Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/175

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165
Mr. Webster on the Strata lying over the Chalk.

that I have described on the north side of the island, under the chalk.

Several of them were composed of a calcareous rock, either of a loose or compact texture; and an attentive consideration of this section, together with those of the opposite coasts of Dorsetshire, Hampshire, and Sussex, convinced me that the date of their origin was posterior to that of the chalk.

No distinct limestone stratum had been hitherto observed above any part of the chalk in this country, although it was well known that such were frequent in France. That this is the real position of the limestones near Paris could not be doubted, since the chalk is always reached in sinking to great depths. But the geognostic place of the strata on the north side of the Isle of Wight, was more difficult to ascertain; and it was only from many combined considerations that I was led to the conclusion, that they might be found to agree with some of those lately described by Cuvier and Brongniart, as contained in the basin of Paris.

These considerations were the following:

The chalk of England, although it appears upon the surface only in detached hills and patches, is actually continuous through considerable tracts of country, where it exists at great depths, as is now ascertained by numerous wells and other sinkings. In the order of position, which the strata of the chalk itself, and those which lie above and below it, bear severally to one another, there has been observed in distant places a remarkable agreement. And although occasional varieties may be noticed, in consequence of the defect or redundancy of any one stratum, yet the law of the Wernerian school seems to hold good; viz. that the order of the beds is never inverted.

This agreement renders it extremely probable that the corresponding strata, found in different parts of the same country, arose from