230 ESSAYS. 
the vegetation which in our day borders the ice, or by ice it- 
self, it is difficult to form more than general conjectures — so 
different and conflicting are the views of geologists upon the 
Glacial period. But upon any, or almost any, of these views, 
it is safe to conclude that temperate vegetation, such as pre- 
ceded the refrigeration and has now again succeeded it, was 
either thrust out of northern Europe and the northern At- 
lantie States, or was reduced to precarious existence and di- 
minished forms. It also appears that, on our own continent 
at least, a milder climate than the present, and a considerable 
submergence of land, transiently supervened at the north, to 
which the vegetation must have sensibly responded by a north- 
ward movement, from which it afterward receded. 
All these vicissitudes must have left their impress upon the 
actual vegetation, and particularly upon the trees.. They fur- 
nish probable reason for the loss of American types sustained 
by Europe. 
I conceive that three things have conspired to this loss. 
First, Europe, hardly extending south of latitude 40°, is all 
within the limits generally assigned to severe glacial action. 
Second, its mountains trend east and west, from the Pyrenees 
to the Carpathians and the Caucasus beyond, near its southern 
border ; and they had glaciers of their own, which must have 
begun their operations, and poured down the northward 
flanks, while the plains were still covered with forest on the 
retreat from the great ice-wave coming from the north. At- 
tacked both on front and rear, much of the forest must have 
perished then and there. Third, across the line of retreat of 
those which may have flanked the mountain-ranges, or were 
stationed south of them, stretched the Mediterranean, an im- 
passable barrier. Some hardy trees may have eked out their 
existence on the northern shore of the Mediterranean and the 
Atlantic coast. But we doubt not, Taxodium and Sequoias, 
Magnolias and Liquidambars, and even Hickories and the 
like, were among the missing. Escape by the east, and re- 
habilitation from that quarter until a very late period, was 
apparently prevented by the prolongation of the Mediterra- 
nean to the Caspian, and thence to the Siberian ocean. If we 
