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would preserve one suite of organisms in England, but a | prolonged.continuance there were not yet Yavourable, they' very different group at the foot of the Himalaya Mountains, soon died out, and the normal fauna of the region resumed yet the deposits at the two places might be absolutely coeval, its occupancy. The deposits formed during these partial even as to months and days. Hence it becomes apparent interruptions, notably graptolitic schists, accompunied by that while strict contemporaneity cannot be predicated of igneous sheets, contain, besides the invading species, remains deposits containing the same organic remains, it may actu- of some of the indigenous forms. Eventually, however, un ally be true of deposits in which they are quita distinct. the final extinction of the second fauna, and, we may supIt, then, at the present time, community of organic forms pose, on the

ultimate demolition of the physical barriers obtains only in districts,.regions, or provinces, it may have lutherto only occasionaliy and temporarily broken, the third been more or less limited also in past time. Similarity fauna, which had already sent successive colonies into the or identity of fossils among formations geographically Bohemian area, now swarmed into it, and peopled it till far apart, instead of proving contemporaneity, ought rather the close of the Silurian period. to be looked upon as indicative of great discrepancies in This original and ingenious doctrine has met with much the relative epochs of deposit. For in any theory of opposition on the part of geologists and paleontologists. the origin of species, the spread of any one species, still of the facts cited by M. Barrande there has been no ques. more of any group of species to a vast distance from the tion, but other explanations have been suggested for them. original centre of dispersion, must in most cases have been It has been said, for example, that the so-called colonies are inconceivably slow. It must have occupied so prolonged merely bands of the Upper Silurian rocks or third fauna, a time as to allow of almost indefinite changes in physical which by great plications have been so folded with the geography, A species may have disappeared from its older rocks as to seem regularly interstratified with them primeval birthplace while it continued to flourish in one or But the author of the Système Šilurien very justly contends more directions in its outward circle of advance. The date that of such foldings there is no evidence, but that, on the of the first appearance and final extinction of that species contrary, the sequence of the strata appears normal and would thus differ widely according to the locality at which undisturbed. Again it has been urged that the difference we might examine its remains

of organic contents in these so-called colonies is dae The grand merch of life, in its progress from lower to merely to a difference in the conditions of water and seahigher forms, has unquestionably been broadly alike in all bottom, particular species appearing with the conditions quarters of the globe. But nothing seems more certain than favourable to their spread, and disappearing when these that its rate of advance has not everywhere been the same. ceased. But this contention is really included in M. It has moved unequally over the same region. A certain Barrande's theory. The species which disappear and re stage of progress may have been reached in one quarter appear in later stages must have existed in the meanwhile of the globe thousands of years before it was reached in outside of the area of deposit, which is precisely what he another; though the same general succession of organic has sought to establish. Much of the opposition, which his forms might be found in each region.

views have encountered has probably arisen from the feeling The geological formations form the records of these ages that if they are admitted they must weaken the value of of organic development In every country where they are palæontological evidence in defining geological horizons A fully displayed, and where they have been properly exa paleontologist, who has been accustomed to deal with mined, they can be separated out from each other according certain fossils as unfailing indications of particular portione to their organio contents. Their relative age within a of the geological series, is naturally unwilling to see his limited geographical area can be demonstrated by the mere generalizations upset by an attempt to show that the fossils law of superposition. When, however, the formations of may occur on a far earlier horizon. distant countries are compared, all that we can safely affirm If, however, we view this question from the broad nat regarding them is that those containing the same or a repre- ural history platform from which it was regarded by M. sentative assemblage of organic remains belong to the same Barrande, it is impossible not to admit that such phenomena epoch in the history of biological progress in each area. as he has sought to establish in Bohemia must have conThey are homotaxial ; but we cannot assert that they are stantly occurred in all geological periods and in all parts of contemporaneous, unless we are prepared to include within the world. No one now believes in the sudden extinction that term a vague period of perhaps thousands of years. and creation of entire faunas Every great fauna in the

