Chapter XIX: Part 7

THE GEOLOGY OF THE COUNTRY FROM YANG-KAO TO K’UEI-HUA-CH’ÊNG, NORTH
SHANSI

As already stated, Yang-kao is situated on the eastern edge of the Ta-t’ung Fu plain. To the north lies a great chain of tall rugged mountains. These seem to be composed mainly of metamorphic rock, gneiss being the only rock we encountered on entering these mountains on our way to K’uei-hua-ch’êng.

The gneiss continued as far as Kuan-t’ung-pu (about 20 miles N.N.W.). West of this place igneous rock prevails, an immense lava flow forming a plateau some ten miles wide (length not ascertained, but considerable). The basalt, which marks the eastern limit of the North Shansi basalt, is typical of the same, being of a dark blue-grey colour, with air holes, usually lined with spar and containing crystals of hornblende. In places where the surface of the plateau is bare of soil the basalt shows distinct hexagonal cleavage, indicating columnar structure beneath. This lava flow, judging from the general contour of the country, is roughly from north to south. The plateau ends abruptly on its western side in a deep river valley, running from north to south. Westward other lesser plateaux occur, however, and travelling along the river valley, which now runs east and west, fine examples of columnar structure are to be seen, notably near Fên-chêng. At this place good clay occurs, enabling extensive pottery work to be carried on.

The volcanic formations continue from here all the way to the T’ai Hai. North of this lake the mountains are entirely of granite as far as Mei-tê-êrh (Mei-teul), at the edge of the K’uei-hua-ch’êng plain.

Some of this granite, notably that occurring up the valley east of Mei-tê-êrh, contains large quantities of garnets, some of which are as large as marbles. All the granite up this way is of a pale buff colour.

The hills south of the lake are of basalt, as also are those on the west as far as the pass beyond Ning-yüan. Here an extensive outcrop of granite, a continuation of that occurring north of the lake, extends as far as Yang-p’o-yao-tzŭ. From this point to the edge of the K’uei-hua-ch’êng plain basalt occurs, showing fine columnar structure. The basalt and granite are frequently superimposed by loess, but not to any very great depth or extent.

No outcrops of any kind occur on the plain, which is mainly alluvial, with patches of wind-deposited sand.

The T’ai Hai (lake) lies in an immense basin some twenty miles long and ten miles wide. This basin is bounded on three sides by low hills of volcanic formation, and on the fourth (the north) by high mountains of granite. It is difficult to explain the existence of this hollow in which the lake lies. The latter is said to be very deep in the centre. At first one might suppose that it occupies the crater of an extinct volcano, but this is by no means certain. Further investigation is needed before such a theory can be confidently advanced. It would, however, be interesting to know the origin of all the basalt, so prevalent in this country.

Referring to the mountains north-west of K’ueihua-ch’êng, where we hunted wild sheep, I find the following notes in my diary:—

“These mountains are entirely plutonic, volcanic, and metamorphic. The low foothills, which run in a series of low parallel ridges, are composed of lava (porphyry). Next (working westward) comes some white and greenish stone, which I take to be a metamorphosed felspar. Beyond this and rising to a great height, with deep cut ravines and valleys, come gneissic and schistose rock, with intrusions of granite. Working still west an extensive outcrop of white marble is crossed. Beyond this again the rock seems to be granitic, gneissic and schistose. The schists, I believe, are chloritic, while the granites certainly have a large proportion of felspar. A certain amount of iron-stone, but no coal, was noticed.”

Probably the mountains north and north-east of K’uei-hua-ch’êng are similar in formation to those north-west.