DESERT (Fr. Lat. dcsertuin. from de screr(% to abandon. from de, from -L RerCrC. to bind). A region which supports little plant and animal life. As thus defined. the term includes all barren areas. whether their barrenness is caused by intense cold, lack of soil, or by in sufficient moisture. Greenland. southern Pata gonia, and the Arctic and Antarctic lands in general are deserts. determined as to character by their situation in high latitudes. In common wage, however, the term is limited to the great continental wa-tes, lying within the tropical and temperate zones, which are scantily watered by rains. The most extensive of these arid deserts are found in Asia. Africa, and Australia: they are much less prominent areally in North and South America, and in Europe they scarcely occur. The Sahara Desert is a part of an arid belt that reaches from the Atlantic coast across the northern limb of Africa to the Bed Sea. and is continued through Arabia, Persia, Turkestan, Sungaria. and Mongolia, almost to the Pacific shores of Asia. The eastern extension of this belt, which is wider than the central portion, is known as the Desert of Gobi. In South Africa the Kalahari Desert occupies a large area between the Zambezi River on I113 north and the Orange and Limpopo rivers on the south. The arid regions of _Australia are situated in the central part of the continent, and are of vast extent. The Atacama Desert, in northern Chile, and the Colorado Desert, in California. are of eomparatively limited area, but they furnish per haps the best illustrations of regions in America having an arid climate.
The arid deserts vary greatly in surface con formation, and often they are far from having the monotonous character which popular imag ination has ascribed to them. The Sahara Desert consists essentially of a series of elevated plains rising in terraces to altitudes of several thousand feet. Within its compass t here are sandy stretches with the surface formed by the winds into shifting dunes, and great areas underlain by stratified rocks, where the surface i- strewn with boulders and has been detply eroded by the rivers that existed in past ages. Oases are found at intervals in deserts wherever there are natural springs or mountains of sufficient height to cause precipitation. Tlw date-palm and other food
plants may flourish here. while in the less favored regions the plant life is limited to representa tives of the more hardy families, such as cacti and artemisia. The dryness of the desert climate and the scanty vegetation give rise to rock sculpturing in columnar, tabular, and fantastic form,. Violent wind - storms, accompanied by whirlwinds, cloudless skies. extraordinary heat by day and rapid fall of the temperature at night, and an annual rainfall that varies from a few inches to an small amount, are characteristic meteorological features.
The small rainfall, upon which the aridity of deserts depends, is due to the following Prevalence of dry winds: isolation by mountain barriers along the borders: great distance from areas of evaporation, or oceans. The Sahara is an illustration of a desert caused by dry winds. In the northern part the prevailing winds blow from the northeast. and rain falls only in winter, when cyclonic storms from the Atlantic pass over the region. The moist winds that have their source in the Gulf of Guinea bring rain to the southern Sahara. but in small amounts only, as their temperature—and consequently their capacity for holding moisture—is increased be fore they reach far into the interior. A similar condition prevails in the Desert of Atacama, where the prevailing winds are from the south. When mountain ranges occupy the borders of a region the winds are deprived of their moisture before they pass beyond the interior slopes. Thus the Kalahari Desert receives a very small rain fall from the east winds, which bring an abun dance tb the region lying between the South African highlands and the Indian Ocean. In America the arid region of Nevada. Utah. and Arizona is shut in from the Pacific Ocean by the Sierra Nevada and the coast ranges. Finally, desert conditions may prevail in regions situated at great distances from oceans. owing to the gradual precipitation of moisture as the winds travel inland. The interior of Asia owes its dry climate to this cause. Consult Neumayr, Erdge schichte (Leipzig. 1895).