and Marine Molmcce. 41 



4. It can be easily conceiyed why the gypsum masses of 

 all formations, though frequently subordinate to rocks full of 

 shells, should never contain any, since fresh-water moluscae 

 cannot exist in water charged with sulphate of lime. 



5, The absence of living organized bodies, in the asphal- 

 tic lake, if it be really true, cannot be attributed to thei 

 great proportion of muriate of soda, since marine moluscae 

 can live in water saturated with it ; — the cause ought rather 

 to be sought in the presence of the bitter muriates of lime 

 and magnesia, which are there in much greater abundance, 

 also perhaps, in that of bituminous substances. 



Q. It is not surprising that masses of rock salt never 

 contain fossil shells, since marine moluscas perish in salt- 

 water as soon as it is over saturated with muriate of soda.* 



7, Lastly, if it is admitted that marine and fresh-water 

 moluscae can, under certain circumstances, live in the same 

 liquid, inhabiting fresh or salt-water does not appear to be 

 a sufficient motive for establishing particular genera ; these 

 distinctions of genera can only be founded on essential and 

 constant difference in the shells, or, which is better, in the 

 animals that inhabit them, when they can be observed. 



* The author could have added another conclusion, from rock salt 

 being always or nearly always accompanied by gypsum ; from which it 

 cannot be doubted that the water that deposited the muriate of soda, wag 

 charged with sulphate of lime. (Note of the editor of the Annales d^s 

 Mines.) 



