THEORY OF THE EARTH. 245 



or cavernous quartz, filled with fresh-water shells, 

 similar to those of our marshes and pools ; under 

 them marls, sandstones, and limestones, all the 

 shells of which are marine, such as oysters, &c. 



At a greater depth are found fresh water for- 

 mations of an older date, and particularly those 

 famous gypsum deposits of the neighbourhood of 

 Paris, which have afforded so much facility in or- 

 namenting the buildings of that great city, and 

 in which we have discovered whole genera of land- 

 animals, of which no traces had been elsewhere 

 perceived. 



They rest upon those not less remarkable beds 

 of limestone, of which our capital is built, in the 

 more or less compact texture of which the patience 

 and sagacity of our naturalists, and of several ar- 

 dent collectors, have already detected more than 

 800 species of shells, all of them marine, but the 

 greater part unknown in the presently-existing 

 sea. They also contain only bones of fishes, and 

 of cetacea and other marine mammifera. 



Under this marine limestone there is another 

 fresh water deposit, formed of clay, in which there 

 are interposed large beds of lignite (brown coal), 

 or that sort of fossil-coal which is of more recent 

 origin than the common or black coal. Among 

 shells, which are always of fresh water origin, there 

 are also found bones in the deposit ; but, what is 

 remarkable, bones of reptiles, and not of mammi- 



