HARSHBERGER: PHYTO-GEOGRAPHIC SKETCH 129 
river, and in the southern Appalachian mountains, generally 
speaking, it lacks many of the peculiar arboreous and herbaceous 
species which characterize the flora of the south and which have 
their nearest living representatives in the flora of eastern China 
and Japan. 
With the retreat of the great ice-sheet, the region once cov- 
ered by the ice was restocked by trees and herbs derived from 
three main sources of supply : (1) Scandinavia, (2) Hudsonian zone 
of the Glacial period, (3) Appalachian forests (north and south). 
The Scandinavian plants migrated eastward during the inter-glacial 
period and tenanted the moraines, nunataks and arctic strip of ter- 
ritory throughout the later glacial epoch. With the retreat of the. 
glaciers, they migrated northward with the ice sheet, or they per~ 
sisted on the tops of high mountains which existed as nunataks: 
during the ice age, or they remained as boreal islands in sphag- 
num-bogs, or in cold and shaded ravines. A northward migra-. 
tion of Hudsonian species and of Appalachian species in concen~ 
tric waves also took place at the close of the Glacial period.* 
The action of the several uplifts and depressions of the earth’s 
surface described was most profound upon this forest, the history 
of which has been traced. With every submergence of the lower 
portions of the creeks of the region and of the Delaware river, 
the forest in the area of submergence was destroyed, or if existing 
on the higher grounds, was subjected to such extensive changes 
of level, as to highly modify its character and the distribution of 
the component species. Many species were crowded together by 
the change of level and the wearing away of the strata to which 
they had become adapted, for ‘“ if we suppose the earlier Mesozoic 
uplands to be the seat of the existing dicotyledons, then by the 
lowering of the surface by gradual consumption of the interstream 
areas, these forms must have been brought into conflict with the 
flora of the lowlands and thereby forced into a contest for 
Supremacy.’’ 
Xerophytes of the hillsides and rock exposures (such as ser- 
s,C. C. Post-Glacial origin and migrations of the life of the north- 
eastern Unied Se , Jour. Geol. x : 303. S 1903. 
t Woodworth, J. B. The meee between baseleveling and organic evolution. 
Am. Geol. 14: Oe O 1894 
