174 FOSSIL REPTILES. 



jaw-bone of castor. These molasse and lignites are said to 

 be invariably lower than the coarse limestone ; but though this 

 point were as well established as it appears to be doubtful ; 

 though it were true, that the molasse and lignites of two dif- 

 ferent eras had not been confounded together, still it must be 

 remembered that the strata resting on the chalk are universally 

 allowed to be the most ancient in which the debris of mam- 

 mifera are observed ; that the chalk itself positively contains 

 none, and still less can they be supposed to exist in strata 

 of an anterior state ; while, on the other hand, the chalk, and 

 most part of these anterior strata, even to the great pit-coal 

 formation, abound, in certain places, with tortoises, lizards, and 

 crocodiles, species which are very rare in the superficial 

 strata. 



We now come to the consideration of another age of the 

 world, an age in which the earth was inhabited only by the 

 cold-blooded reptiles, and in which the sea abounded in 

 ammonites, belemnites, terebratulse, and encrinites, and in 

 which all these genera, now of such prodigious rarity, con- 

 stituted the basis of its population. This age is termed by 

 geologists that of the secondary strata. 



We shall begin with the crocodiles, in our review of the 

 remains of reptiles. 



Fossil Crocodiles. 



The bones of crocodiles are more abundant than those of 

 other reptiles, and more easily recognized. They exist in a 

 great number of strata, both in those of a comparatively middle 

 antiquity, as in the gypsum of Montmartre, or those of an an- 

 tiquity more remote, such as the limestone of the neighbour- 

 hood of Caen, from which the frieze-stones are taken, and the 

 blue calcareous marl of the environs of Honfleur. 



It will be necessary, before we proceed to the consideration 

 of their fossil remains, to say a word or two concerning the 

 distinctive characters of the existing species of crocodiles, and 



