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ground down into sand, and in other places the strata are purely chalky or marly. But the vagueness of the limitations of strata in situation, and still more in time, may be estimated by the fact that we are fully justified in speaking of the chalk formation now going on, as is shown by the investigations of Carpenter and W. Thompson on the constitution of the deep seabottom of the Atlantic. To the early chalk period belongs a great fresh-water deposit, and likewise the Wealden, a formation of peat and bog occasioned by upheavals, which contains a number of remains of freshwater and terrestrial animals, besides a peculiar sort of coal.
The oolitic strata appear more definite, mostly lying regularly over each other in distinct deposits, more rarely, as in the Alps, raised up by later dislocations. The rocks themselves, betray that the depositions took place in wide seas, for the most part calm or deep, and this is rendered a certainty by the scanty vegetal remains and the far more abundant animal remains which they contain. In the apparently very sharp limitation of the oolitic formation, both above and below, the older geology found a main prop for the assertion, that comparatively quiet periods of long duration alternated with catastrophes destroying and re-creating everything. To avoid any misapprehension we must, however, add that the oolitic period already possessed vast and highly integrated continents, as it will likewise be seen that during this era the higher terrestrial animals made their appearance.
The characters shown by the three great divisions of the triassic formation are very various, especially as
they are developed in Germany. The German portion, judging by its influxes, must be regarded as a formation of strands and bays; its more highly integrated equivalent in the Alps as a huge oceanic deposit. The Muschelkalk (which is missing in England), with its layers of rock salt and rich remains of oceanic organisms, is likewise a marine formation. Of the origin of the stratified variegated sandstone, so-called from its varied colouring, with its clays, marls, and frequent vast enclosures of gypsum, we obtain some idea from our present formations of sandy shores and dunes. Like these, the deposition of the variegated sandstone afforded but scanty opportunities of enclosing animal and vegetal remains, but very notable footprints have been preserved, such as might now be formed and preserved, if the marks imprinted on the damp sand were filled up with fine clayey particles torn by a storm from some adjacent shore, and subdivided in the sea.
As the diversified appearance of the superimposed planes of antediluvian plants and animals of course depends essentially on the nature of their former abodes, and as the nature of the individual districts of each plane must then, as now, have influenced the character of the organisms by which it was inhabited, we will indicate the causes which thus affect life in its form and manifold variety. In order to complete our view of the origin of the Earth's crust, and the dependence of the organic on the configuration of the inorganic world, we will leave a geologist, Credner, to describe the relations of the dyassic and carboniferous formations: "In regions where the carboniferous (coal) formation is typically developed, it consists of a series of stratifications, the
lower one chalky (mountain limestone), the middle one conglomerated or arenaceous (millstone grit), and the upper one carboniferous (coal measures); hence a marine, a littoral and a marsh or fresh-water formation. It is easy to imagine the cause of this phenomenon; it depends on the secular elevation of the primæval sea bottom, on which was deposited first the marine mountain limestone; secondly, as it rose to the surface, the shingle and coarse sand of the shore; and finally, on persistent elevation, the products of marshes, lagunes, and estuaries. If it now happened that some portions of the infant continent covered with the latter (that is
say, with the productive carboniferous strata), were seized with an opposite movement, and therefore sank, there would be deposited on the surface now again gradually becoming the bed of the sca, precisely similar forms, only in inverse order to that which occurred during the period of elevation.
And, in fact, this phenomenon is exhibited by those portions of the earth's surface which shortly after the formation of the coal measures again sank below the sea. In Germany and England the productive coal measures are followed by a sandstone and conglomerate, therefore a littoral formation, exactly like the quartzose sandstone and millstone grit which underlies them; and above this a limestone, dolomite and gypsum formation, corresponding to the mountain limestone, the lowest member of the carboniferous system. On account of the division which is displayed in profound palæontological and petrographical diversities, the formation thus developed and composed is designated as the Dyas. The separate phases of this cycle of occur
rences, by which the carboniferous and Dyassic formations were evolved, are accordingly (reading from above downwards):
From this account it is also manifest that in cases of incomplete elevation, such as took place in North America, the formation of the middle period is either disturbed or totally omitted, and that it may depend on local causes and the duration of the oscillations if, as in the Russian Permian formations, corresponding to the German Dyas, the boundaries of the subdivisions are more or less obliterated.
The two series of strata beneath the mountain limestone, and reaching the depth of more than 3000 and 6000 metres, the Devonian and Silurian formations, are the lowest, and therefore the first which clearly bear the mark of their origin as marine deposits. Both
groups were formerly comprised under the name of Transition rocks, or Graywacke formation. In them. also sandy, clayey, and chalky rocks alternate with one another, already exhibiting modifications of a local nature, from which, towards the carboniferous period, issued the first beginnings of continental upheaval.
The granite, gneiss and slate, which as primary rocks, or primitive formations, originated before the Silurian rocks, are for the most part sediments of hot or very warm primæval seas, which have undergone manifold internal changes from pressure and heat. Till recently, they were likewise termed the Azoic group, as containing no vestiges of life, when the discovery of the Eozoon and its unlimited occurrence in the Laurentian strata of Canada, proved that the required conclusion to the series had actually taken place.
With this Eozoon we begin the enumeration of the antediluvian animals from below upwards. The remains of this creature consist of a more or less irregular system of chambers with cretaceous walls, of which the interior is filled with serpentine or pyroxene. It was attempted to deny the organic origin of this cretaceous testa, which may best be compared to the shells of the Foraminiferà: But renewed researches have substantiated that although in the great mass of the Eozoon rocks occurring in vast strata, metamorphosis has rendered it nearly, if not quite, impossible to recognize the true nature of the body, pieces here and there occur with the chambering so distinctly marked, and a tubular structure peculiar to the Foraminifera, which exclude any other interpretation than that of a living being resembling the low Foraminifera. This is of great significance, as the pro