274 MINERALOGY OP THE ENVIRONS OF PARIS* 



THIRD FORMATION.- 



Marine Origin. 



Coarse Marine Limestone, with its Marine Sandstone. 

 This formation presents much greater variety than the 

 chalk. Several different strata, or series of strata, sucli 

 as limestone, clay-marl, limestone-marl, slate-clay, occur 

 in it. These are arranged in a determinate order, and 

 the strata of limestone are well characterized by their ge- 

 ognostic characters and by the petrifactions they contain ; 

 the same system of strata always possessing the same gene- 

 ral characters and species of petrifactions. 



First System of Strata. 



The lowest system of strata, or first system of strata, of 

 the coarse limestone formation, is very sandy, and some- 

 times contains a substance resembling green earth ; it is 

 still better characterized by containing a great variety of 

 well preserved shells, many of which still retain the 

 pearly lustre, and differ more from the present existing 

 species, than those in the upper strata of this formation. It 

 is particularly characterized by the nummulites it con* 

 tains. 



The following are the petrifactions enumerated byCu- 

 vier and Brongniart, as occurring in it. 



Nummulites lasvigata } 



, f These are always found in 



numismalis $ the lowest part of the bed. 

 Madrepora At least three species. 

 Astraea Three species at least. 

 Carophyllia Three simple, and one branched species. 

 Fungites. 



