FIG. 26-Vertical section of portion of Nummulite, showing the Investment of the earlier whorls by the alar prolongations of the later:-a, marginal cord; b, chamber of outer whorl; c, c, whorl invested by a: d, one of the chambers of the fourth whorl from the margin; e, e, marginal portions of the enclosed whorls; f. investing portion of the outer whorl; g. 9, spaces left between the Investing portions of successive whorls; h, h, sections of the partitions dividing these. And by a further increase of this subdivision, a complete reticulation is formed between the successive whorls of the spiral lamina, by the complex inosculation of the septal prolongations. Now, although it would not be diffi cult to arrange a collection of Nummulites under a number of specific types founded on these characters, if account were only taken of the specimens showing the most strongly marked differences, yet when due attention is given to the intermediate forms, they are found to present such a transitional gradation as to make it impossible to draw any absolute differential lines between the numerous components of the series.-The canal system of Nummulina bears a close re semblance to that of Opercu- FIG. 27.-Internal cast of two chambers, a, a, lina; and it is sometimes of Nummulina, the radial canals between them passing into b, marginal plexus. brought into beautiful dis tinctness in fossil specimens by the infiltration of ferraginous or other fossilizing material. And sometimes fragmentary internal casts" present themselves, which admirably display the distribution of parts of the system (fig. 27). We find in the larger forms of the Nummuline type the same tendency to become labyrinthic," by the subdivision of the principal chambers into "chamberlets," that we have seen in the Mili oline. Just as Peneroplis is converted by such subdivision into a spiral Orbiculina, and this, again, by the early exchange of the spiral for the cyclical plan of growth, into the cyclical Orbitolite, so Operculina, without any other departure from the ordinary Nummuline type, becomes Heterostegina (fig. 28); whilst the substitution of the cyclical for the spiral plan of growth FIG 23-Ileterostegina. produces the discoidal Cycloclypeus (fig. 29), the largest existing Foraminifer yet discovered, its diameter sometimes reaching 2 inches. This is the recent representative of the very important fossil type Orbitoides, examples of which present themselves very abundantly in many localities in association with Nummulites (fig. 25, c), which they so closely resemble as to be easily mistaken for them. Some of them are very thin flattened disks, of the proportion shown in vertical section in fig. 30; while others have two or three times the proportionate thickness. Each disk has a central plane of chamberlets (figs. 31, 32, b, b) resembling that of Cycloclypeus, arranged with a general but not constant regularity in concentric circles; but whilst in the recent type this central plane is enclosed above and below by successive lamelle of tubular shell-substance not separated from each other by any apertures in their shell-walls. This arrangement obviously corresponds with that of the most reticulate forms of Nummulites. FIG. 30.-Vertical section of Orbitoides: a, primordial chamber. clypeus is furnished by the disposition of the canal-system, which, Another important link of affinity between Orbitoides and Cycloallowance being made for the cyclical plan of growth of the former, as contrasted with the spiral plan of the latter, is essentially the same in the two types. This, moreover, is beautifully shown in "internal casts" of Orbitoides found by Professor Ehrenberg in the Greensand; which, though fragmentary, display a canalsystem precisely resembling that which the writer had worked out in Cycloclypeus by the examination of sections of the shell. It has been by the study of such "internal casts," recent and fossil, taken in connexion with the microScopic appearances shown in thin sections of its calcareous Orbitoides; showing at b, b the chamberlets of the median plane, and st layers, that the Foraminiferal nature of the Serpentine-limestone of Canada has been elucidated, of which some of Fig. 31.-Horizontal section of disk of the deepest beds of the Laurentian formation (the earliest a, a those of the superposed lamella. series of stratified rocks at present known) are composed, and which has its parallel in certain beds that lie near the base of the "fundamental gneiss" of central Europe. In order that the evidence of the organic origin of this rocka point of the highest paleontological and petrological interest-may be properly understood, regard must be had to what is even now going on in the depths of the ocean. Fia. 32.