so far north, as the banded lemming. The arctic fox is another characteristic 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 temperature 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 necessitate 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
