodontia and ,rhynchocephalia4 ,in the ,rhtic beds of ,britain and in still lower ,triassic beds abroad the orders ,ichthyopterygia and ,sauropterygia 7represented by ,ichthyosaurus and ,plesiosaurus7 are found4 ,the ,triassic rocks also yield the earliest known mammals1 the best known1 ,microlestes1 occurring in the ,triassic rocks of ,britain and the ,continent4 ,these mammals are now placed in a subclass ,metatheria of the order ,monotremata4 ,the marine invertebrate fauna of the normal ,triassic rocks presents some points of considerable interest4 ,as already remarked1 the fauna may be looked upon as a passage fauna between that of ,palozoic and that of ,mesozoic times1 the number of ,palozoic forms which pass into the ,trias being approximately comparable with those which appear here and range upwards into higher ,mesozoic strata4 ,this may be well seen by examining the table given in ,chapter ,,xxi4 of the ,second ,edition of ,sir ,charles ,lyell's ,student's ,elements of ,geology1 in which three columns shew the genera of ,mollusca common to older rocks1 those characteristic of the ,trias1 and those common to newer rocks4 ,amongst the first are ,orthoceras1 ,bactrites1 ,loxonema1 ,murchisonia1 and ,euomphalus1 in the second column are ,ceratites1 ,halobia 7,daonella71 ,koninckina1 and ,myophoria1 and in the third1 ,ammonites1 ,cerithium1 ,opis1 ,plicatula and ,thecidium#ih4 ,footnote #ih3 ,it has been seen that some of the ,ammonites appear earlier1 namely1 in ,permian strata4 ,myophoria is extremely abundant in the ,trias1 but ranges into newer strata4 ,the ,ammonites are largely utilised in the case of the ,mesozoic strata for separation of these strata into zones1 each zone being characterised by some species of ,ammonite1 and the researches of ,mojsisovics have proved that this zonal subdivision1 long adopted for ,jurassic rocks1 is also applicable to those of ,triassic age#ii4 ,he gives the following table of the classification of the ,triassic rocks of the ,mediterranean ,province1 which is reproduced1 as it is founded upon ,palontological evidence1 and will probably be widely adopted4 ,footnote #ii3 von ,mojsisovics1 ,dr ,e41 ,faunistische ,ergebnisse aus der ,untersuchung der ,ammoneen-faunen der ,mediterranen ,trias4 ,abhandl4 der k4 k4 ,geologisch4 ,reichsanstalt1 ,,vi4 ,band #b ,abtheilung4 ,vienna1 #ahic4 ,series ,zonal ,divisions ---------------------------------------- ------------------------------- ,rhtic #a4 ,zone of ,avicula ,contorta ---------------------------------------- ------------------------------- #b4 ,zone of ,sirenites ,argonautae ,upper ,juvavic #c4 ,zone of ,pinnacoceras ,metternichi ,juvavic ,middle ,juvavic #d4 ,zone of ,cyrtopleurites bicrenatus #e4 ,zone of ,cladiscites ruber ,lower ,juvavic #f4 ,zone of ,sagenites ,giebeli ---------------------------------------- ------------------------------- ,upper ,carnic #g4 ,zone of ,tropites subbullatus ,carnic ,middle ,carnic #h4 ,zone of ,trachyceras ,aonoides ,lower ,carnic #i4 ,zone of ,trachyceras ,aon ---------------------------------------- ------------------------------- ,upper ,noric #aj4 ,zone of ,protrachyceras ,noric ,archelaus ,lower ,noric #aa4 ,zone of ,protrachyceras ,curionii ---------------------------------------- ------------------------------- ,upper ,muschelkalk #ab4 ,zone of ,ceratiles trinodosus ,muschelkalk ,lower ,muschelkalk #ac4 ,zone of ,ceratiles binodosus ---------------------------------------- ------------------------------- ,buntsandstein ,werfener ,schichten #ad4 ,zone of ,tirolites ,cassianus ---------------------------------------- ------------------------------- ,,chapter ,,xxii4 ,,the ,,jurassic ,,system4 ,the ,jurassic rocks were formerly separated on account of differences of lithological character into ,oolites and ,lias1 but it was apparent that the ,oolites were more important than the ,lias1 and a fourfold division was made into3-- ,upper or ,portland ,oolites ,middle or ,oxford ,oolites ,malm ,lower or ,bath ,oolites ,dogger ,lias4 ,the ,lias strata have also been spoken of as the ,black ,jura1 the ,lower ,oolites and part of the ,oxford ,oolites as ,brown ,jura1 and the rest of the ,oxford ,oolites with the ,portland ,oolites as ,white ,jura4 ,as the outcome of a detailed study of the faunas of the ,jurassic rocks1 a further subdivision has been made1 partly based upon the original ,british series1 but the divisions are defined with greater accuracy1 so that they are applicable over wider areas4 ,they are as follows3-- ,purbeckian ,upper ,oolites ,portlandian ,kimmeridgian ,corallian ,middle ,oolites ,oxfordian ,callovian ,lower ,oolites ,bathonian ,bajocian ,toarcian ,lias ,liassian ,sinemurian4 ,many of these series have been still farther subdivided into smaller stages1 and the whole differentiated into a number of zones characterised by different forms of ,ammonites4 ,dr ,e4 von ,mojsisovics gives thirty-two ,ammonite zones1 of which fourteen occur in the ,lias1 eight in the ,lower ,oolites1 six in the ,middle ,oolites1 and four in the ,upper ,oolites4 ,characters of the strata4 ,the whole of the ,jurassic rocks and also those of ,lower ,cretaceous age may be regarded as having been deposited during the first shallow water phase of the third marine period1 but this shallow water phase is represented by strata which are varied owing to numerous marine changes resulting in the production of land at times1 and estuarine conditions1 shallow water1 marine conditions1 and somewhat deeper sea conditions respectively at other times1 and accordingly the strata of the ,british ,isles vary greatly when traced laterally4 ,that the uplifts of the ,permo-,triassic periods produced some effect on the nature and distribution of the ,jurassic rocks is certain1 but it is not quite clear how far the ridges produced by these uplifts were submerged and denuded during the deposition of the main portion of the ,jurassic strata4 ,viewed broadly1 the ,jurassic rocks of ,britain may be regarded as consisting of three great clay deposits1 the ,lias1 ,oxford and ,kimmeridge ,clays1 alternating with the deposits of variable lithological characters1 which compose the ,bajocian1 ,bathonian1 ,corallian1 ,portlandian and ,purbeckian subdivisions4 ,this essentially argillaceous character of a large part of the deposits of ,jurassic age is often overlooked1 as1 owing to their sameness and the comparative paucity of organisms constituting the faunas in the clays1 their description in text-books can be given at much shorter length than that of the more variable and highly fossiliferous deposits which separate the clays4 ,the following figure 7,fig4 #bc7 roughly represents the nature of the different divisions of the rocks of this system when traced across ,england from south-west to north-east4 ,illustration3 ,fig4 #bc4 ,vertical scale3 #a in4 about #ajjj feet4 ,it will be seen that the greatest variations in lithological character occur in the ,bathonian and ,bajocian beds1 and it will be of interest to give some account of the principal variations and to attempt to account for them4 ,in so doing it will be convenient to consider the four major divisions of the ,jurassic rocks separately1 and to enter into particulars concerning the local classification applied to the rocks of these divisions4 ,the ,lias4 ,the ,british ,lias deposits are divided into the ,lower ,lias1 the ,marlstone1 and the ,upper ,lias corresponding in general terms only with the ,sinemurian1 ,liassian1 and ,toarcian4 ,the ,marlstone is separated from the ,upper and ,lower ,lias on account of the greater percentage of carbonate of lime which it contains1 so that the bands of argillaceous limestone are much more marked in the ,marlstone than in the upper and lower divisions1 which consist chiefly of clay4 ,the three divisions possess very much the same characters throughout the country1 though the presence of the ,mendip ridge and its continuation beneath ,london is marked by the attenuation of this and succeeding strata1 and by the conglomeratic character of some of the ,liassic strata where they abut against it4 ,the ,british ,lias1 as a whole1 seems to have been deposited in a fairly shallow sea at no great distance from the land4 ,it passes down conformably into the ,rhtic beds1 indeed the zone of ,ammonites 7,aegoceras7 planorbis1 referred by ,british geologists to the ,lower ,lias is included by some continental writers with the ,rhtic beds1 and the plane of demarcation here as in other cases is conventional4 ,the ,lower ,oolites4 ,of all the ,british strata1 these perhaps cause most trouble to the learner1 on account of the different nomenclature applied to the rocks in different parts of ,england1 and the rapid variations in lithological character1 when the beds are traced laterally4 ,the following divisions are usually adopted for the beds of the south-western counties where the most marked marine development occurs3-- ,cornbrash1 ,forest ,marble1 ,great ,oolite 7with ,bradford ,clay71 ,fuller's ,earth1 ,inferior ,oolite4 ,of these divisions1 the uppermost one1 the ,cornbrash1 though thin1 retains its characters with great constancy across the island4 ,of the others the ,forest ,marble may be looked upon as a local development of the upper portion of the ,great ,oolite1 and the ,fuller's ,earth is a local deposit1 so that the ,inferior ,oolite and ,great ,oolite constitute the important divisions of the ,lower ,oolites4 ,the variations in the characters of the rocks may be best shown in tabular form4 ---------------------------------------- ------------------------------- ,gloucestershire1 ,south ,n4 c4 ,northamptonshire ,northamptonshire ,yorkshire and ,lincoln ---------------------------------------- ------------------------------- ,cornbrash ,cornbrash ,cornbrash ,cornbrash ---------------------------------------- ------------------------------- ,great ,oolite ,great ,oolite ,great ,oolite ,clay 7,upper part7 ,great ,oolite ,upper ,limestone ,upper ,estuarine ,northamptonshire ,estuarine 444444444444444 4444444444444444 44444444444444444 4444444444444444 ,series ,series ,lincolnshire ,scarbro' ,limestone ,limestone ,sands ,middle ,estuarine ,series ,inferior ,oolite ,lower ,estuarine ,millepore ,oolite ,series ,lower ,estuarine ,series ---------------------------------------- ------------------------------- ,upper ,lias ,upper ,lias ,upper ,lias ,upper ,lias ---------------------------------------- ------------------------------- ,the dotted line shows roughly the division between ,bathonian and ,bajocian4 ,the changes may be explained very simply if we leave out of account for the moment the development of ,lincolnshire ,limestone1 with its equivalent the ,scarbro' ,limestone1 and the ,millepore series4 ,the beds in ,gloucestershire and other south-western counties are essentially marine2 whilst in ,northamptonshire and ,lincolnshire estuarine conditions set in after the deposition of the ,upper ,lias1 and continued throughout the deposition of the ,bajocian and ,lower ,bathonian beds1 being replaced by marine conditions during the formation of the ,upper ,bathonian strata1 and still further north in ,yorkshire the estuarine conditions generally prevailed throughout ,bajocian and ,bathonian times4 ,these changes point to the existence of land towards the north4 ,the general simplicity is modified by temporary prevalence of marine conditions twice over 7during the deposition of the ,millepore ,oolite and the ,scarbro' ,limestone7 in ,yorkshire1 and once 7during the deposition of the ,lincolnshire ,limestone7 in ,lincolnshire4 ,certain local deposits have not been noticed1 but two of them merit brief reference4 ,at the base of the ,great ,oolite of ,oxfordshire is an estuarine deposit of finely laminated mechanical sediment mixed with calcareous matter known as the ,stonesfield ,slate1 especially interesting on account of its fossils1 while a bed with similar lithological characters but with a different fauna occurring at the base of the ,lincolnshire ,limestone 7of ,bajocian age7 is termed the ,collyweston ,slate4 ,neither of these deposits is a slate in the true sense of the word1 as they have not been affected by cleavage subsequently to their accumulation1 but each has been somewhat extensively used for roofing purposes4 ,the ,middle ,oolites are much less complicated though considerable variations arise with respect to the ,corallian ,rocks4 ,the ,oxfordian with ,callovian consist chiefly of clay1 though the ,callovian of the south of ,england is represented by calcareous sandstone1 with a peculiar fauna which seems to be represented in the lower part of the ,oxford ,clay further north1 though this ,callovian fauna has not been everywhere recognised4 ,the ,corallian of the southern counties consists of limestones with calcareous grits1 the limestones being often largely composed of the remains of reef-building corals1 and a similar development of the rocks of this series is found in ,yorkshire1 while a local development of the same character is found at ,upware in ,cambridgeshire1 though in the other parts of the ,fenland counties the ,corallian is represented by an argillaceous deposit with ,corallian fossils known as the ,ampthill ,clay4 ,the ,upper ,oolites have a tolerably constant base1 the ,kimmeridge ,clay1 usually consisting of laminated bituminous argillaceous material1 but the ,portlandian and ,purbeckian divisions vary greatly1 and are only locally developed1 though their absence in some parts of central ,england is no doubt due to unconformity4 ,the ,portlandian rocks of the south of ,england consist of limestones and sandstones which pass further northward into shallower water mechanical deposits often charged with iron hydrate1 and the beds disappear in ,oxfordshire4 ,the ,purbeckian rocks of the south are also limited as regards area of exposure3 they consist of estuarine deposits with some terrestrial accumulations of the nature of old surface soils4 ,representations of the ,portlandian and ,purbeckian beds are found in ,lincolnshire and ,yorkshire1 as arenaceous deposits in the former county and argillaceous ones in the latter4 ,both are marine deposits of a northern type1 developed elsewhere in northern ,european and circumpolar regions1 and in these counties we find a complete passage from the ,jurassic rocks through the ,cretaceous rocks1 but the exact lines of demarcation between the different series of the passage beds are difficult to define4 ,the foreign ,jurassic rocks of ,europe and of some parts of ,asia strongly resemble in general characters those which have been described above as occurring in ,britain4 ,one of the most remarkable features of the ,jurassic rocks as a whole1 is the absence of the ,lias over wide areas1 the continental period which in ,britain existed in ,permo-,triassic times is elsewhere frequently replaced by one of ,liassic age4 ,the ,jurassic and ,cretaceous rocks are of interest on account of the evidence which they supply as to the existence of climatic zones in these periods1 which run fairly parallel with those at present existing4 ,the late ,dr ,neumayr in a paper already cited divides the world during later ,mesozoic times into four distinct climatic zones1 equatorial1 north and south temperate and boreal zones 7the corresponding austral zone is not known owing no doubt to the extensive sea of ,south ,polar regions and our general ignorance of its lands74 ,in ,europe the ,mediterranean ,province belongs to the equatorial zone1 the ,middle ,european to the ,north temperate zone1 and the ,russian or ,boreal to the ,boreal zone4 ,the last-named is marked partly by negative characters1 the absence of certain ,ammonite-genera and of coral reefs being noticeable1 whilst the lamellibranch ,aucella is very frequent4 ,in the ,north temperate zone1 certain ,ammonite genera as ,aspidoceras and ,oppelia are abundant and there are also extensive coral-reefs4 ,the ,equatorial zone is marked by the ,ammonite-genera ,phylloceras and ,lytoceras and by the ,diphya group of ,terebratul4 ,it is of special interest to note that the fauna of the ,south temperate bears closer relationship to that of the ,north temperate than to that of the intermediate ,equatorial zone4 ,jurassic floras and faunas4 ,the ,jurassic flora is very similar in its characters to that of the ,lower ,cretaceous rocks1 and the two taken together afford a decided contrast with that of later ,palozoic times1 and also with that which succeeds them in the ,upper ,cretaceous rocks1 which bears a marked resemblance to the existing flora4 ,cycads predominate1 accompanied by conifers1 and a fair number of ferns and ,equisetace4 ,the ,jurassic fauna is specially noteworthy on account of the character of the vertebrata1 but some notice of the invertebrates must also be taken4 ,the abundance of corals in the ,temperate zones has already been pointed out1 but the mollusca form the bulk of the invertebrate fauna1 lamellibranchs1 gastropods and cephalopods being all abundant2 of the last-named the ammonites and belemnites contribute most largely4 ,the vertebrates include remains of fishes1 amphibia1 reptiles1 birds and mammals4 ,the ,jurassic reptilia furnish representatives of some modern orders as the ,chelonia and ,crocodilia1 but the most important orders are essentially characteristic of later ,mesozoic times and their representatives abound in the ,jurassic strata4 ,these are the ,sauropterygia 7including the ,plesiosaurs71 the ,ichthyopterygia 7including the ,ichthyosaurs71 the ,dinosauria1 and the ,pterosauria commonly known as ,pterodactyls4 ,no birds have hitherto been discovered in the ,british ,jurassic rocks1 but the ,solenhofen ,slate of ,bavaria 7of ,kimmeridgian age7 has furnished the celebrated ,archopteryx macrura1 which is not only placed in a family but also in an order by itself1 the order ,saurur4 ,many remains of mammals have been extracted from the estuarine deposits of ,stonesfield1 and the old surface soils of the ,purbeckian beds2 representatives of the ,monotremata are furnished by the ,plagiaulacid and ,tritylodontid1 the former family containing the genus ,plagiaulax of the ,purbeck ,beds and the latter1 ,stereognathus of the ,stonesfield slate4 ,the ,marsupialia are represented by the ,amphitherid1 ,spalacotherid and ,triconodontid4 ,some forms have been referred to the ,insectivora1 but there is still disagreement concerning the correctness of this reference4 ,before dismissing the subject of the ,jurassic fossils1 attention may be called to a feature which has been frequently commented upon1 namely1 the general resemblance of the flora and fauna of ,jurassic times to the modern ,australian fauna and flora4 ,the explanation which has been offered to account for this resemblance has been given in a preceding chapter1 where it was stated that ,mr ,a4 ,r4 ,wallace considers1 after review of the geological and biological evidence1 that ,australia was severed from the adjoining continental lands in ,mesozoic times1 and that the higher forms of life which on the larger continents have replaced the earlier and lower forms have not succeeded in obtaining a footing in ,australia1 which therefore furnishes us with a local survival of a once widespread fauna4 ,in connection with this matter the actual existence of the genus ,trigonia 7a form peculiarly abundant in ,jurassic strata and characteristic of ,mesozoic strata in ,britain7 in the ,australian sea is of considerable interest4#ajj ,footnote #ajj3 ,a good account of the ,british ,jurassic rocks will be found in ,mr ,h4 ,b4 ,woodward's ,memoir on ,the ,jurassic ,rocks of ,britain4 ,mem4 ,geol4 ,survey1 #ahic--4 ,,chapter ,,xxiii4 ,,the ,,cretaceous ,,system4 ,classification4 ,the rocks of the ,cretaceous system are conveniently divided into ,upper and ,lower ,cretaceous4 ,the following classification has been widely used for the ,british deposits1 and is founded on lithological characters3 ,upper ,chalk with flints ,middle ,chalk with few flints ,chalk ,upper ,lower ,chalk without flints ,cretaceous ,chalk ,marl ,upper ,greensand ,gault ,lower ,greensand ,lower ,wealden ,cretaceous ,hastings sands ,as the result of examination of the faunas1 a more generally applicable classification has been established and is now largely adopted4 ,it is as follows3 ,danian ,senonian ,upper ,cretaceous ,turonian ,cenomanian ,albian ,aptian ,lower ,cretaceous4 ,neocomian ,in this classification the ,neocomian practically represents the ,wealden and ,hastings beds1 the ,aptian the ,lower ,greensand and the ,albian the ,gault1 placed according to this classification in the ,lower ,cretaceous1 while the ,upper divisions represent the strata above the ,gault1 consisting essentially of ,chalk in ,england4 ,description of the ,strata4 7i7 ,the ,neocomian and ,aptian ,beds4 ,in the south of ,england the ,lower ,cretaceous beds succeed the ,jurassic rocks with little or no break1 and the type of the lower beds is similar to that of the beds deposited during the ,purbeck age1 consisting of estuarine deposits of variable characters1 chiefly arenaceous below 7the ,hastings sands7 and argillaceous above 7the ,wealden series71 though impure limestones are found1 largely composed of the shells of the freshwater ,paludina1 and much ironstone is developed in places4 ,at the close of ,neocomian times1 the freshwater conditions in southern ,england were replaced by marine conditions and the ,lower ,greensand strata with their marine fauna were deposited in the ,aptian sea4 ,the ,neocomian and ,aptian beds thin out westward1 and much more rapidly to the northward1 so that both divisions disappear against the now buried ridge which forms a continuation of the ,mendip axis4 ,north of this they appear in another form4 ,at first the highest ,aptian beds alone are developed as shore deposits4 ,passing into ,norfolk lower beds come in until in ,lincolnshire we get a complete development of the ,neocomian and ,aptian beds with a marine facies1 though of fairly shallow water character1 whilst in ,yorkshire the two divisions are represented by a deeper water clay1 forming the ,upper portion of the ,speeton series4 ,there is a consensus of opinion in favour of the ,neocomian beds of southern ,britain having been laid down in an estuary of a river flowing from the west over a continent now destroyed4 ,to the north of this river stood the ,london ridge of the ,palozoic rocks1 the northern borders of which formed the coast line off which were deposited the sediments of ,neocomian and ,aptian ages which occur in northern ,england4 ,before the deposition of the ,albian beds a considerable upheaval of some parts of ,britain occurred1 and an unconformity separates the higher ,cretaceous beds from older strata of ,cretaceous and ,jurassic ages1 thus complicating the major phases by local changes in the characters of the strata4 7ii7 ,the ,albian and higher ,cretaceous ,beds4 ,the commencement of the deep-water phase of the third marine period may be said to occur in ,albian times in ,britain1 reaching its maximum during the deposition of the chalk4 ,the existence of a deeper sea towards the north of ,england is indicated by the characters of the ,albian and newer strata4 ,the ,albian beds of gault consist of a stiff clay in southern ,england1 replaced by coarser mechanical sediments towards the west4 ,as one passes north from the ,london ridge 7which exerted its influence in ,albian times1 after which it was finally buried in sediment7 the gault thins out1 and becomes gradually replaced by calcareous deposit when it is known as the red chalk which replaces the gault in northern ,norfolk1 ,lincolnshire and ,yorkshire4 ,a local unconformity separating the chalk and gault in parts of ,east ,anglia points to another local uplift with its accompanying complications in the characters of the strata4 ,after the uplift had ceased1 general depression must have occurred1 and the various divisions of the chalk were accumulated in a fairly open sea1 though1 for reasons to be given presently1 this was probably of no great lateral extent1 save when united with the open ocean1 probably in a manner similar to the connexion between the ,gulf of ,mexico and the ,atlantic4 ,the general variations in the lithological characters of the various members of the ,cretaceous system will probably be rendered clearer by reference to the accompanying diagram 7fig4 #bd7 representing the variations when traced across ,england from south to north#aja4 ,footnote #aja3 ,for information concerning the ,british ,cretaceous beds1 see ,topley and ,foster1 ,geology of the ,weald1 ,mem4 ,geol4 ,survey1 #ahge2 ,bristow and ,strahan1 ,geology of the ,isle of ,wight1 ,mem4 ,geol4 ,survey1 #ahhi2 ,lamplugh1 ,on the ,speeton ,clay1 ,q4 ,j4 ,g4 ,s41 vol4 ,,xlv4 p4 #ege1 and ,the ,speeton ,series in ,yorkshire and ,lincolnshire1 ibid41 vol4 ,,lii4 p4 #agi2 ,barrois ,recherches sur le ,terrain ,crtac suprieur de l',angleterre et d',irlande1 ,lille1 #ahgf2 and various papers by ,messrs ,hill and ,jukes-,browne1 in the ,quarterly ,journal of the ,geological ,society and ,geological ,magazine of recent years4 ,for the ,scotch deposits consult a paper by ,prof4 ,judd1 ,q4 ,j4 ,g4 ,s41 vol4 ,,xxxiv4 p4 #gcf1 and for those of ,ireland1 see ,hume1 ,q4 ,j4 ,g4 ,s41 vol4 ,,lii4 p4 #edj4 ,illustration3 ,fig4 #bd4 ,ch4 ,chalk4 ,al4 ,albian4 ,ap4 ,aptian4 ,n4 ,neocomian4 ,j4 ,jurassic4 ,the clue to the physical geography of ,britain during ,cretaceous times is furnished to a considerable extent by study of the foreign deposits4 ,in ,northern ,europe the ,cretaceous beds of ,england are met with in ,northern ,france1 and there the characters are generally speaking similar to those of our ,british deposits4 ,in ,germany shallower water conditions prevailed1 the lower beds gradually disappear1 and the upper beds are replaced by mechanical sediments of various degrees of coarseness1 becoming on the whole coarser1 as one travels eastward1 so that in ,saxony the chalk is partly replaced by arenaceous deposits 7the ',quader' sandstones7 which are responsible for the remarkable scenery of the ,elbe district above ,dresden4 ,in passing northwards1 indications of similar change are noted in the deposits of ,denmark and ,scania1 whilst to the south1 we get a complete change in the character of the rocks1 after crossing the ,loire in ,france1 and a similar change is observable in districts lying further east4 ,furthermore1 as will be noted more fully in a subsequent paragraph1 the character of the ,upper ,cretaceous flora indicates the existence of a large tract of land lying to the north and north-west of ,europe1 so that it would appear that the ,cretaceous rocks of ,northern ,europe were deposited in a gulf-like expansion of a western ocean1 bounded on the north by ,scandinavia1 on the west by eastern ,germany1 and on the south by a ridge running eastward from the mouth of the ,loire#ajb4 ,we may speak of this gulf as the ,chalk gulf4 ,to the south of the presumed ridge the character of the strata alters1 and also that of the included organisms4 ,this southern type of ,cretaceous rocks is one which is very widely spread1 being found in ,europe south of the ,loire1 and of the ,alps1 and in ,greece and ,turkey1 while it also occurs in the northern parts of ,africa4 ,the beds of this type are traceable through ,asia ,minor into ,india and to the shores of the ,indian ,ocean1 indicating the existence of a widespread ,cretaceous ocean1 which is sometimes spoken of as the ,hippurite-limestone sea1 for reasons which will eventually appear4 ,the deposits are largely formed of hard limestone which is very different in its character from the soft chalk of the northern gulf4 ,footnote #ajb3 ,the reader will find the existence of this gulf maintained and supported by a considerable mass of detail in ,mr ,a4 ,r4 ,wallace's ,island ,life4 ,the climatic conditions which prevailed during ,cretaceous times were apparently similar in most respects to those of the preceding ,jurassic period1 and as already stated the climatic zones which ,neumayr defined for ,jurassic times are also maintained by him to have existed during the ,cretaceous period4 ,the existence of cold has sometimes been inferred from the presence of large foreign blocks in the chalk1 especially at its base1 but if these are due to the transport1 they might well be caused by masses of floating ice1 which are often found at considerable distances from the coast in temperate regions after the break-up of the frost which succeeds an unusually hard winter4 ,the flora and fauna are not suggestive of severe conditions4 ,the ,cretaceous flora and fauna4 ,it has been noted in the last chapter that the gymnospermous flora of the ,jurassic period1 in which cycads form a considerable percentage of the whole flora1 was prevalent in ,lower ,cretaceous times4 ,in the ,upper ,cretaceous rocks this flora is replaced by one which consists to a large extent of dicotyledonous angiosperms4 ,these are found in the ,upper ,cretaceous rocks of ,europe and ,north ,america1 and as the researches of botanists indicate their origin in circumpolar regions1 their arrival in ,europe is an additional argument in favour of the existence of an extensive northern continent1 sending a prolongation to the southward in eastern ,europe4 ,the invertebrate fauna bears considerable resemblance to that of ,jurassic times1 and many of the dominant ,jurassic genera are also found in ,cretaceous rocks4 ,a most interesting feature is connected with the character and geographical distribution of the ,ammonites4 ,in ,europe they are almost exclusively confined to the deposits of the northern gulf1 and before their final disappearance they undergo many changes of form4 ,we find the discoid spiral shells of earlier times1 but these are accompanied by shells which are straight1 curved1 boat-shaped1 and coiled into various helicoid spirals1 sometimes having the whorls in contact1 while at other times they are separate4 ,in the chalk of ,britain gastropods are on the whole rare1 and this fact serves to emphasize the palontological break which occurs between the ,cretaceous and ,tertiary rocks2 but when conditions were favourable1 as during the deposition of some of the strata of the ,middle ,chalk1 gastropods are abundant1 and some are related to ,tertiary genera1 so that we may assume that the palontological break alluded to is exaggerated by the difference of conditions which prevailed during the deposition of the earliest ,tertiary and latest ,cretaceous sediments4 ,in the ,cretaceous deposits of the southern sea1 where the ,ammonite tribe is almost unknown1 the remarkable family of the lamellibranchs known as the ,hippuritid furnish the dominant invertebrates of the period1 and the representatives of this family are exceedingly scarce amongst the ,cretaceous strata of the northern gulf1 though they are found on two or three horizons4 ,of vertebrates1 the most interesting are the reptiles4 ,the families which predominate in ,jurassic times have many representatives amongst the ,cretaceous strata also1 but the order ,squamata is represented by the sub-order ,pythonomorpha1 which is characteristic of the ,cretaceous rocks4 ,the best known representative is the gigantic ,mosasaurus4 ,lastly1 we have the remarkable toothed birds or ,odontornithes1 now placed in different orders1 the genus ,hesperornis being the only representative of the sub-order ,odontolc of the ,ratit1 whilst ,ichthyornis and allied forms are placed in the sub-order ,odontorm of the ,carinat4 ,,chapter ,,xxiv4 ,,the ,,eocene ,,rocks4 ,classification4 ,the ,eocene ,beds of the south of ,england have been subdivided according to the variations in their lithological characters1 and the subdivisions have received local names4 ,the following classification is generally adopted1 though the different subdivisions are by no means of equal value3 ,upper ,eocene ,upper ,bagshot ,beds ,barton ,beds ,middle ,eocene ,bracklesham ,beds ,lower ,bagshot ,beds ,london ,clay#ajc ,lower ,eocene ,oldhaven ,beds ,lower ,london ,woolwich and ,reading ,beds ,tertiary ,strata ,thanet ,sands ,footnote #ajc3 ,some writers place the ,london ,clay in the ,middle ,eocene4 ,the deposits vary greatly when traced abroad1 and the exact equivalents of the minor subdivisions of the ,british rocks can seldom be ascertained at any distance from ,england1 though the division into ,upper1 ,middle1 and ,lower ,eocene can be made over wide areas4 ,description of the strata4 ,the character of the strata of ,europe and ,asia indicates the persistence of the northern gulf and southern ocean of ,cretaceous times in ,eocene times also1 though the area of each had shrunk in the meantime1 owing to the physiographical changes which occurred at the end of ,cretaceous times1 giving rise to more extended land areas1 and producing a shallow water phase over wide extents of ocean1--the final shallow water phase of the third and last great marine period of the ,british area4 ,it is difficult to ascertain the exact importance of the physical break between ,cretaceous and ,eocene rocks in the south-east of ,england1 owing to the subterranean solution of the upper part of the chalk1 subsequently to the deposition of the ,eocene strata1 but the contraction of the ,cretaceous gulf is shown in several ways1 one of the most significant being the distribution of ,cretaceous and ,eocene rocks in the south-west of ,england4 ,the existence of an outlier of ,cretaceous rock at ,buckland ,brewer in ,north ,devon1 only three miles from the ,atlantic ,ocean1 indicates the former extension westward of the ,upper ,cretaceous beds1 while the occurrence of an outlier of ,eocene rocks at ,bovey ,tracey in ,south ,devon1 resting not on ,cretaceous but on ,palozoic rocks1 shows that there was an uplift after the deposition of the ,cretaceous rocks and before the ,eocene rocks were deposited there1 and that during the period of uplift the ,cretaceous rocks were removed4 ,owing to these physical changes1 the ,eocene rocks of ,britain are mainly mechanical sediments1 some1 as the ,oldhaven beds1 being composed of coarse pebbles over a fairly wide district1 while some of the earlier ,eocene rocks are estuarine or fluvio-marine4 ,the ,eocene rocks of ,britain occur in four areas1 namely1 the ,london ,basin1 the ,hampshire ,basin1 the ,bovey ,tracey outlier1 and the north-east of ,ireland and western ,isles of ,scotland4 ,the deposits of the three southern areas may be considered together1 and give general indications of an approach to land when passing westward4 ,the ,lower ,london ,tertiary strata are fluvio-marine at the east end of the ,london ,basin2 they become shallower water deposits when traced westward1 and begin to disappear4 ,the ,london ,clay is an estuarine deposit1 which is generally supposed to have been laid down at the mouth of a large river flowing from the west4 ,it is absent in the ,bovey ,tracey outlier4 ,local disturbances caused the existence of a shallow water region in the east during the deposition of the ,middle and ,upper ,eocene deposits1 and accordingly the well-marked marine deposits which form the representatives of these divisions in ,hampshire are replaced by the ,bagshot beds of the ,london ,basin1 consisting chiefly of coarse mechanical sediments with a poor marine fauna1 but even in the west shallow water prevailed at times during the accumulation of various plant-bearing strata4 ,the ,middle ,eocene beds only are found in the ,bovey ,tracey outlier1 though the ,upper ,eocene beds may originally have been laid down in that area1 and subsequently denuded4 ,the fourth area displays a very different succession of ,eocene