-Chamberlets of the superposed lamella a, and of the median plane b of Orbitoides, more highly magnified. The animals that form the enormous mass of globigerina ooze at present in course of deposit over vast areas of the sea-bottom increase and multiply by limited gemmation; that is, the size of each individual shell, which depends upon the number of segments of which it is composed, is restricted by the cessation of continuous gemmation after a definite number of segments has been produced. An indefinite extension of the type, however, is provided for by the detachment of further segments, which, increasing by gemmation, in their turn give origin to new shells. In the larger Foraminiferal types last described, on the other | larly confirmed by the fact ascertained by Dr Sterry Hunt, hand, continuous gemmation proceeds much further; and that in certain Silurian Limestones from Wales and New thus we may have in an Orbitolite, a Nummulite, or a Brunswick, the segments of Crinoidal stems have the soft Cycloclypeus, hundreds or even thousands of chambers, all animal tissue, which originally filled the interspaces of their formed by the segmental extension of the animal body from calcareous network, replaced by a silicate of alumina, iron, one "primordial segment." Further, in Polytrema we find magnesia, and potass-intermediate between glauconite a rotaline shell extending itself by the continuous gemma- and serpentine. Now, the Serpentine-limestone that lies tion of the animal, without any definite limit either of size near the base of the Laurentian formation in Canada, is or shape,its increase taking place by vertical as well as by ordinarily composed of alternating layers of carbonate of horizontal gemmation, so that it develops itself into forms lime (in the condition of calcite) and of silicate of magnesia which are essentially zoophytic. Hence there is nothing (serpentine), these layers being superposed upon one in the nature of Foraminiferal organization in the least another with great general regularity (as shown in fig. 33), degree inconsistent with the idea that a shell essentially and frequently exceeding fifty of each kind in number. In "Nummuline" in its character should extend itself some localities, however, the calcite is replaced by dolomite indefinitely by the continuous gemmation of the animal (magnesian limestone), while the serpentine is replaced that forms it, not merely over horizontal planes, but also in either by loganite (a compound of silex, alumina, magnesia, the vertical direction, so as to produce solid massive struc- and iron), or by some other magnesian silicate; but the altertures bearing a strong general resemblance to Coral growths. Again, the dead shells of Foraminifera brought up from many parts of the sea-bottom are found to have their cavities filled with green or ochreous ferruginous silicates, which seem allied in composition to the "glauconite" of the Greensand formation; and these mineral deposits occupy not merely the chambers of the shell, but its canalsystem also; so that when the calcareous shells have been dissolved away by dilute acid (which does not act on their contents), internal casts are obtained, which are perfect models, not only of the soft sarcodic segmented body of the animal, but also of its extensions into the canal-system that traverses the substance, of the intermediate skeleton (figs. 21, 27). Yet further, this mineral deposit sometimes penetrates the minute tubuli of the shell itself; so that the surface of the internal cast of each chamber is beset with little points which represent the pseudopodia that extended themselves into those tubuli from each sarcodic segment. There can be no reasonable doubt that these "internal casts" are formed by a process of chemical " substitution," the animal body, in the progress of its decay, being replaced, particle by particle, by ferruginous silicates precipitated from sea-water by the liberation of ammonia. And the explanation of the fact that this replacement only occurs in particular localities (notably in the Ægean, over the Agulhas bank near the Cape of Good Hope, and on certain parts of the Australian coast) probably lies in some local peculiarity in the composition of the sea-water, which may not improbably be due to the discharge from submarine springs of water containing an unusual quantity of the materials of the deposit. Now there is ample evidence. that a similar process has taken place at various geological periods. For, as was first pointed out by Professor Ehrenberg, the green sands which occur in different formations from the Silurian to the Tertiary epoch (being especially characteristic of the earlier Cretaceous) consist very largely (though not exclusively) of the "internal casts" of Foraminifera,-as is shown by microscopic examination of their grains. Examples of such casts, which can be referred without the least difficulty to known Foraminiferal types, have been already given (figs. 17, 27). Hence there is no inherent improbability in such an occupation of the chamber-cavities, of the canalsystem, and even of the minute, tubulation, of a still earlier Foraminiferal structure, formed by the indefinite extension of a Nummuline growth into coral-like masses. And as there is every reason to believe that the composition of ocean-water has varied greatly at different geological periods, and especially that it contained magnesian salts at earlier epochs in much larger quantity than at present, it might be expected that the silicates which replace the soft tissues of the animals of the earliest organisms should be essentially magnesian. This expectation has been singu FIG. 33.