CAEBOXLFEEOUS SYSTEM. 275 



four to twelve inches; it is generally, however, quite regular, 

 from five to eight inches thick, and very seldom entirely 

 absent ; though sometimes it is represented by a band of 

 rather compact lenticular masses of limestone, as is the case 

 on Mosquito creek, in Dallas county. The following species 

 of fossils occur in this bed: Crinoidal remains, Productus 

 muricatus. P. longispinus,very rare; P. aquico status, Chonetes 



mesoloba, Hemipronites crassus, (?), Distinct , Atliyris, 



subtilita, Martinia planoconxexa, M. lineata, Spirt ferina 



Kentuckensis, RJiynclionella, , Pernopecten, (?) , 



Aviculopecten rectilateraria, , , 



Better oplion carbonaria, B. , B. , Euomplialus, 



(sp. undet,), Pleurotomaria , P. , Orthoceras, 



, Nautilus . 



No. 11. Brown, rotten shales at base, overlaid by bluish, 

 gritty shales, eight feet. Local deposit, Mosquito creek. 



No. 12. Dark, indurated calcareous shales. Six to 

 eighteen inches. A locally developed, intercalated layer, 

 seen at Piatt's mine on Mosquito creek, where it affords the 

 following fossils: Productus ozquicostatus, P. muricatus, 

 Hemipronites crassus (?), Atliyris subtilita. 



No. 13. Variegated blue, gray and chocolate-colored 

 shales, sometimes slightly arenaceous. Five to fifteen feet. 

 A band of dark, plastic clay occurs locally near the top. 



No. 14. Limestone, impure, soft, bluish-gray, in two to 

 four thin layers separated by marly partings. One to four 

 feet. The continuity of this bed is uninterrupted; although it 

 loses its upper layer in the southern extension of the forma- 

 tion, and wherever it is exposed it presents the same 

 lithological and palseontological characters, which easily 

 distinguishes this from all other horizons in the formation. 



14a. Usually forms an eight to twelve inch layer, some- 

 times in two thin bands, and is particularly characterized by 

 the prevalence of Productus muricatus; besides this fossil, 

 the following species have been found in this layer: crinoidal 



remains, Piscina , Chonetes mesoloba, Hemipronites 



crassus (?) Atliyris subtilita, Martinia planoconvexa > 



