THE CANADIAN ENTOMOLOGIST. 165 



had been prepared for the encounter. We may expect that multitudes of 

 specific forms ultimately perished, of whose remains no traces have been 

 preserved. 



Such being a brief statement of the outlines of the opening of the 

 glacial epoch, 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 of the North American 

 continent, in regions offering analogous conditions of climate to those 

 obtaining on the summits of these mountains. The genera Oeneis and 

 Brenthis among the Butterflies, and Anarta and Agrotis among the Moths 

 are represented by the same or similar species in all of the above 

 mentioned localities. In the case of the White Mountain butterfly, 

 Oeneis se/nidea, we have a form sustaining itself on a very limited Alpine 

 area on the top of Mount Washington.* Although there is some doubt 

 that precisely the same form of Oeneis has been discovered in Colorado, 

 the fact remains that Oeneis butterflies exceedingly like it, though registered 

 by us under different specific names, live in Labrador and Colorado. 

 Whether the White Mountain butterfly, Oeneis semidea, be, as suspected 

 by Lederer, a modification of some of the Labradorian forms of the 

 genus, or not, the geographical distribution which its genus enjoys cannot 

 be meaningless. The question comes up, with regard to the White 

 Mountain butterfly, as to the manner in which this species of Oeneis 

 attained its present restricted geographical area — How did the White 

 Mountain butterfly get up the White Mountains ? And it is this question 

 that I am disposed to answer by the action attendant on the decline of 

 the glacial epoch. 



I have before briefly outlined the phenomena attendant on the advance 

 of the ice-sheet, and I now dwell for a moment on the action which must 

 equally be presumed to have accompanied its retirement. Many of the 



* See Mr. Scudder's article in the "Geology of New Hampshire,'' 1, 342. Mr. 

 Scudder first pointed out the existence of Alpine and sub- Alpine faunal belts on 

 Mount Washington, and interestingly remarks, "that if the summit of Mount 

 Washington were somewhat less than two thousand feet higher, it would reach the 

 limit of perpetual snow." 



