THE TUNDRAS AND STEPPES OF PREHISTORIC EUROPE. 323 



so far north, as the banded lemming. The arctic fox is another charac- 

 teristic member of the tundra fauna, having a high northern range. 

 It occasionally wanders south to the sixtieth parallel, but that is only 

 in treeless regions, for it everywhere avoids the forest, seeming to 

 prefer the barest and most sterile lands. Another common denizen of 

 the tundras is the arctic or mountain hare. This is the same species 

 so commonly met with above the limits of the forests in the mountains 

 of temperate Europe. A closely allied form (polar hare) frequents the 

 barrens of North America. The reindeer must also be included in the 

 tundra fauna, although in winter it ranges far into the forest zone. 

 The muskox, formerly a native of Eurasia, is now confined to North 

 America. Like the arctic fox it avoids the forests, ranging north of 

 these from the the sixtieth parallel up to the highest latitudes. 



Such are the most characteristic mammals of the tundras. There 

 are many other animals, however, which frequent the same regions, 

 more especially in summer. Among these may be mentioned glutton, 

 voles, ermine, weasel, wolf, common fox, and brown bear. The summer 

 visitors also include a vast host of birds, especially water birds. 



The climate of all these northern plains is extreme — the winter tem- 

 perature falling upon an average to 27° below zero, while in summer 

 the average temperature is about 50° F. The actual range in certain 

 regions is of course considerably greater. These conditions necessarily 

 give rise to annual migrations. Only a few mammals, as we have seen, 

 brave the long winter of the tundras, where river and lake are often 

 frozen solid, and the whole land is sheeted in snow. During the great 

 frosts the air is remarkably still, but as winter draws to a close storms 

 of wind and snow become frequent. Wide regions are then often swept 

 bare, and the snow is blown into every abrupt hollow and depression in 

 the plains, and into the gullies and ravines of the hills, where it becomes 

 so beaten as often to bear the weight of a man. Not only snow, but 

 sand and dust, are thus swept forward. The sand and dust are no 

 doubt largely obtained from the great river valleys and deltas, but no 

 inconsiderable proportion is derived also from the bare rocky hills and 

 mountains, which in many places diversify the surface of the circum- 

 polar plains. Frost is a great pulverizer of rocks, not only splitting 

 them into fragments, but disintegrating their surfaces into grit, sand, 

 and dust. It is remarkable how in the highest northern regions the 

 surface of the snow often becomes discolored with fine sand and dust 

 derived in this way from exposed rock surfaces. 



We need not enter into further details as to the physical conditions 

 of the tundras. It will be sufficient to sum up here the points which 

 are most deserving of our attention. Briefly they are these: 



1. The climatic conditions of the tundras are extreme, and necessi- 

 tate annual migrations. 



2. The flora is represented chiefly by mosses and lichens. Here and 

 there, however, tracts of grassy meadow occur, while inlets and oases 



