276 MINERALOGY OF THE ENVIRONS OP PARIS. 



Of these petrifactions, the most characteristic is the 

 eerites. 



Third System of Strata.* . 



The third system of strata is already less abundant in 

 petrifactions, and contains fewer species than the two 

 preceding. The following have been observed. 



Miliolites Very rare. 

 Cardium Lima, et obliquum, 

 Lucina saxorum. 

 Ampullaria spirata. 



Cerithium tuberculatum. } . 



... I Almost all the other species, 



mutabile. 



... > with exception of the gi- 



lapidum. 1 



\ ganteum. 

 petncolum. 



Corbula anatina ? 



striata. 

 Also impressions of the leaves of a fucus. 



The strata of the second and third systems sometimes 

 contain beds of sandstone, or masses of hornstone filled 

 with marine shells. Tn some cases the sandstone takes 

 the place of the limestone. Land shells and fresh-water 

 shells (Limncea et Cyclostomce) have also been observed in 

 this sandstone. The sandstone and the hornstone, con- 

 taining marine shells, rest either immediately on the ma- 

 rine limestone, or are contained in it. The following 

 list contains the names of those species of petrifactions 

 which occur most frequently in the sandstone. 



Calyptraea trochiformis ? 

 Oliva laumontiana. 



* This is the limestone used for building at Paris. 



