FOSSIL REPTILES. 247 



species, is completely made out. This must be evident even 

 from the necessarily abridged account to which our limits con- 

 fine us. It is scarcely necessary, as the Baron remarks, to 

 reply to those who would explain the extraordinary differences 

 of those bones from those of the gavial, by the influence of age^ 

 of nutriment, of climate, or of the passage to a state of petri- 

 faction. Could all these causes united, continues this distin- 

 guished philosopher, place in front the convexity which the 

 other crocodiles have behind in the vertebrae ? Or could they 

 change the origin of the transverse apophyses, flatten the edges 

 of the orbits, diminish or augment the number of the teeth ? 

 As well might it be said that all our living species are derived 

 from one another. 



Having noticed the remains of the most ancient croco- 

 diles which belong to the formations called Jurassic, we must 

 now mention such as are a little more recent^ and appertain to 

 the age of the chalk. Crocodiles have been discovered in the 

 ferrugineous sands under the chalk in this country — in the 

 chalk at Meudon ; and immediately under the chalk in lignites 

 and plastic argile in several places. Unfortunately_, there have 

 not been collected specimens in a sufficient state of preserva- 

 tion to determine the species : all, therefore, that can be said 

 respecting them is reduced to mere indications. 



A tooth from the chalk of Meudon, in its form, curve, and 

 slight ridge on one side, much resembled that of the common 

 crocodiles. The individual from which it came might have 

 been twenty feet long. 



Our countryman^ Mr. Mantell, in his " Illustrations of the 

 Geology of Sussex," has described the fossil remains in the dif- 

 ferent strata of that county very minutely. He has given a very 

 particular account of those which are found in vast abundance 

 in the forest of Tilgate, near Horsham^ and has determined the 

 strata of which the soil of this forest is composed. These are such 

 as are immediately below the chalk formation. After the com- 

 mon chalk with silex, comes a lower chalk, without silex, then a 



