Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/228

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Mr. Webster on the Strata lying over the Chalk.

there, and consequently the last marine deposits would be placed immediately upon the lower ones, and would be less easily distinguished, as is frequently the case in the basin of Paris, where we are informed that the sandstone without shells, which is over the marls belonging to this formation, is placed immediately upon the siliceous limestone of the lower marine formation, on the heights to the east of Melun and of Samoineau; the gypsum being wanting there. But as it forms the summits of almost all the bills and plateaux where the gypsum beds are found, they form a separation between the upper and lower marine strata, and render their distinction no longer uncertain. In the counties of Suffolk and Norfolk, there are very extensive beds of marine shells, imbedded chiefly in a ferruginous sand, and lying above the London clay, which have been described under the name of Crag pits. Among the fossils which have been enumerated as belonging to these beds, many agree with those in the upper marine formation in the Paris basin, and others do not appear to differ from the recent shells of the neighbouring seas.

Fossil shells agreeing with the recent occur also in many other parts of the kingdom, now considerably removed from the sea, and are often buried under beds of gravel. These probably belong to the last states of the earth, and might; serve as a clue to unravel geological mysteries.

If we depend upon fossils as a principal means of identifying strata, we shall see great reason to believe that the last of our marine depositions are nearly allied to the upper marine formation of the basin of Paris.

In this stratum in the Isle of Wight I found the following fossils.