-Section of the Eozoic Serpentine-limestone of Canada, showing alternation of calcareous (light) and serpentinous (dark) lamellæ. nation of calcareous and siliceous lamella is just as regular in these cases as in the typical ophicalcite, and there is every probability that the dolomitic layers were originally formed as calcite, and subsequently metamorphosed by magnesian infiltration. The regularity of this alternation of calcareous and siliceous lamellæ, which has no parallel in any undoubted mineral, taken in connexion with the resemblance of the entire formation (extending continuously over hundreds of square miles) to ancient coral reefs, having suggested to Sir William Logan its organic origin, a careful microscopic examination of specimens that seemed to have been least altered by metamorphic action was made at his instance by Dr Dawson of Montreal, with results that left him in no doubt either of the organic nature of the calcareous lamellae, or of the Foraminiferal affinities of the organism. These results were confirmed by the writer of this article, whose re-examination of the subject, to meet the objections raised from time to time against Dr Dawson's conclusions, has only had the effect of strengthening his original conviction of their truth. And the following general sketch of the structure of Eozoön canadense is here presented with full confidence, as expressing, not merely his own views, but those of the numerous eminent naturalists who have examined for themselves the evidentiary facts placed before them.1 1 Of those who may be considered as qualified by special study of the Foraminifera to form a judgment on this matter, Mr H. Carter is the only one who has expressed his dissent; and he has never seem FIG. 34. Calcareous skeleton of Eocoon canadense: A, Al, chambers of lower story; A2, A3, chambers of upper,story, imperfectly divided at a, a; B, B, tubulated or Nummuline layers; cc, intermediate skeleton; D, large passage from one story to another; E, Z, Z, branching canal-systems. opening one into the other, as at a, a, like apartments en suile, but being occasionally divided by complete septa, as at b, b, which are traversed by passages of communication between the chambers they separate. Each layer of shell consists of two finely-tubulated.or "Nummuline" lamellæ, B, B, which form the boundaries of the chambers above and beneath, and of an intervening deposit of homogeneous shell-substance, c, c, which constitutes the "intermediate skeleton." The amount of this varies considerably in different layers, while the thickness of the "proper wall" of the chambers (or "Nummuline lamella ") remains almost constant, the distinction between the two being just as marked (in well-preserved specimens) as it is in the recent Calcarina (fig. 19). The tubuli of the "Nummuline" lamellae are usually filled up (as in the Nummulites of Nummulitic Limestone) by mineral infiltration, so as to present only a fibrous appearance in thin transparent sections; but it fortunately happens that, through its having escaped such infiltration, the tubulation (fig. 35, a, a) is occasionally as distinct as it is in recent Nummuline shells, bearing a strong resemblance in its occasional waviness (as at a', a') to that a crab's claw. The "intermediate skeleton," whenever it forms a thick layer, is penetrated by arborescent systems of canals (fig. 34, E, E), which are often distributed so extensively and so minutely through its substance as to leave very little of it without a branch. These FIG. 35-Highly-magnified section of a portion of the calcareous skeleton of Eozoon canadense: a, a, Nummuline layer showing parallel tubuli with a wavy bend along the plane a', a'; b, origins of canal-system penetrating the Intermediate skeleton c, c, which is traversed obliquely by cleavage-planes that pass on into the Nummuline layer. canals (fig. 35, b, b) take their origin, not directly from the chambers, but from irregular lacunae or interspaces between the outside of the proper chamber-walls and the "intermediate skeleton," exactly as in Calcarina,-the extensions of the sarcode-body which occupied the most characteristic specimens of Eozoic structure. On the other hand, the late Professor Max Schultze, who took up the enquiry towards the end of his life, not only publicly and most explicitly expressed his conviction that the canal-system found in the calcareous lamelle must be organic, but left behind him an elaborate Memoir on the subject, with ample illustrations, which unfortunately still remains unpublished. them having apparently been formed by the coalescence of the pseudopodial filaments which had issued forth