Doctrine of Colonies.-M Barrande, the distinguished earth's history must have gradually grown out of some preauthor of the Système Silurien de la Bohême, drew attention existing one, and must have insensibly graduated into that more than a quarter of a century ago to certain remarkable which succeeded. The occurrence of two very distinct intercalations of fossils in the series of Silurian strata of faunas in two closely consecutive series of strata does not Bohemia. He showed that, while these strata presented a prove that the one abruptly died out and the other suddenly normal succession of organic remains, there were neverthe appeared in its place. It only shows, as Darwin has so well less exceptional bands, which, containing the fossils of a enforced, the imperfection of the geological record. In the higher zone, were yet included on different horizous among interval between the formation of two such contrasted groups inferior portions of the series. He termed these precursory of rocks the fauna of the lower strata must have continued bands “colonies," and defined the phenomena as consisting to exist elsewhere, and gradually to change into the newer in the partial co-existence of two general faunas, which, con facies which appeared when sedimentation recommenced sidered as a whole, were nevertheless, successive.

with the upper strata Distinct zoological provinces have posed that during the later stages of his second Silurian no doubt been separated by narrow barriers in former geo fauna in Bohemia the first phases of the third fauna had logical periods, as they still are today. There seems, already appeared, and attained some degree of development therefore, every probability that such migrations as M. in some neighbouring but yet unknown region. At inter- Barrande bas supposed in the case of the Silurian fauna of vals, corresponding doubtless to geographical changes, such Bohemia have again and again taken place. Two notable as movements of subsidence or elevation, volcanic eruptions, examples will be given in later pages, one in the Lower and &c, communication was opened between that outer region one in the Upper Old Red Sandstone of Scotland. and the basin of Bohemia. During these intervals a greater Gaps in the Geological Record.—The history of life has w less number of immigrants succeeded in making their been very imperfectly preserved in the stratified parts of the way into the Bohemian area, but as the conditions for their earth's crust. Apart from the fact that, even under the

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most favourable conditions, only a small proportion of the from the one facies of fossils to the other must represent a total flora and fauna of any period could be preserved in the long interval of time which has not been recorded by the fussil state, enormous gaps occur where no record has been deposit of strata. Professor Ramsay, who called attention preserved at all. It is as if whole chapters and books were to these gaps, termed them “breaks in the succession of missing from an historical work. Some of these lacune are organic remains.” He showed that they occur abundantly sufficiently obvious. Thus, in some cases, powerful disloca- among the Palæozoic and Secondary rocks of England. It tions have thrown considerable portions of the rocks out of is obvious, of course, that these breaks, even though tracesiglit. Sometimes extensive metamorphism has so affected able over wide regions, were not general over the whole them that their original characters, including theirorganic globe. There have never been any universal interruptions contents, have been destroyed. Oftenest of all, denudation in the continuity of the chain of being, so far as geological has come into play, and vast masses of fossiliferous rock evidence can show. But the physical changes which caused have been entirely worn away. That this cause has operated the breaks may have been general over a zoological district frequently is shown by the abundant unconformabilities in or minor region. They no doubt often caused the comble structure of the earth's crust.

plete extinction of genera and species which had a small While the mere fact that one series of rocks lies uncon- geographical range. formably on another proves the lapse of a considerable From all these facts it is clear that the geological record, aterval between their respective dates, the relative length as it now exists, is at the best but an imperfect chronicle of If this interval may sometimes be demonstrated by means geological history. In no country is it complete.' The of fossil evidence and by this alone. Let us suppose, for lacuuæ of one region must be supplied from another. Yet Example, that a certain group of formations has been dis- in proportion to the geographical distance between the turbed, upraised, denuded, and covered unconformably by localities where the gaps occur and those whence the misa second group. In lithological characters the two may sing intervals are supplied, the element of uncertainty in closely resemble each other, and there may be nothing to our reading of the record is increased. The most desirable show that the gap represented by their unconformability is method of research is to exhaust the evidence for each 'area not of a trifling character. In many cases, indeed, it would or province, and to compare the general order of its succesbe quite impossible to pronounce any well-grounded judg- sion as a whole with that which can be established for other ment as to the amount of interval, even measured by the provinces. It is, therefore, only after long and patient vagus relative standards of geological chronology. But it observation and comparison that the geological history of each group contains a well-preserved suite of organic re different quarters of the globe can be correlated mains, it may not only be possible, but easy, to say exactly Subdivisions of the Geological Record by means of Fossils. -: how much of the geological record has been left out between As fossil evidence furnishes a much more satisfactory and the two sets of furmations. By comparing the fossils with widely applicable means of subdividing the stratified rocks those obtained from regions where the geological record is of the earth's crust than mere lithological characters, it is more complete, it may be ascertained perhaps that the made the basis of the geological classification of these.rocks lower rocks belong to a certain platform or stage in geologi- Thus we may find a particular stratum marked by thu cal history which for vur present purpose we may call D,. occurrence in it of various fossils, one or more of which and that the upper rocks can in 'like manner be paralleled may be distinctive, either from occurring in no other bed with stage H. It would be then apparent that at this above and below, or from special abundance in that stratum. locality the chronicles of three great geological periods E, These species might therefore be used as a guide to the ocF, and G were wanting, which are elsewhere found to be currence of the bed in question, which might be called by the intercalated between D and H. The lapse of time repro- name of the most abundant species. In this way a geological sented by this unconformability would thus be equivalent horizon or zone would be marked off, and geologists would to that required for the accumulation of the three missing thereafter recognize its exact position in the series of formaformations in those regions where sedimentation went on tions. But before such a generalization can be safely made, undisturbed.

