In summer, great heat is encountered here on the relatively low (3000-4600 feet), gravelly expanses on the north and on those of the south (4000-5000 feet); but on the higher ground between, which in the Pe-shan ranges ascends to , there is great cold even in summer, and a wide daily range of temperature. Above the broad and deep accumulations of the products of denudation which have been brought down by the rivers from the Tian Shan ranges (e.g. the Karlyk-tagh) on the north and from the Nanshan on the south, and have filled up the cauldron-shaped valleys, there rises a broad swelling, built up of granitic rocks, crystalline schists and metamorphosed sedimentary rocks of both Archaic and Palaeozoic age, all greatly folded and tilted up, and shot through with numerous irruptions of volcanic rocks, predominantly porphyritic and dioritic. On this swelling rise four more or less parallel mountain ranges of the Pe-shan system, together with a fifth chain of hills farther south, all having a strike from west-northwest to east-northeast. The range farthest north rises to above the desert and above sea-level, the next two ranges reach above the general level of the desert, and the range farthest south or an absolute altitude of , while the fifth chain of hills does not exceed in relative elevation.