Ch. XVIII.] PARIS BASIN. 249 



action of denuding causes. At Valmondois, for example, a 

 deposit of the upper marine sandstone is found *, in which 

 rolled blocks of the calcaire grossier with its peculiar fossils, and 

 fragments of a limestone resembling the calcaire siliceux, occur. 

 These calcareous blocks are rolled and pierced by perforating 

 shells belonging to no less than fifteen distinct species, and they 

 are imbedded, as well as worn shells washed out from the cal- 

 caire grossier, with the ordinary fossils of the upper marine 

 sand. 



We have seen that the same earthquake in Cutch could raise 

 one part of the delta of the Indus and depress another, and 

 cause the river to cut a passage through the upraised strata and 

 carry down the materials removed from the new channel into 

 the sea. All these changes, therefore, might happen within a 

 short interval of time between the deposition of two sets of 

 strata in the same delta f- 



It is not improbable, then, that the same convulsions which 

 caused one part of the Paris basin to sink down so as to let in 

 the sea upon the area previously covered by gypsum and fresh- 

 water marl, may have lifted up the calcaire grossier and the 

 siliceous limestone, so that they might be acted upon by the 

 waves, and fragments of them swept down into the contiguous 

 sea, there to be drilled by boring testacea. 



It is observed that the older marine formation at Laon is 

 now raised 300 metres above the sea, whereas the upper marine 

 sands never attain half that elevation. Such may possibly 

 have been the relative altitude of the two groups when the 

 newest of them was deposited. 



Third fresh-water formation. We have still to consider 

 another formation, the third fresh-water group (No. 5 of the 

 preceding tables). It consists of marls interstratified with beds 

 of flint and layers of flinty nodules. One set of siliceous layers 

 is destitute of organic remains, the other replete with them. 



* M. Deshayes, Memoires de la Soc. d'Hist. Nat. de Paris, torn. i. p. 243. 

 The sandstone is called, by mistake, gres marin infericur, instead of supericur, to 

 which last the author has since ascertained it to belong. 



t Vol. i. 2d Edit. chap, xxiii, - 3 vol. il 1st Edit. chap. xvi. 