we must be sure that the species in question really never But fossil evidence may be made to prove the existence does appear on any other platform. This evidently demands of gaps which are not otherwise apparent. As has been wide experience over an extended field of observation. The already remarked, changes in organic forms must, on the assertion that a particular species occurs only on one horizon whole, have been extremely slow in the geological past. manifestly rests on negative evidence as much as on positive. The whole species of a sea-floor could not pass entirely The palæontologist who makes it cannot mean more than away, and be replaced by other forms, without the lapse that he knows the fossil to lie on that horizon, and that, pf long periods of time. If then among the conformable so far as his own experience and that of others goes, it has stratified formations of former ages we encounter sudden never been met with anywhere else. But a single example and abrupt changes in the facies of the fossils, we may of the occurrence of the fussil on a different zone would pe certain that these. must mark omissions in the record, greatly damage the value of his generalization, and a few which we may hope to fill in from a more perfect series such cases would demolish it altogether. Hence all such elsewhere. The complete contrasts between unconformable statements ought at first to be made tentatively. To estabstrata are sufficiently explicable. It is not so easy to give lish a geological horizon on limited fossil evidence, and then à satisfactory account of those which occur where the beds to assume the identity of all strata containing the same are strictly conformable, and where no evidence can be fossils, is to reason in a circle and to introduce utter conobserved of any considerable change of physical conditions fusion into our interpretation of the geological record. The at the time of deposit. A group of strata having the same first and fundamental point is to determine accurately the general lithological characters throughout may be marked order of superposition of the strata. Until this is done by a great discrepance between the fossils above and below detailed paleontological classification may prove to be wortha certain line. A few species may pass from the one into legs. But when once the succession of the rocks has been the other, or perhaps every species may be different. In fixed palæontological evidence may become paramount. cases of this kind, when proved to be not merely local but From what has been above advanced it must be evident persistent over wide areas, we must admit, notwithstanding that, even if the several groups in a formation or system of the apparently undisturbed and continuous character of the rocks in any district or country have been minutely srub original deposition of the strata, that the abrupt transition | divided by means of their characteristic fossil- and if, after