through the tubulated famella. It is to be remarked that the substance, not merely of the intermediate skeleton, but of the Nummuline layer, is traversed by oblique lines, indicating the cleavage-planes of calcite. This is what is constantly seen in fossilized calcareous organisms such as the shells and spines of Echinida, or the stems of Crinoidea-which retain their organic arrangement unchanged, and thus affords no basis whatever for the contention that these calcareous layers are purely mineral. On the other hand, the fact that the portions of the canal-system, shown in thin sections (fig. 35), continually cross the cleavage planes, instead of lying between them, furnishes a strong objection to the hypothesis that the appearances which have been interpreted as indicating a regular distribution of ramifying canals can have been produced by mineral infiltration. Further, the distinct continuity of these cleavage-lines through the "Nummuline layer" (fig. 35, a, a) proves this layer to be essentially calcareous,-the layer of serpentine-fibres which is commonly found in its place after decalcification being a secondary deposit, formed in the manner to be presently described. an When a well-preserved fragment of Eozoon has been treated with dilute acid, so as to dissolve away the calcareous lamelle, we have "internal cast" in serpentine, which gives us a precise model of the sarcodic body by which the cavities of the calcareous struc ture were originally occupied. We see, in the first place (fig. 36), FIG. 36.—Internal cast, in Serpentine, of the animal body of Eozoon canadense, that each of the layers of serpentine forming the lower part of such a specimen shows more or less of a segmental arrangement,-being, in fact, made up by the coalescence of a number of minute serpencing in the upper part of the figure. This shows that there is not tinous granules, such as are shown separately or but slightly coalesthat difference between the regularly "lamellated" and the "acervuline" plans of growth which might at first sight be sup posed,-the chambers having been separate in the latter, whilst in the former they constituted imperfectly subdivided galleries. In those wider spaces between the serpentine-layers, which were origin. ally occupied by the thicker calcareous layers forming the "intermediate skeleton," we find internal casts of the branching canal-system; and the development of this system is found, as in recent Foraminifera, to bear a constant relation to the amount of the secondary calcareous deposit. But further, in specimens in which the "Nummuline" layer was originally well preserved, and in which the decalcifying process has been carefully managed, that layer is represented by a thin white film covering the exposed surfaces of the segments; as is shown superficially over the upper part of fig. 36, and in section, along the margins of the serpentine layers, in the lower. When this film is examined with a sufficient magnifying power, it is found to consist of extremely minute needle-like fibres of serpentine; which sometimes stand upright, parallel, and almost in contact with one another, like the fibres of asbestos, but which are frequently grouped in converging brush-like bundles, so as to be very close to each other in certain spots at the surface of the film, whilst widely separated in others,-thus indicating exactly the same irregularities in the grouping of the tubuli that (as already mentioned) we find in recent Nummulines. And it is not unfrequently seen that where bundles of these fibres converge towards the surface, so that the pseudopodial threads they represent would have issued forth in clusters, the internal casts of the canal-system take their origin in such aggregations. We have here, in fact, in this most ancient of all fossils at present known, the most complete model we possess of any extinct animal, extending even to its soft sarcodie threads of less than th of an inch in diameter,-this model being conformable in all essential particulars to the "internal casts" of existing Foraminifera which are at present in course of produc tion on the sea-bottom. Geographical Distribution.-Most of the Families of thie group have a very wide geographical distribution, this being especially the case with the smaller and simpler re- | found, it may even be said that all other fossils are modern presentatives of them that range over those vast areas in by comparison. For the interval between the formation of the deep oceanic basins, of which the bottom-temperature the Canadian Eozoön and the period represented by the is kept down by the polar underflow. A striking resem- oldest fossils of the Lower Cambrian series seems blance has long been noted between the poor and feeble undoubtedly to have been quite as great-geologically Foraminiferal fauna of shallow waters in colder-temperate speaking-as that which intervened between the latter seas, and that of great depths in tropical seas; and this and the existing epoch, if not greater,—the “fundamental