THE WILLOWS AND POPLARS 91 



European and Arctic records a petrified piece of a poplar root has 

 been described from the Upper Cretaceous of Japan, indicating 

 that Asia had its species then as now.^ 



During the succeeding Eocene period there were upwards of 

 50 species, or twice as many as are living at the present time. 

 The rising land of what is now the Rocky Mountain country 

 shut off the moisture laden winds from the Pacific and the lessen- 

 ing rainfall made of this vast region a quite different country from 

 what it had been during the Upper Cretaceous. In the continental 

 deposits of the Eocene, that is, deposits laid down on the bosom 

 of the land rather than in the sea— the deposits of wind blown 

 materials and volcanic dust, laid down in lakes, streams, flood- 

 plains, etc. — deposits referred to the Fort Union formation, leaves 

 of poplars are the most abundant fossils. 



Poplars appear to have covered at this time all of the plains and 

 mountain country of the West in great variety, extending north- 

 ward from the western provinces of the United States and Canada 

 to Alaska and the mouth of the Mackenzie River, and encircling 

 the globe in high latitudes. They have been recorded from Green- . 

 land, Grinnell Land, Spitzbergen, Sachalin, Siberia and Manchuria. 

 A few are found in central Europe, but the great bulk are American 

 and Arctic, and the climate of more southern lands appears to have 

 been too warm for their presence in any great numbers, for in the 

 abundant Eocene floras of southeastern North America we find no 

 traces of poplars but in their place a warm climate flora of figs, 

 laurels, bread fruit, rain trees and their allies, thatch and date 

 palms, nutmegs,' pond apples and similar types unfamihar to 

 dwellers in the Temperate Zone. This warm flora extends as far 

 north as the mouth of the Ohio in America and a similar warm 

 flora extends to southern England in Europe. 



During the Ohgocene, which succeeded the Eocene, the scanty 

 records have yielded few poplars. Three species have been de- 

 scribed from deposits of this age in the West and 4 or 5 are 



^ Many of these early poplars are thought by some students to represent an 

 altogether different family of plants — the Trochodendraceae. 



