338 A. R. Grote—Hffect of the Glacial Epoch, ete. 
which latter journeyed northward, following the course of the 
retirement of the main ice-sheet. They had found in elevation 
their congenial climate, and they have followed this gradually 
to the top of the mountain, which they have now attained and 
from which they cannot now retreat. Far off in Labrador the 
descendants of their ancestral companions fly over wide stretches 
of country, while they appear to be in prison on the top of a 
mountain. I conceive that in this way the mountains may 
generally have secured their alpine animals) The Glacial 
period cannot strictly be said to have expired. It exists even 
now for high levels above the sea, while the Esquimaux finds 
it yet enduring in the far north. Had other conditions been 
favorable, we might now find Arctic man living on snow- 
capped mountains within the Temperate zone. 
At a height of from 5,600 to 6,200 feet above the level of the 
sea, and a mean temperature of about 48 degrees during a short 
summer, the White Mountain butterflies (Oeneis semidea) yet 
enjoy a climate like that of Labrador within the limits of New 
Hampshire. And in the case of moths an analogous state of 
things exists. The species Anarta melanopa is found on Mount 
Washington, the Rocky Mountains and Labrador. <Agrolis 
Islandica is found in Iceland, Labrador, the White Mountains, . 
and, perhaps in Colorado. As on islands in the air, these 
insects have been left by the retiring ice-flood during the open 
ing of the Quarternary. : 
On inferior elevations, as on Mount Katahdin, in Maine, 
where we now find no Oeneis butterflies, these may formerly have 
existed, succumbing to a climate gradually increasing in warmth 
from which they had no escape; while the original colonization. 
in the several instances, must have always greatly depended 
upon local topography. 1% 
I have briefly endeavored to show, that the present distribu- 
tion of certain insects may have been brought about by the 
phenomena attendant on the Glacial period. The discussion 
‘of matters connected with this theoretical period of the earth’ 
ane, as it now ap 
act of its actuality. I hope that my present meer 
matter, seeing that we have in our own country fields for its 
full exploration. 
