40 OEIGIN 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 again, 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 

 th,e 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. 



