THE BASIN OF THE HWANG-HO.—This region may be considered as including the six provinces grouped along the course of the Hwang-ho, viz., Kansu, Shensi (north of the Tsin-ling), Shansi, Honan, Chili, and Shantung, though it may be noted that the greater part of Chili is drained by the Pei-ho and tributaries of the Liao, much of Shantung by short rivers running directly to the sea, and the south-eastern parts of Honan by the affluents of the Hwai.
Kansu, Shensi, Shansi, and the west of Honan are mountainous, while the east of Honan, the greater part of Chili, and the west of Shantung belong to the Great Plain. In the east of Shantung is an isolated mountain mass formed largely of Archman rock. Throughout the greater part of the mountainous area in Kansu, Shensi, Shansi, and Honan, the river basins are covered over with, and the rugged outlines of the mountains smoothed down by, large deposits of loess. The loess is, according to Richt hof en, " an earth of brown-yellow colour, so soft that one can easily rub it to pieces with the fingers, and yet at the same time so firm that in places where through erosion, as by running water, large masses are broken off, it remains standing in perfectly vertical walls several hundred feet high It is so fine that one can rub most of it into the pores of the skin ; nothing then remains but some fine grains of sand, of which there are sometimes more, some times less. . . By repeated washing with water one can separate this from a much greater mass of material that may be called clay, and is tinted brownish-yellow by iron. A third important element is carbonate of lime . . . . On every bit of loess, even the smallest, one may recognise a certain texture, which consists in that the earth is traversed by long-drawn-out tubes which are in part extraordin arily fine, and in part somewhat coarser ; which branch downward after the manner of fine rootlets and generally are coated with a thin crust of carbonate of lime." To discuss here the various theories held as to the origin of this loess would involve too long a digression. Richthofen himself believed that it was due to the outflowing winds of Central Asia depositing the dust obtained from prolonged denudation of the rocks in regions unprotected by vegetation and exposed to great extremes of heat and cold, while the vertical cleavage of the loess he attributed to the pores left by the decay of grass roots as each successive layer of vegetation was covered up by fresh deposits of sand. A more recent theory
involves the action of water as well as of wind in the transportation of the loess, and explains the vertical cleavage by the action of physical principles. Whatever be the true solution, the fact remains that the loess gives to Northern China some of its most characteristic features. Its great fertility is probably due in part to the organic remains of a former vegetation, and in part to capillary action drawing up from below ground water containing lime derived from the underlying limestone rocks. On the other hand, owing to its porous nature, it requires much water in order to render it productive, and irrigation is difficult as the rivers have cut their beds downward on to the rocks below.
The plain of the Hwang-ho, which in appearance is a wide alluvial flat, is also covered with loess to a great extent. This loess has been brought down as the alluvium of the Hwang-ho and other rivers, and has been resorted by the action of wind and water. Near the rivers sandy soils and fine sands are found, while in the open spaces intervening between them loess is the prevailing formation. The poorer soils have, however, often been improved by flooding them with water from the Hwang-ho, in order that the loess which it contained might be deposited.
The loess region is generally well cultivated, though in some places, as in Shansi, it suffers severely from the want of sufficient moisture. The lowlands are, as a rule, more productive than the uplands, and the valley of the Wei in Shensi, the plain of Taiyuen in Shansi, the region drained by the Lo in Honan, and various parts of the Great Plain are noted for their fertility. The staple food crops (wheat, millet, peas, and beans) are widely grown, and some rice is produced in the valley of the Wei. Opium was until recently a flourishing crop in Northern China, which produced much of the best native varieties. Cotton is cultivated, but not to the same extent as in the Yangtse basin where climatic conditions are more favourable. Wild silk is obtained from silkworms, which thrive upon the leaves of the oak in several provinces, but chiefly in Shantung.