Plant-Beds of Western América. 403 
genera to which they are supposed to belong afford only nega- 
hve evidence of the strata that contain them.* 
It is by no means insisted that we must find in America the 
plants of the European Kocene, before we can be said to have 
an Eocene flora, since, during the Hocene period, the physical 
geography of Europe was such as to give it a very different 
flora from any that ever grew on the North American continent. 
During the deposition of the Eocene strata, the great mountain 
trier which extends from the Bay of Biscay to the China 
sea—formed by the Pyrenees, Alps, Carpathians, Caucasus 
and Himalayas—existed, if at all, only in embryo. The Medi- 
terranean communicated with the Indian Ocean, the south 
shore of Europe was washed by a tropical sea, and the land 
was covered with a sub-tropical, Indo-Australian flora. en, 
however, the great mountain barrier, to which I have referred, 
Was raised, these Austral influences were cut off, the climate of 
‘urope was rendered temperate, and the surface was gradually 
Covered with a temperate flora which, because it included a 
large number of American plants, Liriodendron, Liquidambar, 
Magnolia, &e., we may call the American flora. This was the 
flora of the Miocene, of which we have illustration in the 
fossil plants of Fort Union in Dacotah, Greenland, Iceland, 
eningen, &. This flora seems to have urope up 
to the advent of the ice period. By the advancing cold, it was 
driven to the shores of the Mediterranean, and there extermi- 
It is an important in this connection, that Lesquereux identifies a num- 
ber of the epecies of plants of the Lignite beds with Miocene species of Europe. 
See the last volume of this Journal, page 448.—Ens. 
