Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/259

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249
Mr. Webster on the Strata lying over the Chalk.

phenomenon of strata formed in freshwater appearing over marine strata, I shall leave to be determined by those who are competent to such a task.

Of the unfathomable antiquity of these great and numerous collections of freshwater in the ancient world we have however abundant proofs, in the admirable researches of Cuvier on the extinct genera of animals which inhabited their borders.

It would perhaps be impossible for us now clearly to ascertain what could have furnished the prodigious quantity of calcareous, and still more the siliceous matter which they held completely in solution; in modern lakes we have examples of strata now forming of marle arising from the shells of the numerous freshwater animals which inhabit these shells, but these beds (as far as is yet known) are not consolidated.

Was a portion of the calcareous part of these ancient strata derived from the surrounding calcareous hills, which might have been lofty? If we examine the section of the Isle of Wight, the probability appears considerable, that the strata of chalk must have stood at a considerable height above the lake; although it has subsequently undergone the same levelling process, to which all the surface of the island has been subjected.

As connected with this subject, I shall quote a passage from Bergman's Physical Geography published in Swedish in 1769.

“At Langesaltza in Thuringia, they find under the vegetable earth a calcareous and porous tufa; in other parts a fine white sand mixed with river shells; below, a bed of hard stone, under which is a bank of porous stone or sand. Lower still they find a bed of hard stone, then tender stone and sand; afterwards peat formed of a mixture of leaves, barks of wood, roots, river shells, &c. Lower, yellow sand; and finally, grey fullers' earth mixed

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