DIFFERENT FORMATIONS CONTEMPORARY. 31

SECTION III.

DIFFERENT FORMATIONS MAY BE CONTEMPORARY.

THE next circumstance to be considered is, whether all the sedimentary strata have been deposited one after the other from the primary starta onwards to the most recent tertiary beds, in a regular sequence of time, or whether several of the groups have not had a contemporaneous formation. There can be no doubt, but that some of the formations have been regularly deposited, one after the other, which is proved by their positions, line of stratification, and from some of the newer strata, containing fragments of the older; but, then, it cannot be so easily demonstrated that this has been the case with the whole. It cannot be proved, for instance, that the great carboniferus groups may not have been partly deposited during the period when the lias and oolite were in the process of formation; or that a contemporary deposition has not taken place among some of the other members of the newer formations.

As to position in England, and the corresponding portion of the continent of Europe, the boundaries of these respective strata can be traced by well defined lines of separation.

The great coal fields of Britain lie in hollow troughs or valleys, formed by the previous disturbance of the mountain limestone and older sedimen

tary strata on which they rest. These coal beds have most probably been accumulated by the action of rivers carrying down vegetable and earthy matter into the basins of estuaries. The lias and oolite again seem more strictly the production of littoral oceanic currents sweeping along the shallow shores. Yet, with some trifling exceptions, the latter formations are not superimposed upon those of the coal measures, but lie in distinct beds. We do not at present take into consideration the characteristic fossils of each, because this subject will be treated of afterwards.

We think it admits of demonstration, too, that the last great change on the British strata, by which they were finally elevated above the ocean, took place at one period, or, at least, at periods nearly contemporaneous.

Thus, if the northern coal fields of England and those of Scotland were elevated above the level of the sea, at a period long antecedent to the existence of the lias and oolite beds of the south-east of England, where are the traces on the surface of the

operations which must have taken place in the long period necessary for the production of the latter? We have no formation older than the carboniferous sandstone, from Newcastle to the Grampian moun→ tains of Scotland, with the exception of a few local patches of new red sandstone. The strata of the coal measures are seen tilted up to the surface; a few feet of diluvial gravel and clay are superimposed, but from the period when the matter forming the carboniferous series ceased to be deposited, till the commencement of the system of vegetation which at present exists on the surface, there are no geological records to mark the lapse of any considerable period of time.* That the superimposed diluvial matter was deposited at the period of the elevation of the sandstone rocks, and could not be of a more recent era, is also demonstrable from its containing the same coprolites as the shale of the inferior strata. These clay ironstone nodules are found among this diluvium in all parts of the country, and lying immediately above the tilted up strata of the carboniferous limestone, as well as the various beds of the coal measures; and though they are in composition exactly the same, and contain the same coprolites and portions of fishes and plants, yet many of them have a less compact structure, and are of a lighter ochrey appearance, than

* See Section and Note I.

those found in the shale,-a proof that they are not part of those latter broken up, and scattered by a more recent denudatory process, but originally from one common source, part having been enveloped in the shale and part in the diluvial detritus. It may be asserted, that denudation may have swept away any newer formations; but the sharp and unworn edges of the sandstone, the total absence of all traces of a newer formation, while the cracks and fissures of the strata are universally filled with the matter of the superimposed diluvium, in which are mingled portions of the trap rocks, which were the elevating agents indicate the total improbability of the existence of any such newer strata. To the north of the Grampians, again, where the coal series is wanting, we find small patches of the lias formation, accompanied by the new red sandstone, both lying immediately above the old red sandstone conglomerate. Now, as regards the older or primary strata, the south and north sides of the Grampians exhibit an exact similarity, the same central granitic ridge having elevated both at the same period; but on the south of the Tay and Frith of Forth, the carboniferous limestone and sandstone have been largely deposited, while on the north no such deposit has taken place; but instead of it is found a noncarboniferous sandstone in extensive beds, above which are traces of the lias limestone, with its peculiar fossils. Now, the question is, when was this

lias deposited, if not during some part of the era of the coal deposition?

If, then, the northern part of England became dry land at the same period as the south-western, the deposition of part at least of the carboniferous strata must have been contemporary with that of the lias and oolite.

If, on the other hand, the reverse be maintained, that while the south of England was dry land, the northern portions of the island were covered by the ocean, the same arguments apply. For either the deposition of the coal strata was going on contemporaneously with the formation of the oolitic beds, or some equivalent system of operations must have been apparent above the coal measures.