The climate at Lop-nor is very different in winter and summer. In winter the temperature falls to 22 deg. below zero, and rises in summer to 104 deg. Large variations like this always occur in the interior of the great continents of the world, except in the heart of Africa, close to the equator, where it is always warm. On the coasts the variation is smaller, for the sea cools the air in summer and warms it in winter. In the Lop-nor country the rivers and lakes are frozen hard in winter, but in summer suffocating heat prevails. Men are tortured by great swarms of gnats, and cattle are devoured by gadflies. It has even happened that animals have been so seriously attacked by gadflies that they have died from loss of blood. Fortunately, the flies come out only as long as the sun is up, and therefore the animals are left in peace at night. During the day horses and camels must be kept among the reeds, where the flies do not come. Incredible numbers of wild geese and ducks, swans and other swimming birds breed at Lop-nor, and the open water is studded all over with chattering birds. In late autumn they fly southwards through Tibet, and in winter the lakes are quiet, with yellow reeds sticking up through the ice. WILD CAMELS The level region over which the Lop-nor has wandered for thousands of years from north to south is called the Lop desert. Its stillness is broken only from time to time by easterly storms which roll like thunder over the yellow clay ground. In the course of ages these strong spring storms have ploughed out channels and furrows in the clay, but otherwise the desert is as level as a frozen sea, the places where Lop-nor formerly spread out its water being marked only by pink mollusc shells. On the north the Lop desert is bounded by the easternmost chains of the Tien-shan, which the Chinese also call the "Dry Mountains." They deserve the name, for their sides are hardly ever washed by rain; but at their southern foot a few salt springs are to be found. Round them grow reeds and tamarisks, and even in other places near the mountains some vegetation struggles for existence.