Cenozoic Floras Around the Northern Pacific 77 



is numerically unimportant. A significant example of this ele- 

 ment is Ulmus brotvnellii, a species with small leaves having 

 simple-serrate margins, first reported from the lower Miocene of 

 Oregon, and ranging as far east as Colorado before the end of 

 that epoch. Elm leaves of the same characteristic appearance 

 have recently been recorded from the lake beds of Pliocene age 

 in Shansi Province, China,^ and U. parvifolia, the modern 

 equivalent of both fossil species is today widespread in the cooler 

 and drier forested areas of northern China. Here is an example 

 of a tree the leaf characters of which permitted its survival in 

 western America long after most deciduous types, including sev- 

 eral species of its own genus, had become extinct, and which has 

 survived down to the present in the somewhat more favorable 

 habitat afforded in northeastern Asia. 



As is true of the Pliocene floras of western North America, 

 the known vegetation of this epoch in Asia is essentially like that 

 now occupying the same areas. Acer, Amelanchicr, Picea, and 

 Ribes are among the other genera recorded in Shansi. To the 

 west, in Sinkiang and adjacent provinces of northwestern China, 

 a small but critically important flora has recendy been described,^* ^^^ 

 all of whose species have closely related living equivalents in 

 central Asia at the present time. The two common trees are a 

 poplar whose leaves are indistinguishable from those of the 

 Populus euphratica now occupying river borders and sand 

 washes in the interior of Asia Minor, and an elm that is essen- 

 tially like Ulmus pumila, which occupied the arid portions of 

 central and northern China, including the borders of the Gobi 

 Desert of Mongolia. Associated with the leaf impressions of these 

 and other species of the sand washes and canyons, there have 

 been recorded the remains of an aquatic element which occupied 

 the lake basins in which the sediments were accumulated. Leaves 