similarity is now explained by the correspondence of the gneiss" of Sir Roderick Murchison, which represents in centemperature to which these two fauna are subjected. The tral Europe the Laurentians of Canada, and near the base of larger and most developed examples of existing Fora- which is found the kindred Eozoön bavaricum, having a minifera, on the other hand, are limited to the shallower thickness estimated at 90,000 feet, and being overlaid by a seas near tropical shores, or covering coral reefs where the great thickness of other non-fossiliferous rocks. Hence the bottom-temperature is comparatively high; or to partially determination of the organic origin of this Ophicalcite, and enclosed seas, like the Mediterranean and Red Sea, which of its Foraminiferal affinities, which has been effected by are cut off from the polar underflow by the shallowness of the examination and comparison of parts of specimens so the straits which connect them with the oceanic basin. It minute as to be scarcely visible to the naked eye, must be is in such seas that we meet with the largest Orbiculina, considered as one of the most remarkable results of microand the most complex Orbitolites and Alveolina,—the first scopic research-fully equal in importance, when considered of these "imperforate" types being generally abundant in in all its bearings, to the discovery by Prof. Ehrenberg of tropical shore-sands, the second in shallow dredgings along the Foraminiferal origin of Chalk.3 the Australian coast, the great barrier-reef, and the lagoons of "atolls" in the Coral Sea, while the third seems to attain its highest development in the Philippine Seas. So, again, among the "perforate Lagenida, we find the "nodosarian and "cristellarian" types attaining a very high development in the Mediterranean; the most complex forms of the "rotalian" type, including the zoophytic Polytrema, are only met with in tropical or sub-tropical seas; while, with the exception of small and modified Polystomella and dwarfed Operculina, there are no known representatives in the colder-temperate or polar seas either of the gigantic Cycloclypeus, or of the large Operculina and Heterostegina of the tropics. But while the Foraminiferal fauna thus obviously depends on an elevated temperature for the attainment of its highest development as regards the size and complexity of its individual members, the numerical multiplication of its lower forms (as is the case in many other groups) seems to be favoured by a much lower degree of warmth; so that we find the vast area of "globigerina-ooze" extending to the borders of the Polar There, however, it ceases almost abruptly, the place of this calcareous deposit being taken by an accumulation of the siliceous skeletons of Radiolarians and Diatomaces. seas. It is not a little curious, however, that recent researches should have disclosed the fact, that the existing Arenaceous Lituolida attain their highest development-in regard no less to size and complexity of structure than to number -on the deep sea-bottom,-the additions to our previous knowledge of the Foraminiferal fauna made by the dredgings of the "Porcupine," the "Valorous," and the "Challenger" having been far greater in this section than in either of the calcareous-shelled groups. And it would hence appear that an elevated temperature is not as essential to the high development of the Foraminifera which construct "tests" by gluing together grains of sand, as it is to that of the shell-forming types which separate the material of their "porcellanous" or "vitreous" skeletons from the seawater in which they live. Geological Distribution.-There is no division of the Animal Kingdom whose range in time (so far as is at present known) can be compared with that of the Foraminifera. Looking, indeed, to the vast series of ages that must have been required for the deposit of that long succession of Upper Laurentian and Huronian rocks which intervenes between the Eozoic Limestone of the Lower Laurentians of Canada, and the lowest strata in which the most ancient representatives of the Paleozoic fauna have as yet been 1 Appearances resembling Annelid burrows have been found in Laurentian rocks; but these cannot be safely relied on as evidence of the existence of Marine Worms at that epoch. | Indications of Eozoic structure have been found in various strata of uncertain age underlying the Silurians of North America, and also in some of the older rocks of the Scandinavian series; and there is no improbability in the idea that its existence may have been prolonged through the whole of that long period, commonly regarded as azoic, which has been designated by Prof. Dana as Archæan. In the earliest strata usually accounted fossiliferous there are found, alike in the old and new continents, a number of curious organisms, sometimes of considerable size, which have received the names Archæocyathus, Stromatopora, and Receptaculites. The nature of these is still problematical, their internal structure not having yet been