THE EARLY MAN OF NORTH AMERICA. 591 



north. But year after year it got warmer, and the local glaciers 

 shortened, extending less and less into the valleys. The trapped 

 insects could not then rejoin their mates, but instead climbed the 

 mountain, dwelling farther and farther up as time progressed and the 

 climate changed. At length they reached the summit of Mount Wash- 

 ington, where we still find some of them, and whence there is no 

 escape. The plants formed patches in congenial spots on the sides 

 of the mountain, driven upward by the new flora filling the valley 

 from the southward. Now, in examining these colonists, we find 

 among them the herb-like willow (Salix herbacea), its short stems 

 hardly rising above an inch from the ground, and other species of 

 plants which we have to go far north to meet again. There, too, 

 the White Mountain butterfly (CEneis semidea) appears year by year, 

 swaying in feeble flight over its narrow range, while its congeners are 

 found one thousand miles to the northward in Labrador. These ex- 

 amples could be easily multiplied. 



But this sort of mountain-trap was not large enough to hold such 

 game as men and reindeer. These both went northward, and are not 

 to be found alive with us ; but the one left his implements, and the 

 other its bones, to tell of their presence at that time, and in these 

 latitudes. 



When we come to the question as to the descendants of this early 

 North American man, we cannot avoid studying for a moment the 

 movements or migrations of man over the surface of the earth gener- 

 ally. I think we may divide his migrations into two main classes 

 from their motives : 



A primitive migration one influenced solely by physical causes 

 affecting his existence, and which must have been in more extended 

 operation in early times when he was unprovided with means of his 

 own invention against a change in his surroundings. Such migra- 

 tions are operative now among certain of our Indians, who move from 

 place to place with the game upon which they subsist and with the 

 season. 



A culture migration one arising from a certain stage of intellect- 

 ual advancement when the movements of man are determined by 

 ultimate and not immediate considerations. The movements of the 

 Indo-European races fall within this category. Besides these, there 

 are to be distinguished accidental migrations, which man submitted 

 to against his will. We know that insects and plants are so trans- 

 ported. Birds and ocean-currents carry seeds from land to land; In- 

 sects on a blade of grass or a fallen bough are carried down a river by 

 the current to found colonies of their race far from their place of ori- 

 gin. And such circumstances give rise to races and varieties among 

 species modifiable by the peculiarities of their new localities. The 

 accidental migrations of man may be considered as belonging to the 

 epoch of culture-migration, since they must more usually have oc- 



