Mr. Webstetl on the Strata lying over the Chalk, 249 



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 col- 

 lections of freshwater in the ancient v^rorld we have however abund- 

 ant 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 marie 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 sub- 

 sequently 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 j and finally, grey fullers' earth mixed 



Vol. II. 2 I 



