OF UPPER EOCENE CLIMATES. 13 



benefit of this drift of warm oceanic waters, whereas the most south- 

 ern locaHties, which here mark the upper Eocene southern limit of 

 alders, birches, hazels, etc., are found at about Latitude 45° North in 

 North America, and fairly well away from coasts in a region where 

 it is reasonable to assume a continental climate may have prevailed, 

 especially if there were mountains intervening, as the textbooks would 

 have us believe. 



None of these most southern Eocene floras of the cool-Temperate 

 type come within many degrees of reaching the existing southern 

 limits of their well-determined genera. For example, the hazel 

 (Corylus) has its present southern limit at Latitude 31° North, 

 whereas in Eocene time this limit was at about Latitude 45° North. 

 At the time these Temperate types were extending their range north- 

 ward, almost to the pole itself, warm temperate or sub-tropical types 

 had invaded our Gulf States as well as southern and central Europe. 



The conclusion seems probable that the whole world had, at that 

 time, a more or less mild and equable climate, prevailingly of the 

 oceanic type, and that the primary cause of this oceanic climate was the 

 diminished and low-lying land areas, and the increased sea areas ; so 

 arranged as to permit a maximum of circulation between equatorial 

 and polar regions. The floras show that in spite of this relatively 

 mild and equable climate, then as now, the polar regions were con- 

 siderably cooler than the equatorial regions. At the present time, 

 because of the great expanse of the Pacific ocean in the equatorial 

 region, its average surface temperature is 19.1° C, as compared with 

 16.9° C. for the Atlantic and 17° C. for the Indian ocean. 



The consensus of opinion that the land masses of the Northern 

 Hemisphere were the main theater of evolution of late Mesozoic and 

 Tertiary terrestrial life, both animal and vegetable, may seem to be 

 opposed to such a free oceanic circulation between the equatorial and 

 polar regions as I have indicated, but this is only an apparent and not 

 a real difficulty. The land emergence whose culmination furnishes 

 geologists with the basis for a boundary between Mesozoic and Ceno- 

 zoic afforded abundant land paths for the dispersal of terrestrial 

 animals and plants, as witness the essential community of the faunas 

 and floras of early Eocene time throughout the whole of Holarctica. 



