NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 95 



member of the Conemaugh series, must be conceded, since no red beds whatever 

 are found from the base of the Pottsville up to the top of the Allegheny, and none 

 worth considering until after the epoch of the Upper Mahoning sandstone. 



The sudden appearance or disappearance of red sediments after their absence 

 from a great thickness of strata is always accompanied by a great change in forms, 

 and the present one is no exception. In fact, the invasion of the red sediments suc- 

 ceeding the Mahoning sandstone epoch of the Conemaugh may well be considered 

 as the 'beginning of the end' of the true Coal Measures, both from a lithological 

 as well as a biological standpoint, and hence it is possible that the best classification, 

 aside from the convenience of the geologist, would leave the Mahoning sandstone 

 in the Coal Measures, and place the rest of the Conemaugh, as well as the Mononga- 

 hela series above, in the Permo-Carboniferous. This reference is also confirmed by 

 the character of the fauna and flora, both of which contain many forms that charac- 

 terize the Permo-Carboniferous beds of Kansas and the West, as may be seen in the 

 lists published on a subsequent page under the detailed description of the principal 

 Conemaugh strata." 



If this sudden change has the significance attributed to it by White, we 

 are justified in regarding the appearance of the forms beneath the Ames 

 limestone as marking the advent of a new fauna, by evolution or migration, 

 which apparently spread over the whole of North America, as evidenced by 

 its discovery in localities from Prince Edward Island to New Mexico. This 

 fauna, so far as we know, appeared at an earlier date in the eastern part of 

 North America than in the western, suggesting the general route of immigra- 

 tion or spreading from its point of inception. 



The red shale series mentioned by White ^ is the equivalent of the Pitts- 

 burgh Red Shale. The Ames limestone Hes just above it. This last is 

 "almost exactly the middle of the Conemaugh series, 315 feet below the base 

 of the Pittsburgh coal, and 695 feet below the base of the Dunkard series 

 (Permian) . The Ames limestone is about 300 feet above the Freeport coal 

 (top of the Allegheny series)." (Statement in a letter from Dr. Raymond.) 

 It is evident, then, that the lower horizon of the reptiles is carried at least 

 into the Allegheny at Linton. 



The exact age of the beds in Illinois and Prince Edward Island, in which 

 similar forms occur, is not yet determined. 



The limit recognized for the Permo-Carboniferous fauna is, then, from 

 the Pittsburgh Red Shales to the top of the Clear Fork. The stratigraphic 

 extent of the space delimited it is impossible to state, as there is no direct 

 correlation of the eastern and western beds possible, but it may be roughly 

 stated as from the middle of the Conemaugh to near the top of the Permo- 

 Carboniferous. The limits of the fauna in America, however, are not those 

 of Europe; the fauna was there continued into the Triassic. 



* White, Geol. Surv. West Virginia, vol. ii, p. 263. 



