290 MINERALOGY OF THE ENVIRONS OF PARIS* 



Planorbis prevostinus. 

 Limneus corneus. 



fabulum. 



ventricosus. 



inflatus. 

 Bulimus pygmeus. 



terebra- 

 Pupa Defrancii. 

 Helix Lamani. 



Desmarestina. 



Dicotyledonous wood, petrified with silica. 

 Stems of arundo or tipha. 

 Articulated stems, resembling the thorn. 

 Peniculated ov.oidal grains. 

 Canaliculated cylindrical grains. 

 Olive-shaped bodies, with an irregular streaked surface- 



The potamides, helicites, and limneus corneus, are the 

 petrifactions that most frequently characterize this second 

 fresh water formation,, and the cyclostoma mumia has 

 never been found in it. The first or lowest fresh water 

 formation, on the contrary, has its characteristic petrifac- 

 tions, the cyclostoma mumia, and Limneus longiscatus, 

 and palludinus, but it never contains potamides, or heli- 

 cites. It is remarkable that no bivalve shells occur in 

 this formation, and that it contains numerous small round- 

 ish groved bodies named Gyrogonites, whicjh appear to 

 be the fruit of a marsh plant of the Chara tribe. 



This second fresh water formation extends for thirty 

 leagues to the south of Paris, and has also been met with 

 in the department of Cher, Alliere, Nievre, Cantal, Puy 

 de Dome, Tarn, Lot, and Garonne, in the southeast of 

 France, and more lately the same interesting formation 

 has been discovered in the Roman states^ in Tuscany, and 



