Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/263

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253
Mr. Webster on the Strata lying over the Chalk.

But I shall now venture with less hesitation to draw an important conclusion from the section of the Isle of Wight, which has been already described, and which of itself forms a volume in which we may read the geological history of several of the latest revolutions which our earth has experienced.

The idea I allude to is, that the last freshwater formation, as well as all the other strata which we have been considering, is anterior to the great event which gave the last shape and surface to our land.

In the highly inclined and vertical positions of the strata of Alum bay, we see the effects of some great convulsion of nature, previous to the formation of the last strata.

In the horizontal deposits of the North side, we see strata of great extent and antiquity yet formed at a later period. But in the outline exhibited by the surface of the island, and which has no reference whatever to that of the strata, is plainly to be perceived the effect of a general and powerful agent, which has subsequently formed the whole of the contour by one bold and sweeping outline.

It may be interesting to see how the same result can be obtained by a careful survey of different portions of the globe.

Messrs. Cuvier and Brongniart have laid considerable stress on the observation, that the outline of the present surface has no resemblance whatever to the undulations of the strata derived from the irregularity of the bottom of the basin. But how much more striking is this in the Isle of Wight? By no ingenuity of reasoning can the present form of its surface be derived from the bottom of that ocean which deposited the chalk; nor would it be produced by any of the causes now acting; and nothing remains for us but to admit that it has been the effect of an extraordinary and an extensively acting cause.