THE CASPIAN SEA AND ITS NEIGHBORS 357
their flocks southward in winter to the warm plains of India. In the Lop basin an opposite state of affairs pre-
vailed, and conditions were highly favorable. The rivers were full of water ; Lop-Nor was the " Great Salt Lake;" the desert was comparatively small and the zone of vegetation extensive; and on all sides there was a density of population and a degree of prosperity far beyond those of to-day. And in the Turfan basin the same was probably true.
A great change took place throughout the six basins during the early centuries of the Christian era. The lakes of Gyoljuk, Seyistan, the Caspian, Lop-Nor, and presumably Turfan were greatly reduced in size. In the case of the first three, parts of the old lake-beds were utilized as sites for villages. Except in Kashmir, the change of climate appears to have brought disaster, although in Turkey the question has not yet been investigated. In the other regions, scores of once prosperous oases were abandoned for lack of water. A few of the displaced inhabitants probably went into the mountains and dug canals such as those of Son Kul. Others perhaps went to Kashmir, which now became warm enough for agriculture, and hence able to support a far larger population. The rest appear to have been impelled to start hither and thither in waves of migration to confound the civilized world.
Again there came a change. The process of desiccation gave place to a slight, but important tendency toward increased rainfall and lower temperature. Kashmir became colder and more snowy, and hence more isolated ; the rivers of Lop and Turfan gained greater volume; and the lakes of Lop, the Caspian, and Seyistan expanded once more. The
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