fully eluci dated; but while it seems probable, on the one hand, that among the organisms whose similarity of external conformation has led to their association under these names, there may be several types of structure essentially different, there seems considerable reason to believe that some among them are really gigantic Foraminifera, presenting approximations to calcareous Sponges. The Limestones of the Silurian period have not been as yet minutely searched for the smaller forms of Foraminifera; but green sands of Silurian age occur in various localities, the grains of which can be identified as "internal casts" of Foraminiferal shells. It is in the Carboniferous Limestone that we first recognize a varied and abundant Foraminiferal fauna, which has recently been made the subject of special study by Mr H. B. Brady, whose very interesting results may be summed up as follows. (1) Of the "imperforate" or "6 porcellanous" Foraminifera no examples have been detected. (2) Of the "perforate" or "vitreous" series, on the other hand, each principal group is represented: the Lagenida very slightly; the Globigerinida by Textularia and various Rotalian types; while of the Nummulinida we find, not only three generic forms that are at the same time individually small and scantily diffused, but (in certain localities) such an accumulation of comparatively large shells of Fusulina (fig. 20), that they constitute almost the sole material of calcareous beds extending over large areas. (3) A large proportion of the foraminiferal types of this period belong to that "arenaceous" group which at present contains not merely the Lituolida, whose "tests" are entirely made up of cemented sand-grains (among which "The discovery of organic remains in the crystalline limestones of the ancient gneiss of Canada," says Prof. Gümbel, the accomplished director of the Geological Survey of Bavaria, "for which we are indebted to the researches of Sir William Logan and his colleagues, and to the careful microscopic investigations of Drs Dawson and Carpenter, must be regarded as opening a new era in geological science." Monograph of the Carboniferous and Permian Foraminifera, published by the Palæontographical Society, 1876. the Saccamina, fig. 5, a, b, is distinctiy recognizable), but | metamorphism. Now, since it is here that we also find also a number of generic types more or less allied to the the most extensive development of Fusulina-limestone in recent Valvulina, in which there is a "vitreous" shelly the place of those sub-crystalline beds which elsewhere basis, more or less thickly incrusted by an arenaceous form the great bulk of the Carboniferous Limestone, there envelope. The " isomorphism" of these with true "nodo- seems exactly the same reason for regarding such a Forasarines" and "rotalines" suggests the question whether miniferal deposit as the original form of those beds. And they are not really in an evolutionary stage between the this view derives remarkable confirmation from the phenorue sandy-tested and the completely calcareous-shelled mena presented by the Carboniferous Limestone of Ireland, types. which has been recently studied with great care by Prof. Hull This formation extends over a very considerable area of the island, constituting in its central portion an elevated plateau, whose nearly horizontal strata present no indication of lateral thrust, whilst along the margin of this area the calcareous strata have been elevated into ridges by thrust from the outside, with more or less of plication and contortion. Now, in these marginal ridges the traces of organic origin are scanty,-the presence of fossils, whether large or minute, being the exception and not the rule. In the level strata of the central plateau, on the other hand, the evidence of organic origin is almost everywhere complete; and whilst fossil Corals, Mollusks, Crinoids, &c., are abundant in particular beds, great masses of the limestone are found by microscopic examination to consist of little else than minute Foraminiferal shells. A very strong case, then, seems made out for the belief that Foraminiferal life has contributed very largely to the production of those vast beds of Carboniferous Limestone (often exceeding 1500 feet in thickness) in which scarcely any trace of organic origin can now be found,-this share bearing to that of the Corals, which are generally credited with the whole, somewhat of the same proportion that the Foraminiferal ooze of the deep-sea-bottom at the present time does to the Coral reefs of shallow waters, and the shells of Mollusks and Echinidans that live among them. But there is a larger question even than this, namely, whether those massive beds of Carboniferous Limestone whose texture is sub-crystalline, and in which scarcely any traces of organic structure are now discernible, do not owe their origin, like analogous beds of the Cretaceous forma tion, to Foraminiferal life. The general tendency of recent geological opinion has been to account for the absence of all