arisk branches, and narrow passages ; at the top, one looked out upon what seemed to be a thick growth of bushy vegetation perched upon hills and fading away in the near distance in a dense haze of dust. The scenery was most monotonous and gloomy. No'sun broke through the haze; no landmarks appeared; there was nothing to guide us save
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the compass. Even with that I found it most difficult to make our countless minute zigzags balance one another, and thus to preserve a straight course.
The tamarisk mound is highly significant as an indicator of changes of climate. One finds it in every stage of development, from one foot high with a vigorous growth of slender flourish ng bushes, to sixty feet high with nothing but huge, gnarled trunks, dead for hundreds of years. During seven years in Asia, so far as I remember, I have never seen young tamarisk bushes growing anywhere except upon the flood-plains of streams, or in other places where the ground was thoroughly saturated with water. On flood-plains from which the water has been diverted by man for four or five years, half or more of the tamarisks are usually dead or dying. In later stages still more die, and only those with very deep roots persist. Then the wind begins to dissect the dry plain, carrying away the finer materials from the parts where the plants have died, and heaping up the coarser grains of sand in the protected spots where living bushes check its force. Thus mounds are formed, and their height is increased by œolian erosion at the base and by œolian deposition at the top. The depth to which erosion can proceed is limited by the level of underground water, and the amount of deposition is limited by the amount of sand avail-
IIIFカラー高解像度
