Henry Newton Dickson

“ DESERT, a term somewhat loosely employed to describe those parts of the land surface of the earth which do not produce sufficient vegetation to support a human population. Few areas of large extent in any part of the world are absolutely devoid of vegetation, and the transition from typical desert conditions is often very gradual and ill-defined. ”

“ When water can be obtained and distributed over an arid region by irrigation, the surface as a rule becomes extremely productive. Natural springs give rise to oases at intervals and make the crossing of large deserts possible. Where a river crosses a desert at a level near that of the general surface, irrigation can be carried on with extremely profitable results, as has been done in the valley of the Nile and in parts of the Great Basin of North America; in cases, however, where the river has cut deeply and flows far below the general surface, irrigation is too expensive. ”

“ Where the line of elevated land runs east and west, as in Asia, the desert belt tends to be displaced into higher latitudes, and where the line runs north and south, as in Africa, America and Australia, the desert zone is cut through on the windward side of the elevation and the arid conditions intensified on the lee side. Desert conditions also arise from local causes, as in the case of the Indian desert situated in a region inaccessible to either of the two main branches of the south-west monsoon. ”