MARINE LIMESTONE FORMATION. 277 



Ancilla canalifera. 

 Voluta harpula. 

 Fusis bulbiformis. 

 Cerithium serratum. 



tuberculosum. 



coronatum. 



lapidum. 



mtitabile. 

 Ampullaria acuta, or spirati. 



patula. 



Nucula deltoidea. 

 Cardiura lima. 

 Venericardia imbricata. 

 Cytherea nitidula. 



elegans. 



teilinaria. 

 Venus callosa ? 

 Lucina circinaria. 

 saxorum. 



Two species of oyster still undetermined ; the one ap- 

 pears allied to ostrea deltoidea, the other to ostrea cym- 

 bula. 



Fourth System of Strata. 



This set of strata consists of hard calcarious marl, soft 

 calcarious marl, clayey marl, and calcarious sand, which 

 is sometimes agglutinated, and contains horizontal layers 

 of hornstone, crystals of quarte, and rhomboidal crystals 

 of calcarious spar, and small cubical crystals of fluor spar. 

 Petrifactions occur very rarely. 



FOURTH FORMATION. 



Siliceous Limestone without Shells. 

 This formation occurs alongside the coarse marine 

 limestone, on the same level with it, and in no instance 



