steeply sloping piedmont region of coarse gravel, and reaches the flatter region of fine sand and impervious
clay, it approaches the surface, or rather the surface ap-
proaches it, until finally, near the end of the last fine gravels, the ground becomes permanently damp close to the sur-
face. The phenomenon is the same as the so-called spring-line in northern Italy, where the water from the Alps, after flowing underground through piedmont gravels, forms a line of springs. In the Lop basin, where the surface of the ground becomes damp, an abundant growth of vegetation, chiefly reeds, tamarisks, and poplars, is able to flourish without the help of rain. The zone of vegetation thus formed varies in width from nearly twenty miles between Khotan and Keriya, to a few hundred yards at the eastern end of Lop-Nor, but its character is everywhere much the same. It is unmistakable along the entire south side of the basin for nearly a thousand miles, and is almost equally continuous, I believe, on the north side, though there it is much less noticeable because its location is almost coincident with that of the similar zone of vegetation of the eccentrically placed Tarim River. The only part of the basin where the zone cannot be detected is the northeast corner, which is exceptional in many other ways also. Most of the towns of the Lop basin are located in the zone of vegetation ; the chief roads follow it, and from the point of view of geography or the relation of the organic to the inorganic, it is the most important feature of the country.
The areas of sand and lacustrine deposits comprised in the central plain are notable as examples of the kinds of regions not adapted to life of any form. They are more
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