strata1 and one of extreme interest4 ,mechanical sediments and plant-bearing clays and lignites alternate with a vast accumulation of basaltic lavas1 indicating the outbreak of the volcanic forces in the ,british area1 after a period of quiescence which lasted through the greater part of ,mesozoic times4 ,the region in which these lavas were poured out was probably a land area during the greater part of the period of volcanic activity1 but the horizontal lie of the lava flows and their wide extent indicate the existence of a flat tract of country1 gradually raised into a plateau by the accumulation of sheet over sheet of basalt4 ,how far this plateau extended it is impossible to say4 ,the distribution of the lavas at the present day is somewhat limited in our isles1 but there is no sign of dying out at the present margins of the accumulations1 and they have probably escaped denudation in these regions1 as maintained by ,professor ,judd1 on account of the faults which have depressed them1 while the portions which were not depressed have been removed by denudation4 ,two views as to the origin of the lavas have been put forward3 according to ,prof4 ,judd1 they were poured forth from gigantic volcanoes1 while ,sir ,a4 ,geikie maintains that they represent portions of massive or fissure eruptions1 the molten rock having welled out from great cracks in the earth1 which are now filled by once molten rock in the form of dykes4 ,as these dykes extend far away from the present volcanic plateau1 one actually extending to the ,yorkshire coast1 we may well believe1 whatever was the origin of the sheets of lava1 that they were formerly spread far away from their present terminations#ajd4 ,without entering here into a discussion of the exact nature of extrusion of these igneous sheets1 it will suffice to say that all the evidence points to the formation of extensive plateaux1 which must have presented a fairly uniform surface1 similar to that which is still found characterising the volcanic districts of the western territories of ,north ,america4 ,footnote #ajd3 ,prof4 ,judd's views will be found in a series of papers by him on the ,secondary ,rocks of ,scotland1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxix4 p4 #ie1 ,,xxx4 p4 #bbj1 ,,xxxiv4 p4 #ffj1 while ,sir ,a4 ,geikie's explanation is advanced in a paper in the ,transactions of the ,royal ,society of ,edinburgh1 vol4 ,,xxxv42 see also the same author's ,ancient ,volcanoes of ,great ,britain4 ,the ,eocene rocks of the north-west of ,europe possess characters very similar to those of the south of ,england1 and there are indications that the northern gulf had diminished in extent towards the east as well as towards the west4 ,passing to southern ,europe1 ,central ,asia and northern ,africa1 we find the conditions of ,cretaceous times reproduced1 and an extensive series of marine deposits extends very widely over these regions1 the most persistent deposit being a mass of limestone of ,middle ,eocene age1 which is almost entirely composed of the tests of ,nummulites1 whence the development is known as the ,nummulitic ,limestone facies1 and we may speak of the ocean as the ,nummulitic ,limestone ,sea4 ,the incoming of shallow water conditions marked by accumulation of coarse mechanical sediments towards the end of the ,eocene period in some parts of the southern ,european area indicates the setting in1 even then1 of those continental conditions which culminated during the ,miocene period4 ,in ,north ,america we get similar evidence of the contractions of the oceans which in ,mesozoic times occupied large expanses of our present continents4 ,the climatic conditions of ,eocene times have been noticed in passing in chapter ,,ix41 and evidence was given to prove the prevalence of a warmer climate over the ,british area than that which now exists4 ,a study of the floras of various parts of the northern hemisphere suggests that climatic zones1 whose lines of demarcation ran practically parallel with the ,equator1 existed in ,eocene times also1 though further information upon this subject is desirable4 ,the ,eocene flora and fauna4 ,the flora of prevalent dicotyledonous angiosperms1 which appeared in ,upper ,cretaceous times1 also marks the ,eocene and later deposits1 but a study of the floras indicates that the differentiation which now marks off the floras of different areas from one another had not occurred to so great an extent as at the present time4 ,the existence of a rich flora in the ,eocene beds of circumpolar regions in the northern hemisphere should be noted1 though perhaps its importance has been somewhat exaggerated4 ,the invertebrate fauna shows an approximation to that of the present day4 ,the remarkable ammonite fauna of ,mesozoic times has disappeared1 and gastropods and lamellibranchs predominate1 many of the forms belonging to existing genera1 though very rarely to existing species4 ,the ,nummulites are the most characteristic ,eocene fossils1 and the period may be spoken of as the ,nummulitic ,period1 though it is now known that ,nummulites are not confined to the ,eocene strata4 ,the vertebrate fauna is very noteworthy4 ,the fishes and reptiles are closely related to existing forms1 and the orders of reptiles which predominated in ,mesozoic times have completely disappeared4 ,but the mammals are the most interesting vertebrates of the ,eocene period4 ,instead of the lowly organised forms of ,mesozoic times1 we find representatives of many orders1 including the highest1 the ,primates4 ,the generalised forms which serve as links between groups which are now separated to a considerable extent are of particular importance4 ,they have been detected in ,eocene rocks of various regions1 though the most complete series have been obtained from the ,eocene rocks of ,north ,america and made known to us through the numerous memoirs of ,professors ,cope and ,marsh#aje4 ,footnote #aje3 ,the ,eocene floras of ,britain are described by ,mr ,j4 ,starkie ,gardner and ,baron von ,ettingshausen in the ,monographs of the ,palontographical ,society2 other ,monographs of the same ,society contain an account of the ,eocene ,mollusca by ,mr ,f4 ,e4 ,edwards and ,mr ,s4 ,v4 ,wood4 ,an idea of the generalised forms of ,mammalia may be obtained by perusal of that portion of ,nicholson and ,lydekker's ,manual of ,palontology in which the latter author treats of the ,mammalia1 and in this connexion the reader will do well to read ,prof4 ,huxley's ,lecture on ,fossil ,horses1 reprinted in his ,american ,addresses4 ,,chapter ,,xxv4 ,,the ,,oligocene ,,and ,,miocene ,,periods4 7i7 ,the ,oligocene ,beds4 ,classification4 ,the ,oligocene ,beds of ,britain are classified as follows3-- ,upper ,wanting ,middle ,hempstead ,beds ,bembridge ,beds ,lower ,osborne ,beds ,headon ,beds ,description of the strata4 ,little need be said of the deposits of this period1 either in ,britain or abroad1 except to remark that they show the further spread of continental conditions over the regions now occupied by land4 ,the ,british deposits are now seen in the ,hampshire ,basin only1 and have been spoken of as the fluvio-marine series1 as many of the strata were laid down in continental sheets of water1 while the true marine sediments are thin and infrequent4 ,the lithological characters of deposits formed under these conditions naturally vary greatly1 consisting of different kinds of mechanical sediments occasionally mixed with thin freshwater marls and limestones4 ,on the ,continent similar conditions prevailed1 though the occurrence of fairly wide tracts of level surface is indicated by the widespread distribution of beds of brown coal or lignite1 and the coarse and thick ,oligocene 'nagelfluh' of ,switzerland points to the elevation of mountain ranges in the neighbourhood4 ,the flora and fauna4 ,the remarks made concerning the ,eocene flora and fauna are generally applicable to those of ,oligocene times1 except that the ,oligocene fossils bear a still closer resemblance to living forms1 and the ,nummulites are no longer dominant4 7ii7 ,the ,miocene ,period4 ,beds of ,miocene age are wanting in ,britain1 and on the ,continent they occur in isolated basins deposited in gulf-like prolongations of the ocean1 never very far from land4 ,a description of the strata and their fossil contents would be of little use for our present purposes1 and the remarks made concerning the ,oligocene beds will apply to the ,miocene strata also4 ,the period was mainly remarkable on account of the important physical changes which occurred1 to which we must devote some consideration4 ,commencing with the ,british area1 we find in the south evidence of the separation of the ,london and ,hampshire ,basins at this time1 for the ,oligocene beds of ,hampshire are tilted up on the south side of an anticline1 which separates the ,hampshire ,basin from that of ,london1 indicating that the movement was post-,miocene1 while in ,kent1 beds of ,pliocene age rest on the denuded top of the chalk1 showing that the elevation and denudation which accompanied it were pre-,pliocene2 the great ,wealden anticline is thus seen to be of ,miocene age4 ,on the north side of the ,london ,basin the line of demarcation between ,eocene and ,mesozoic beds runs approximately parallel to the strike of the latter in that part of ,britain1 and this points to the elevation of the ,mesozoic strata which gave them their present south-easterly dip about the same period1 though in the absence of ,oligocene rocks it cannot be definitely stated that the movement was altogether post-,oligocene4 ,the present physical geography of considerable parts of ,britain must date from ,miocene times4 ,important as the changes were in ,britain1 they were slight as compared with those which affected ,europe and many parts of ,asia4 ,the great mountain chains of the ,old ,world received their maximum uplift during this great period of earth-movement1 and orogenic structures were impressed upon the rocks of many regions1 for the ,tertiary ,mountain ,chains of the ,old ,world have an ,alpine structure impressed upon them as the result of intense lateral pressure1 accordingly we find the ,eocene strata lifted far above their original level to heights of #h1jjj feet in the ,alps and over #ab1jjj feet in the ,himalayas4 ,away from these marked uplifts epeirogenic movements caused the disappearance of the seas of earlier ,eocene times1 so that towards the close of the ,miocene ,period1 the main features of the ,eurasian continent were much as they are now4 ,the present drainage-systems must have originated at the same time1 and the sculpture of our continent has been carried on more or less continuously by subaerial agents from ,miocene times to the present day4 ,that any addition to the total area of land was made is doubtful4 ,the land which appears to have existed to the west of ,britain during ,cretaceous and ,eocene times finally disappeared beneath the waters of the ,atlantic ,ocean1 and the movement probably gave rise to the prominent submarine feature which now exists at some distance from the coast of ,ireland4 ,a great marine period is now existent in our ocean areas1 but so far as the existing continents are concerned1 we are living on the fourth continental period which practically came into existence in ,miocene times4 ,the strike of the uplifted strata naturally coincides on the whole with the axes of the major uplifts1 and accordingly we find the ,mesozoic and early ,tertiary strata folded around axes which have a prevalent east and west direction1 with others which have a trend at right angles to this4 ,the strike of the ,british ,mesozoic rocks seems to have been determined by each of these sets of movements1 so that although it is east and west in the south of ,england1 it runs north and south in the eastern counties north of the ,thames4 ,in ,america1 although epeirogenic movements had occurred before ,miocene times1 with the formation of wide continental tracts1 these appear to have been of the nature of plains1 diversified by extensive inland sheets of water1 and uplift of orogenic character converted these plains into uneven tracts in ,miocene times4 ,many of the movements in ,america1 which like those of ,europe are still progressing with enfeebled power1 differ from those of ,eurasia1 giving rise to raised monoclinal blocks rather than to violent folds of ,alpine character1 as seen in the western territories of ,north ,america1 and as proved also by the differential movements which are now known to affect the ,atlantic coast of that continent4 ,accompanying these changes in the earth's crust were others which affected the climate1 at any rate locally4 ,the warm climate of ,eocene times gradually gave way to a cooler climate in ,oligocene times1 and this lowering of temperature was still further advanced in ,miocene times1 though there is evidence that the temperature of those parts of ,europe which have strata representative of the ,miocene period was higher than it is at the present day4 ,owing to the changes which occurred in ,miocene times1 the area of sedimentation was extensively shifted to our present oceans1 and accordingly we find that the times subsequent to those of the ,miocene uplifts are marked by scattered accumulations of continental character1 with a few insignificant marine strata seldom found far inland from the present coast-lines4 ,,chapter ,,xxvi4 ,,the ,,pliocene ,,beds4 ,classification4 ,the ,italian ,pliocene ,beds which have long been known have been divided into three stages1 to which names have been applied which are somewhat widely used1 though the division of the ,british deposits into the same three stages has not been made4 ,the stages are3-- ,astian4 ,plaisancean4 ,zanclean4 ,the classification of the ,british deposits may be made as follows3-- ,cromer ,forest ,series4 ,weybourne ,crag and ,bure ,valley ,beds4 ,chillesford ,crag4 ,norwich ,crag and ,red ,crag4 ,upper ,coralline ,crag4 ,lower ,coralline ,crag4 ,as the ,english deposits are somewhat scattered it is difficult to make out the exact order of succession1 but the above shows the classification which is adopted by the best authorities1 the ,norwich ,crag 7or ,fluvio-marine ,crag as it is sometimes termed7 being now supposed to represent the upper portion of the ,red ,crag4 ,description of the strata4 ,the ,british deposits are chiefly found in the counties of ,norfolk and ,suffolk1 but isolated patches have been detected in ,kent and at ,st ,erth in ,cornwall2 while the inclusion of ,pliocene fossils in the glacial deposits of ,aberdeenshire and on the west coasts and islands of ,great ,britain suggests the occurrence of ,pliocene beds beneath sea-level1 around the ,british coasts1 at no great distance from the land4 ,the term ',crag' has been applied to shelly sands of which the ,british ,pliocene beds are largely composed4 ,the oldest ,british ,pliocene strata are supposed to be the ,lenham ,beds1 occurring in 'pipes' on the ,chalk of the ,north ,downs1 which are referred to the ,lower ,coralline ,crag1 and some writers believe that the ,st ,erth beds of ,cornwall are of similar age#ajf4 ,the former are ferruginous sands1 and the latter shelly sands and clays4 ,the higher beds of the ,coralline ,crag are found in ,suffolk1 and are largely calcareous1 being made of remains of polyzoa1 molluscs1 and other invertebrates4 ,they were probably deposited in deeper water than the rest of the ,british ,pliocene strata1 and contain a far larger percentage of carbonate of lime4 ,the ,red ,crag consists of ferruginous shelly sands1 of the nature of sand-banks1 formed near land2 while the ,norwich ,crag is of a still more littoral character1 and contains remains of land shells and the bones of mammalia mingled with the marine shells of the coast4 ,the higher ,pliocene deposits are also coastal accumulations1 even the so-called ,forest bed being a deposit and not a true surface soil1 as proved by the observations of ,mr ,clement ,reid4 ,at the summit of the ,cromer ',forest' ,series1 however1 is a true freshwater bed4 ,these ,british deposits appear to have been laid down on a coast line which formed one side of the estuary of a large river1 of which the present ,rhine is the 'betrunked' portion 7to use a term introduced by ,prof4 ,w4 ,m4 ,davis7#ajg4 ,footnote #ajf3 ,see ,clement ,reid1 ,nature1 #ahhf1 p4 #cdb2 and ,kendall and ,bell1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlii4 p4 #bja4 ,footnote #ajg3 ,see a paper by ,mr ,f4 ,w4 ,harmer1 ,on the ,pliocene ,deposits of ,holland1 and their relationship to the ,english and ,belgian ,crags1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,lii4 p4 #gdh4 ,on the ,european continent1 marine ,pliocene beds are found in ,belgium and ,italy4 ,the former deposits greatly resemble our ,crags1 whilst the latter are of interest on account of the mixture of volcanic beds with marine sediments in ,sicily1 showing that the formation of ,etna commenced in ,pliocene times4 ,various deposits formed in inland basins are found in ,france and ,germany1 but the most remarkable occur in the ,vienna basin1 where ,caspian conditions prevailed over large areas1 and the ordinary strata alternate with chemical deposits of which the best-known are the celebrated rock salt masses of ,wieliczka1 near ,cracow4 ,at the same time volcanic activity was rife to the south of the ,carpathian mountains4 ,other deposits1 which are partly referable to the ,pliocene period1 occur in ,greece at ,pikermi1 and in ,india in the ,siwalik hills2 these are celebrated for their remarkable mammals1 as are the ,pliocene strata of the ,western territories of ,north ,america4 ,the occurrence of marked earth-movements since ,pliocene times is indicated by the nature of the deposits of ,barbadoes1 where radiolarian cherts have furnished two echinids