Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/238

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Mr. Webster on the Strata lying over the Chalk.

are not subdivided into distinct beds, are parts of extreme compactness, so as to acquire a porcellanous character. Other parts contain masses of loose chalky matter, most of which are of a roundish form; and among these also are many beds of a calcareous matter, extremely dense, and much resembling those incrustations that have been formed by deposition from water on the walls of ancient buildings in Italy.

Through all these last strata are veins, frequently several inches in thickness, of very pure carbonate of lime, which is crystallized, frequently in a radiated form.

This stratum may be seen in many parts of the Isle of Wight, north of the middle range of chalk hills. On the western coast it does not extend farther than Totland bay, but occurs again at Warden point, forming the summit of the cliff.

Numerous blocks of it lie loose in the soil in many parts about Cowes, Binstead, and Bembridge. But in the neighbourhood of Calbourne, and between that place and Thorley, several quarries are opened in it, and afford an excellent stone. The fossil shells are here larger than I have observed them in any other part, the planorbes being full two inches in diameter, and the cyclostomæ nearly as large. The rocks at Bembridge ledge and Whitecliff bay, on the east side of the island, must also be referred to this formation.

It appears therefore to have originally extended over the whole of the northern half of the island; but I have not yet been able to find it on this side of the water, and it is still uncertain whether it ever existed here, or whether it has disappeared amidst the last revolutions to which the surface of the earth has been subjected.

This formation may be considered as the latest in this country which we have as yet been able to detect: and of all those above