The place where the ferry-boat was frozen in for the winter is called New Lake (see map, p. 90). Just at this spot the Tarim bends southwards, falling farther down into a very shallow lake called Lop-nor. The whole country here is so flat that with the naked eye no inequalities can be detected. Therefore the river often changes its bed, sometimes for short and sometimes for long distances. Formerly the river did not bend southwards, but proceeded straight on eastwards, terminating in another lake also called Lop-nor, which lay in the northern part of the desert, and which is mentioned in old Chinese geographies. The peculiarity of Lop-nor is, then, that the lake moves about, and, in conjunction with the lower course of the Tarim, swings like a pendulum between north and south. I made many excursions in that part of the desert where the Lop-nor formerly lay, and mapped out the old river-bed and the old lake. There I discovered ruins of villages and farms, ancient canoes and household utensils, tree trunks dry as tinder and roots of reeds and rushes. In a mud house I found also a whole collection of Chinese manuscripts, which threw much light on the state of the country at the time when men could exist there. These writings were more than 1600 years old. The explanation of the lake's wanderings is this. At the time of high water the Tarim is always full of silt, and the old lake was very shallow. The lake, therefore, was silted up with mud and decaying vegetation, and by the same process the bed of the river was raised. At last came the time when the Tarim sought for an outlet to the south, where the country was somewhat lower. The old bed was dried up by degrees and the water in the lake evaporated. The sheet of water remained, indeed, for a long time, but it shrank up from year to year. At last there was not a drop of water left, and the whole country dried up. The poplar woods perished, and the reeds withered and were blown away by the wind. The men left their huts and moved down the new water channel to settle at the new lake, where they erected new huts. The Tarim and Lop-nor had swung like a pendulum to the south, and men, animals, and plants were obliged to follow. The same thing then occurred in the south. The new river and lake were silted up and the water returned northwards. Thus the water swung repeatedly from north to south, but of course many hundreds of years elapsed between the vibrations.