38 Cincinnati Society of Natural History. 



Maysville stage. — During the Maysville stage, the supply 

 of mud was lessened, as is shown by the increased proportion 

 of limestone upward in the formation. It is not known 

 whether this clearing of the seas was due to "an actual 

 diminution in the amount of mud supplied, or to a deepening 

 of the sea which would reduce the amount of terrigenous 

 material brought to this place. But we do know that at 

 times the sea was quite shallow, for in the Fairmount mem- 

 ber where limestone is relatively more abundant than at 

 any lower horizon in the Cincinnatian, there are several 

 waved limestone strata. As these are composed largely of 

 fragmental material, they could not have been deposited 

 at a depth greater than that at which such material can be 

 agitated by the waves. The Maysville stage was a time 

 favorable to the existence of abundani animal life, and 

 especially to such forms as brachiopods and bryozoans 

 which inhabited clear waters. 



Richmond stage. — During *the Richmond stage, con- 

 ditions changed frequently, as is shown by the alternation 

 in the character of the rock. These varying conditions 

 were probably produced by epeirogenic movements. The 

 Arnheim (basal Richmond) was a time of deposition of 

 shaly limestone and of shale. The change from clear water 

 conditions of the McMillan stage to the muddy waters of 

 Arnheim time affected the life of the seas very strongly as 

 is shown by the scarcity of fossils in the lower division of 

 the Arnheim (Sunset). Later in the Arnheim time (Ore- 

 gonia), life became abundant, but the species and even the 

 genera were largely different from those of the previous 

 stage. The Arnheim time was transitional between the 

 McMillan and the Richmond stages. Muddy water con- 

 ditions inaugurated during the Arnheim time prevailed 

 during the deposition of the Waynesville, and in accord 

 with this, species closely related to those of the previous 

 muddy water stage, the Eden, appeared, such as Dahnanclla 

 meeki, Lepiaena rhomhoidalis, and many bryozoans. Follow- 

 ing the AVaynesville time the seas again cleared, inaugurating 



