Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/179

From Wikisource
Jump to navigation Jump to search
This page has been validated.
169
Mr. Webster on the Strata lying over the Chalk.

with the vertical beds without suffering any considerable change in their dip, it should seem that they have been deposited on the sides of this basin subsequently to the disturbance of the strata already spoken of.

The above conclusions are confirmed by other circumstances.

These horizontal beds have no agreement with any of those beneath the chalk, nor indeed with any others yet observed in Great Britain; their mineralogical characters, and their fossils, are peculiar and distinctive. The calcareous beds contain numerous petrifactions[errata 1] of freshwater shells, and in others are found marine fossils agreeing with those described by Lamarck in the strata of the Paris basin. But fortunately, the inspection of specimens from the basin of Paris enabled me no longer to depend upon conjecture only as to the similarity of these formations. They had been given by M. Brongniart himself, in illustration of his memoir, to the Count de Bournon, who had deposited them in the museum of the Geological Society. The agreement of the strata of the two basins, not only with respect to the external characters of the calcaire d'eau douce, but also to its fossils, was thus rendered evident: and these specimens, so well authenticated, added one more proof (if more could be wanting) of the utility of such collections, and of the advantages to be derived from a liberal communication between men of science.

It is unnecessary to inform the Society that this circumstance produced another visit to the Isle of Wight and its vicinity, for the purpose of examining more particularly its basin, and the remains of its ancient lake. From this, compared with my former survey, I was enabled to add to the British strata the following, of later formation than the London clay.

  1. A calcareous stratum, containing only freshwater shells.
  2. Greenish marl, with marine shells.

Errata

  1. Original: petrefactions was amended to petrifactions: detail

Vol. II.Y