Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/219

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209
Mr. Webster on the Strata lying over the Chalk.

the same quality, which appears to be owing to calcareous spar cementing the parts together. In our blue clay there is a considerable quantity of carbonat of lime in a sparry state, as is evident from the septaria.

The middle and upper beds of the French calcaire grossier frequently contain a sandstone, with marine shells which agree, though not entirely, with those of the calcaire. This sandstone is sometimes white and friable, and sometimes shining and almost translucent. The shells are frequently white, calcareous, and well preserved, though sometimes broken and mixed with pebbles.

The sandstone which forms the uppermost beds of the rocks of Bognor, already described, do not differ much from this description. It contains some fossil shells of the same species, though not in such numbers as the lower beds; and some of those in the lower beds, as the pinnæ, are not met with in the upper beds; the shells also are frequently whitened.

By connecting all the above circumstances it would appear, that if we could suppose a blending or mixture between the French plastic clay, which is blackish and contains organic bodies, and the lower beds of the calcaire grossier with its green earth and fossils, we should have a compound agreeing sufficiently near with our London clay under all its varieties; with this difference, that that of the French basin would have a greater proportion of calcareous, and ours of argillaceous matter. We may therefore fairly infer that they belong to the same epoch. But with respect to the upper beds of the calcaire grossier of France, no strata have yet been discovered in this country that correspond to them. Whether any such ever existed, and whether any traces yet remain, may perhaps prove a fit subject for future enquiry.


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