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-ivater 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 inferieur, instead of superieur, to 
which last the author has since ascertained it to belong. 
f Vol, i, 2d Edit, chap.xxiii.; vol. ii, 1st Edit. chap. xvi. 
