Miscellaneous. 441 



The genera (Eneis 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 ((Eneis semidea) we have a form 

 sustaining itself on a very limited alpine area on the top of Mount 

 Washington*. Although there is some doubt whether precisely the 

 same form of (Eneis has been discovered in Colorado, the fact remains 

 that (Eneis butterflies exceedingly like it, though registered by us 

 under different specific names, live in Labrador and Colorado. 

 Whether the White-Mountain butterfly ((Eneis semidea) be, as sus- 

 pected 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 (Eneis 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 period. 



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 "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 mountain-ravines, thus running at 

 variance with the main body of the glacier, being determined by 

 local topography. 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 period the geographical 

 distribution of the genus (Eneis 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, detained 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 flitting (Eneis 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 



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

 Mr. Scudder first pointed out the existence of alpine aud subalpine 

 fauual belts on Mount Washington, and makes the interesting remark 

 " that if the summit of Mount Washington were somewhat less than 

 2000 feet higher, it would reach the limit of perpetual snow." 



Ann. & Mag. N. Hist. Ser. 4. Vol. xvi. 31 



