Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/354

 to be shells strictly belonging to the subjacent stratum, but which having lain uppermost, became involved in the first or lowest deposition of the blue clay,

Immediately beneath the clay there is found a line of about three or four inches of the preceding shells imbedded in a mass of calcareous matter, the result of their disintegration. Beneath this are numerous alternating layers of shells, marl, and pebbles, for about twelve or fifteen feet. The shells are those which have been already mentioned; but are very rarely to be met with whole, and when entire are so brittle as to be extricated with much difficulty. In some of these layers scarcely any thing but the mere fragments of shells are to be found, and in others a calcareous powder only is left.

The pebbles are almost all of a roundish oval form, many of them being striped, but differing from those of the superior gravel stratum, in being seldom broken, in there being few large ramose masses, and in their not bearing any marks or traces of organization. Many of these pebbles are passing into a state of decomposition, whence they have in some degree the appearance of having been subjected to the action of tire: small fragments of shells are every where dispersed amongst them.

Beneath the pebbles is a stratum of light fawn-coloured send of about ten feet in depth, and immediately under this is the stratum of white sand, which is about five and thirty feet deep, and is here seen resting immediately on the chalk.

At Plumstead, about a mile distant in a south-eastern direction, there is a pit, in which the shells, about two years ago, were to obtained in a much better state of preservation than at New Charlton; but this seam of shells, as the pit has been dug further in, has by degrees become so narrow as to be now nearly lost. In this pit, not only the shells already mentioned were found, but many tolerably perfect