40 
ORIGIN OF LIFE IN AMERICA 
in America before the time when the glacial drift was de¬ 
posited, or, in other words, when the northern ice-sheets were 
supposed to have advanced to their southern limits. The 
glacial drift, I may mention agqin, is the mantle of clay, sand 
and boulders believed to have been left by the ice as it 
retreated northward. Whether this drift or boulder clay really 
is the product of immense glaciers, or whether it was deposited 
in the sea by floating icebergs, it is evident that wherever the 
country is covered by it the pre-existing fauna and flora must 
have been destroyed. The evidence seems to me all in 
favour of destruction rather than emigration. 
The idea of a gradual southward withdrawal of the fauna 
and flora, that they fled like a conquered army before an ad¬ 
vancing foe, sounds very plausible, but is there any foundation 
for such a belief ? 
No evidence can be adduced from fossil specimens that 
any members of what I have called the European invasion 
ever penetrated southward of the limits of the drift in North 
America. They do not seem to have been pushed south in front 
of the advancing masses of northern ice. Theoretically, they 
ought to have survived the Ice Age somewhere in south-eastern 
North America. If they did, they must subsequently have 
reoccupied the very parts, viz., Labrador, Newfoundland and 
the coast of New England, where they originally set foot 
on American soil after completing their travels across the 
North Atlantic land bridge. But is it possible that they 
quitted the south-eastern States without leaving a trace of 
their former presence there ? As Dr. Harshberger * points 
out, not a single species of thirty-four plants characteristic 
of the area just south of the glacial drift deposits, is a native 
of Europe. On the other hand, of the plants growing on 
the drift itself, about one-third are common to northern 
Europe and America. All the available evidence, therefore, 
points to a survival of the European element within the 
glaciated area. 
Could any islands have existed in the midst of this glaciated 
area, where this assemblage of European plants and animals 
* Harshberger, J. W., “ Comparative Age of Floristic Elements,” 
p. 606. 
