514 F. H. K^'OAVLTOX EVOLUTION OF GEOLOGIC CLIMATES 



devoid of frosts. "We therefore conclude that after Middle Devonian time the 

 climate of the world was as a rule uniformly warm and more or less humid 

 and remained so to the close of Upper Carbonic time." 



Permian flora and its climatic significance. — The Permian flora pre- 

 sents many points of extreme interest. As already stated, during and 

 at the close of Stephanian or Pennsylvanian Carboniferous time, the 

 climate was uniform and mild — perhaps subtropical — and as a conse- 

 qnence the plants in practically identical assemblages were almost world- 

 wide in distribution. Distinct botanical provinces are not known. 



The incoming of the Permian inaugurated a series of events that pro- 

 duced a very profound modification of both climate and plant life — 

 that is, the so-called "Permo-Carboniferous^^ glaciation. This glacia- 

 tion, which occurred very early in the Permian and was probably of 

 comparatively short duration, was principally about the Indian Ocean, 

 and affected wide areas in India, South Africa, Australia, and eastern 

 South America. This created two sharply marked botanical provinces — 

 a northern and a southern province. In the northern province, which 

 includes Xorth America, Europe, and northern Asia, the Stephanian 

 flora was able to continue with comparatively slight change, while in tlie 

 south the original flora was mainly wiped out, and later succeeded by the 

 so-called Gangamopteris or Glossopteris flora. The dominant types arc 

 Gangamopteris, Glossopteris Vertebraria, Xeuropteridium, Xoeggera- 

 thiopsis, Phyllotheca, Schizoneura, Ottokaria, etcetera. This is not 

 strictly a glacial flora, though in some places, as in Australia, it is found 

 in a higher inter-glacial epoch. It is persumed to have originated on a 

 land mass (Gondwana Land) about the South Pole, and being a terres- 

 trial flora there must have been practical land connection essential to 

 its passage from these now widely separated areas — India, South Africa, 

 Australia, and Brazil. The existence of this former land bridge is 

 greatly strengthened by the finding of Glossopteris by the Scott Antarctic- 

 Expedition within 5 degrees of the South Pole. 



During the time of actual glacial occupancy the climate was un- 

 doubtedly severe, and this influence extended over a wider area than was 

 dominated by the Pleistocene glaciation. Thus, in certain woods found 

 rather closely associated with these early boulder beds in Australia and 

 South Africa, the growth rings are indicative of sharp seasonal changes, 

 but it is evident that very soon after the close of glacial activity greatly 

 ameliorated climatic conditions were soon restored, for woods in the 

 higher beds, as in South America, show very little evidence of seasonal 

 growth rings. This early restoration of favorable climatic conditions 



