Out of two hundred and ninety species of shells from the faluns Mr Lyell says he found seventy-two identical with recent species, and that out of the whole three hundred and two in his possession forty-five only were found to be common to the suffolk crag. Nevertheless a similarity of mineral composition, and the general analogy of the fossil shells and zoophytes, together with the perfect identity of certain species, strongly justifies the opinion that has long been pronounced, that the faluns of Touraine, and the Suffolk crag are nearly contemporaneous.
To this brief outline of what may properly be termed the regular stratifications of Touraine, it only remains to be stated, that they are frequently concealed by considerable deposits of alluvial and diluvian beds of flinty gravel, sand, and adventitious clays, in some of which numerous specimens of the rocks and fossils to be found existing in situ in the neighbourhood are interspersed.
It is almost impossible to contemplate even the comparatively scanty catalogue of geological facts just adverted to, without being forcibly reminded of the remarkable physical transformations which the surface of the country must have undergone, at distinct, and incalculably distant epochs; and to speculate on the causes which effected; and the peculiar circumstances characterizing those revolutionizing periods.
Geology, may indeed, be truly said to be an inductive science, and while pondering over its natural inferences we find ourselves most marvellously progressing through a long concatenation of pre-existing realities, which at every remove may be said to assume more and more the features of romance!
During the cretaceous period, Touraine had not emerged from the Ocean, which here was probably studded with Islands constituted of the primary rocks of Brittany, and those of the older secondary formations we have noticed as now principally occupying the more southern provinces. These lands, we may reasonably infer, were adorned by the luxuriant vegetation of a tropical climate, the fossil remains of which, are found abundantly dispersed throughout the first formed members of the tertiary series.
Subsequent to the deposition of the chalk, a retiring of the sea from this region, and a period of repose, are indicated by the presence of the freshwater formation, but on examining the overlying deposits of faluns, we have the most indubitable evidence, that this quiescent state, was succeeded by another irruption of the Ocean, which desolated the land, and deposited the wrecks of its animal and vegetable productions as now discovered in that formation. As yet, the geologian maintains, man had not been called into existence, and therefore the huge quadrupeds whose remains are found in the faluns, unmolestedly ranged through the umbrageous wilds of nature absolute Lords of the creation.
While the imagination is startled at the mystic nature of these successive cosmological revolutions, it is no less puzzled to account for the mighty causes which have effected them. The geologist however has discovered in various parts of the world, the most positive evidence of the upheaving and subsidence of immense tracts of territory, by the stupendous operations of subterranean convulsions.
At Alum Bay in the Isle of Wight we have an extraordinary and complete example of this description; in the remarkable vertical position of the beautiful and variously coloured arenose stratifications of the plastic clay, we are enabled to discover that the ponderous substrata of chalk were uplifted subsequently to the deposition of the tertiary formation. And it would not be unreasonable to believe that the same, or a similar convulsion, finally raised the lands of Touraine to their present elevation above the level of the sea.
We have however in this country, as in almost every other part of the globe, the most striking proofs of the mighty modifying operations of the last grand cataclysm, the erosive power of whose turbulent waters have denudated or scooped out deep vallies, frequently leaving—as instanced in the faluns detached and widely scattered masses of pre-existing formations, and heaping up their debris in the vast and variously shaped accumulations designated as diluvial deposits.
These popular speculations have been touched upon rather with the view of exciting the attention of the curious, and inviting the disquisitions of the able student of nature, than a desire to attach any absolute importance to existing theories; for in a progressive science like geology, new and amazing facts are continually being developed, and it is only when an immensely increased accumulation of such existing evidences has been thoroughly scrutinized by the penetrating and comprehensive genius of a Newton in geology, that we can hope to arrive at any thing approaching a correct explication of its remarkable and interesting phenomena.