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the lapse of many years, no discovery has occurred to alter as already mentioned, is often knunn by the name of a the established order of succession of these fossils, neverthe- typical fossil, as the different zones in the Lias are by their less the subdivisions can only be held good for the region special species of ammonite. A series of such zones, united in which they have been made. They must not be supposed by the occurrence among them of a number of the same to be strictly applicable everywhere. Advancing into species or genera, is called a group. A series of groups another district or country where the petrographical char- similarly related constitute a formation, and a number of acters of the same formation or system indicate that the formations may be united into a system. The terminology original conditions of deposit must have been very employed in this classification will be discussed in the different, we ought to be prepared to find a greater or following part. less departure from the first observed or what might be regarded as the normal order of organic succession. PART VI.-STRATIGRAPHICAL GEOLOGY. There can be no doubt that the appearance of new organic forms in any locality has been in large measure connected This branch of the science arranges the rocks of the with such physical changes as are indicated by diversities earth's crust in the order of their appearance, and interprets of sedimentary materials and arrangement. The Upper the sequence of events of which they form the records. Its Silurian formations, for example, as studied by Murchison province is to cull from all the other departments of geology in Shropshire and the adjacent counties, present a clear the facts which may be needed to show what has been the sequence of strata well defined by characteristic fossils. But progress of our planet, and of each continent and country. within a distance of 60 miles it becomes impossible to estab- from the earliest times of which the rocks have preserved lish these subdivisions by fossil evidence. If we examine any memorial. Thus from mineralogy and petrography it corresponding strata in Scotland, we find that they con- obtains information regarding the origin and subsequent tain some fossils which never rise above the Lower Silurian mutations of minerals and rocks. From dynamical geology formations in Wales and the west of England. Again, it learns by what agencies the materials of the earth's crust in Bohemia and in Russia we meet with still greater depart have been formed, altered, broken, upheaved, and melted Ilres from the order of appearance in the original Silurian From structural geology it understands how these materials area, some of the most characteristic Upper Silurian organ- were put together so as to build up the complicated crust of isms being there found far down beneath strata replete with the earth. From palæontological geology it receives in wellrecords of Lower Silurian life. Nevertheless the general determined fossil remains a clue by which to discriminate succession of life from Lower to Upper Silurian types re

the different stratified formations, and to trace the grand mains distinctly traceable. Such facts warn us against the onward march of organized existence upon this planek danger of being led astray by an artificial precision of Stratigraphical geology thus gathers up the sum of all that palæontological detail. Even where the paleontological is made known by the other departments of the science, and sequence is best established, it rests probably in most cases

makes it subservient to tho interpretation of the geological not merely upon the actual chronological succession of history of the earth. organic forms, but also, far more than is usually imagined, The leading principles of stratigraphy may be summed upon original accidental differences of local physical condi- up as follows :tions. As these conditions have constantly varied from 1. In every stratigraphical research the fundamental reregion to region, it must hardly ever happen that the same quisite is to establish the order of superposition of the strata. migute paleontological subdivisions, 80 iinportant and Until this is accomplished it is impossible to arrange the instructive in themselves, can be identified and paralleled, dates and make out the sequence of geological history. except over comparatively limited geographical areas, 2. The stratified portion of the earth's crust, or geological

It cannot be too frequently stated, nor too prominently record, as it has been termed, may be subdivided into natkept in view, that, although gaps occur in the succession of ural groups or formations of strata, each marked throughout organic remains as recorded in the rocks, there have been by some common genera or species, or by a general resemno such blank intervals in the progress of plant and animal blance in the type or character of its organic remaius. life upon the globe. The march of life has been unbroken, 3. Many living species of plants and animals can be onward and upward. Geological history, therefore, if its traced downward through the more recent geological formarecords in the stratified formations were perfect, ought to. tions; but they grow fewer in number as they are followed show a blending and gradation of epoch with epoch, so that into more ancient deposits. With their disappearance we no sharp divisions of its events could be made. But the encounter other species and genera which are no longer progress has been constantly interrupted; now by upheaval, living. These in turn may be traced backward into earlier now by volcanic outbursts, now by depression. These formations, till they too cease, and their places are taken by interruptions serve as natural divisions in the chron- yet older forms. It is thus shown that the stratified rocks icle, and enable the geologist to arrange his history into contain the records of a gradual progression of organic fornis. periods. As the order of succession among stratified rocks A species which has once died out does not seem ever to was first made out in Europe, and as many of the gaps in have reappeared. But as has been already pointed out that succession were fouud to be widespread over the in reference to Barrande’s doctrine of colonies, & species European area, the divisions which experience established may within a limited area appear in a formation older for that portion of the globe came to be regarded as typical, than that of which it is characteristic, having temporarily and the names adopted for them were applied to the rocks migrated into the district from some neighbouring region of other and far distant regions. This application has where it had already established itself. brought out the fact that some of the most marked breaks 4. When the order of succession of organic remains in the European series do not exist elsewhere, and, on the among the stratified rocks has been determined, they becomo other hand, that some portions of that series are much more an invaluable guide in the investigation of the relative age complete than in other regions. Hence, while the general of rocks and the structure of the land.' Each zone and similarity of succession may remain, different subdivisions formation, being characterized by its own species or genera, aud nomenclature are required as we pass from continent may be recognized by their means, and the true succession to continent.

of strata may thus be confidently established even in a A bed, or limited number of beds, characterized by one country which hus been shattered by dislocetion, or where ce more distinctive fossils, is termed a zone or horizon, and, the rocks have been folded and inverted,

area.

