FOSSIL REPTILES. 251 



tracts inhabited by mammifera, previously to the invasion of 

 the sea, by which the cerithian limestone was formed. 



The crocodiles, however, give rise to no doubts of this 

 description. We see them appear in the very first secondary 

 strata. The monitors of the coppery schistus alone precede 

 them in point of time, but they show themselves immediately 

 after in the lias in this country, the banc bleu of Normandy, or 

 in the bluish and pyritous calcareous marie, which has so 

 much analogy with the coppery schistus. 



From then, until the epoch of the last catastrophe but one, 

 some species of them have always subsisted, and in consider- 

 able abundance. To those of the different strata of the Juras- 

 sic formation, succeed those of the chalk. There are some 

 above the chalk in the lignites of Auteuil and Mimet, and in 

 the sandstone of Kent. Above the cerithian limestone, which 

 the French call calcaire grossier, some are found in the marly 

 fresh-water formation of Argenton, and in the gypsum of Paris. 

 Finally, there even may be some in the loose and superficial 

 strata, in which so many remains of elephants and other 

 large quadrupeds are buried, if the small number of fragments 

 collected at Brentford were not brought there from some other 

 position. 



It must be confessed, however, that they are of exceeding 

 rarity in the last-mentioned depositions. None have been 

 seen in the immense collections of bones made from the 

 valley of the Arno, nor in those from any part of Germany or 

 France. This is the more extraordinary, as the crocodiles of 

 the present day live in the torrid Zone with the elephant, the 

 hippopotamus, and all the other genera which have furnished 

 those remains. Some few, indeed, are said to have been 

 recently found in the superficial strata of the Vale of Arno. 



