266 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



The middle of Conemaugh time saw the beginning of the end of the fixed 

 environment of the amphibia and the first reptiles. The change began on 

 the eastern side of the continent and the record as shown by the deposits 

 has long been recognized. Girty says:^ 



"The Upper Carboniferous, rather in contrast with the Lower, was a period 

 of emergence of shores and of shallowed waters, and it presents the variety that 

 appertains to such conditions. In considering the stratigraphic relations of eht 

 Pennsylvanian and Permian one can not fail to be struck by the local character 

 of the phenomena, and the vast amount of detail, from which it is difficult to 

 disengage facts of broader significance." 



" Lithologically the beds of the Upper Carboniferous^ and Permian present 

 the greatest variety, and about the only truth of broad applicability has long 

 been known. I mean that in eastern North America the sediments of the Upper 

 Carboniferous are chiefly shales, sandstones, and conglomerates, with some thin 

 limestones, while in the West the limestones have a much larger development, 

 and coals, which toward the east play so important a part, if not in thickness at 

 least economically and significantly in the Carboniferous sediments, are there 

 practically absent. From this it has been justly inferred that the character of 

 the eastern Carboniferous indicates shore and estuarine conditions of deposition, 

 while that of the western indicates marine conditions of deposition." 



The variety of sediments emphasized by Girty is, however, rather a 

 repetition of a relatively few kinds of beds than an evidence of varied 

 habitat. 



The same change is recognized by David White,^ who notes that the 

 beginning of Stephanian time dates from the Hercynian uplift in Europe, 

 but that the abrupt differences of level and vegetation do not appear in 

 America: 



"In view, however, of the paleobotanical evidence indicative of a point near 

 the Allegheny-Conemaugh boundary, I, personally, am inclined to regard the 

 formation of the Mahoning sandstone (conglomeratic), the changed sedimentation 

 of the Conemaugh formation, the probable upwarp of the southern Appalachian 

 region which later resulted in the exclusion of the sea from the northern area 

 also, and the consequent climatic changes, as due to the same great orogenic 

 influence. Accordingly I would provisionally place the greater part, if not all, 

 of the Conemaugh together with the Monongahela in the Stephanian. 



"The final exclusion of the sea from the Appalachian trough appears to have 

 occurred soon after the deposition of the Ames limestone, near the middle of the 

 Conemaugh, since, according to reports, only fresh or possibly brackish water 

 mollusca occur in the higher terranes. It is probable that the Monongahela 

 was never deposited in the southern Appalachian region, from portions of which 

 the Conemaugh may also have been absent, the red oxidized sediments of the 

 latter being in part derived, I believe, from the eroded unconsolidated older 

 Pennsylvanian to the southeastward." 



• Girty, G. H., Outlines of Geological History, p. 124, 1910. 



^ Idem, p. 126. 



' White, David, Outlines of Geologic History, p. 148, 1910. 



