336 = A. «RB. Grote—LHffect of the Glacial Epoch upon the 
American continent. These facts, in the present instance, are 
furnished by a study of our Lepidoptera, or certain kinds of 
butterflies and moths now inhabiting the United States and 
adjacent territories. Before proceeding with the subject, a 
brief statement of the phenomena assumed to have attended 
the advent of the Glacial period is necessary. 
At the close of the Tertiary, the temperature of the earth’s 
surface underwent a gradual change by a continuous loss of 
hea he winters became longer, the summers shorter. The 
tops of granitic mountains in the east and west of the North 
American continent, now in summer time bare of snow and 
harboring a scanty flora and fauna, became, summer and winter, 
covered with congealed deposits. In time the mountain snows 
movement from north south, absorbed the local glacial 
streams in their course, and extended over all physical barriers. 
e Appalachians an ky Mountains are supposed to have 
e 
After this brief statement of the outlines of the opening of 
the Glacial period, we turn to some facts offered by a study 
of certain of our existing species of butterflies and moths. 
The tops of the White Mountains and the ranges of mountain 
elevations in Colorado offer us particular kinds of insects, living 
in an isolated manner at the present day, and confined to their 
respective localities. In order to find insects like them we 
have to explore the plains of Labrador and the northern portion 
