A COLONY OF BUTTERFLIES. 83 



more snow fell than was melted, and this snow 

 stayed, sum.mer and winter, and accumulated more 

 and more. It consolidated into iiche and glacial 

 ice. Forming on the highest lands, the ice-rivers 

 filled the ravines and joined, upon the plains, the 

 main body of ice which was pressing southward 

 from the pole. Summer and winter still alternated, 

 but, as is the case now in the extreme north, the 

 summers were short and the winters long. The 

 advancing ice destroyed, or drove before it, the 

 insects and animals of the warmer climates, which 

 it chilled by its approach. But it was kind to its 

 own children. It brought down with it the Oeneis 

 butterflies and the reindeer. Before its feet it 

 spread food for both of these, year by year, always 

 pushing food and animals to the south. At the 

 probable rate of less than a mile in a hundred 

 years, it brought them at last from the farthest 

 north into Virginia; not the Virginia of to-day, 

 but Virginia changed into an Arctic scene*. 



At length the climate began again to change. 

 The point of farthest advance reached, the ice com- 

 menced to retrace its steps. And it called its own 

 back with it, alluring them by their food, scattered 

 ever farther and farther to the north. At some 

 time, the lengthening summers and shortening 

 winters brought the main Ice-sheet back into New 

 Ensrland. Prom Southern New York to Connecti- 

 cut, to Massachusetts, to Vermont, to New Hamp- 



* Consult A. R. Grote, ' Proceedings of the American Association 

 for the Advancement of Science,' p. 222 (1875) ; also ' Silliman's 

 Journal ' for the same year. 



