150 DAVID WHITE 



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. 



Floral characters. — The Stephanian is marked by the great 

 development of Pecopteris, Callipteridium, and Odontopteris of the 

 true type. It witnessed the nearly complete disappearance of 

 Alethopteris, Sigillaria, and Lepidodendron. Neuropteris of the 

 large-pinnuled forms enters its period of decadence. Before its close 

 appear the first representatives of Callipteris, Walchia, Taeniopteris 

 of the simple type, Pterophyllum, Zamites, and Plagiozamites, all 

 characteristic of the Permian or later periods. 



In eastern America, where the relations of land and water were but 

 gradually altered and the sedimentation was continuous, the passage 

 to the Stephanian flora has no line of sharp paleobotanical demarka- 

 tion. The change appears to be gentle and the older forms drop out 

 more slowly. In Europe, on the other hand, the contrast is a little 

 sharper; the old types disappear more abruptly and many new ones 

 take their places. A number of these new types have not yet been 

 found in the Permian of this country. Among these are the four 

 Permian coniferal and cycadalean genera above mentioned. 



Source and distribution of the flora. — It is clear that the new ele- 

 ments 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 atmospheric composition may have played a subtle if not 

 important part. It seems hardly possible that the tremendous 