which are described by ,dr ,gregory as deep-sea forms4 ,these beds were once referred to the ,miocene period1 but there is good reason for assigning them to a later date1 and correlating them with the ,pliocene beds of other areas1 in which case there must have been a considerable uplift in this region since ,pliocene times1 a fact of great theoretical importance4 ,the climatic conditions of ,pliocene times show steady fall of temperature4 ,the early ,pliocene beds of ,britain were deposited during the prevalence of warmer temperatures than those which now exist in the same area1 but during later ,pliocene times1 the temperature was at first similar to that now prevailing1 and afterwards distinctly colder1 and we find in the upper ,pliocene beds the remains of organisms of a northern type4 ,in the uppermost deposit of the ,cromer ',forest' ,series1 the arctic birch and arctic willow indicate the commencement of the cold which culminated in the succeeding ',great ,ice ,age4' ,the flora and fauna4 ,little need be said of the ,pliocene fossils3 the flora approaches that of present times1 and the invertebrates are in most cases specifically identical with those now living4 ,the vertebrates alone differ markedly from living forms1 being chiefly of extinct species1 and in many cases belonging to extinct genera4 ,it is interesting to find that the mammalian fauna of ,pliocene times resembles the existing fauna of the area in which the beds are found1 a fact long ago observed by ,darwin4 ,thus the ,european ,pliocene mammals are like existing ,european forms1 whilst in ,australia the mammalian terrestrial fauna consists of ,marsupials1 and in ,south ,america there are ,edentata of ,pliocene age#ajh4 ,footnote #ajh3 ,the ,pliocene fauna of ,britain is described by ,mr ,searles ,v4 ,wood in the ,monographs of the ,palontographical ,society4 ,,chapter ,,xxvii4 ,,the ,,pleistocene ,,accumulations4 ,classification4 ,the term ,pleistocene1 as used here1 is approximately equivalent to the expressions ',glacial ,period' and ',great ,ice ,age' of some writers2 but ,i have adopted it in preference to these expressions1 because it may eventually be possible to define the ,pleistocene period in such a manner as to give the term a strictly chronological meaning1 whereas the other terms indicate the existence of climatic conditions which must have ceased in some areas sooner than in others4 ,at present1 climatic change gives us the best means for separating the accumulations formed subsequently to the ,pliocene period over large parts of the ,eurasian land-tract1 and the most convenient division of these continental accumulations is to refer them to three periods1 viz43-- ,the ,forest ,period 7in which we are now living74 ,the ,steppe ,period4 ,the ,glacial ,period4 ,some of the accumulations which were formed during the ,steppe period are included in the ,pleistocene period by many writers1 but ,i prefer to treat of them as post-,pleistocene4 ,in the present state of our knowledge of the glacial deposits any attempt to make a classification applicable over very wide areas is doomed to failure1 and the very principles upon which the classification should be based are a subject of disagreement4 ,the most promising basis for classification is founded on alternate recession and advance of land-ice1 though the proofs that advance takes place simultaneously over very wide areas are not yet forthcoming4 ,dr ,j4 ,geikie in the last edition of his work ,the ,great ,ice ,age adopts four periods of glaciation1 with intervening periods of recession1 and this division accords with the observations of many foreign geologists4 ,in order to understand the method of classification upon this basis1 a few words concerning glacial deposits in general will not be out of place4 ,glacial accumulations may be divided into three classes3--7i7 true glacial accumulations1 formed on1 in1 and under the ice1 and left behind upon its recession1 7ii7 marine glacial deposits1 laid down in the sea1 when floating ice is extensively found on its surface1 and 7iii7 fluvio-glacial deposits1 laid down by streams which come from the ice4 ,the two former indicate glacial conditions1 while the occurrence of fluvio-glacial deposits overlain by true glacial deposits indicates an advance of land-ice1 for the fluvio-glacial deposits are accumulated in front of those which are truly glacial4 ,accordingly if we find alternations of glacial and fluvio-glacial deposits on a large scale1 we may fairly infer the alternation of periods of great glaciation with others when the ice diminished1 or in other words of glacial and interglacial periods4 ,there is1 however1 in many cases great difficulty in distinguishing glacial deposits from marine glacial ones1 while some of the true glacial deposits formed in the ice 7englacial deposits7 cannot readily be distinguished from those of fluvio-glacial origin4 ,furthermore1 as the terminal moraines of land-ice often rest upon other true glacial deposits1 it is often difficult to know whether we are dealing with the products of one or two glaciations over limited areas4 ,the test of superposition is often applicable1 and one is enabled to obtain some clue as to the relative order of events4 ,in ,england at least three periods of glaciation seem to be indicated by the glacial deposits4 ,on the east coast the ,cromer ,forest ,series is succeeded by the ,cromer ,till1 and in ,yorkshire the ,basement ,clay occupies a similar position with regard to the overlying glacial accumulations to that of the ,cromer ,till4 ,whether these deposits be marine or terrestrial1 and the evidence is not yet sufficient to settle this question to the satisfaction of all geologists1 there is no doubt that they are glacial4 ,above them1 in ,east ,anglia1 lies the ,contorted ,drift1 the origin of which is still a moot point1 and it is overlain by the great ,chalky ,boulder ,clay1 which extends far and wide over ,east ,anglia1 the ,midland ,counties and into ,yorkshire4 ,evidence has been adduced to connect this with the till or boulder clay which spreads over the upland districts of the north of ,england at the foot of the main hill-systems4 ,this set of deposits indicates a second glaciation4 ,as the upland till is often ploughed out by glaciers which have left their traces in the form of moraines in our upland regions1 we seem here to have evidence of a third glaciation1 which naturally leaves no traces in the southern districts1 and the exact age of this cannot be ascertained in the absence of fossil evidence1 though we may provisionally refer it to the ,pleistocene period4 ,another attempt has been made to classify the glacial deposits1 on the supposition that there have been periods of elevation and depression of the land during ,pleistocene times4 ,some writers advocate one interglacial period when the land was depressed to an extent of #adjj and perhaps #bjjj feet1 while others have advocated the occurrence of a number of such interglacial marine periods4 ,the evidence for the supposed oscillations is furnished by the existence of shell-bearing sands associated with boulder clays at high levels1 the best known being on ,moel ,tryfan in ,caernarvonshire1 near ,macclesfield in ,cheshire1 and near ,oswestry in ,shropshire4 ,as many geologists believe that these shells have been carried to their present position by ice in a way which it is not our province to discuss here1 we may dismiss this method of classification as based upon events which cannot be proved to have occurred4 ,in the present state of our knowledge1 it is indeed best to avoid1 as far as possible1 classifications which are intended to be applicable over wide regions1 and to devote our attention to local details1 gradually piecing together the evidence which is obtained as the result of exhaustive examination of each separate area#aji4 ,footnote #aji3 ,the glacial literature of our own island only1 is so extensive that the student may well be bewildered when he attempts to grapple with it4 ,he is recommended to read the following general works3 ,j4 ,geikie1 ,the ,great ,ice ,age4 #crd ,edition1 #ahid4 ,h4 ,carvill ,lewis1 ,the ,glacial ,geology of ,great ,britain and ,ireland4 #ahid4 ,g4 ,f4 ,wright1 ,man and the ,glacial ,period1 #ahib1 and ,the ,ice ,age in ,north ,america1 #ahij4 ,sir ,c4 ,lyell1 ,antiquity of ,man4 #dth ,edition1 #ahgc4 ,for the glacial geology of special regions the following papers may be consulted3 ,the ,lake ,district and adjoining neighbourhood4 ,e4 ,h4 ,tiddeman1 ,evidence for the ,ice ,sheet in ,north ,lancashire c4 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxviii4 p4 #dga4 ,j4 ,g4 ,goodchild1 ,glacial ,phenomena of the ,eden ,valley c4 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxi4 p4 #ee1 and ,j4 ,c4 ,ward1 ,mem4 ,geol4 ,survey1 ,the ,geology of the ,northern half of the ,lake ,district4 ,yorkshire4 ,g4 ,w4 ,lamplugh1 ,drift of ,flamborough ,head1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlvii4 p4 #chd4 ,lincolnshire4 ,a4 ,j4 ,jukes-,browne1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xxxv4 p4 #cig and ,,xli4 p4 #aad4 ,east ,anglia4 ,clement ,reid1 ,mem4 ,geol4 ,survey1 ,the ,geology of the district around ,cromer4 ,north ,wales4 ,t4 ,mc,k4 ,hughes1 ,drifts of the ,yale of ,clwyd c4 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xliii4 p4 #gc1 and ,a4 ,strahan1 ,glaciation of ,south ,lancashire1 ,cheshire1 and the ,welsh ,border1 ibid41 vol4 ,,xlii4 p4 #dhf4 ,switzerland4 ,c4 ,s4 du ,riche ,preller1 ,on ,fluvio-glacial and ,interglacial ,deposits in ,switzerland1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,li4 p4 #cfi and ,on ,glacial ,deposits1 ,preglacial ,valleys and ,interglacial ,lake formations in ,sub-,alpine ,switzerland1 ibid41 vol4 ,,lii4 p4 #eef4 ,the reader will find references to other works on the ,glacial ,geology of other districts by consulting the general works referred to on the preceding page4 ,the foregoing remarks will convince the student that any attempt to show the distribution of land and sea during any part of the glacial period is not likely to meet with general acceptance1 as so much depends upon the terrestrial or marine origin of the deposits of the lowlands1 and the mode of formation of the shell-bearing drifts of high levels4 ,the occurrence of elevation to a greater height than that which our country at present possesses during portions at any rate of the glacial period has been inferred on general grounds1 but direct evidence in favour of it is furnished by the existence of a number of ancient valleys on the land around our coasts1 whose floors are often considerably below sea-level1 while the valleys are now completely filled up with glacial accumulations1 except where they have been partially re-excavated by streams which for some distance run above the courses of the ancient streams4 ,the climatic conditions of glacial times can only be briefly touched upon in this place4 ,if the periods of advance can be proved to be contemporaneous over wide areas1 this points to alternations of colder and warmer periods1 or at any rate of drier and wetter periods1 though local advance may be due to a number of causes4 ,it must be borne in mind that with the temperature remaining the same1 advance of ice can be brought about by increased precipitation of aqueous vapour in the form of snow4 ,the question of the cause of the glacial period is one that only indirectly affects the stratigraphical geologist until he has accumulated sufficient evidence to indicate the cause4 ,it must suffice to observe that the extremely plausible hypothesis of ,croll 7for which the student should consult ,dr ,croll's ,climate and ,time7 does not explain the apparent gradual lowering of climate throughout ,tertiary times till the cold culminated in the ,pleistocene period1 and the student will do well to remain in suspense concerning the cause of the ,ice ,age until further evidence has been brought to bear upon it4 ,the glacial flora and fauna4 ,the glacial deposits naturally yield few traces of life1 except those which have been derived from other deposits1 and we are dependent for our information concerning the fauna and flora of the glacial period upon the remains furnished by the interglacial deposits4 ,unfortunately it is very hard to ascertain which deposits are interglacial1 and many which have been claimed as such are either preglacial or postglacial4 ,the meagre evidence which we possess points to the existence of an arctic fauna or flora in ,britain during the prevalence of this glacial period4 ,a question which has received much attention of recent years is that of the existence of preglacial or interglacial man1 on which much has been written4 ,the existence of man in glacial times is probable1 but it is the opinion of many of those who are most competent to form a judgment1 that it has not been proved in the only conclusive way1 namely1 by the discovery of relics of man in deposits which are directly overlain by glacial deposits1 or which at any rate are demonstrably older than glacial deposits#aaj4 ,footnote #aaj3 ,on the question of preglacial and interglacial man1 see ,w4 ,boyd ,dawkins1 ,early ,man in ,britain2 ,h4 ,hicks1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlii4 p4 #c1 ,,xliv4 p4 #efa1 and ,,xlviii4 p4 #dec2 ,t4 ,mc,k4 ,hughes1 ibid41 vol4 ,,xliii4 p4 #gc2 ,sir ,j4 ,evans1 ,presidential ,address to ,british ,assoc4 #ahig4 ,,chapter ,,xxviii4 ,,the ,,steppe ,,period4 ,the occurrence of a period marked by dry climate over wide areas of the ,eurasian continent1 and possibly also in ,north ,america1 is evidenced by the widespread distribution of an accumulation known as loess1 concerning the origin of which there has been much difference of opinion1 though that it was formed subsequently to the glacial period seems to be generally admitted1 inasmuch as it is largely composed of rearranged glacial mud4 ,the formation of the loess as a steppe-deposit was first advocated by ,baron von ,richthofen1 and his views were supported by ,nehring after study of the loess-fauna4 ,richthofen's explanation of the loess as due to the spread of dust by wind in a dry region is becoming widely accepted1 and it necessitates the widespread occurrence of steppe conditions1 as the loess has a very extensive geographical range1 and may be truly regarded as the normal continental deposit of ,eurasia during the period immediately succeeding the glacial period4 ,in our own country1 as the sea cannot have been far distant during these times the normal loess is not found1 but several accumulations occur1 which on stratigraphical and palontological grounds must be regarded as synchronous with the formation of the loess4 ,these are certain rubble-drifts of the southern counties1 the older river-gravels of southern ,england1 and some of the older cave deposits of various parts of ,england4 ,it is doubtful whether any classification into minute subdivisions can be adopted for them1 though ,prof4 ,boyd ,dawkins has advocated their separation into an older age of ,river ,drift ,man1 and a newer period of ,cave ,man1 on account of the evidences of a lower state of civilisation afforded by examination of the ,river ,drift implements when compared with those fashioned by ,cave ,man4 ,roughly speaking1 the ,steppe period corresponds with the period during which ,palolithic man existed1 at any rate in north-west ,europe1 and we may speak of the ,steppe period as the ,palolithic period1 without asserting that ,palolithic man necessarily disappeared at the time when the climate changed and caused the replacement of ,steppe conditions by others favourable to forest-growth4 ,description of the accumulations4 ,the loess consists of unstratified calcareous mud or dust1 with a peculiar vertical fracture1 and is interesting rather on account of the nature of its fossils and of its distribution than for its lithological characters4 ,as it is not found in ,britain it is not necessary to say much about it1 but merely to refer to the published descriptions#aaa4 ,footnote #aaa3 ,an account of ,richthofen's views by that author will be found in the ,geological ,magazine1 ,dec4 #b1 vol4 ,,ix4 7#ahhb71 p4 #bic1 and the fauna of the loess is described by ,nehring 7,ibid41 p4 #egj74 ,the ,british deposits require some notice1 as their characters and mode of occurrence are of some significance4 ,along the south coast are deposits of coarse rubble which have yielded some organic remains1 which have been described by ,mr ,clement ,reid#aab1 who also discusses their origin4 ,the rock1 also known as the ,elephant ,bed1 consists of angular fragments of flint and chalk1 and seems to have been produced by streams which were able to flow over the surface of the chalk when it was frozen4 ,many other similar deposits in the south of ,england1 which are found on the open surface1 may have had a similar origin4 ,footnote #aab3 ,c4 ,reid1 ,origin of ,dry ,chalk ,valleys and of ,coombe ,rock1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xliii4 p4 #cfd4 ,the ,palolithic river-gravels are found at various distances above present river-levels1 and are the surviving relics of alluvial deposits which were laid down when the rivers ran at a higher level than they now do4 ,that they are newer than the main glacial drifts of the region in which they occur is indicated by the frequent presence in them of boulders derived from the drift4 ,their antiquity is shown by the physical changes which have occurred since their deposition 7there having been sufficient time since then to allow of the excavation of some river-valleys to a depth of over one hundred feet beneath their former level71 and also by the character of the included mammals which will presently be referred to4 ,the deposits vary in coarseness1 like those of modern alluvial flats1 