242 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



America the line between the Westphalian and the Stephanian is not yet accu- 

 rately drawn, the fossil floras being not studied in sufficient detail. 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 Cone- 

 maugh 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. * * * 



"It is clear that the new elements of our Stephanian flora are chiefly, at 

 least, of European origin, the plant life there having been directly influenced by 

 the important physical changes to which it was immediately subjected. The 

 various exotic types migrated to North America, probably, along or near the 

 general route traversed by their Westphalian predecessors. Also, since the 

 Stephanian flora of the American basins seems to afford no evidence of a rapid 

 or strongly pronounced climatic alteration, it becomes fairly probable that the 

 more abrupt plant changes described in western Europe were induced chiefly 

 by the sweeping orogenic effects of the Hercynian movement, rather than by a 

 great climatic change of world-wide extent. This does not, however, preclude a 

 moderate but far-reaching modification of climate', in which changes in the atmos- 

 pheric composition may have played a subtle if not important part. It seems 

 hardly possible that the tremendous amounts of carbon then being stored away 

 in the coal fields as the result of plant extraction from the air could have failed 

 to produce some effect on the atmospheric content of CO 2 . * * * 



"The coming of the Permian is characterized not only by orogenic movements 

 in the eastern hemisphere, but also by indications of increasing climatic differences. 

 The first paleobotanical effect of these is the extinction of nearly all characteristic 

 Carboniferous types, except in Pecopteris, Cordaites, and Neuropteris, the latter, 

 however, disappearing nearly completely by the close of the Autunian or lower 

 stage. They are replaced by varied forms of Callipteris, the lingulate Odontopteris, 

 and the ribbon-like Tceniopteris, together with expanding gymnospermous types, 

 such as Walchia, Dicranophyllum, Doleropteris, Psygmophyllum, and Ginkgo- 

 phyllum. Later, in the Saxonian, or Middle Permian, Voltzia, with the thick- 

 leaved Equisetites, appears, while more of the older types go out; and in the Thur- 

 ingian, or Zechstein (Upper Permian), Rhipidopsis, Araucarites, Gomphostrobus, 

 Voltzia, and Ullmannia become the characteristic genera, while Pecopteris, domi- 

 nant in the Stephanian, has nearly vanished. Though lacking the abundant 

 Cycad and Cladophlebis-Asterocarpus elements, the Upper Permian is in many 

 respects transitional to the older Mesozoic flora. * * *" 



" ' PERMO-CARBONIFEROUS CLIMATES.' 



"Climate of the Carboniferous. The climate of the Pennsylvanian ('Upper 

 Carboniferous') as viewed in perspective was mild and relatively humid, and, 

 above all, equable over the greater part of the earth. It was moderate in tem- 

 perature, not tropical, possibly not even subtropical, but, during the Westphalian 

 at least, always and everywhere equable. It was truly temperate. The criteria 

 which may be interpreted in support of this generally accepted proposition 

 include: 



"i. The tremendous size and great height of the types, and their rank foliar 

 development, indicating favorable conditions of environment and vigorous 

 nutrition. 



