DEVELOPMENT OF VERTEBRATE LIFE IN PERMO-CARBONIFEROUS 267 



The same change is noted by I. C. White, 1 who, however, emphasizes 

 the change in life which followed the change in environment: 



"Viewed from the standpoint of change in physical conditions the proper 

 place for such a dividing-plane between the Conemaugh and Allegheny beds 

 would be the first general appearance of red rocks, near the horizon of the Bakers- 

 town coal, about 100 feet under the Ames or crinoidal limestone horizon. That 

 a great physical change took place soon after the deposition of the Mahoning 

 sandstone rocks, the present basal members 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 life 

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

 succeeding 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 conveniences of the geologist, would leave the 

 Mahoning sandstone in the Coal Measures, and place the rest of the Conemaugh, 

 as well as the Monongahela 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 characterize 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." 



In previous pages emphasis has been placed upon the physical change 

 which began on the eastern side of the continent and spread to the west. 

 The land was gradually elevated east of the coal basins and a cooler and 

 less humid climate accompanied the elevation. It has been pointed out by 

 David White, Stevenson, and others that the eastern half of the Southern 

 Subprovince continued to sink for some time after middle Conemaugh time, 

 as it received the added load derived from the rising land to the east, but 

 the change of the sediment and, above all, the new elements in the fauna 

 and flora, show that the climatic change was having its effect. Beyond the 

 limits of the basin in all directions the lack of accumulating sediments 

 permitted the elevation to have full effect. 



The fauna, long restrained from any expression of its evolutionary 

 tendencies, full fed, and in the vigor of its youth, responded at once to the 

 change, and new forms appeared so suddenly as to be unheralded in the 

 preserved remains. This is of course more apparent than real, but there was 

 unquestionably a rapid evolution amounting to vigorous radiation, expressed 

 especially in those features which were adapted to life upon a drier land or 

 in aquatic areas of far wider possibilities of varied habitat than in the enor- 

 mous and monotonous swamps. Either of these conditions, rapidity of evolu- 

 tion or life away from favorable conditions for the preservation of the remains, 

 would lessen the probability of the preservation of the connecting forms. 



There can be no question, however, that the response to the changed 

 environment was rapid and in favorable localities very complete. The 



1 White, I. C., West Virginia Geological Survey, vol. n, p. 226, 1903. 



