FOSSIL MAMMALIA. 25 



readers here, that both these formations, agreeing in their cha- 

 racter of uncompactness, but differing in their antiquity, are 

 alike termed loose, or alluvial^ by Cuvier and other geologists. 

 We do not altogether deviate from this usage in our subse- 

 quent account of the fossil species ; but when we use the term 

 alluvial, in relation to organic debris, we must be understood 

 to mean the diluvial formations. 



Between this diluvium and the chalk formation are strata 

 alternately filled with fresh and salt water productions. These 

 mark the irruptions and retreats of the sea to which our por- 

 tion of the globe has been subjected, subsequently to the for- 

 mation of the chalk. First come marly beds, and cavernose 

 silex, similar to those of our ponds and morasses. Under 

 these are marie again, sandstone, and limestone, containing 

 nothing but marine productions. 



At a greater depth we find fresh-water strata, of an era more 

 remote. Among these are reckoned the celebrated plaster- 

 quarries in the neighbourhood of Paris, where the remains of 

 entire genera of terrestrial animals have been found, which 

 exist no longer. 



These last-mentioned strata rest on beds of calcareous stone, 

 in which an immense number of sea-water shells have been 

 collected, the great majority of which belong to species un- 

 known in the existing seas. In this formation are also found 

 the bones of fishes, cetacea, and other marine mammalia. 



Under this marine limestone we have again another fresh- 

 water stratum, composed of argilla, in which are interposed 

 considerable beds of lignite, or that species of coal which is of 

 a more recent origin than our pit-coal. Here are found shells 

 only of the fresh water, and bones among them, not of mammi- 

 ferous animals, but of reptiles. It is filled with crocodiles and 

 tortoises, &c., whereas the mammiferous genera contained in the 

 gypsum are not seen there. They did not yet exist in the coun- 

 try when the argilla and hgnites were in a course of formation. 



This last fresh-water formation, which supports all the 



