62 R' W. Chancy 



latitude the major factor in determining these differences seems 

 to be the position of the two areas with relation to prevailing 

 circulation of air and water currents. The resemblance of these 

 early Tertiary floras of Alaska and northeastern Asia to the 

 Miocene floras of Oregon and adjacent states will be seen by 

 reference to the list of Miocene genera on page 68. It seems 

 possible to conclude that in the early part of the Tertiary period 

 there was no such uniformity of climate over a wide range of 

 latitude as has been pictured by earlier writers, some of whom 

 are responsible for the myth of the occurrence of tropical floras 

 in the Arctics. The existence of such floras has been so frequendy 

 disproved by Berry^' and others in recent years that their sup- 

 posed climatic implications can be wholly disregarded. The 

 fossil plant record indicates that there were differences in tem- 

 perature and humidity along the Pacific Coast of North America 

 during the Eocene which, though perhaps not as marked as 

 those of today, indicate that latitude was a controlling factor, 

 with subtropical vegetation toward the south and progressively 

 more temperate floras northward into Alaska. The diiferentia- 

 tion of Tertiary vegetation into a series of climaxes, or a cHsere, 

 in response to differences in latitude and altitude was suggested 

 by Clements almost twenty years ago." 



This change in the character of the vegetation because of the 

 influence of latitude makes possible certain important inferences 

 concerning the nature of the upland forests during the Eocene 

 and subsequent epochs. The fossil record is of necessity in- 

 complete, since it is usually preserved at sites of deposition situ- 

 ated on the lowlands. Studies of the dispersal of modern leaves 

 and fruits from the trees on which they grew indicate that under 

 normal conditions of transportation they are rarely deposited 

 except in the immediate vicinity of the parent trees. The assump- 