traces of organic structure in such beds by the "metamorphism" they have undergone subsequently to their original deposition. Of the completeness with which such metamorphism may obliterate the evidence of organic origin in calcareous rocks it is impossible to have more "pregnant instances" than those afforded by the purely crystalline marble of Carrara, which is unquestionably a metamorphic Oolite, and the crystalline conversion of the Antrim Chalk in the neighbourhood of the basaltic outburst which forms the Giant's Causeway. The abundance of Corals, however, in various beds of Carboniferous Limestone, accompanied by such accumulations of Brachiopods, Crinoids, &c., as might have been associated with them on coral reefs, taken in connexion with the fact that the substance of existing reef-building corals, when raised by upheaval, sometimes exhibits a metamorphism that causes it to bear a close resemblance to carboniferous limestone, has seemed to favour the belief that the azoio sub-crystalline bors of that formation had their origin in Coral growths. Against this, however, it may be urged that we have at the present time no continuity of Coral-growth over areas that are at all comparable to those which we find continuously covered with Carboniferous Limestone; that the real parallel to these is presented by the continuous beds of Chalk formerly deposited over vast marine areas, by those of the Nummulitic Limestone of the succeeding period, and by those of Globigerina-ooze still in progress of production; and that, if the tropical sea-bottom were now elevated into dry land, we should find over the deeper areas a continuous Foraminiferal deposit, interrupted in particular localities by upheaved reefs of Coral, whose slopes would be covered with calcareous-shelled Mollusks, Echinoderms, &c., bearing a general correspondence with the great Carboniferous Lime stone formation. In the earlier Secondary rocks we do not find by any means the same evidence of abundant Foraminiferal life; but this is very probably to be accounted for by the conditions of their deposition. For during the Triassic period we find no representative of a deep oceanic calcareous deposit,—the only considerable limestone bed (the muschelkalk) being obviously composed of the remains of the more developed fauna of comparatively shallow water. It is interesting, however, to find certain clay beds of the New Red Sandstone yielding Foraminifera, chiefly of the Cristellarian type, which can be identified-not only generically and specifically, but even varietally-with forms common in the Italian Tertiaries, and still living in the Mediter ranean. In many of the Liassic clays Foraminifera are found in great abundance; and here the "porcellanous" group first characteristically shows itself under one of its Moreover, it has now come to be generally admitted that least modified types, the Spiroloculina. In the formation "metamorphism" is connected with mechanical disturbance, of many Oolitic Limestones it seems probable that Forami and especially with that "lateral thrust" which is the prin-nifera had a considerable share. For while the material of cipal source of the plication and contortion of strata, and which must have given rise to the evolution of great heat. That such a change was extensively produced in the Carboniferous rocks of Great Britain at the end of the Paleozoic period, when the horizontal and continuous Coal-fera, that we seem justified in regarding those beds as measures were thus broken up into separate basins," bordered by intervening ridges formed by the uplifting of their subjacent limestone, is universally recognized. But, on the other hand, over the vast area of Russia that lies between the Baltic and the Ural mountains, there seems to have been no such force in action. Its strata are so nearly level that the determination of their order of superposition has been difficult. And there is such a remarkable absence of metamorphism even in those of Silurian age that we there find what are elsewhere slates represented by beds of clay, constituting the original form of that deposit which has elsewhere acquired the slaty character by subsequent many of the calcareous beds belonging to this formation was obviously furnished by debris of Corals, Echinoderms, and Mollusks, the nuclei of the component grains of the true Oolitic beds are so often found to be minute Foramini. having been formed by a sub-aerial metamorphosis of shore sands largely composed of the minute shells belonging to that group, like many tropical shore-sands of the present time. It was by the comparative study of specimens of Chall brought from different localities that Professor Ehrenberg was first led to the conclusion that this vast formation was mainly produced by the progressive accumulation and subsequent disintegration of the minute shells of various 1 Physical Geography and Geology of Ireland, 1878. Ueber die Bildung der Kreidefelsen und des Kreidemergels durch unsichtbare Organismen," Berlin, 1888. |