242 FOSSIL REPTILES. 



than the immense mass of chalk which rests upon them, and 

 much anterior to those which contain the bones of even the 

 most ancient quadrupeds^ such as the gypsum of Paris ; for 

 this gypsum rests upon the most common coquillaceous lime- 

 stone, which last rests upon the chalk. 



The substance of the bones is of a very deep brown, and 

 takes a fine polish. It is soluble in acids, and assumes a red- 

 dish tint, which shows that it is coloured by iron. It has, 

 however, preserved a portion of its animal nature. The great 

 cavities of the bones, as the box of the cranium, the canal of 

 the nostrils, and that of the vertebrae, are filled with the same 

 hard and greyish marie which envelopes their exterior. But the 

 pores, or small cells, are occupied by a calcareous demi-trans- 

 parent spath, sometimes tinted with yellow. Each cellule is 

 usually carpeted with pyrite, Avhich envelopes the spath with 

 a thin and brilliant bed. The interior of the shells found here 

 is also, sometimes, furnished with it ; and some are found 

 whose substance has been entirely replaced by the pyrite. 



The most considerable piece in the collection of which we 

 are now to speak, is a lower jaw almost complete. The arti- 

 cular extremity of the branches appears to be all that is 

 wanting. 



This jaw bears the most incontestable characters of the cro- 

 codile. The teeth are conical and striated. The majority are 

 broken, but some are entire, and the two trenchant ridges very 

 distinguishable. Many of those which are in their places show 

 in their cavities the little germ which was to replace them. 



The sutures which divide this jaw into six bones on each 

 side are easily distinguished. They are pretty nearly in the 

 same positions, and of the same form, as those which compose 

 the jaw of the gavial. Still, an attentive examination soon 

 leads to the discovery of characters which distinguish it very 

 clearly from the last-mentioned species. 



The branches are much longer in proportion than the ante- 

 rior or symphysized part, which they exceed by some thirds of 



