50 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



Most of Pennsylvania, western West Virginia, and the adjacent portions 

 of Ohio and Kentucky were occupied by a basin wherein continuous terres- 

 trial deposition took place from about middle Conemaugh time on. It is 

 commonly stated that no marine fossils are found above the Ames limestone, 

 but I. C. White states that some have been found at slightly higher horizons. 

 But no doubt it may be accepted that middle Conemaugh time saw the 

 beginnings of new conditions in the type area of the Eastern Province. 



A strong indication of this change of conditions is the presence of heavy 

 layers of red shales and sandstones, as the Pittsburgh red shales in Penn- 

 sylvania and the equivalent horizons in West Virginia. It must be recog- 

 nized that, as I. C. White has so strongly insisted, the change in the sediments 

 marks a decided change in the environment of life, and though Permo- 

 Carboniferous (Permian) plant remains do not commonly occur until much 

 higher horizons, the presence of favorable conditions can be recognized and 

 the younger flora, and part, at least, of the fauna could now appear, either 

 by development or migration. 



It must be clearly understood that the author proceeds upon the thesis, 

 right or wrong, that favorable conditions for any type of life or group of 

 forms must precede the life forms, which follow either as determined by the 

 direct action of the environment or as permitted by the environment, 

 evolution being determined by other forces. If this be so, then an interval 

 of geological time begins when the conditions fitted for the life of that time 

 appear, not when the first typical fossils of the time appear, which may be 

 at a somewhat or even considerably later date. From this it follows that 

 to understand the life conditions of the closing period of the Paleozoic era 

 it is necessary to start somewhat further back than is ordinarily done. 



In order to describe most clearly the conditions of the Eastern Province, 

 it is desirable to divide it into two subprovinces — a Northeastern Sub- 

 province, including New England and the Maritime Provinces of Canada, 

 and a Southern Subprovince, including Pennsylvania, West Virginia, Ohio, 

 Indiana, Illinois, and Kentucky. To the latter subprovince belongs, per- 

 haps, Michigan, though deposits of that State have added nothing to the 

 discussion or solution of the question. 



The deposits of these two areas are separated by a considerable interval 

 occupied by both older and younger rocks, and it is questionable if they 

 were ever connected, but the similarity of the deposits is such as to permit a 

 correlation of the conditions, at least, under which they were laid down. 

 The physiography of the two areas during the time of deposition was so dif- 

 ferent as to constitute in itself a sufficient cause for the observed differences in 

 the deposits. In the Northeastern Subprovince the accumulation took place 

 in long parallel troughs which were largely if not completely isolated from 

 each other and which received accretions of material derived from a closely 

 adjacent source. Moreover, these troughs were in the line of a movement of 

 earth folding and faulting which was at that time undergoing a constant 



