Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/206

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Mr. Webster on the Strata lying over the Chalk.

Other beds of sand succeed, and on the top there is a stratum of dark blue clay a few feet thick.

This bed, which is frequently referred to by Woodward in his history of fossils, has also excited the particular attention of Mr. Parkinson: but its fossils differ so much from those usually found in the London clay, that it is not easy to decide upon the place to which it ought to be referred; particularly since it is not even covered by a bed that can be identified with the London clay. Bivalves, resembling those of Woolwich, have been brought up in digging wells at other places on the banks of the Thames, but I am not aware that cerithia and the other fossils of this stratum have been so found. This bed is known to extend for a considerable distance on the south of the Thames, in the counties of Kent and Surrey. It is found at Bexley and Plumstead, at which latter place a thin stratum of minute fossil shells was laid open a few years ago, but which now appears to be lost.

At Bromley, which is not far above the chalk, vast quantities of oysters are found imbedded in a calcareous cement and forming, together with rounded pebbles, a sort of rock. It has been observed that these oysters are found adhering to the pebbles, indicating the formation of the latter previous to the growth of the former.

Woodward, in his catalogue, frequently mentions a bed of stone as occurring at Stifford in Essex, and containing fossil shells which agree with those at Woolwich and Bexley. In a late visit which I made to that part of the country for the purpose of ascertaining this fact, I was not fortunate enough to procure specimens of the rock. It is not indeed new to be seen where it is described by that author, being probably concealed by cultivated ground: but I learned that a stone did exist under the soil, which the labourers frequently came to in ditching, and I mention this in the hope that some one residing in that neighbourhood may examine into this matter.