194 
was so gradual that it did not destroy the temperate flora, or at 
least not those forms enumerated by Gray in his table as existing 
species.“ These and their fellows, or such as survived, must have 
Laney 
be- 
tween them and the ice there was doubtless a band of subarctic and 
been pushed on to lower latitudes as the cold advanced, anc 
arctice vegetation,—portions of which, retreating up the mountains 
as the chmate ameliorated and ice receded, still scantily survive 
upon our highest Alleghenies, and more abundantly upon the colder 
summits of the mountains of New York and New England :—dem- 
onstrating the existence of the present arctic alpine vegetation 
during the glacial area; and that the change of climate at its close 
was so gradual that it was not destructive of vegetable species.” 
“ As the temperature rose, and the ice gradually retreated, the 
surviving temperate flora must have returned northward pari 
passu, and—which is an important point—imust have advanced 
much farther northward, and especially northwestward, than it 
now does; so far, indeed, that the temperate floras of North 
America and [astern Asia, after having been for long ages most 
” 
widely separated, must have become a second time conterminous. 
All t 
the two continents before the ice age were very nearly the same 
— 
ie evidence shows that the temperature differences between 
as now, the isothermal lines having in earlier times turned north- 
ward on our eastern, and southward on our northwest coast, as 
act 
that the interchange of species took place in high northern lati- 
they do today. This fact of similarity of climates and the 
ee 
tudes, “are points which go far towards explaining why [astern 
North America, rather than Oregon and California, has been 
mainly concerned in this interchange.” 
The descendants of the forms that became stranded at or near 
the summits of the higher peaks remain today as arctic-alpine 
‘ ” 
“islands” of plant and animal life, having affinities with forms 
found elsewhere only in more northern latitudes. 
The summit of Mount Washington (altitude 6284 ft. U.S, 
G. S. bench mark) and other peaks of the Presidential Range of 
the White Mountains possess today an “island” of vegetation 
and animal life related to the plants and animals of Labrador and 
Greenland, a thousand miles away, but not related to the flora and 
fauna on the lower slopes of the same mountains and the sur- 
