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Show 32 STEPPES AND DESERTS. ture, described the Deserts of Northern Africa, of Yemen, of Kerman, and Mehan (the Gedrosia of the Greeks), and even as far as Moultan, as forming a single connected sea of sand. (21) In addition to the action of these hot winds, there is (so far as we know) an absence or comparative paucity in Africa of large rivers, of widely extended forests producing coolness and exhaling 'moisture, and of lofty mountains. Of mountains covered with perpetual snow, we know only the western part of the Atlas, (22) whose narrow range, seen in profile from the Atlantic, appeared to the ancient navigators when sailing along the coast as a single, detached, lofty, sky-supporting mount. The eastern prolongation of the chain extends nearly to Dakul, where Carthage, once mistress of the seas, now lies in mouldering ruins. As forming a long extended coastchain, or Gretulian rampart, the effect of the Atlas range is to intercept the cool north breezes, and the vapors which ascend from the Mediterranean. The Mountains of the Moon, Djebel-al-Komr1 ( 28) (fabulously represented as forming part of a mountainous parallel extending from the high plateaux of Habesh, an African Quito, to the sources of the Senegal,) were supposed to rise above the limit of perpetual snow. The Cordillera of Lupata, which extends along the eastern coast of Mozambique and Monomotapa, as the Andes along the western coast of Peru, is believed to be covered with perpetual snow in the gold districts of Machinga and Mocanga. But all these mountains, with the abundant waters to which they give rise, are far remote from the immense Desert which stretches from the southern declivity of the Atlas to the Niger. Possibly, however, all the causes of heat and dryness which have been enumerated may have been insufficient to transform such considerable parts of the African plains into a dreadful desert, without ihe concurrence of some revolution of na,ture-such1 for instance, as an irruption of the ocean, whereby these flat regions may have been despoiled of their coating of vegetable soil, as well as of the plants which it nourished. Profound obscurity veils the period of such an event, and the force which determined the irruption. Perhaps it may have been caused by the great "rotatory current" (24 ) which sends the warmer water of the Mexican gulf over the banks |