& The relative chronological value of the divisions of the needful is it to bear in mind that the cassation of one or geological record is not to be measured by mere depth of more species at a certain line among the rocks of a partieustrata. While it may be reasonably assumed that a great lar district may mean nothing more than that, owing to some thickness of stratified rock must mark the passage of a long change in the conditions of life or of deposition, these period of time, it cannot safely be affirmed that a much less species were compelled to migrate or became locally exthickness elsewhere represents a correspondingly diminished tinct at the time marked by that line. They may have conperiod. This may sometimes be made evident by an uncon- tinued to flourish abundantly in neighbouring districts for formability between two sets of rocks, as has already been a long period afterward. Many examples of this obvious explained. The total depth of both groups together may truth might be cited. Thus in a great succession of be, say 1000 feet. Elsewhere we may find a single un- mingled marine, brackish-water, and terrestrial strata, like broken formation reaching a depth of 10,000 feet; but it that of the Carboniferous Limestone series of Scotland, would be utterly erroneous to conclude that the latter repre. corals, crinoicis, and brachiopods abound in the limestones sents ten times the length of time shown by the two former. and accompanying shales, but disappear as the sandstones, So far from this being the case, it might not be difficult to ironstones, clays, coals, and bituminous sbales supervene. show that the minor thickness of rock really denoted by far an observer meeting for the first time with an instance of the longer geological interval If, for instance, it could the disappearance, and remembering what he had read be proved that the upper part of both the sections lay on about "breaks in succession," might be tempted to specu. one and the same geological platform, but that the lower late about the extinction of these organisms, and their reunconformable series in the one locality belonged to a far placement by other and later forms of life, such as the ferns, lower and older system of rocks than the base of the thick lycopods, ganoid fishes, and other fossils so abundant in the conformable series in the other, then it would be clear that overlying strata. But further research would show him the gap marked by the unconformability really indicated a that high above the plant-bearing sandstones and coals longer

period than the massive snecession of deposits. other limestones and shales might be observed, once more 6. Fossil evidence fornishes the chief means of comparing charged with the same marine fossils as before, and still the relative value of formations and groups of rock. À farther overlying groups of sandstones, coals, and carbonabreak in the succession of organic remains marks an inter- ceous beds followed by yet higher marine limestones. Ho val of time often unrepresented by strata at the place where would thus learn that the same organisms, after being the break is found. The relative importance of these breaks, locally exterminated, returned again and again to the same and therefore, probably, the comparative intervals of time After such a lesson he would probably pause before which they mark, may be estimated by the difference of the too confidently asserting that the highest bed in which we facies of the fossils on each side. If, for example, in one can detect certain fossils marked really their final appearance case we find every species to be dissimilar above and below in the history of life. A break in the succession may thus. a certain horizon, while in another locality only half of the be extremely local, one set of organisms having been driven species on each side are peculiar, we naturally'infer, if the to a different part of the same region, while another set total number of species seems large enough to warrant the occupied their place until the first was enabled to returdi. inference, that the interval marked by the former break was 7. The geological record is at the best but an imperfect very much longer than that marked by the second. But chronicle of the geological history of the earth. It abounds we may go further and compare by means of fossil evidence in gaps, some of which have been caused by the destruction the relation between breaks in the succession of organic of strata owing to metamorphism, denudation, or otherwise, remains and the depth of strata between them.