from the coarse gravels of the river-beds to the fine loams and marls of the flood-plains4 ,they are found1 in ,britain1 with their typical mammalian remains1 south-east of a line drawn from the mouth of the ,tees to the ,bristol ,channel4 ,the cave-deposits have a wider distribution than those which have just been noticed1 being also found to the north-west of the above-mentioned line in ,yorkshire1 and in ,north and ,south ,wales4 ,in the south of ,england they are found as far east as ,ightham in ,kent1 and in a westerly direction to ,torquay and ,tenby4 ,the ,ightham deposits occur in fissures and consist of materials which were apparently introduced from above by river action#aac4 ,the cave-deposits of limestone areas are sometimes found in fissures1 but at other times in caverns with a fairly horizontal floor1 on which the various accumulations lie in order of formation4 ,the deposits vary in character and may be divided into three groups1 though accumulations of intermediate character are found2 the first group consists of cave-earths and cave-breccias--formed by weathering of the limestone1 and the retention of the insoluble residue1 as a more or less ferruginous mud1 mixed with angular fragments of limestone1 and with the remains of creatures which inhabited the caves2 the second group consists of true deposits laid down under water1 as gravels1 sands1 and laminated clays2 while the third is composed of limestone deposited from solution in water1 in the form of stalagmite#aad4 ,footnote #aac3 ,the ,ightham fissures and their contents are described by ,messrs ,abbot and ,newton1 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,l4 pp4 #aga and #ahh4 ,footnote #aad3 ,the reader should consult ,prof4 ,w4 ,boyd ,dawkins' works on ,cave ,hunting and ,early ,man in ,britain1 for information concerning the ,cave ,deposits4 ,see also ,sir ,c4 ,lyell1 ,antiquity of ,man2 ,sir ,j4 ,evans1 ,ancient ,stone ,implements of ,great ,britain1 and ,sir ,j4 ,lubbock1 ,prehistoric ,times4 ,in these works references will be found to papers by ,messrs ,pengelly1 ,magens ,mello1 ,tiddeman and others on the ,caves of ,devon1 ,derbyshire and ,yorkshire4 ,references have already been made to papers upon the ,caverns of ,north ,wales4 ,the organic contents of the ,palolithic period are of much interest1 and it is desirable to discuss their character before making further observations upon the physical conditions of the period4 ,the ,palolithic flora and fauna4 ,the plants of some of the earlier deposits of the age we are considering show the prevalence of cold conditions during their accumulation1 for instance the ,arctic birch and ,arctic willow are found in the accumulations beneath the implement-bearing ,palolithic deposits of ,hoxne in ,suffolk#aae4 ,the invertebrate fauna consists essentially of the remains of molluscs4 ,the loess molluscs are chiefly pulmoniferous gastropods which lived upon the land1 though swamp forms are occasionally associated with them4 ,the palolithic river-gravels have yielded numerous land- and freshwater-molluscs of living species1 though some which are abundant in the ,british gravels are now extinct in ,britain1 e4g4 ,cyrena 7,cobicula7 fluminalis and ,unio littoralis4 ,marine deposits of this age are occasionally found1 as at ,march1 in ,cambridgeshire1 where the fauna closely resembles that of our present sea-shores4 ,footnote #aae3 ,these beds are described by ,messrs ,reid and ,ridley1 ,geol4 ,mag4 ,dec4 ,,iii4 vol4 ,v4 p4 #dda4 ,see also ,c4 ,reid on the ,history of the ,recent ,flora of ,britain1 ,annals of ,botany1 vol4 ,,ii4 ,no4 #h1 ,aug4 #ahhh4 ,the vertebrate remains are much more remarkable1 and it is not quite clear that the association of forms whose living allies now live under widely different conditions has been satisfactorily explained4 ,the river-gravels and cave-deposits contain remains of temperate forms1 as the bison1 and brown bear1 associated with those of northern forms1 as the mammoth1 woolly rhinoceros1 glutton1 reindeer1 and musk ox1 and also with those whose living allies are inhabitants of warmer regions1 like the lion1 hyna1 and hippopotamus4 ,one of the most remarkable creatures is the sabre-toothed lion or ,machairodus1 remains of which have been discovered in ,kent's ,cavern1 ,torquay1 and in the caves of ,cresswell ,crags1 ,derbyshire4 ,the loess fauna consists of characteristic steppe animals1 such as the jerboa1 ,saiga antelope and steppe-porcupine1 and it is interesting to find an indication of this fauna in the ,ightham fissures4 ,the first undoubted relics of mankind are found in the ,palolithic deposits1 which are very widely spread over the ,eurasian continent4 ,they consist mainly of implements of bone and stone1 the latter being chipped1 but never ground or polished1 though both bone and stone implements are frequently ornamented with engraved figures4 ,the cave-deposits have furnished implements of a higher type than those usually found in the river-drifts1 but the latter are also found in caverns in deposits beneath those containing the higher type1 hence the division of the period into two minor periods1 that of river-drift man1 and that of cave-man#aaf4 ,footnote #aaf3 ,concerning this matter1 the reader should consult ,prof4 ,boyd ,dawkins' ,early ,man in ,britain4 ,sir ,j4 ,prestwich has argued in favour of the existence of a group of implements found on the plateau south of the ,thames of an age antecedent to that of the ordinary river-drift implements4 ,see ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlv4 p4 #bgj4 ,there are several questions of interest connected with the ,palolithic fauna1 three of which deserve some notice here4 ,the absence of the relics of the ,palolithic mammalia and of the human implements in the river-gravels north-west of the line drawn between the ,tees and ,bristol ,channel1 and the presence of the mammalian remains in the caverns of that area requires some explanation4 ,one such explanation assumes that the relics were destroyed in the open country to the north-west of that line1 owing to glaciation1 but it is not by any means universally accepted4 ,another difficulty which in the opinion of some writers has not been fully cleared up is the mixture of apparently southern forms like the ,hippopotamus1 with others of northern character like the ,musk ox1 under such conditions as to show that the creatures lived in the ,british area contemporaneously4 ,seasonal migration might account for it1 but the wide belt of overlap of apparent northern and southern forms requires something more1 though secular changes of climate might shift the belt of seasonal overlap from one place to another1 causing the entire belt of overlap to extend over a considerable distance4 ,the third1 and perhaps most important difficulty is the abrupt change from the ,palolithic type of implement to the ,neolithic type1 characteristic of the next period4 ,some implements1 as those of the kitchen-middens of ,denmark1 and those found at ,brandon and ,cissbury in this country1 have been appealed to as intermediate in character1 but evidence has been brought forward to show that each set is truly ,neolithic1 the one being the implements of the lowly fisher-folk who lived contemporaneously with the makers of the highly finished polished implements of ,denmark1 while the others are unfinished implements thrown away during the manufacture on account of flaws or accidental fractures4 ,the difficulty is increased when we take into account the great physical and faunistic changes which occurred between ,palolithic and ,neolithic times4 ,the country was undoubtedly more elevated than it is at present during portions if not during the whole of ,palolithic times1 as shown by the appearance of the great mammals in ,britain1 the discovery of their remains beneath sea-level1 and especially the occurrence of remains in the caverns of rocky islands such as those of the ,bristol ,channel1 where they could not possibly have existed unless the present islands were connected with the mainland4 ,the fossils of the times between the ,glacial period and the ,neolithic period indicate variations of climatic conditions4 ,upon this point ,i cannot do better than quote the words of ,sir ,john ,evans in his ,presidential ,address to the ,british ,association at ,toronto#aag4 ,at ,hoxne the interval between the deposit of the ,boulder clay and of the implement-bearing beds is distinctly proved to have witnessed at least two noteworthy changes in climate4 ,the beds immediately reposing on the clay are characterised by the presence of alder in abundance1 of hazel1 and yew1 as well as by that of numerous flowering plants indicative of a temperate climate very different from that under which the ,boulder clay itself was formed4 ,above these beds characterised by temperate plants1 comes a thick and more recent series of strata1 in which leaves of the dwarf ,arctic willow and birch abound1 and which were in all probability deposited under conditions like those of the cold regions of ,siberia and ,north ,america4 ,at a higher level1 and of more recent date than these--from which they are entirely distinct--are the beds containing the ,palolithic implements1 formed in all probability under conditions not essentially different from those of the present day4 ,footnote #aag3 ,report ,brit4 ,assoc4 for #ahig1 p4 #ac4 ,,chapter ,,xxix4 ,,the ,,forest ,,period4 ,subsequently to ,palolithic times1 the physical conditions over ,eurasia changed greatly1 and at the commencement of ,neolithic times the conditions were favourable for the growth of forests over wide regions of that continent4 ,at the commencement of the ,forest period the physical conditions were very much the same as they are at present1 though minor changes have of course taken place since then1 including probably a submergence of large parts of ,britain to a depth of about fifty feet beneath its former level1 as indicated by the existence of ,neolithic submerged forests round many parts of our coast-lines4 ,the ,forest period may be best subdivided for local purposes by reference to the civilisation of mankind at different times1 and in this way we obtain the following divisions3 ,historic ,iron age4 ,prehistoric ,iron age4 ,bronze age4 ,neolithic age4 ,a classification may also be based upon changes in the flora4 ,in ,denmark the peat deposits of this age are divisible into five layers1 characterised by different dominant forms of trees4 ,these are as follows in descending order3 ,fifth layer3 ,beech 444 ,iron age ,fourth layer3 ,alder ,third layer3 ,oak 444 ,bronze age ,second layer3 ,scotch ,firs 444 ,neolithic age ,lowest layer3 ,poplar4 ,in our own country the forest growth has been much interfered with by man1 but the lower fenland peat gives a good example of the material formed by forest growth4 ,it is not necessary to touch on the various accumulations which are now being formed in different parts of our island1 except to remark that the deposits of the ,forest period give indications of earth-movements on a small scale1 which is well seen in the fenland1 where the forest peat is covered in places by a buttery clay with ,scrobicularia piperata indicating submergence1 and above this is a marsh peat4 ,the flora and fauna of the ,forest period are practically those of the present day1 though the larger forms of mammalia have disappeared one by one4 ,the ,irish elk and ,bos primogenius probably became extinct early in the period1 while as far as ,britain is concerned the wolf1 bear1 and beaver have disappeared within historic times4 ,the relics of man deserve passing notice4 ,the ,neolithic period is characterised by the absence of metal instruments1 though those made of stone were much more highly finished than those of ,palolithic times1 and were often ground and polished4 ,the first metal which was largely worked was bronze1 which gradually replaced stone1 though stone was extensively used in the ,bronze age1 as indicated by the imitation of bronze implements in stone4 ,the ,bronze age in turn was replaced by the ,prehistoric iron age2 at first1 when iron was scarce1 bronze implements were merely tipped with iron1 but ultimately the one metal was practically replaced by the other4 ,the date of the ,palolithic period is unknown2 no approximate date can be satisfactorily assigned to it1 but various calculations1 founded on different data1 have been made as to the age of the ,neolithic period1 and several of them agree in placing it at about #gjjj years from the present time4 ,it will be seen that no sudden and violent change marks the incoming of the human race1 which to the geologist is but one of a large number of events which have followed each other in unbroken sequence1 and accordingly the thread of the story where abandoned by the geologist is taken up by the antiquary1 and passed on by him to the historian#aah4 ,footnote #aah3 ,the student may obtain information concerning the ,neolithic age in ,britain in ,boyd ,dawkins's ,early ,man in ,britain2 ,sir ,j4 ,evans' ,early ,stone ,implements of ,great ,britain1 and ,sir ,j4 ,lubbock's ,prehistoric ,times4 ,in the latter work he will find a good account of the ,neolithic remains of ,denmark and of the ,swiss ,lake dwellings4 ,for information concerning the ,bronze age he should consult ,evans' ,ancient ,bronze ,implements of ,great ,britain4 ,the varied ,danish antiquities of ,neolithic and ,bronze ages are figured in ,h4 ,p4 ,madsen's ,antiquits ,prhistoriques du ,danemark4 ,the ,prehistoric fauna of the fenlands is described in ,sir ,r4 ,owen's ,history of ,british ,fossil ,mammals and ,birds4 ,,chapter ,,xxx4 ,,remarks ,,on ,,various ,,questions4 ,there are many problems connected with geology which can only be solved by detailed study of the stratified rocks1 and when solved the principles of the science will be more fully elucidated4 ,in the present state of our knowledge some of these problems are ripe for discussion1 others can merely be indicated1 while others again have probably remained hidden1 though it will be the task of the geologist of the future to clear them up4 ,among the many questions which demand knowledge of stratigraphical geology for their right understanding are the following1 which will be briefly considered in this chapter3--the changes in the position of land and sea in past times1 and the growth of continents2 the replacement of a school of uniformitarianism by one of evolutionism2 and the duration of geological time4 ,changes in the position of land and sea4 ,certain physicists have arrived at the conclusion that the general position of our oceans and continents was determined at a very early period in the earth's history1 and that the changes which have occurred in their position since then have been comparatively insignificant4 ,the wide extent of land over which stratified rocks are distributed at once indicates that from the point of view of the geologist the changes have been very important1 and it is worth inquiring whether they are not sufficiently important to prove that the primitive oceans and continents have undergone so much alteration as to be unrecognisable4 ,some authorities1 while recognising the great changes which have occurred in the relative position of land and sea during those periods of which geologists have direct information1 suppose that the changes took place to a large degree in certain 'critical areas' bordering the more stable areas of permanent ocean on the one side and permanent land on the other4 ,in discussing the question of general permanence of land and ocean regions it will be convenient to commence with a study of the present land areas1 and at the outset we may take into consideration the present distribution of marine sediment over different parts of the land1 using the last edition of ,m4 ,jules ,marcou's geological map of the world for the purpose#aai4 ,a glimpse at this map indicates that more than half of the land areas are occupied by rocks which are as yet unknown 7many of which may be marine sediments71 or by crystalline schists of which the mode of origin has not yet been fully explained1 so that a large part of ,central ,asia1 the interior of ,africa1 and of ,south ,america may have existed as land from very early times1 and the same may be said of smaller portions of ,europe and ,north ,america4 ,actual observation of a geological map therefore indicates the possibility that about half of the land surfaces may have existed as such through very long periods1 but though there is a possibility of this1 the probability is not very great4 ,the unknown regions1 as remarked above1 may consist to a considerable extent of marine sediments1 and the existence of isolated patches of late ,palozoic and of ,mesozoic strata in the heart of ,central ,asia1 points to the submergence of much wider regions than those in which these isolated patches have been found4 ,again1 the character of the sediments when they abut against the crystalline schists frequently proves that these sediments once extended further over the crystalline schists1 and have since been removed by denudation1 so that even if we assume that the crystalline schists are all of very early date1 and not necessarily formed in any case from marine sediments1 we cannot suppose that all the area occupied by them has existed as land for long periods of time4 ,on the other hand1 the major part of ,europe and ,north ,africa1 extensive tracts in ,asia1 the greater part of ,australia1 a very large part of ,north ,america and considerable tracts of ,south ,america give proofs of having been occupied by the oceans in ,palozoic and later times4 ,footnote #aai3 ,a reduced copy of this map will be found opposite the title-page of the first volume of ,prof4 ,prestwich's ,geology4 ,it may be answered that most of these