166 College of Forestry 
(3) That species which made up the flora were not all ex- 
terminated, for we have many of them still. 
It is reasonable to assume therefore that these species — 
or many of those which covered the region invaded by glacial 
ice — migrated southward. Personally I like the view that 
the climatic conditions incident to the prevalence of such a 
field of ice so far south of the arctics would be equivalent to 
moving the climatic zones southward and one may imagine 
the zones of vegetation correspondingly pushed southward * 
Thus we may imagine a zone of tundra vegetation fronting 
the glacial margin, the boreal conifers next southward or at 
lower elevations, the Appalachian highland and the zone of 
deciduous forest still southward or below this, and warmer 
climate vegetation correspondingly displaced by the south- 
ward shift of climatic zones. 
I think we must hold to the idea in any event that the 
floristic stock which now composes the essential body of New 
York species lay during the glacial epoch, in the Appalachian 
and adjacent regions to the south of the glaciated territory, 
and it was chiefly from this source that the returning vegeta- 
tion came. 
The course of their return is speculative. Jf one could 
hold to the comfortable theory that we have in all this glacial 
and post-glacial history an oscillation of zones from north to 
south and back, the matter would be for a broad view rela- 
tively simple. Adams * suggests that the northward migra- 
tion following the retreating glacier would comprise three 
great waves of life. First, a wave of glacial or arctic vegeta- 
tion of which we have remnants in New York on Mt. Marcy 
and two or three other high peaks. Second, a wave compris- 
17Tn this connection Chamberlin and Salisbury (Vol. III, p. 531) say: 
“ Following the last ice-retreat the life of each of these sections moved 
northward, each biotic zone, arctic, subaretic, cold-temperate and tem- 
perate expanding as it went. I+ was as though the life-zones were 
elastic bodies which had been compressed to narrow limits about the 
edge of the advancing ice and then recovered their normal breadth as 
the ice pressure was withdrawn.” 
2Adams, C. C.  Post-glacial origin and migrations of the Life of 
Northeastern U. S., Jour. Geog. I, 1902, p. 308 and fcllowing. 
