The traveller who quits the great plain of Chihli [which terminates at Fu-ch’eng-i, a small market-town, two days from Pao-ting.—H. C.] for “the kingdom of Taianfu,” _i.e._ Northern Shan-si, enters a tract in which predominates that very remarkable formation called by the Chinese _Hwang-tu_, and to which the German name _Löss_ has been attached. With this formation are bound up the distinguishing characters of Northern Interior China, not merely in scenery but in agricultural products, dwellings, and means of transport. This _Löss_ is a brownish-yellow loam, highly porous, spreading over low and high ground alike, smoothing over irregularities of surface, and often more than 1000 feet in thickness. It has no stratification, but tends to cleave vertically, and is traversed in every direction by sudden crevices, almost glacier-like, narrow, with vertical walls of great depth, and infinite ramification. Smooth as the löss basin looks in a bird’s-eye view, it is thus one of the most impracticable countries conceivable for military movements, and secures extraordinary value to fortresses in well-chosen sites, such as that of Tung-kwan mentioned in Note 2 to chap. xli. Agriculture may be said in N. China to be confined to the alluvial plains and the löss; as in S. China to the alluvial plains and the terraced hill-sides. The löss has some peculiar quality which renders its productive power self-renewing without manure (unless it be in the form of a surface coat of fresh löss), and unfailing in returns if there be sufficient rain. This singular formation is supposed by Baron Richthofen, who has studied it more extensively than any one, to be no subaqueous deposit, but to be the accumulated residue of countless generations of herbaceous plants combined with a large amount of material spread over the face of the ground by the winds and surface waters. [I do not agree with the theory of Baron von Richthofen, of the almost exclusive Eolian formation of _loess_; water has something to do with it as well as wind, and I think it is more exact to say that loess _in China_ is due to a double action, Neptunian as well as Eolian. The climate was different in former ages from what it is now, and rain was plentiful and to its great quantity was due the fertility of this yellow soil. (Cf. _A. de Lapparent, Leçons de Géographie Physique_, 2ᵉ éd. 1898, p. 566.)—H. C.]