regions containing marine sediments occur in critical areas1 which have undergone a certain amount of oscillation owing to earth-movements1 and that the interior parts of the great continental masses have been practically stationary4 ,but if these lands had been land-areas through geological ages they must have been acted upon by the agents of subaerial denudation1 throughout these ages1 and long ago reduced to peneplains#abj unless the action of these subaerial agents was counteracted by that of elevating forces1 but if these forces were sufficient to counteract the action of subaerial denudation through countless ages1 they were also sufficient to raise extensive tracts of land above sea-level1 and materially to alter the distribution of land and sea1 and if elevation could go on to this extent1 why not also depression8 ,footnote #abj3 ,a term proposed by ,prof4 ,w4 ,m4 ,davis for a nearly level surface of subaerial denudation1 as opposed to a plain of marine denudation4 ,proceeding a step further1 and examining the character of the sediments as well as their geographical distribution1 we find further evidence of great crust-movements4 ,it has been urged that deep-water sediments do not occur amongst the strata found on the continents1--that there are no representatives of the abysmal deposits of recent ocean floors amongst the strata of the geological column#aba1 but the researches of the last two decades have brought to light foraminiferal and radiolarian deposits1 pteropodal deposits1 and possibly deep-sea clays1 which are comparable with those in process of formation at great depths in existing oceans1 and though the proofs of their deep-sea origin are not always as full as might be desired in the case of the older rocks#abb1 we can speak with greater certainty when we examine those of ,tertiary age1 and if the deep-sea accumulations of this late date can be uplifted above sea-level1 this is much more likely to have occurred with those of past times4 ,when a deposit like the radiolarian rock of ,barbadoes1 the deep-water character of which has been conclusively proved1 can be elevated into land since ,miocene or possibly ,pliocene times1 it is evident that the crust-movements have been sufficient to produce the most profound changes in the distribution of land and sea during the long ages which are known to us4 ,another argument against the occurrence of extensive changes has been derived from an examination of those islands which are spoken of as oceanic islands4 ,strictly speaking an oceanic island is one in which the present fauna and flora give indications of their introduction by transport across intervening sea1 and no indications of the existence of forms of life which inhabited it when it was once united to a continent2 it may be inferred with a considerable degree of certainty that these islands have been isolated for long periods of time4 ,it has been stated that these oceanic islands never contain marine sediments of any considerable degree of antiquity1 and that there are therefore no traces of former continents over those wide tracts of ocean which are occupied by oceanic islands4 ,the evidence is of a negative character4 ,the islands would be less likely to exhibit ancient sediments than continents1 for being near the ocean1 they would be readily submerged1 and the older deposits masked by newer ones1 though this need not necessarily account for the entire absence of ancient rocks amongst them4 ,the danger of the argument lies in the fact that we do not yet know how far these old rocks really are absent1 as the geology of the oceanic isles has not been fully explored from this point of view1 and already several cases of the asserted presence of ancient rocks on these islands have been recorded4 ,footnote #aba3 ,see ,mr ,a4 ,r4 ,wallace's ,island ,life4 ,footnote #abb3 ,see chapter ,,ix4 ,the argument derived from the present distribution of organisms is far too complex to be discussed here1 and the student is recommended to read a masterly review of the evidence in ,dr ,w4 ,t4 ,blanford's ,presidential ,address to the ,geological ,society in #ahij1 on the question of the ,permanence of ,ocean ,basins#abc4 ,after reviewing the evidence furnished by a study of modern distribution he concludes that it is far too contradictory to be received as proof of the permanence of oceans and continents4 ,footnote #abc3 ,quart4 ,journ4 ,geol4 ,soc41 vol4 ,,xlvi41 ,proc41 p4 #ei4 ,the existence of former extensive land tracts over regions now occupied by sea is naturally more difficult to prove than that of sea over land1 as we depend upon inference rather than actual observation to a much greater degree than when considering the permanence of continents1 nevertheless a considerable amount of indirect evidence in favour of the existence of widespread land tracts over our present ocean regions has been accumulated and will be briefly noticed4 ,we may take first the evidence derived from the nature of sediments1 and afterwards that which has been acquired by studying distribution of organisms in past times4 ,the indications of existence of an extensive tract of continent over the ,north ,atlantic ,ocean1 during ,palozoic times have already been considered1 and it was seen that the thinning out of the ,palozoic sediments when traced away from the present ,atlantic borders in an easterly direction over ,europe and in a westerly one over ,north ,america pointed to the existence of this ,palozoic ',atlantis1' as maintained by ,prof4 ,hull in his work1 ,contributions to the ,physical ,history of the ,british ,isles4 ,this writer gives some reasons for supposing that the continental mass began to break up towards the end of ,palozoic times1 though it is not clear that complete replacement of land by sea occurred1 and the nature of the ,wealden deposits has been pointed to as evidence of the existence of an extensive tract of land to the west of ,britain during the ,cretaceous period4 ,the ,palontological evidence in favour of destruction of ancient continental areas and their replacement by the sea is more satisfactory than that which is based on physical grounds4 ,the distribution of the ,glossopteris flora of the ,permo-,carboniferous period points to the former existence of a great southern continent1 including the sites of ,australia1 ,india1 ,south ,africa and ,south ,america1--the ,gondwanaland of ,prof4 ,e4 ,suess#abd4 ,footnote #abd3 ,on this question and that of the other destroyed continental areas noted here1 see ,w4 ,t4 ,blanford's ,presidential ,address1 loc4 cit4 ,again1 a study of ,jurassic and ,cretaceous faunas has led palontologists to conclude that there was a connexion betwixt ,s4 ,africa and ,india in ,mesozoic times across a portion of the area now occupied by the ,indian ,ocean1 and also between ,s4 ,africa and ,s4 ,america1 and these inferences are supported by study of the distribution of existing forms4 ,the sudden appearance of the ,dicotyledonous ,angiosperms in ,upper ,cretaceous rocks has also been used as evidence of destruction of considerable tracts of land subsequently to ,upper ,cretaceous times1 and there is a certain amount of evidence in favour of the existence of this land in the north polar region1 in an area now largely occupied by water1 though relics of it are left1 as the ,faroe ,isles1 ,spitsbergen1 ,novaya ,zembla and ,franz ,josef ,land4 ,i cannot conclude the consideration of the question of permanence of oceans and continents more fitly than by quoting from ,dr ,blanford's address4 ,he says1 ,there is no evidence whatever in favour of the extreme view accepted by some physicists and geologists that every ocean-bed now more than #ajjj fathoms deep has always been ocean1 and that no part of the continental area has ever been beneath the deep sea4 ,not only is there clear proof that some land-areas lying within continental limits have at a comparatively recent date been submerged over #ajjj fathoms1 whilst sea-bottoms now over #ajjj fathoms deep must have been land in part of the ,tertiary era1 but there are a mass of facts both geological and biological in favour of land-connexion having formerly existed in certain cases across what are now broad and deep ocean#abe4 ,footnote #abe3 ,loc4 cit41 ,proc4 p4 #ajg4 ,growth of continents4 ,whatever view as to the general permanence of continents and oceans be ultimately established1 the occurrence of widespread changes in the position of land and sea is indisputable1 and it is of interest for us to consider the nature of these changes in the formation of continents4 ,prof4 ,j4 ,d4 ,dana has put forward a hypothesis of growth of continents by a process of accretion1 causing diminution in the oceanic areas1 which at the same time became deeper3 such growth need not always take place in exactly the same way1 and study of the distribution of the strata of the ,north ,american continent suggests that the growth there was endogenous1 the older rocks lying to the west and north forming a horseshoe shaped continent enclosing a gulf-like prolongation of the ,atlantic1 which became contracted by deposition and uplift in successive geological periods1 though it is still partly existent as the ,gulf of ,mexico4 ,the ,eurasian continent1 especially its western portion1 suggests more irregular growth around scattered nuclei of older rocks1 though the process is not completed1 and many gulf-like prolongations1 as the ,baltic and the ,mediterranean1 still remain as water-tracts1 which have not yet been added to the continents4 ,although extensive additions to continents may be and no doubt are often largely due to epeirogenic movements1 the influence of orogenic movements on continent-formation is very pronounced4 ,as the result of orogenic movements1 the rocks of portions of the earth's crust become greatly compressed1 and give rise to masses which readily resist denudation2 moreover1 these comparatively rigid masses1 as shown by ,m4 ,bertrand1 tend to undergo elevation along the same lines as those which formed the axes of previous elevations1 and accordingly after a continental area has undergone denudation for a considerable period1 the uplands consist of rocks which have undergone orogenic disturbance1 while the tracts of ground which are occupied by rocks which have not suffered disturbances of this character1 even if originally uplifted far above sea-level1 tend to be destroyed1 and ultimately occupied by tracts of ocean4 ,stumps of former mountain chains may be again and again established as nuclei of continents and as every period of orogenic movement will add to the number of these nuclei1 the continental areas must in course of time become more complex in structure4 ,moreover1 as some areas are affected by orogenic movements to a greater extent than others1 the complexity of different continental masses will vary4 ,thus1 western ,europe has been affected by orogenic movements during many periods since the commencement of ,cambrian times and its structure is extremely complex1 while the central and western parts of ,russia have not been subjected to violent orogenic disturbances since ,cambrian times1 and accordingly we find the structure of that area comparatively simple2 the greater part of ,africa seems to have escaped these movements since remote times1 and the structure of that continent is extremely simple when compared with the ,eurasian continental tract4 ,it need hardly be stated that the formation of extensive chains composed of volcanic material1 by accumulation of lavas and ashes on the earth's surface1 may give and often has given rise to more rigid tracts1 which will bring about the same effects as those produced by orogenic disturbance as illustrated on a small scale by the ,lower ,palozoic volcanic rocks of ,cambria and ,cumbria4 ,uniformitarianism and ,evolution4 ,according to the extreme uniformitarian views held by some geologists1 the agents which are in operation at the present day are similar in kind and in intensity to those which were at work in past times1 though no geologist will be found who is sufficiently bold to assert that this holds true for all periods of the earth's history1 but only for those of which the geologist has direct information derived from a study of the rocks1 and he is content to follow his master ,hutton in ignoring periods of which he cannot find records amongst the rocks4 ,the modern geologist1 however1 while rightly regarding the rocks as his principal source of information finds that he cannot afford to ignore the evidence furnished by the physicist1 chemist1 astronomer and biologist1 which throws light upon the history of periods far earlier than those of which he has any records preserved amongst the outer portions of the earth itself1 just as the modern historian is not content with written records1 but must turn to the 'prehistoric' archologist and geologist for information concerning the history of early man upon the earth4 ,interpreting the scope of geology in this general way1 rigid uniformitarianism must be abandoned4 ,assuming that the tenets of the evolutionist school are generally true1 the question is1 how far does this affect the geologist in his study of those periods of which we have definite records amongst the rocks8 ,this is a question which cannot readily be answered at the present day1 for our study of the rocks is not sufficiently far advanced to enable us to point out effects amongst the older rocks which were clearly caused by agents working with greater intensity than they do at present1 but as1 on the other hand1 we cannot prove that these effects are due to agents working with no greater intensity than that which now marks these operations1 it is unphilosophical to assume the latter4 ,no student of science at the present day would state that because there has been no observed case of incoming of fresh species within the time that man has actually observed the present faunas and floras1 the hypothesis of evolution of organisms is disproved1 for the time of observation has been too short1 and similarly the time which has elapsed since the formation of1 say1 the ,cambrian rocks may have been too short1 as compared with the time which has elapsed since the formation of the earth1 to allow of any important change in the operation of the geological agents4 ,leaving out of account1 for the moment1 the actual evidence which has been derived from a study of the rocks1 we may briefly consider the theoretical grounds upon which the substitution of an evolutionist school of geology for one of uniformity has been suggested#abf4 ,the principal sources of energy which have exerted an influence upon geological changes are the heat received from the sun and that given off from the earth itself1 both of which must have diminished in quantity throughout geological ages4 ,to the former source we largely owe climatic changes and the operations of denudation1 and accordingly of deposition2 to the latter1 those of earth-movement and vulcanicity4 ,it by no means follows that because the agents were once potentially more powerful than now1 they would necessarily produce greater effects1 for that depends to some extent upon the various conditions which prevailed at different times4 ,to give an example3--if there had at any time been a universal ocean of considerable depth1 however active the agents of denudation were then1 they could produce no effect whatever1 having nothing to work upon2 to take a less extreme case1 if our continents at any past time were smaller and less elevated than at present1 agents of denudation working with greater intensity than that of the present agents need not necessarily have produced a greater amount of denudation than that which is going on at the present day4 ,again1 let us consider vulcanicity3 ,it is as certain1 says ,lord ,kelvin1 that there is less volcanic energy in the whole earth than there was a thousand years ago1 as it is that there is less gunpowder in a ',monitor' after she has been seen to discharge shot and shell1 whether at a nearly equable rate or not1 for five hours without receiving fresh supplies than there was at the beginning of the action4 ,but it does not follow that the manifestations of volcanic activity were necessarily more violent in early geological times than now1 for the degree of violence would be affected by other things than the volcanic energy1 such as the thickness of the earth's crust4 ,footnote #abf3 ,the student may consult an interesting article by ,prof4 ,sollas bearing on this subject4 ,see ,geol4 ,mag4 ,dec4 #b1 vol4 ,,iv4 p4 #a4 ,and now1 let us consider briefly the characters of the rocks of the crust1 to see if they throw any light upon this question4 ,the earliest sediments of which we have any certain knowledge resemble in a striking manner those formed at the present day1 and they seem to have been formed under very much the same conditions1 though further work may show that there were somewhat different conditions which did produce definite differences in the characters of the earlier strata#abg4 ,our knowledge of earth-movement and vulcanicity which took place in past times is still too small to enable us to draw any certain conclusions connected with the subject under discussion from it4 ,perhaps the most suggestive indication of one set of conditions having been generally similar in those early periods of which we have definite records amongst the rocks is furnished by study of past climate4 ,if we accept the nebular hypothesis as a starting point1 we must admit that in the early stages of the earth's history the temperature of the surface1 which would then be largely dependent upon the amount of heat given out from the earth itself as well as upon that received from the sun1 must have been much higher than it is at the present day1 and indeed the mere diminution of