some by original non-deposition, as above explained. Three formations of fossiliferous strata, A, C, and H, may Nevertheless from this record alone can the progress of the occur conformably above each other. By a comparison of earth be traced. It contains the registers of the births the fossil contents of all parts of A, it may be ascertained and deaths of tribes of plants and animals which have from that, while some species are peculiar to its lower, others to time to time lived on the earth. But a small proportion its higher portions, yet the majority extend throughout of the total number of species which have appeared in the formation. If now it is found that of the total num- past time have been thus chronicled, yet by collecting the ber of species in the upper portion of A only one-third broken fragments of the record an outline at least of the passes up into C, it may be inferred with some probability bistory of life upon the earth can be deciphered. that the time represented by the break between A and C The nomenclature adopted for the subdivisions of the was really longer than that required for the accumulation geological record bears witness to the rapid growth of geoof the whole of the formation A. It might even be pos- logy. It is a patch-work in which no system nor language sible to discover elsewhere a thick intermediate formation has been adhered to, but where the influences hy which B filling up the gap between A and C. In like manner the progress of the science has been moulded may be were it to be discovered that, while the whole of the forma distinctly traced. Some of the earliest names are lithologi. tion C is characterized by a common suite of fossils, not one. cal, and remind us of the fact that miveralogy and petroof the species and only one half of the genera pass up into graphy preceded geology in the order of birth - Chalk, H, the inference could hardly be resisted that the gap Oolite, Greensand, Millstone Grit. Others are topograbetween the two formations marks the passage of a far phical, and often recall the labours of the early geologists longer interval than was needed for the deposition of the of England-London Clay, Oxford Clay, Purbeck, Portland, whole of -C. And thus we reach the remarkable con- Kimeridge beds. Others are taken from local English clusion that, thick though the stratified formations of a provincial names, and remind us of the debt we owe to country may be, in some cases they may not represent so William Smith, by whom so many of them were first used long a total period of time as do the gaps in their suc- -Lias, Gault, Crag, Cornbrash. Others of later date recog. cession,-in other words, that non-deposition was more nize an order of superposition as already established among frequent and prolonged' than deposition, or that the formations-Old Red Sandstone, New Red Sandstone. intervals of time which have been recorded by strata have By common consent it is admitted that names taken from not been so long as those which have not been so recorded. the region where a formation or group of rocks is typically

In all speculations of this nature, however, it is necessary developed, are best adapted for general use. Cambrian, to reason from as wide a basis of observation as possible, Silurian, Devonian, Permian, Jurassic, are of this class, seeing that so much of the evidence is negative. Especially and have been adopted all over the globe.

a

Alluvium.

Recent or Terrace.

But whatever be the name chosen to designate a particu.

I. ARCHIÆAR. lar group of strata, it soon comes to be used as a chronologi. cal or homotaxial term, apart altogether from the strati- Underneath the oldest unaltered stratified and fossiliferous graphical character of the strata to which it is applied. formations in Europe there occur masses of gneiss and Thus we speak of the Chalk or Cretaceous system, and other crystalline schistose rocks belonging perhaps to widely embrace under that term formations which may contain po different geological periods, but, from want of satisfactory chalk; and we may describe as Silurian a series of strata means of discrimination, decessarily united provisionally in utterly unlike in lithological characters to the formations one common series. That they aro separated by a vast inin the typical Silurian country. In using these terms we terval of time from the rocks which lie upon them is shown unconsciously allow the idea of relative date to arise by the strong unconformability with which they are related to prominently before us. Hence such a word as chalk or every formation of younger date than themselves. Everycretaceous does not suggest so much to us the group of where thoroughly crystalline, they are disposed in rude, strata so called, as the interval of geological history which crumpled, often vertical beds, out of the ruins of which these strata represent. We speak of the Cretaceous, Jurassic, the overlying formations have been partly built. ard Cambrian periods, and of the Cretaceous fauna, the BRITAIN.In no part of the European area are these Jurassic flora, the Cambrian trilobites, as if these adjectives ancient rocks better seen than in the north-west of Scotland. denoted simply epochs of geological time.

Their position there, previously indicated by MacCulloch The geological record is classified into five main divisions: and Hay Cunningham, was first definitely established by -(1) the Archæan, Azoic (lifeless), or Eozoic (dawn of Murchison, who showed that they possess a dominant strike life) Periods ; (2) the Primary or Palæozoic (ancient life) to N.N.W., and are unconformably overlaid by all the other Periods; (3) the Secondary or Mesozoic (middle life) rocks of the Scottish Highlands. They consist of a tough Periods; (4) the Tertiary or Cainozoic (recent life); and massive gneiss usually hornblendic, with bands of horn(5) the Quaternary or Post-Tertiary Periods. These divi- blende-rock, hornblende-schist, quartz-felsite, granite, and sions are further ranged into systems, each system into other crystalline rocks. In two or three places they encloso formations, each formation into groups, and each group or bands of limestone, but neither in these nor in any other series into single zones or horizons. The subjoined gene parts of their mass has the least trace of any organic strucralized table exhibits the order in which the chief sub- ture been detected. It is impossible at present to offer any divisions appear.

conjecture as to their probable thickness. It must be many Order of Succession of the Stratified Formation of the Earth's Crest tainable, will only be made out after the region where they

thousand feet; but its approximate amount, if ever ascerBritain

occur has been mapped in detail These gneisses and Continental Europe.

