THE EOCENE PERIOD. 227 



Eocene, the prolific Alum Bay (England) plant-beds record a flora 

 "the most tropical in general aspect which has yet been studied in 

 the northern hemisphere/' 1 while the abundant Bournemouth (Eng- 

 land) flora, perhaps a little later "suggests a comparison of its climate 

 and forests with those of the Malay Archipelago and tropical America." 

 It was an epoch of palms in mid-latitudes. The Mid-Eocene series of 

 America in temperate latitudes contains palms and bananas mingled 

 with many similar mild temperate trees, implying sub-tropical or warm- 

 temperate conditions. 



Some of the leading plants of the middle and late Eocene of Europe 

 and America were allied to types that now prevail in India and Aus- 

 tralia, and hence the Eocene flora is often said to have had an Australian 

 facies, an expression liable to misinterpretation. The facts do not im- 

 ply that these types originated in Australia, or were even necessarily 

 living there in Eocene times, but merely that the descendants of the 

 Eocene plants now live there. It is the more needful to observe this, 

 because the nearest living relatives of another part of the Eocene plants 

 of America and Europe are now found in portions of tropical Africa 

 and America, while those of still another part are found in temperate and 

 even boreal latitudes in America. An adaptive differentiation seems 

 to have taken place since, attended by a dispersal of the differen- 

 tiated groups to different climatic zones. Probably the true view is 

 that the mixed or undifferentiated flora of the Cretaceous and Eocene, 

 when it came to be subjected later to severe climatic and other crucial 

 conditions, became modified into adaptive groups, some of which came 

 to be restricted to the tropical regions and are now known as tropical 

 plants, others to the temperate, and still others to boreal regions, ac- 

 quiring corresponding designations. These later meanings can be car- 

 ried back to the ancestral plants only at a certain risk of error. It is 

 doubtless wise to make some discount in the direction of intermediate 

 conditions, the conditions from which all probably diverged. 



The flora as food-supply. — The presence of the angiospermous flora 

 in the northern continents at the time of the appearance of the placental 

 mammals, without doubt had far-reaching biological consequences. The 

 rapid development of the ancestral herbivores, rodents, sloths, and 

 lemurs, was doubtless, in some large measure, controlled by adaptation 



1 Geikie, Text-book of Geology, 3d ed., p. 974. 



