74 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



the site of nearly continuous though variable epeirogenic action. Consequently 

 the formations are in general thicker and more arenaceous toward the east side 

 of the basin. The greatest thickening is toward the southeast, where at the 

 edge of the Cretaceous overlap in Alabama, the Pottsville, or lower division, 

 probably exceeds 7,500 feet. Marine or brackish- water faunas, extending over 

 wide areas, occur at numerous stages except in the later Pennsylvanian, thus 

 showing frequent accessibility to marine life, though the conditions of sedimenta- 

 tion in the Appalachian trough were generally less favorable for open-water 

 marine mollusca than in the eastern interior arm. The subsidence kept, on the 

 whole, relatively close pace with loading, so that, though the warping was unequal, 

 there is slight evidence of the contemporaneous formation of new basins as the 

 result of the erogenic changes." 



The Allegheny series: 1 



"It embraces the softer sediments of more quiescent waters intervening 

 between the arenaceous invading Pottsville and the Mahoning and other sand- 

 stone and shale members of the overlying Conemaugh formation * * *. As 

 compared with the Pottsville the members of the Allegheny are relatively regular 

 and continuous, and the occurrence in them of marine mollusca is comparatively 

 common." 



The main strata of the Allegheny beds, according to Orton and I. C. 

 White, can be traced across Ohio from Columbiana County to Kentucky, 

 250 miles, beyond the Pennsylvania line. Considering with this the extent 

 and persistence of the Allegheny series in Pennsylvania and West Virginia, 

 there is, apparently, a Pennsylvanian base for a Permo-Carboniferous series, 

 quite similar to the condition which prevails in the western provinces, but 

 at a considerably lower stratigraphic level. 



The Conemaugh, in strong contrast to the Allegheny, has an irregularity 

 in the beds far exceeding even that of the Pottsville. The different layers 

 vary in thickness and in many places some are absent, but there are some 

 which are very persistent. The limits of the Conemaugh have been arbi- 

 trarily fixed, mostly for convenience in mapping; there is the same shading 

 from persistent dominantly calcareous beds below into more shaly and irreg- 

 ular beds above, with a rapid appearance of red beds such as occurs in the 

 Plains Province and parts of the Basin Province. The Monongahela is, 

 like the Conemaugh, variable in character, but contains much limestone 

 and coal. The bulk of the red and green sandstone and shale is in the 

 southern portion of the Monongahela; towards the north the deposits are 

 more normal in color. 



The Dunkard in its maximum thickness consists of 16 to 18 members, 

 being alternations of limestone, coal, and sandstone. According to Steven- 

 son, 2 the Dunkard is smaller in extent than the Monongahela and confined 

 to a limited area in the adjoining portions of Pennsylvania, Ohio, and West 



1 White, David., loc. cit., p. 434. 



2 Stevenson, J. J., Carboniferous of the Appalachian Basin, Bull. Geol. Soc. Amer., vol. 18, 



p. 160, 1907. 



