786 GEOLOGY 



is not surprising, therefore, that the rise of the mammals drove the 

 clumsy, affectionless, small-brained reptiles either into extinction, 

 or to the assumption of new and smaller forms. 



The angiosperms may have been a factor in the placental dis- 

 persion, through the fact that they are a staple source of food of 

 the mammals. It may have been the spread of this flora from its 

 originating tract, until it came into contact with the primitive 

 placentals in their originating tract, that caused the rapid spread 

 and evolution of the latter. 



The Vegetation 



In plant history, the Eocene was not the dawn of the recent, 

 for the great change from medieval to modern plants took place in 

 the Comanchean period. The Eocene was not even the period of 

 any radical innovation. There was, however, much progress 

 toward living species, and toward present adaptations of plants 

 to climate, soil, and topography, and to each other. 



Among the plants of the earliest known Tertiary flora of Europe 

 were oaks like those of the present elevated districts of warm 

 temperate zones. With them were willows, chestnuts, laurels, 

 ivies, aralias, etc., which have been likened to the flora of southern 

 Japan. 



The flora of the Denver beds (p. 752), contains figs, poplars, 

 laurels, magnolias, and many ferns. The early Eocene flora <>f 

 southern Canada 1 included similar forms, together with oaks, 

 beeches, etc., a flora indicating a temperate climate. 



The Middle Eocene flora of England records a flora "the most 

 tropical in general aspect which has yet been studied in the north- 

 ern hemisphere," 2 while a later flora "suggests a comparison of its 

 climate and forests with those of the Malay Archipelago and tropical 

 America." The Mid-Eocene series of America in temperate lat- 

 itudes contains palms and bananas, mingled with many other 

 trees of similar climatic significance. 



1 Penhallow. Tertiary Plants of British Columbia, Can. Ki-pt. <f Mini's, 

 1908. 



2 Geikir, Text-book of Geology, 3d ed., p. 974. 



