166 THE CANADIAN ENTOMOLOGIST. 



features of its advance were repeated, in reverse order, on the subsidence 

 of the main ice-sheet or glacial sea. The local glaciers appeared again, 

 separate from the main body of ice, and filled the valleys and the moun- 

 tain ravines, thus running at variance with the main body of the glacier, 

 being determined by local topograph}'. A reversal of the temperature 

 shortened the winters and lengthened the summers. Ice-loving insects, 

 such as our White Mountain butterfly, hung on the outskirts of the main 

 ice-sheet, where they found their fitting conditions of temperature and 

 food. The main ice-sheet had pushed them insensibly before it, and 

 during the continuance of the glacial epoch, the geographical distribution 

 of the genus Oeneh had been changed from a high northern region to one 

 which may well have included portions of the Southern States. And, on 

 its decline, the ice-sheet drew them back again after itself by easy stages ; 

 yet not all of them. Some of these butterflies strayed by the way, delayed 

 by the physical nature of the country and destined to plant colonies apart 

 from their companions. When the main ice-sheet left the foot of the 

 White Mountains, on its long march back to the pole, where it now seems 

 to rest, some of these wayward, Hitting, Oeneis butterflies were left behind. 

 These had strayed up behind the local glaciers on Mount Washington and 

 so became separate from the main body of their companions, 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 Labra- 

 dor 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 epoch 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 /one. 



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 Labra- 

 dor within the limits of New Hampshire. And in the case of the moths an 

 analogous state of things exists. The species Anuria melanopa is found 

 on Mount Washington, the Rocky Mountains and Labrador. Agrotis 

 islandica is found in Iceland, Labrador, the White Mountains, and, per- 



