OV ARTS AND SCIENCES. 1 25 



region that it " gives off three long arms or chains of islands, 

 which reach far south along three great mountain systems of 

 the United States — an eastern arm in the Alleghanies, a central 

 arm in the Rocky Mountains, and a western arm in the Cas- 

 cades and Sierra Nevada." It is with the first of these that we 

 have to do in this paper. 



In his study of the distribution of animals in America, Dr. 

 Merriam found that of the 130 genera of non-pelagic mammals 

 inhabiting North America north of Panama, there are only six 

 genera each of which ranges over large parts of both Boreal 

 and Sonoran regions, including, of course, the transition zone 

 between. They are Sciiiroptems , Sciicrus, Spennophiliis ^ Le- 

 pus, Canis, and Lutra. These genera — ^comprising the squir- 

 rels, the rabbits, the wolves, and the otters — are all of great an- 

 tiquity, the remains of most of them having been found as low 

 down as the Miocene. They were early diffused over the con- 

 tinent, and their peculiar habits of life, although so dissimilar, 

 enabled them to survive the great mutations of these land areas 

 since Miocene times. 



It is well established that during the Glacial Epoch many 

 genera formerly represented in North America perished utterly. 

 But upon the advance of the great ice sheet and its attendant 

 cold, the wolves, the rabbits and the otters retreated southward, 

 and with them went the squirrels to find new homes in the trop- 

 ics, somewhat over-crowded, doubtless, but able to adapt them- 

 selves to their new surroundings and bide their time. 



When the ice began its final retreat, and vegetation slowly 

 reasserted its dominion, a few of the hardier and more adven- 

 turous of the squirrels pushed their way along the sea coast and 

 up the river valleys. Among these were they of the vermicu- 

 lated bellies and the black band near the tip of the tail. They 

 multiplied, spread over the land, and undoubtedly had things 

 much their own way for a time — perhaps for many centuries. 

 Then a horde of their cousins began to press on from behind. 

 These new-comers were less showy in their rusty-red coats, but 

 they were larger, more noisy, and more aggressive. The effect 

 was similar to that of the Teutonic invasion upon the Celts. 



