NIAGARA PERIOD — CLINTON EPOCH. 



233 



2. Animals. 

 The arenaceous and shaly character of the beds is unfavorable 

 for Radiates, and only a rare coral or Crinoidal fragment has been 

 met with. 



Figs. 358-363. 



Fig. 



Arthropbycus Harlani ; 359, Lingula cuneata; 360, Modiolopsis orthonota ; 361, M. 

 primigenius ; 362, Pleurotomaria litorea; 363, Bucania trilobata. 



Of Molluslcs, the most common species is the Brachiopod Lingula 

 cuneata (figs. 359 and 63), which sometimes thickly covers large- 

 surfaces, and is a good mark of the epoch. 



Among the few other species there are the following : — Fig. 360, 3Iodiolopsix 

 orthonota; 361, M. ? ■primigenius ; 362, Pleurotomaria litorea H. ; 363, Bucania 

 trilobata, different views. Orthocerata are occasionally met with. 



The only Crustacean described is the Ostracoid Leperditia cylindrica. 



The Medina epoch is closely related in its rocks and fossils to the 

 Clinton epoch. 



3. CLINTON EPOCH (5 c). 

 I. Rocks : kinds and distribution. 



The Clinton rocks have a wide range over the country. In the 

 Interior Continental basin they fail in New York on the Hudson ; but, 

 commencing near Canajoharie, they stretch westward across the 

 State beyond Lake Ontario, through Canada. They occur farther 

 west, in Michigan, Ohio, and the States west, to the Mississippi, and 

 perhaps also beyond the Mississippi, in Iowa. The formation is 

 200 feet thick in some parts of New York ; to the west it is very 

 thin, and in the States bordering on the Mississippi it is seldom 

 recognizable. 



In the Appalachian region the strata have been observed in Penn- 



