226 GEOLOGY. 



the land connections from migratory facilities for the animals, to their 

 function in plant distribution. Not only because of this possible func- 

 tion of the vegetation, but because of its incontestible agency in direct- 

 ing the evolution of the mammals, we turn to it first in sketching the 

 life of the Eocene. 



The Eocene Vegetation. 



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

 for the great change from the medieval to the modern, in its main 

 essentials, had taken place in the Early Cretaceous. The Eocene was 

 not even the period of any radical innovation. There was, however, 

 much progress toward the specific forms that now live, and toward the 

 more recent adaptations to climate, soil, and topography, and toward 

 those relationships of plant to plant that have worked out into the 

 present plant societies. In Cretaceous times there was much mixture 

 of forms that have since become dissociated, and the mixed state con- 

 tinued in large measure through the Eocene. On account of this mix- 

 ture, climatic inferences have to be drawn with some caution. Where 

 palms and poplars grow together, it is not quite clear whether the pres- 

 ent environment of the palms or that of the poplars is implied. Very 

 likely conditions not quite like either of these are implied, but rather 

 climates of a less differentiated or less diversified nature. 



The temperate (?) flora of the earliest Eocene. — The plants of the 

 Heersian system (Heers, Belgium), the earliest known Tertiary flora of 

 Europe, interpreted from the present adaptations of the species, imply 

 a temperate climate. Most abundant among them were oaks like those 

 of the present elevated districts of warm temperate zones. With these 

 were associated willows, chestnuts, laurels, ivies, aralias, and other plants, 

 making up an interesting group which Saporta likens to that of southern 

 Japan, and Prestwich regards as very different in significance from the 

 tropical palms, tree-ferns, and associated plants of a later stage of the 

 Eocene. An assemblage of similar temperate facies occurs in the Paris 

 basin, and in the Lower Eocene of England. The American flora of this 

 stage yet awaits determination. 



The tropical (?) flora of the Middle Eocene. — In a later stage of the 

 Lower Eocene (London clay), a rich assemblage of trees grew in England, 

 embracing palms, figs, cinnamon, and many others which, interpreted 

 by present ranges, imply a somewhat tropical climate. In the Middle 



