SZECHUAN, the largest province of China Proper, area formerly nearly 220,000 sq.m., but after the institution of Kham (Chwanben) reduced to 16o,000--185,000 sq.m., with a popula tion only less dense than that of Shantung, recent estimates varying from 54,500,000 to about 76,613,000. The heart of Szechuan is the plateau known as the Red basin, a region that continued as a gulf of the sea for some time, in later Palaeozoic period, after the north Mongolian region became land, and changed to a freshwater lake during the Mesozoic, with deposition of the post-Rhaetic red sandstones, later wrinkled and converted into land. The province is bordered on the west by the immense eastern Tibetan fault-zone, which gives a rapid rise from the Min-ho (less than 1,500 ft. above sea-level) by broad terraces to great north-south mountain lines, the greater part of which is well over the 12,000 ft. level. Most of these western highlands were included in the province of Kham (Chwanben) save that the Liangshan and some other mountains involved in great river-bends remained in south-west Szechuan. There is much evidence of a long continuance of earth movement along this great fault line, and the river courses of the highland have adapted them selves to the changes involved, running southward between the ranges turning eastwards into south-west Szechuan and north Yunnan, eventually uniting in the north-eastward course of the Yangtze-Kiang. The mountain courses of the rivers are tor rential; in the Red basin the rivers are generally navigable and afford the best means of communication. On the north-east, the Red basin grades up to the Tapaling or Tapashan, beyond which, to the north, is the great west-east range of the Tsinlingshan. The Tapaling (Tapashan) end in a great fault against the Hupeh basin, eastwards ; and the latter is much lower than the Red basin. The Yangtze-Kiang makes its way from the one down to the other through the famous gorges of the north-east frontier of Szechuan to Ichangin Hupeh. Von Richtofen thought that the sinking of the Red basin, as compared with the Tibetan high land, has continued until recent times, whereas that of the Hupeh basin, as compared with the Tapaling and the Red basin, ended earlier. The result would be a tilt, lessening the slopes in the west of Szechuan, within the basin, but increasing them in the north-east ; this furnishes at least a supplementary interpreta tion of the Yangtze-Kiang (q.v.) gorges, which are so notable a feature of China's physical geography, and have played such a part in isolating Szechuan from Hupeh. The Yangtze and its feeders within the basin in the west are less closely encased, so there are considerable alluvial plains, as around Cheng-tu, the capital, where irrigation is highly developed. Beyond the Yang
tze-Kiang, to the south-east, stands the limestone horst of the province of Kweichow, with its border towards the Red basin, often at an altitude of 4,500 ft., drained by streams which reach the deep channel of the Yangtze by narrow valleys. The name Szechuan means four rivers, and the Yangtze-Kiang is made up of the Min, To, Fu and Kialing, flowing north to south into the Red basin, where they meet the Kin-Sha or Upper Yangtze, which has also been formed of north to south streams and has then rounded the Liangshan and flowed north along its eastern side, really entering the basin at Sui-fu (Su-chow-fu) where the Min, from Chengtu, joins it.
The climate of the Red basin may be studied from data for Chung-king, at the junction of the Kialing with the Yangtze. The monthly average temperatures vary from 49° F in December and January to F in July and August. The average mini mum per month is not more than below the average, so, in the Red basin, snow and frost are not often lasting. The rainfall, very low under the influence of the Central Asiatic anti cyclone in December, January and February, but March has a rainfall of 2.8 in., April a rainfall of 4 in., and so the amount increases up to a maxima of about 11 in. in each of the months of June and August. The early onset of rain before the summer monsoon has begun is probably explained by the heating of the air in the deep basin and the consequent development of cyclones, which thus milden the climate of a region in the heart of a conti nent. The winter is not too cold for growth of cereals (wheat, barley, oats, millet) and the summer monsoon gives opportuni ties for almost tropical crops at low levels, and rice (especially on irrigated alluvium near Chengtu), sugar, hemp, sesamum, pulses, mulberry, oranges, maize and tobacco are thus grown. Wax trees are important around Kiating-fu. (See Sui-Fu.) Until the last millennium B.C. Szechuan was entirely non Chinese. and was under Indian culture influence. the results of which persist in the cultivation of sugar-cane, the use of great water-wheels for irrigation, and the presence of the zebu and water-buffalo. The Tsin dynasty incorporated Szechuan within the empire, but its isolation has often made it a basis for sepa ratist movements. The population within the basin has become definitely Chinese, though almost forming a separate nationality within the Chinese group. The western highlands have a sparse Tibetan population, while in the south-west are non-Chinese groups, Lolo, Sifan, Miautse, some probably of very long standing locally, others of relative late, if still pre-Chinese, entry.