In the struggle for existence in the vegetable world, the tree line pushes as far up the mountain as conditions of climate and soil will permit.  Then comes a season of fiercer storms, intenser cold and invading ice upon the peaks.  Havoc is wrought, and the forest drops back across a zone of border warfare—­for war belongs to borders—­leaving behind it here and there a dwarfed pine or gnarled and twisted juniper which has survived the onslaught of the enemy, Now these are stragglers in the retreat, but are destined later in milder years to serve as outposts in the advance of the forest to recover its lost ground.  Here we have a border scene which is typical in nature—­the belt of unbroken forest, growing thinner and more stunted toward its upper edge, succeeded by a zone of scattered trees, which may form a cluster perhaps in some sheltered gulch where soil has collected and north winds are excluded, and higher still the whitened skeleton of a tree to show how far the forest once invaded the domain of the waste.

[Sidenote:  Oscillating boundaries]

The habitable area of the earth everywhere shows its boundaries to be peripheral zones of varying width, now occupied and now deserted, protruding or receding according to external conditions of climate and soil, and subject to seasonal change.  The distribution of human life becomes sparser from the temperate regions toward the Arctic Circle, foreshadowing the unpeopled wastes of the ice-fields beyond.  The outward movement from the Tropics poleward halts where life conditions disappear, and there finds its boundary; but as life conditions advance or retreat with the seasons, so does that boundary.  On the west coast of Greenland the Eskimo village of Etah, at about the seventy-eighth parallel, marks the northern limit of permanent or winter settlement; but in summer the Eskimo, in his kayak, follows the musk-ox and seal much farther north and there leaves his igloo to testify to the wide range of his poleward migration.  Numerous relics of the Eskimo and their summer encampments have been found along Lady Franklin Bay in northern Grinnell Land (81 deg. 50’ N. L.), but in the interior, on the outlet streams of Lake Hazen, explorers have discovered remains of habitations which had evidently, in previous ages, been permanently occupied.[326] The Murman Coast of the Kola Peninsula has in summer a large population of Russian fishermen and forty or more fishing stations; but when the catch is over at the end of August, and the Arctic winter approaches, the stations are closed, and the three thousand fishermen return to their permanent homes on the shores of the White Sea.[327] Farther east along this polar fringe of Russia, the little village of Charbarova, located on the Jugor Strait, is inhabited in summer by a number of Samoyedes, who pasture their reindeer over on Vaygats Island, and by some Russians and Finns, who come from the White Sea towns to trade with the Samoyedes and