INTRODUCTION 



The Geological Record 



A study of the fossil plants shows beyond question thai through- 

 out the greater part of geological time the rail IT- climate * 

 much more uniform than at present. It has been claimed ' that 

 the zonal climates now existing, were scarcely recognizable in the 

 earlier geological periods, but are first clearly defined in the 

 Pliocene — the era just preceding the succession of glaciations 

 constituting the great ice age. 



While the great fluctuations in the distribution of land and 

 water areas during the ages undoubtedly exercised a very gre 

 influence on the prevailing climate, it is difficult to see how under 

 any conditions, conceivable at the present day, it would be possible 

 for such trees as magnolias, figs, walnuts and sequoias to live in 

 the latitude of Spitzbergen and Greenland as they undoubtedly 

 did in the Eocene. 



It is true that in regions with an insular climate, such as smith- 

 eastern Alaska and New Zealand there is a luxuriant vegetation 

 in relatively high latitudes, due to heavy rain-fall and absence <»f 

 severe cold; but such conditions are hardly conceivable at the 

 present day in regions less than ten degrees from t he pole. 



Especially during the Carboniferous was the flora of the earth 

 extremely uniform. "We find practically identical assembly 

 of plants wide spread over western Europe, central and i stern 

 Asia, South Africa, eastern North America and probably southern 

 South America." 2 



Even more widely spread floras occur in the Jurassic, which are 

 known to range from Franz Josef Land, 82° N.. to I Iraham I.ai d. 

 63° S., and to extend practically completely round the world. 



From the nature of the plants of these periods, one may conclude 



that the climate was a mild— perhaps subtropical our. and that 

 there was very heavy precipitation. Such a climate seems to 

 have prevailed during much of geologic time. 



There were, however, periods of lower temperatures, indi 

 bv evidences of extensive glaciation, especially during I he Permian. 

 At that period, there are abundant evidences of extensive glacia- 



« Knowlton, F. H., " Evolution of < Geologic < Jlimatee/' Bull. Q 

 Vol. XXX, pp. 499-566, 1919. 

 2 Knowlton, loc. cit., p. 51-'. 