North America.

schists possess a massiveness and rudeness of bedding which

strongly distinguishes then from all the other and younger Recent-Alluvium,

metamorphic rocks of Britain. They form nearly the Champlain

whole of the Outer Hebrides, and occupy a variable belt of the western parts of the counties of Sutherland and Ross.

Murchison proposed to term them the Fundamental or Plioceno - Crag de Pliocene-Tvgel, Dino

Lewisian Gneiss from the isle of Lewis the chief of the posits of Norfolk and Suffolk.

Hebrides. Afterwards he called them Laurentian, regard. Miocene-Lignite of Miocene-Leithakalk,

ing them as the equivalent of some part of the great Bovey Tracey Mull, Upper Molasze.

Laurentian system of Canada.
Oligocene Lower Mo-

In recent years Mr Hicks and others have endeavoured
lasse, Grès de Fontaine-
Bleau, &c.

to show that in Wales there exist here and there protrusions Eocene-Tertiaria of Eocene-Nummalite- Alabama Hampshire Basin, limestone, Flysch. Lignitie

of an old crystalline group of rocks from beneath the Cam. and Isle v Wighi.

brian sysiem, and they have described these "pre-Cambrian" Upper Senonlan-Craie blanche Fox-Hills group.

masses as overlaid unconformably by younger formations, et tuff'eau, Upper Qua

as in the north-west of Scotland. Professor Ramsay, however, who with his colleagues in the Geological Survey mapped the Welsh areas in detail, contends that the sup

posed older gneiss is merely a metamorphosed portion of Upper. Upper or White Jara (Malm).

the Cambrian rocks. Lower.

CONTINENTAL EUROPE-On the continent of Evrope (Dogger).

poorly developed

numerous areas of ancient gneiss rise from under the oldest s Upper Rhætic beds, Keuper.

fossiliferous formations. In Scandinavia the structure of

part of the country resembles that of the north-west of Lower.

Scotland: the fundamental-gneiss (Urgneiss), covering a Dyas or (Zechstein,

large area, is overlaid unconformably by red sandstones Permian Rothliegendes. Terrain houiller, Stein

which underlie tlie most ancient strata containing organic

remains. The gneiss and its accompanying rocks range
Sub-Carboniferous.
Flötzleerer Sandstein
Calcaire Carbonifère,

through Finland into the north-west of Russia, reappearing Kohlenkalk, Kulm. Devonlan and Old Red Devonian

in the north-east of that vast empire in Petchora Land

down to the White Sea, and rising in the nucleus of the Silurlan (Transition or Grauwacke system).

chain of the Ural Mountains, and still further south in Cambrian.

Primordial Silurian, older Primordial Silurlan Podolia. In Central Europe they appear as islands in the

grauwacke and slate. and Cambrian. Primitive schists Huronian.

midst of more recent formations. In the midst of the Carpathian Mountains they protrude at a number of points,

but westwards in the Alpine chain they rise in a more con. Fundamental gnelss. Ur-gneiss.

Laurentian..

tinuous belt in the central portion of these crests, and show numerous mineralogical varieties, including protogine, mica-schist, and many other schists, as well as limestone

Post-Tertlary or Qolterary

Diluvian

peat, &c. Pleistocene-Care

deposits Glacial drit.

Glacial.

Sumter.

thereum-Sand.

Yorktown

Tertiary or Calnozoic.

Cretaceous.

Upper Misc souri Ragion.

Lower.

dersandstein.
Turonian-Plänerkalk.

Pierre group
Cenomanian-Grès vert. Niobrara group.
Gault.

Benton group.
Neocomlan.

Dakotah group.

Jurassic rocks ap
Middle or Browu Jura

pear to be but

Secondary or Mesozoic.

Jurassic.

Qolitic

Llassic.

Lower or Black Jura

(Lias).

in N. America

Trassie

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