MODES OF LIFE IN DESERTS AND POLAR REGIONS THE great deserts that border the torrid zone comprise the intensely hot and dry regions of Arabia, the Sahara, the Kalahari, central Australia, northern Mexico, and northern Chile. These regions are all alike in having the following characteristics: (1) slight rainfall; (2) scanty vegetation; (3) practically no agriculture; (4) dependence of man on animals; (5) a sparse nomadic popula tion; and (6) low civilization.
If we examine the whole world we find that certain other regions also have these six qualities. These other regions are of two types, (1) continental deserts and (2) polar regions. The continental deserts are in most respects like the trade wind deserts. The chief difference is that although most of the year they are hot like the trade wind deserts, they have a period when they are cold like the polar deserts. Nevada and Utah are mild examples of this kind, while the deserts of Central Asia from the Caspian Sea to the borders of Man churia are extreme examples. The polar regions, which have the six characteristics named above, are not deserts in the ordinary sense for they are covered with snow much of the time and the ground is moist when this melts. Yet in their effect on man the cold regions of Greenland, the northern parts of North America and Asia, the vast continent of Antarctica, and many limited regions at high altitudes like Tibet are much like deserts. Hence in this chapter we shall treat these cold wet polar deserts as well as the ordinary hot dry deserts.
Sparsity of Desert Population.—The sparsity of desert population is astonishing. For instance, the desert part of Arabia, omitting the fairly well-watered regions of Yemen and Oman, is as large as the United States east of the Mississippi River. Yet its population is probably less than 2,000,000, while the corresponding portion of the United States has 70,000,000. In southern Arabia over 300,000 square miles of absolute desert have never been explored and probably contain no inhabitants. This area equals Germany and Italy,
combined, which contain 100,000,000 people. The great Sahara, which is as large as the United States, probably has less people than the Arabian desert, while the Australian desert has least of all among the dry deserts. In our own country, Nevada has only one person for each square mile, and most of these are gathered in oases such as Reno at the eastern base of the Sierras. Contrast this with Massachusetts, which has 450 people per square mile.
Cold deserts have even fewer people than dry deserts. For in stance, if we omit the Labrador coast and the Yukon mining district, the northern provinces of Canada, with an area of 2,000,000 square miles have only about 20,000 inhabitants. This part of Canada is as large as all Europe aside from Russia, but it has only one inhabitant where the European countries have 16,500. Antarctica, the greatest of all deserts, has not a single inhabitant.
The Effect of Scanty Rainfall on the Appearance of Dry Deserts. —Dry deserts present a peculiar appearance. Parts consist of moun tains and parts of plains. Among mountains the bare rock every where sticks out, often painting the landscape with weird colors.
Sometimes it is shattered and broken by the action of frost and sun. Elsewhere it is roughly pitted by the wind. Only in the higher parts of the mountains is the climate moist enough so that there is a fairly deep cover of soil held in place by vegetation.
The weathered rock and soil from the mountains are washed down to the lowlands by the occasional violent rains which fall even in deserts. At the base of the mountains the wet weather torrents deposit their load in great tracts of sloping gravel like enormous beaches from 1 to 40 miles wide. Close to the mountains the gravel consists of large rough fragments, but farther away the materials be come more pebbly and sandy, and finally they merge into plains of sand and clay. Often the sand is heaped into dunes while the clay is scoured by the wind into fantastic pillars and tables.