DESERT (ckstrtus, solitary), a term used to denote any portion of the earth's surface which, from its barrenness, as in the case of the arid places of northern Africa and Arabia, or from its rank exuberance, as in the case of the silvas of South America, is unfitted to be the site of great commercial and industrial communities. Many names, each differing in meaning to some extent, are employed to designate the desert-plains of different countries. The desert proper may be said to signify the vast sandy plains of Africa and Arabia; while the flats extending from the Black sea on the n., and from Persia on the s., onward across Thibet and Tartary to the north-eastern coasts of Asia, are called steppes; those in the northern division of South America, silvan or desert-for ests; those in the other portions of South America, llanos and pampas; and those in North America, prairies or savannahs. All these, though widely differing in individual characteristics, have in common the important physical features of wide extent and uni form general level. The oases, which are occasional spots in the desert where springs arise, and where the waste is enlivened by the presence of vegetation, are usually lower than the general level of the surrounding plain. The great and famous desert-ground, however, is to be found in the old world. A huge tract of comparatively rainless coun try stretches almost continuously from the north Atlantic to the shores of the north Pacific, thus forming a great belt of sand from c. to w., along the whole extent of tho
eastern hemisphere. Beginning from cape Nun on the n.w. coast of Africa, the Great Sahara, the grand type of all desert-grounds, stretches away eastward from the shores of the Atlantic to the banks of the Nile, its eastern division being frequently called the desert of Libya. Crossing the Nile, by the irrigation and inundations of which alone Egypt is preserved from subsiding into the waste condition of the surrounding country, the desert is again found, interposing a strip of hot sand .between the right bank of the Nile and the western border of the Red sea, upon whose shores no rain ever falls. On the right shore of the Red sea, desert-grounds unvisited by any rains prevail over the greater portion of Arabia, and stretch onward, with occasional inter ruption, over Persia, Thibet, and the Tartaries. The most extensive desert in the eastern portion of these arid districts is called the desert of Gobi, whiCh extends from the west ern extremity of Whet me. to the shores of lake Baikal. The cause of this extraordinary zone of parched land and of similar smaller tracts in other parts of the world, will be best explained under the head of RAIN.