82 A COLONY OF BUTTERFLIES. 



grapher was Thomas Say, who described it in the 

 year 1828. Previously, Mr. Thomas Nuttall, the 

 botanist, had collected specimens of the butterfly, 

 while Say's original figure of the species was drawn 

 from an individual presented to him by Mr. Charles 

 Pickering, of Salem. 



It is 1800 miles west from Mount Washington to 

 Long's Peak, Colorado. In this direction, over all 

 the level stretch of country, no butterflies like our 

 White-Mountain butterfly are to be met with. But, 

 in Colorado, species similar to the White-Mountain 

 butterfly, and probably one exactly like it, are 

 found again occupying elevated lands. To the 

 northward it is 1000 miles to Hopedale, Labrador, 

 and here again very similar butterflies are found 

 living in that barren region. 



This is a strange distribution for a butterfly, and 

 so the question comes up as to the manner in which 

 it was brought about. By comparing what has 

 been found out, with regard to past conditions of 

 the earth and the present state of things, a solu- 

 tion of the question has been offered. This solu- 

 tion gives us the Ice period in North America as 

 the agent, which induced the j)resent distribution 

 of the genus to which the White-Mountain butterfly 

 belongs. And the colonization of the butterfly, on 

 our New-England mountains, would have been 

 effected in this wise. 



Before the Ice reign commenced in New Eng- 

 land, it had extended itself over the north of the 

 continent. The ice gradually and very slowly 

 advanced, year by year, to the southward. Always 



