2 MM. Cuvier a>id Brongniart on 



1. On the Calcaire Grossier of Paris*. 



The calcaire grossier does not always rest immediately on 

 the (plastic) clay, being often separated from it by a bed of 

 sand. We cannot state whether this sand belongs to the for- 

 mation of the limestone or that of the clay. We have not, 

 it is true, found fossil shells in it, in the few places where we 

 have observed it, — which circumstance would seem to refer it 

 to the (plastic) clay formation ; but as the lowest calcareous 

 bed usually contains sand, and as it is always full of shells, we 

 do not yet know whether this sand differs from the former, or 

 belongs to the same deposit. We may be led to suppose it 

 different, since the sand of the clay that we have seen is in 

 general tolerably pure, though of a red or blueish-gray colour; 

 it is refractory (r^r«c^«/re), and often very-large-grained. This 

 sand sometimes contains masses or beds of tolerably pure and 

 solid sandstone. 



The calcaire grossier, after quitting this sand or sandstone, 

 is composed of alternating beds of coarse limestone more or 

 less hard; of argillaceous marl, often in very thin beds, and of 

 calcareous marl : it must not however be supposed that these 

 various beds occur without order ; they are always found in 

 the same order of superposition throughout the considerable 

 extent of country that we have examined. Many of them are 

 occasionally either wanting or very thin; but that bed which 

 is inferior in one district is never superior in another. 



This constancy in the superposition of even the thinnest 

 beds, over an extent of at least twelve myriameters, is, in our 



* From the Description Geologique des Environs de Paris, by Baron 

 G. Cuvier, and M. Alex. Brongniart. 



"This rock, the equivalent of our London clay, forms such an important 

 part of the superior or tertiary rocks, that the excellent general account 

 here given of its mode of occurrence, and of its characteristic fossils, be- 

 comes highly valuable. We should indeed expect very considerable modifi- 

 cations in these respects, in such a comparatively modern rock, at points 

 distant from each other; and we do accordingly find them, more particularly 

 in its mineral composition, as for instance, in the case of the London clay; 

 yet keeping in mind the more essential characteristics here detailed, we 

 are enabled to recognise strata, formed at the same geological epoch with 

 this, amid the superior or tertiary rocks of other countries. This has al- 

 ready been done not only in our own country, but also in Switzerland, 

 Italy, the Netherlands, Austria, Hungary, Poland, &c. It is also stated to 

 exist in the north of Africa. Humboldt {Essai sur le Gisemcnt des Roches) 

 ■ considers some of the rocks of Equinoctial America as equivalent to this 

 formation. However this may be, it is certain that tertiary rocks are not 

 wanting in the West Indian Islands ; and I have myself observed them oc- 

 cupying a considerable extent of country, and of great thickness, in Ja- 

 maica," — Trans. 



estimation, 