the amount of heat received from the sun would probably be sufficient to account for a very marked lowering of the temperature4 ,besides this change of temperature1 resulting in gradual lowering of temperature over the whole earth's surface1 we have other changes dependent upon different conditions1 as proved by the fact1 that there have been alternations of glacial and genial periods4 ,if the general temperature had been very high in the early periods of which we have actual records1 the oscillations would not be sufficient to produce a lowering of temperature sufficient to cause glacial periods1 whereas if it had not been appreciably higher than now1 glacial periods might be produced4 ,this may be represented diagrammatically4 ,footnote #abg3 ,on this matter see ,teall1 ,j4 ,j4 ,h41 ',presidential ,address to ,section ,c1' ,report of the ,british ,association1 #ahic4 ,let a represent the temperature at the commencement of earth-history and b that necessary for glaciation1 and bc the lapse of time between then and now4 ,the curved line indicates the gradual fall in temperature due to diminution of the amount of heat1 while the zigzag line represents the oscillations due to secular climatic changes4 ,if the ,cambrian period x occurred comparatively soon after the commencement of earth-history as shown in fig4 ,a1 no glaciation could be produced1 even during periods when secular changes caused colder conditions than the mean1 whereas if the ,cambrian period occurred at a time very remote from the commencement of earth-history as shown in ,b1 glacial conditions could be produced then as now1 for the mean temperature1 as shown by the distance of the curve from the line bc1 would be practically as it now is4 ,the studies of the last few decades have brought into prominence the occurrence of glacial periods in remote times1 probably in early ,palozoic times2 and as far as the mean temperature of the earth's surface is concerned1 it would appear1 from the knowledge in our possession1 that matters were not very different in those early times from what they now are4 ,illustration3 ,fig4 #be4 ,some further remarks will be made in subsequent paragraphs concerning the period of the earth's history at which the geologist is first furnished with definite records1 but in the meantime it may be observed that the geologist will do well1 when working amongst the strata1 to consider that the more active operation of agents1 even in times of which he has definite knowledge1 may have produced effects which he should be prepared to discover1 as their discovery would be of considerable importance1 and that he should not be content to infer that because it has been proved that agents operating with the same intensity as that which they have at present1 may have produced all the effects which he can actually observe1 they therefore necessarily did produce them4 ,recurrences4 ,absolute uniformity of conditions is impossible1 even in a single area4 ,every change which takes place upon the earth produces conditions somewhat dissimilar from those which previously existed1 and these will leave their effects upon the physiography of the area4 ,for this reason1 assuming that the conditions have gradually changed from simpler to more complex1 every period of time will have been marked by conditions which never prevailed before or afterwards1 and these will leave their impress upon the deposits of the period4 ,it is doubtful for instance1 as already remarked1 whether the exact conditions which gave rise to the extensive deposits of vegetable matter in ,carboniferous times which now form coal1 ever occurred to a like extent in previous or subsequent periods1 and accordingly1 though we have deposits of coal of other ages1 none are so extensive as those of the ,coal ,measures4 ,again1 as the strata of one period are largely composed of denuded particles of pre-existing strata1 which were derived directly or indirectly from igneous rock1 the soluble material existing in the igneous rocks must have been gradually eliminated unless restored by other processes1 and we might expect to find that early sediments have1 on the whole1 a larger proportion of soluble silicates than the later ones4 ,besides these changes1 there are physical changes which are recurrent1 and cause conditions generally similar to pre-existing ones to occur in an area after an interval of dissimilar ones4 ,we have seen that deposits tend to vary according to the distance from the coast1 limestone being succeeded by mud1 this by sand and gravel1 and after subsidence the sand and gravel are succeeded by mud1 and that by limestone4 ,these changes will produce some effect upon the organisms1 and the recurrence of organisms is a well-known event1 of which cases have been cited in a former chapter4 ,again we find1 as already pointed out1 recurrence of climatic changes1 with alternation of glacial and warmer periods1 and these may have been very widespread1 and would influence the other physical conditions1 as well as the distribution of the organisms4 ,vulcanicity may have been more rife at some periods than others1 for instance there seems1 in the present imperfect state of our knowledge1 evidence of enfeebled vulcanicity in later ,mesozoic times1 and of its renewed activity in ,tertiary times4 ,again1 orogenic movements seem to have occurred more extensively at some times than others1 as for instance in early upper ,palozoic times1 at the end of the ,palozoic epoch1 and in early ,tertiary times1 though this may also be an apparent and not an actual truth1 due to imperfect knowledge4 ,in any case1 in limited areas1 there seem to have been alternations of periods of uplift accompanied by marked orogenic movements1 and of widespread depression1 accompanied by sedimentation4 ,the subject of rhythmic recurrence is worthy of further study4 ,this recurrence in combination with evolutionary change may account for the apparent marked difference between ,cambrian and ,precambrian times1 a difference which strikes some geologists as being too great to be accounted for as due to our ignorance only4 ,organic evolution4 ,this subject is too wide for more than passing notice in a work of this character4 ,the evidence of ,palontology is of extreme importance to the biologist1 and indeed1 the way in which evolution of organisms has occurred can only be actually demonstrated by reference to ,palontology1 and the study of ,palontology has already given much information concerning the lines on which evolution has proceeded in different groups of organisms4 ,it must be remembered that the major divisions of the invertebrata were in existence in very early times2 indeed representatives of most of them are found in the rocks containing the earliest known fauna1 that of the ,olenellus beds of ,cambrian age4 ,if our present views as to evolution be correct1 there is no doubt that the period which elapsed between the appearance of life upon the globe and the existence of the ,olenellus fauna must have been very great1 possibly1 as ,huxley suggested1 much greater than that which has elapsed between early ,cambrian times and the present day4 ,if this be so1 however probable it is that we shall carry our knowledge of ancient faunas far back beyond ,cambrian times1 it is extremely improbable that we shall ever get traces of the very earliest faunas which occupied our earth4 ,geological time4 ,various attempts have been made to give numerical estimates of the lapse of time which occurred since the earth was formed1 or since the earliest known rocks were deposited4 ,these attempts may be classed under two heads1 namely1 those made by physicists1 mainly on evidence obtained otherwise than by a study of the rocks1 and those made by geologists by calculating the mean rate of denudation and deposition of the rocks1 and estimating the average thickness of the rocks of the geological column4 ,the calculations of physicists as to the age of the earth vary3--,lord ,kelvin assigned #bj1jjj1jjj years as the minimum and #ajj1jjj1jjj as the maximum duration of geological time4 ,prof4 ,tait has halved ,lord ,kelvin's minimum period1 while ,prof4 ,g4 ,darwin admits the possibility of the lapse of #ejj1jjj1jjj years4 ,the estimates made by geologists1 which will appeal more directly to the geological student1 also vary considerably1 though they bear some proportion to those which have been put forward by the physicists4 ,prof4 ,s4 ,haughton#abh assigned a period of #bjj1jjj1jjj years for the accumulation of the rocks of the geological column2 ,mr ,clifton ,ward#abi one of #fb1jjj1jjj years1 after studying the rocks of the ,english ,lake ,district1 and allowing for the gaps in the succession2 ,mr ,a4 ,r4 ,wallace#acj further lowers the time for the formation of the column to #bh1jjj1jjj years2 ,sir ,a4 ,geikie#aca gives #gc1jjj1jjj years as the minimum and #fhj1jjj1jjj as the maximum2 while ,mr ,j4 ,g4 ,goodchild has lately#acb estimated the period at over #gjj1jjj1jjj years4 ,footnote #abh3 ,nature1 vol4 ,,xviii4 p4 #bfh4 ,footnote #abi3 ,ward1 ,j4 ,c41 ',the ,physical ,history of the ,english ,lake ,district1' ,geol4 ,mag4 ,dec #b1 vol4 ,,vi4 p4 #aaj4 ,footnote #acj3 ,wallace1 ,a4 ,r41 ,island ,life1 ,chap4 ,x4 ,footnote #aca3 ,geikie1 ,sir ,a41 ',presidential ,address to the ,british ,association1' ,report ,brit4 ,assoc41 #ahib4 ,footnote #acb3 ,goodchild1 ,j4 ,g41 ,proc4 ,roy4 ,soc4 ,edinburgh1 vol4 ,,xiii4 p4 #bei4 ,interesting as these figures are1 they probably convey little to the ordinary reader1 and it is doubtful whether the geologist is really affected by them to any extent when picturing to himself the vast duration of geological time4 ,one numerical estimate probably does impress him1 namely that made by ,croll as to the date of the ,great ,ice ,age1 for if the ,ice ,age be so remote as ,croll imagined1 the commencement of earth-history must be inconceivably more remote2 as ,croll's estimate is not generally accepted1 it is doubtful how far geologists are thus influenced1 and probably the fact which does impress them most1 leaving fossils out of account1 is the very little change which has occurred in historic or even in prehistoric times as compared with the vast changes which are familiar to them after studying the strata of the geological column4 ,it is1 after all1 the succession of varied faunas which really gives students of the rocks the most convincing proof of the vast periods of geological time4 ,if anyone doubts this assertion1 let him consider what impression would be made upon him by observing the several thousand feet of strata of the column if none of them contained any organisms4 ,cognisant as he is of the slow rate of change of existing organisms1 the fact that fauna has succeeded fauna in past times brings home to him in an unmistakeable manner the great antiquity of the earliest fossiliferous rocks1 and as our detailed knowledge of these faunas increases the impression of great lapse of time is intensified4 ,and if the earliest fossiliferous rocks be of such vast antiquity1 and1 as has been remarked1 the period of their formation is comparatively recent with reference to the actual commencement of earth-history1 the latter must indeed be inconceivably remote1 and numerical estimates can do but little to familiarise us with the significance of the vast time which has rolled by since the world's birthday4 ,,index4 ,abraum salts1 #bab olian rocks1 #bd1 #ii1 #ajj ,age1 definition of1 #fj ,albian series1 #bcf1 #bch ,algonkian rocks1 #add ,ampthill clay1 #bcb ,angelin1 ,n4 ,p41 #afa1 #afb1 #afe ,aptian series1 #bcf1 #bcg ,aqueous rocks1 #bd ,archan rocks1 #acb ,ardmillan series1 #agj ,ardwick stage1 #aib ,arenaceous rocks1 #bi ,arvonian rocks1 #ada ,asaphus fauna1 #afe ,ashgill series1 #afd1 #afe1 #afg-afi ,ashprington series1 #ahd ,astian series1 #bef ,atlantis1 #bhc ,aveline1 ,w4 ,t41 #afd ,aymestry limestone1 #age1 #agf ,bagshot beds1 #bdd1 #bdf ,bajocian series1 #bbg1 #bca ,bala limestone1 #afg ,bala series1 #afd ,barr series1 #agj ,barrande1 ,j41 #ec1 #ee1 #aei1 #afa1 #afc ,barrois1 ,c41 #bci ,barrow1 ,g41 #ach ,barton beds1 #bdd ,bath oolites1 #bbf ,bathonian series1 #bbg1 #bca ,bed1 #bg ,bedding plane1 #bg ,bell1 ,a41 #beg ,belt1 ,t41 #aec1 #afb ,bembridge beds1 #bea ,bertrand1 ,m41 #hg1 #bhf ,birkhill shales1 #agg ,black ,jura1 #bbf ,blake1 ,j4 ,f41 #ach-adj ,blanford1 ,w4 ,t41 #bjf1 #bjh1 #bag1 #bhb1 #bhd ,bonney1 ,t4 ,g41 #gf1 #ada1 #adb ,boulder clay1 #bfb ,bracklesham beds1 #bdd ,bradford clay1 #bcj ,break1 palontological1 #fa2 physical1 #fj ,bristow1 ,h41 #bci ,brockram1 #baa ,brgger1 ,w4 ,c41 #afa-afc ,brongniart1 ,h41 #ah ,brongniart1 ,c41 #bjj ,bronze age1 #bge-bgg ,brown ,jura1 #bbf ,bunter sandstone1 #bah1 #bbj-bbb ,bure valley beds1 #bef ,buttery clay1 #bgf ,caerfai beds1 #aeb1 #aed1 #aef ,calcareous rocks1 #bi ,caldicote series1 #aci ,callaway1 ,c41 #ach-adj ,callovian series1 #bbg1 #bcb ,cambrian faunas1 #aeh-afc ,cambrian system1 #aeb-afc ,caradoc series1 #afe1 #afh-aga ,carbonaceous rocks1 #bi ,carboniferous fauna and flora1 #aii-bja ,carboniferous limestone1 #aib1 #aid1 #aie ,carboniferous system1 #aib-bja ,carnic beds1 #bbe ,cataclastic rocks1 #bd ,cave man1 #bfh ,cenomanian series1 #bcf ,ceratopyge fauna1 #afb ,chalk1 #bcf1 #bch1 #bci ,chalk marl1 #bcf ,chemically-formed rocks1 #bi1 #aja ,chillesford crag1 #bef ,chronological terms1 #fj ,clastic rocks1 #bd ,climatic conditions1 #ajc1 #aab1 #bij1 #bia ,climatic zones1 in ,jurassic times1 #bcc2 in ,cretaceous times1 #bda ,clymenian beds1 #ahc ,coal1 #aif-aii ,coal measures1 #aib2 mode of formation of1 #aie-aii ,coblenzian beds1 #ahd ,collyweston slate1 #bca ,colonies1 theory of1 #ee ,contemporaneity of strata1 #dh ,continents1 growth of1 #bhe-bhg ,cope1 ,e41 #bdi ,corallian series1 #bbg1 #bcb ,coralline crag1 #bef1 #beg ,cornbrash1 #bcj ,cornstones1 #ahf ,coutchiching series1 #add ,crags1 #bef-bei ,cretaceous fauna and flora1 #bda-bdc ,cretaceous system1 #bcf-bdc ,croll1 ,j41 #bfe1 #bie1 #bif ,cromer ,forest series1 #ajj1 #bef1 #bei ,cromer till1 #bfb ,cuculla beds1 #ahc ,cuvier1 ,baron ,g41 #ah1 #bj ,dalradian rocks1 #acg ,dana1 ,j4 ,d41 #bhe ,danian series1 #bcf ,darwin1 ,c41 #bj1 #gf ,darwin1 ,g41 #bie ,daubre1 ,a41 #hh ,david1 ,t4 ,w4 ,e41 #bjf ,davis1 ,w4 ,m41 #beh1 #bhj ,dawkins1 ,w4 ,b41 #bff1 #bfh1 #bgj1 #bgb1 #bgg ,deep-sea deposits1 #aji ,de ,hayes1 ,g4 ,p41 #ai ,de la ,beche1 ,sir ,h41 #ib ,deposition1 order of1 #cg1 #aaf ,derivative rocks1 #bc ,devonian flora and fauna1 #ahi-aia ,devonian system1 #ahc-aia ,dictyograptus fauna1 #afb ,dimetian rocks1 #ada ,dogger1 #bbf ,downtonian beds1 #age ,dwyka conglomerate1 #bjf ,edwards1 ,f4 ,e41 #bej ,eifelian beds1 #ahd ,encrinurus fauna1 #ahe ,englacial deposits1 #bfa ,entomis slates1 #ahc ,eocene fauna and flora1 #bdh1 #bdi ,eocene rocks1 #bdd-bej ,eozoon canadense1 #adc ,eparchan rocks1 #acb ,epeirogenic movements1 #cb ,epiclastic rocks1 #bd2 simulation by cataclastic rocks1 #ch1 #hj ,epoch1 definition of1 #fj ,estuarine series1 #bcj ,etheridge1 ,r41 #ai ,ettingshausen1 ,baron von1 #bej ,evans1 ,sir ,j41 #bff1 #bgj1 #bgd1 #bgg ,evolution1 #bhg1 #bic ,feistmantel1 ,o41 #bjh ,fenland1 #bgf ,fluvio-glacial deposits1 #bfa ,foreland grits1 #ahd ,forest marble1 #bcj ,forest period1 #bfj1 #bge-bgg ,fossils1 #db2 strata identifiable by1 #dj2 mode of occurrence of1 #dd2 relative value of1 #dg2 remani1 #eb2 geographical distribution of1 #ee2 as indicative of physical conditions1 #ajd ,fossil zone1 #fg ,foster1 ,c4 ,le ,n41 #bci ,fox1 ,h41 #aie ,freshwater deposits1 #ajd2 distinction from marine1 #aje ,fuller's earth1 #bcj ,fusulina beds1 #bja ,gala beds1 #agg ,gannister stage1 #aib ,gardner1 ,j4 ,s41 #bej ,gault1 #bcf1 #bch ,geikie1 ,sir ,a41 #fj1 #hd1 #ie1 #abe1 #acj1 #acg1 #ada1 #adb1 #add1 #ahf1 #ahh1 #aii1 #bdg1 #bie ,geikie1 ,j41 #bfc ,girvan type1 #agj ,glacial deposits1 permo-carboniferous1 #bjf2 ,pleistocene1 #bfj-bff ,glacial period1 #bfj-bff ,glenkiln shales1 #afi1 #agj ,glossopteris flora1 #bjg1 #bjh1 #bad ,godwin-,austen1 ,r4 ,a4 ,c41 #bj ,gondwana series1 #bjg ,gondwanaland1 #bjg1 #bhd ,goniatite beds1 #ahc ,goodchild1 ,j4 ,g41 #hg1 #acj1 #bfc1 #bie ,great ice age1 #bie1 #bif ,great oolite1 #bcj1 #bca ,gregory1 ,j4 ,g41 #beh ,green1 ,a4 ,h41 #abb1 #aci1 #aic ,greensand1 ,lower1 #bcf2 ,upper1 #bcf ,groom1 ,t4 ,t41 #agh ,gshellian beds1 #aic1 #bja ,hampshire basin1 #bde ,hangman grits1 #ahd ,harker1 ,a41 #cj1 #hh ,harkness1 ,r41 #afa ,harmer1 ,f4 ,w41 #beh ,harpes fauna1 #age ,harrison1 ,w4 ,j41 #acj ,hartfell shales1 #afi1 #agj ,hastings sands1 #bcf1 #bcg ,haughton1 ,s41 #bie ,headon beds1 #bea ,heim1 ,a41 #cb ,hempstead beds1 #bea ,hercynian systems of folds1 #bjc ,hicks1 ,h41 #acd1 #ada1 #aec1 #aed1 #afj1 #afa1 #afc1 #afg1 #ahd1 #bff ,hickson1 ,s4 ,j41 #aji ,hill1 ,a41 #bci ,hill1 ,e41 #adb ,hilton shales1 #baj1 #baa ,hind1 ,w41 #aif ,hinde1 ,g4 ,j41 #afi1 #aie ,hippurite limestone1 #bda1 #bdb ,hirnant limestone1 #afg ,homotaxis1 #dh ,hughes1 ,t4 ,mc,k41 #ada1 #bfd1 #bff ,hull1 ,e41 #abj1 #abb1 #aic1 #bhc ,hume1 ,w4 ,f41 #bci ,hunt1 ,a4 ,r41 #aja ,huronian system1 #adc ,hutton1 ,j41 #bhg ,huxley1 ,t4 ,h41 #ej1 #bej ,igneous rocks1 #ba-bc ,ilfracombe beds1 #ahd ,inferior oolite1 #bcj ,inverted strata1 #cb2 detection of1 #cb ,iron age1 #bge1 #bgf ,judd1 ,j4 ,w41 #bci1 #bdg ,jukes1 ,j4 ,b41 #hd ,jukes-,browne1 ,a4 ,j41 #abf1 #bci1 #bfd ,jurassic beds1 #bbe ,jurassic fauna and flora1 #bcd1 #bce ,jurassic system1 #bbf-bce ,kayser1 ,e41 #abe1 #aia ,keewatin series1 #add ,kelvin1 ,lord1 #bhi ,kendall1 ,p41 #beg ,keuper beds1 #bah1 #bba1 #bbb ,kidston1 ,b41 #aii ,kimmeridge clay1 #bcb ,kimmeridgian series1 #bbf ,king1 ,w41 #bag ,kjerulf1 ,th41 #hh ,koninck1 ,l4 de1 #bja ,kupferschiefer1 #bji ,lake1 ,p41 #abf1 #agh ,lamina1 #bg ,lamplugh1 ,g4 ,w41 #hj1 #aai1 #bfd ,lapworth1 ,c41 #cb1 #ach1 #aci1 #aef1 #afh-agj1 #agc1 #agh1 #agi ,laurentian rocks1 #adc ,lawson1 ,a4 ,c41 #add1 #ade ,lehmann1 ,j41 #gg ,lenham beds1 #beg ,lewis1 ,h4 ,c41 #bfc ,lias1 #bbf1 #bbi ,liassian series1 #bbg1 #bbi ,lincolnshire limestone1 #bcj1 #bca ,lincombe and ,warberry grits1 #ahd ,lindstrm1 ,g41 #aad ,lingula flags1 #aeb1 #aee1 #aef ,linnarsson1 ,j4 ,g4 ,o41 #afa ,llandeilo limestone1 #afg ,llandeilo series1 #afe1 #afg ,llandovery series1 #agd-agg ,loess1 #bfg ,logan1 ,sir ,w41 #bj ,london ,basin1 #bde ,london clay1 #aac1 #bdd1 #bdf ,longmyndian rocks1 #ach ,lower ,london ,tertiary beds1 #bdd1 #bdf ,lubbock1 ,sir ,j41 #bgj1 #bgg ,ludlow series1 #agd-agf ,lydekker1 ,r41 #bej ,lyell1 ,sir ,c41 #f1 #ab1 #ai1 #ajf1 #abi1 #bbd1 #bfc1 #bgj ,lynton slates1 #ahd ,mc,coy1 ,sir ,f41 #bja ,mc,mahon1 ,c4 ,a41 #gg ,madsen1 ,h4 ,p41 #bgg ,magnesian ,limestone1 #bji-baa ,malm1 #bbf ,maps1 geological1 #hd1 #acj2 use of1 #hf1 #abj1 #aba ,marcou1 ,j41 #acj1 #bgi ,marine deposits1 #ajb2 nature of fossils in1 #ajg ,marl slate1 #bji1 #baj ,marlstone1 #bbi ,marsh1 ,o4 ,c41 #bdi ,marwood beds1 #ahc ,matthew1 ,g4 ,f41 #afj-afb1 #ahj ,meadfoot sands1 #ahd ,mechanically formed rocks1 #bi1 #ajb ,mello1 ,j4 ,m41 #bgj ,mendip system of folds1 #bjc ,menevian beds1 #aeb1 #aed1 #aef1 #afa ,metamorphic rocks1 #be ,miall1 ,l4 ,c41 #abb ,michell1 ,j41 #aj1 #aa ,millepore oolite1 #bcj1 #bca ,miller1 ,h41 #ahi ,millet seed sands1 #ajj ,millstone grit1 #aib ,miocene period1 #beb-bee ,moffat shales1 #afi1 #agg ,mojsisovics1 ,e4 von1 #bbd1 #bbg ,morgan1 ,c4 ,ll41 #ada ,morte slates1 #ahd ,moscovian beds1 #aic1 #cja ,mountain limestone1 #aib ,murchison1 ,sir ,r4 ,i41 #ai1 #bj1 #agd1 #agi ,murray1 ,sir ,j41 #cj ,muschelkalk1 #bah1 #bba1 #bbb ,nehring1 ,a41 #bfg1 #bfh ,neobolus fauna1 #afj ,neocomian series1 #bcf-bch ,neolithic age1 #bge-bgg ,neumayr1 ,m41 #aae1 #bcc ,newton1 ,e4 ,t41 #de ,nicholson1 ,h4 ,a41 #ahi1 #bej ,noachian ,deluge1 #h ,noetling1 ,f41 #afj ,nordenskjld1 ,a4 ,e41 #aac1 #aad ,noric beds1 #bbe ,northamptonshire sands1 #bcj ,norwich crag1 #bef1 #beg ,nummulitic limestone1 #bdh ,old red sandstone1 #ahc1 #ahe1 #ahf1 #ahh1 #aia ,oldham1 ,r4 ,d41 #bjh ,oldhaven beds1 #bdd1 #bde ,olenellus fauna1 #acd1 #aec1 #aef-afj ,olenus fauna1 #aeb1 #afa1 #afb ,oligocene beds1 #bea1 #beb ,oligocene fauna and flora1 #beb ,oolite1 #bbf ,ordovician faunas1 #agb1 #agc ,ordovician system1 #afd-agc ,organically formed rocks1 #bi1 #ajb1 #aji ,orogenic movements1 #cb ,osborne beds1 #beg ,owen1 ,sir ,r41 #bgg ,oxford clay1 #bcb ,oxford oolite1 #bbf ,oxfordian series1 #bbg1 #bcb ,palolithic fauna and flora1 #bgj-bgd ,palolithic man1 #bfh1 #bgb-bgd ,palolithic period1 #bfg-bgd ,palontological break1 #fa ,palo-physiography1 #abj ,paradoxides fauna1 #aeb1 #afj1 #afa ,peat deposits1 #bge1 #bgf ,pebble beds of ,bunter1 #bah ,pebidian rocks1 #adj ,pengelly1 ,w41 #bgj ,pennant stage1 #aib ,pennine system of folds1 #bjc ,penrith sandstone1 #ge1 #baj1 #baa ,period1 definition of1 #fj ,permanence of ocean basins1 #bgh-bhe ,permian fauna and flora1 #bad-baf ,permian system1 #bji-bag ,permo-carboniferous fauna and flora1 #bjg1 #bjh ,permo-carboniferous glacial deposits1 #bjf ,permo-carboniferous period1 #bje-bjh ,phillips1 ,j41 #aj1 #aa1 #bja ,physical break1 #fj ,pickwell ,down sandstone1 #ahc ,pilton beds1 #ahc ,plaisancean series1 #bef ,planes of lamination1 #bg ,planes of stratification1 #bg ,pleistocene fauna and flora1 #bfe1 #bff ,pleistocene period1 #bfj-bff ,pliocene fauna and flora1 #bei ,pliocene period1 #bef-bei ,portland oolites1 #bbf ,portlandian series1 #bbf1 #bcb ,prado1 ,c4 de1 #afa ,precambrian rocks1 #acb2 mode of formation of1 #adf ,preller1 ,c4 ,s4 du ,r41 #bfd ,prestwich1 ,sir ,j41 #ai1 #acj1 #bgi ,productus limestones1 #bje1 #bjf1 #bad ,protolenus fauna1 #afj ,pseudo-stromatism1 #gf ,purbeckian series1 #bbf1 #bcb ,pyroclastic rocks1 #bd ,quader sandstone1 #bdj ,ramsay1 ,sir ,a4 ,c41 #acj1 #aec1 #afc1 #ahh ,reading beds1 #bdd ,recurrences1 #bib ,red crag1 #bef1 #beg ,reid1 ,c41 #de1 #beg1 #bfd1 #bfh1 #bga ,renard1 ,a41 #cj ,reversed fault1 #cd ,rhtic beds1 #bah ,rhiwlas limestone1 #afg ,richthofen1 ,baron von1 #bfg1 #bfh ,ridley1 ,h4 ,n41 #bga ,river drift man1 #bfh ,rotherham red rock1 #bjb ,rothliegende1 #bji ,rouelle1 #ac ,st ,bees sandstone1 #baj ,st ,erth beds1 #beg ,salopian beds1 #age ,salter1 ,j4 ,w41 #afa1 #afb1 #ahf ,scarbro' limestone1 #bcj1 #bca ,schists1 crystalline1 #gf1 #gg1 #acc1 #adg ,scilla1 ,a41 #ac ,screes1 #aja ,scrope1 ,g4 ,p41 #gf ,sections1 geological1 #hd2 use of1 #hh ,sedimentary rocks1 #bc ,sedgwick1 ,a41 #af1 #ai1 #bj1 #aec1 #agd ,senonian series1 #bcf ,series1 definition of1 #fj ,seward1 ,a4 ,c41 #aac1 #bjh ,sigmoidal structure1 #cc ,siliceous rocks1 #bi ,silurian faunas1 #agi1 #ahj ,silurian system1 #agd-ahb ,simulation of structures1 #gb ,sinemurian series1 #bbg1 #bbi ,smith1 ,w41 #h1 #ab-ah1 #eg1 #he ,soil1 #ajj ,solenhofen slate1 #bcd ,sollas1 ,w4 ,j41 #bhh ,solva beds1 #aeb1 #aed1 #aef1 #afa ,speckled sandstone1 #bje1 #bjf ,speeton series1 #bch ,spencer1 ,h41 #ej ,spirorbis limestone1 #bja ,stages1 definition of1 #fj ,steppe period1 #bfj1 #bfg-bgd ,stonesfield slate1 #bca ,strachey1 ,j41 #aj ,strahan1 ,a41 #bci1 #bfd ,strata1 #bg2 classification of1 #eh1 #abe ,stratification1 #bf ,stratified rocks1 #bc2 composition of1 #bh2 origin of1 #bi2 classification of1 #bh1 #abe2 symbols to represent1 #ij ,stratigraphical geology1 aim of1 #a2 ,w4 ,smith1 founder of1 #h1 #ab-ah ,suess1 ,e41 #aaj1 #abc1 #bjg1 #bhd ,superposition1 law of1 #ca ,surveying1 geological1 #hd ,systems1 definition of1 #fj ,talchir stage1 #bje1 #bjf ,tarannon shales1 #agd-agg ,teall1 ,j4 ,j4 ,h41 #bhi ,terrestrial rocks1 #ii ,thanet sands1 #bdd ,thinning out1 #bh ,thrust plane1 #cd2 detection of1 #ce1 #hb ,tiddeman1 ,b4 ,h41 #hg1 #bfc1 #bgj ,till1 #bfb ,time1 geological1 #bid-bif ,toarcian series1 #bbg1 #bbi ,topley1 ,w41 #acj1 #bci ,torridonian beds1 #ace-acg ,tremadoc slates1 #aeb1 #aee1 #afb1 #afc ,triassic fauna and flora1 #bbc-bbe ,triassic system1 #bah-bbe2 ammonite zones of1 #bbe ,trinucleus fauna1 #afe ,tullberg1 ,s4 ,a41 #afb ,turonian series1 #bcf ,unconformity1 #fj1 #gh1 #ih ,underclays1 #aig ,uniformitarianism1 #bhg-bib ,uriconian rocks1 #ach ,ussher1 ,w4 ,a4 ,e41 #ahc ,valentian beds1 #age ,verneuil1 ,e4 ,p4 de1 #afa ,volcanic rocks1 ,cambrian1 #aee2 ,carboniferous1 #aii2 ,devonian1 #ahd1 #ahf2 ,eocene1 #bdf1 #bdg2 ,ordovician1 #afe-agj2 ,precambrian1 #adf ,vulcanicity1 #bhi ,waagen1 ,w41 #bac1 #bad ,walcott1 ,c4 ,d41 #add1 #aeh1 #afj1 #afa1 #agc ,wallace1 ,a4 ,r41 #abd1 #bce1 #bdj1 #bha1 #bie ,ward1 ,j4 ,c41 #hg1 #hh1 #bfc1 #bie ,warming1 ,e41 #aae ,watts1 ,w4 ,w41 #adb1 #afh1 #agh ,wealden beds1 #bcf1 #bcg ,webster1 ,t41 #ah ,weissliegende1 #bad ,wenlock limestone1 #age1 #agf ,wenlock series1 #agd-agg ,wenlock shale1 #age-agg ,werfener ,schichten1 #bbe ,werner1 ,a4 ,g41 #ab ,weybourne crag1 #bef ,whewell1 ,w41 #ej ,whidbourne1 ,g4 ,f41 #ia ,white ,jura1 #bbf ,whitehaven sandstone1 #bjb ,whitehurst1 ,j41 #aa1 #ab ,wiman1 ,c41 #df ,wood1 ,s4 ,v41 #bej1 #bei ,woodward1 ,h41 #aia ,woodward1 ,h4 ,b41 #fh1 #acj1 #aca ,woodward1 ,j41 #h-aj ,woodward1 ,s4 ,p41 #ajh1 #aaa ,woolhope limestone1 #age ,woolwich beds1 #bdd ,wright1 ,g4 ,f41 #bfc ,yoredale series1 #aib ,zanclean series1 #bef ,zechstein1 #bji ,zone1 fossil1 #fg2 ammonite1 #bbe1 #bcg2 graptolite1 #fi ,,cambridge3 ,,printed ,,by ,j4 ,,and ,c4 ,f4 ,,clay1 ,,at ,,the ,,university ,,press4 ,cambridge ,natural ,science ,manuals4 ,,biological ,,series4 ,general ,editor1 ,a4 ,e4 ,shipley1 ,m4,a4 ,elementary ,palontology--,invertebrate ,h4 ,woods1 ,m4,a41 ,f4,g4,s4 #fs4 ,elements of ,botany ,f4 ,darwin1 ,m4,a41 ,f4,r4,s4 #ds4 #f;d4 ,practical ,physiology of ,plants ,f4 ,darwin1 ,e4 ,h4 ,acton1 ,m4,a4 #ds4 #f;d4 ,practical ,morbid ,anatomy ,h4 ,d4 ,rolleston1 ,m4,d41 ,f4,r4,c4,p4 ,a4 ,a4 ,kanthack1 ,m4,d41 ,m4,r4,c4,p4 #fs4 ,zoogeography ,f4 ,e4 ,beddard1 ,m4,a41 ,f4,r4,s4 #fs4 ,flowering-,plants and ,ferns ,j4 ,c4 ,willis1 ,m4,a4 ,in two vols4 #ajs4 #f;d4 ,the ,vertebrate ,skeleton ,s4 ,h4 ,reynolds1 ,m4,a4 #abs4 #f;d4 ,fossil ,plants ,a4 ,c4 ,seward1 ,m4,a41 ,f4,g4,s4 #b vols4 ,vol4 ,i4 #abs4 ,outlines of ,vertebrate ,palontology ,a4 ,s4 ,woodward4 #ads4 ,the ,soluble ,ferments and ,fermentation ,j4 ,reynolds ,green1 ,sc4,d41 ,f4,r4,s4 #abs4 ,zoology ,e4 ,w4 ,mac,bride1 ,m4,a4 and ,a4 ,e4 ,shipley1 ,m4,a4 ,in the ,press4 ,,physical ,,series4 ,general ,editor1 ,r4 ,t4 ,glazebrook1 ,m4,a41 ,f4,r4,s4 ,heat and ,light ,r4 ,t4 ,glazebrook1 ,m4,a41 ,f4,r4,s4 #es4 in two separate parts each #cs4 ,mechanics and ,hydrostatics ,r4 ,t4 ,glazebrook1 ,m4,a41 ,f4,r4,s4 #hs4 #f;d4 in three separate parts ,part ,i4 ,dynamics #ds4 ,,ii4 ,statics #cs4 ,,iii4 ,hydrostatics #cs4 ,solution and ,electrolysis ,w4 ,c4 ,d4 ,whetham1 ,m4,a4 #gs4 #f;d4 ,out of print4 ,electricity and ,magnetism ,r4 ,t4 ,glazebrook1 ,m4,a41 ,f4,r4,s4 ,in ,preparation4 ,,geological ,,series4 ,petrology for ,students ,a4 ,harker1 ,m4,a41 ,f4,g4,s4 #gs4 #f;d4 ,handbook to the ,geology of ,cambs ,f4 ,r4 ,c4 ,reed1 ,m4,a4 #gs4 #f;d4 ,the ,principles of ,stratigraphical ,geology ,j4 ,e4 ,marr1 ,m4,a4 #fs4 ,crystallography ,prof4 ,w4 ,j4 ,lewis1 ,m4,a4 #ads4 ,net4 99 99 99 99 99 ,laboratory ,note-,books of ,l4 ,r4 ,wilberforce1 ,m4,a41 and ,elementary ,physics ,t4 ,c4 ,fitzpatrick1 ,m4,a4 ,i4 ,mechanics and ,hydrostatics4 ,,ii4 ,heat and ,optics4 ,,iii4 ,electricity and ,magnetism4 each #as4 ,other volumes are in preparation and will be announced shortly4 ,press ,opinions4 ,,biological ,,series4 ,a ,manual and ,dictionary of the ,flowering ,plants and ,ferns4 ,morphology1 ,natural ,history and ,classification4 ,alphabetically arranged4 ,by ,j4 ,c4 ,willis1 ,m4,a41 ,gonville and ,caius ,college4 ,in ,two ,volumes4 ,crown #hvo4 ,with ,illustrations4 #ajs4 #f;d4 ,bookman4 ,one of the most useful books existing for students of botany4444 ,the student who has this book and the chances which ,kew1 or even one of the smaller gardens1 affords him1 will make a steady and really scientific progress4 ,elements of ,botany4 ,by ,f4 ,darwin1 ,m4,a41 ,f4,r4,s4 ,second ,edition4 ,crown #hvo4 ,with numerous ,illustrations4 #ds4 #f;d4 ,journal of ,education4 ,a noteworthy addition to our botanical literature4 ,practical ,physiology of ,plants4 ,by ,f4 ,darwin1 ,m4,a41 ,f4,r4,s41 ,fellow of ,christ's ,college1 ,cambridge1 and ,reader in ,botany in the ,university1 and ,e4 ,h4 ,acton1 ,m4,a41 late ,fellow and ,lecturer of ,st ,john's ,college1 ,cambridge4 ,with ,illustrations4 ,second ,edition4 ,crown #hvo4 #ds4 #f;d4 ,nature4 ,the authors are much to be congratulated on their work1 which fills a serious gap in the botanical literature of this country4 ,zoogeography4 ,by ,f4 ,e4 ,beddard1 ,m4,a41 ,f4,r4,s4 ,with ,maps4 #fs4 ,daily ,chronicle4 ,although included in the series of ,cambridge ,natural ,science ,manuals1 and therefore designed chiefly for students of biology1 ,mr ,beddard deals with his subject in a clear and graphic way that should commend his book to the general reader interested in the question4 ,his style1 while never lacking dignity1 avoids the dulness which too often accompanies that virtue4 ,elementary ,palontology--,invertebrate4 ,by ,henry ,woods1 ,m4,a41 ,f4,g4,s4 ,with ,illustrations4 ,crown #hvo4 ,second ,edition4 #fs4 ,nature4 ,as an introduction to the study of palontology ,mr ,woods's book is worthy of high praise4 ,outlines of ,vertebrate ,palontology for the use of ,students of ,zoology4 ,by ,a4 ,s4 ,woodward1 ,assistant ,keeper in the ,department of ,geology in the ,british ,museum4 ,demy #hvo4 #ads4 ,athenum4 ,mr ,woodward1 in studying vertebrate fossils for the purpose of this volume1 takes the biological view1 and has designed his work primarily for the assistance of students of vertebrate morphology and zoology4 ,mindful1 however1 of the geological side of the subject1 he has introduced a chapter on the succession of the vertebrate faunas1 offering a brief but convenient summary of the distribution of vertebrate life throughout geologic time4 ,the author is to be congratulated on having produced a work of exceptional value1 dealing with a difficult subject in a thoroughly sound manner4 ,the ,vertebrate ,skeleton4 ,by ,s4 ,h4 ,reynolds1 ,m4,a41 ,trinity ,college4 ,crown #hvo4 #abs4 #f;d4 ,british ,medical ,journal4 ,a volume which will certainly take its place amongst the standard text-books of the day4 ,,biological ,,series4 ,practical ,morbid ,anatomy4 ,by ,h4 ,d4 ,rolleston1 ,m4,d41 ,f4,r4,c4,p41 ,fellow of ,st ,john's ,college1 ,cambridge1 ,assistant ,physician and ,lecturer on ,pathology1 ,st ,george's ,hospital1 ,london1 and ,a4 ,a4 ,kanthack1 ,m4,d41 ,m4,r4,c4,p41 ,lecturer on ,pathology1 ,st ,bartholomew's ,hospital1 ,london4 ,crown #hvo4 #fs4 ,british ,medical ,journal4 ,this manual can in every sense be most highly recommended1 and it should supply what has hitherto been a real want4 ,the ,soluble ,ferments and ,fermentation4 ,by ,j4 ,reynolds ,green1 ,sc4,d41 ,f4,r4,s41 ,professor of ,botany to the ,pharmaceutical ,society of ,great ,britain4 ,demy #hvo4 #abs4 ,nature4 ,it is not necessary to recommend the perusal of the book1 to all interested in the subject since it is indispensable to them1 and we will merely conclude by congratulating the ,cambridge ,university ,press on having added to their admirable series of ,natural ,science ,manuals an eminently successful work on so important and difficult a theme1 and the author on having written a treatise cleverly conceived1 industriously and ably worked out1 and on the whole1 well written4 ,brewer's ,journal4 ,it will of course find a place in every brewer's library1 and will be a work much studied and much pondered over by the thoughtful and highly trained men who now represent our profession4 ,,physical ,,series4 ,mechanics and ,hydrostatics4 ,an ,elementary ,text-book1 ,theoretical and ,practical1 for ,colleges and ,schools4 ,by ,r4 ,t4 ,glazebrook1 ,m4,a41 ,f4,r4,s41 ,fellow of ,trinity ,college1 ,cambridge1 ,director of the ,national ,physical ,laboratory4 ,with ,illustrations4 ,crown #hvo4 #hs4 #f;d4 ,also in separate parts4 ,part ,i4 ,dynamics4 #ds4 ,part ,,ii4 ,statics4 #cs4 ,part ,,iii4 ,hydrostatics4 #cs4 ,knowledge4 ,we cordially recommend ,mr ,glazebrook's volumes to the notice of teachers4 ,practical ,teacher4 ,we heartily recommend these books to the notice of all science teachers1 and especially to the masters of ,organised ,science ,schools1 which will soon have to face the question of simple practical work in physics1 for which these books will constitute an admirable introduction if not a complete vade mecum4 ,heat and ,light4 ,an ,elementary ,text-book1 ,theoretical and ,practical1 for ,colleges and ,schools4 ,by ,r4 ,t4 ,glazebrook1 ,m4,a41 ,f4,r4,s4 ,crown #hvo4 #es4 ,the two parts are also published separately4 ,heat4 #cs4 ,light4 #cs4 ,journal of ,education4 ,we have no hesitation in recommending this book to the notice of teachers4 ,practical ,photographer4 ,mr ,glazebrook's text-book on ,light cannot be too highly recommended4 ,,geological ,,series4 ,handbook to the ,geology of ,cambridgeshire4 ,for the use of ,students4 ,by ,f4 ,r4 ,cowper ,reed1 ,m4,a41 ,f4,g4,s41 ,assistant to the ,woodwardian ,professor of ,geology4 ,with ,illustrations4 ,crown #hvo4 #gs4 #f;d4 ,nature4 ,the geology of ,cambridgeshire possesses a special interest for many students4444 ,there is much in ,cambridgeshire geology to arouse interest when once an enthusiasm for the science has been kindled1 and there was need of a concise hand-book which should clearly describe and explain the leading facts that have been made known4444 ,the present work is a model of what a county geology should be4 ,the ,principles of ,stratigraphical ,geology4 ,by ,j4 ,e4 ,marr1 ,m4,a41 ,fellow of ,st ,john's ,college1 ,cambridge4 ,crown #hvo4 #fs4 ,nature4 ,the work will prove exceedingly useful to the advanced student2 it is full of hints and references1 gathered during the author's long experience as a teacher and observer1 and which will be valuable to all who seek to interpret the history of our stratified formations4 ,university ,extension ,journal4 ,mr ,marr is an old ,university ,extension lecturer1 and his book1 which is distinguished by the lucidity and thoroughness which characterise all his work1 cannot fail to be of service to ,university ,extension students who are making a serious study of ,geology4 ,crystallography4 ,by ,w4 ,j4 ,lewis1 ,m4,a41 ,professor of ,mineralogy in the ,university of ,cambridge4 ,demy #hvo4 #ads4 net4 ,athenum4 ,prof4 ,lewis has written a valuable work4444 ,the present work deserves to be welcomed not only as a greatly needed help to advanced students of mineralogy1 but as a sign that the study itself maintains an honoured place in the university ,science ,course4 ,nature4 ,the author and the ,university ,press may be congratulated on the completion of a treatise worthy of the subject and of the ,university4 ,petrology for ,students4 ,an ,introduction to the ,study of ,rocks under the ,microscope4 ,by ,a4 ,harker1 ,m4,a41 ,f4,g4,s41 ,fellow of ,st ,john's ,college1 and ,demonstrator in ,geology 7,petrology7 in the ,university of ,cambridge4 ,crown #hvo4 ,second ,edition1 ,revised4 #gs4 #f;d4 ,nature4 ,no better introduction to the study of petrology could be desired than is afforded by ,mr ,harker's volume4 ,london3 ,c4 ,j4 ,,clay ,,and ,,sons1 ,,cambridge ,,university ,,press ,,warehouse1 ,,ave ,,maria ,,lane ,,and ,h4 ,k4 ,,lewis1 #acf1 ,,gower ,,street1 ,w4,c4 ,medical ,publisher and ,bookseller4 ,transcriber's ,note ,any obsolete or alternate spelling and grammar was retained4 ,all obvious typographical errors were corrected4 ,although hyphenation of words has been standardized to the most prevalent occurrence1 the six occurrences of fresh-water were not converted to freshwater 7#cj occurrences7 due to usage4 ,corrected spellings3 ,godwin-,austen 7p4 #bj72 ,whidbourne 7p4 #aia72 and ,ichthyopterygia 7p4 #bbc74