Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/218

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Mr. Webster on the Strata lying over the Chalk.

These beds of Liancourt contain also masses of sandy limestone filled with chlorite: and Stubbington is remarkable for the quantity of green earth which it contains.

A circumstance is mentioned by the French authors which appears to point out a remarkable era in the history of these strata. They observe, that in the beds of the lower marine formation, and particularly in those of Liancourt, natural wells of considerable size are sometimes found, filled with ferruginous and sandy clay and water-worn siliceous pebbles. These wells do not pierce through all the beds of the calcaire grossier; but begin at the same level, and are covered and closed by the uppermost beds: shewing that they were formed after the period of the formation of the lowest, and before that of the upper beds; which points out a very long interval, and the action of violent causes during this time.

It may be remarked, that this is exactly the period to which we must look for the subversion of the strata of the Isle of Wight, and the formation of its basin. If therefore the deposition of the upper beds of the calcaire grossier was general, and extended to this part of the globe, it must be placed at the lowest part of the Isle of Wight basin, and probably therefore at an inaccessible depth.

The rocks of Bognor and Selsea appear to be the most easily referable to some of the beds of the calcaire grossier of France. The correspondence in their geognostic situation, in the nature of their materials, and in the fossils which they contain, sufficiently justify the supposition.

Although in general the beds of the calcaire grossier maintain a regularity remarkable and distinctly to be traced, yet that is not always the case, the quarries of Saillancourt being cited as an exception to this rule: all the beds are there united, and nearly of