156 DAVID WHITE 



account of the strange character of the flora, I am inchned to regard 

 the pecuHar floral association as due to the extension of the early 

 Gondwana climatic influence into north-central Asia and the subse- 

 quent isolation of the flora from western influences. This theory is 

 supported by the presence of the older Gondwana flora in the coalfield 

 of Shensi in China. On the other hand the floral differences between 

 the Ural and eastern localities may be due to geographic position of the 

 latter in the interior of the great Asiatic continent while the Ural 

 flora which has more elements in common with the western w^orld is 

 located on the west coast of this continent. 



The contrast is certainly not due to mere latitude, nor can it be 

 credited wholly to aridity; for the eastern plants are associated in 

 great series with coals in each region. A few stray wood fragments 

 of uncertain location and age appear to offer slight evidence of sea- 

 sonal changes, but the criteria deserve careful re-examination both 

 as to this point and as to the geological horizon of the material 

 described. 



It would be most interesting to know to what extent the plant life 

 of Permian time on the west coast of North America was influenced 

 by the Gondwana glacial climate and as to how far it was allied to the 

 older Gondwana floras. 



The sharp contrast between the Chinese Gondwana plants and 

 the floras of the very latest Stephanian in the same region involves 

 a pronounced break either in climate or in time in that quarter of the 

 globe. Probably both are concerned. The most satisfactory illumi- 

 nation of the stratigraphical and paleontological history of this 

 period will probably be found in China or southern Siberia. 



" PERMO-CARBONIFEROUS CLIMATES" 



Climate oj 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 temperature, 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 in- 

 clude: 



