Chapter XIV: Part 2

THE GEOLOGY OF THE COUNTRY TRAVERSED BY ANDERSON AND THE AUTHOR IN 1908:
NORTHERN SHENSI, THE ORDOS AND WESTERN SHANSI

On my journey with Anderson through North Shensi, along the Ordos border and into Western Shansi, I kept some note of the geological formations.

PLATE XVII.

A TOWER OF THE GREAT WALL, ORDOS BORDER.
]

LOESS RAVINE IN NORTH SHENSI.

_Opposite p. 258._]
]

As the Clark Expedition subsequently traversed a good portion of our route, and as I have already published notes on the geological formations along that portion, there is no need to go over it again here.

From Yen-an Fu to Ching-pien Hsien we travelled up the valley of the Yen-shui, and noted that the sandstone strata, usual in North Shensi, occurred all the way, without fault and practically horizontal. As far as I can make out this sandstone belongs, or at least corresponds, to the Red Beds, which form the upper strata of the Shansi formation. What corroborates this supposition is the fact that no coal seams appear along the ravines, as is the case in the coal-producing districts of Shansi, yet coal is extensively mined throughout North Shensi, vertical shafts being sunk to reach the seams. As the average altitude of the upper surface of the sandstone strata does not exceed 3,000 feet, it follows that the Shansi coal measures are very much higher than those of Shensi. Further, there seems to be no reason to suppose that they are two distinct systems, so that one can only suppose that the strata of North Shensi must lie in an extensive and shallow synclinal fold, or that they have become depressed below those of Shansi owing to faults somewhere along the course of the Yellow River. We know that there is a series of faults with downthrow on the west, running roughly parallel with the Yellow River, marking out the course of the Fên Ho in Shansi. There seems to be no special reason why there should not be a second series of faults down the course of the Yellow River. As a matter of fact, wherever I have crossed the latter from Shansi into Shensi, I have noticed that the mountains on the Shansi side are higher and more precipitous than those on the Shensi side, while the strata on either side do not correspond at all well.

Near the head of the Yen-shui valley red sandstone replaces the grey or yellow. Here the loess mantle is very much thicker than elsewhere. At Ching-pien Hsien no outcrop of sandstone is visible, as the course of the stream cuts deeply through hardened sand and dark sun-baked mudstone.

Continuing into the desert we encountered nothing but sand, alternating with stretches of pale blue-grey clay, in which were lagoons and small lakes. As we travelled north-eastward from here, along the border, we again encountered the red sandstone lying beneath the enormous deposits of sand, or in places sand and clay mixed. Near Yü-lin Fu this gave place to yellow-grey sandstone once more, which continued till we again neared the Shansi border, when the shales, typical of the Shansi series, once more presented themselves, underlying the sandstone. Again at Pao-tê Chou the difference in levels of the strata was very noticeable. Working south-east from Pao-tê Chou, we shortly encountered limestone, belonging to the Ki-ch’ou formation, the strata of which dipped gently to the west. Rising steadily up through this, we reached a high ridge of limestone, descending from which we again reached the sandstone of the Shansi formation, in which the town of K’o-lan Chou is situated, and which extends eastward from here to the Fên Ho. Though we had crossed the great ridge dividing the basin of the Fên Ho from the Yellow River, we did not encounter any of the usual archaic formations. This then forms one of the few breaks in the continuity of the archaic ridge, which runs from Ning-wu Fu to Yung-ning Chow in Western Shansi.

From K’o-lan Chou we journeyed northward to Wu-tsai Hsien, crossing a low ridge in the Shansi formation, and from Wu-tsai eastward to Ning-wu Fu, crossing a somewhat higher ridge in the same formation. Here we noticed bituminous coal being mined close to the city. Northward from Ning-wu Fu I noticed the Shansi formation extending for some distance, but I did not pursue my investigation very far in this direction.

Leaving Ning-wu Fu we journeyed eastward, soon encountering the Sinian limestone, followed by limestone of the Hu-t’o series, originally described from close to this very region by Bailey Willis. A little to the west of T’ai-niu-tien, the limestone is cut through by a dyke of granite, probably belonging to the T’ai-shan complex, which forms the basal complex of the formations of the Wu-t’ai Hsien district.

We crossed the alluvial plain and reached Hsin-chou, at which point we joined the route taken by Bailey Willis’ party on its way from Wu-t’ai Hsien to T’ai-yüan Fu.

Striking south from Hsin-chou, we crossed the south-western terminus of the Ki-ch’ou Shan, where occur the typical Sinian limestones, which Bailey Willis has called the Ki-ch’ou formation, and which are of the Cambro-Ordovician period.

The Ki-ch’ou Shan run from north-east to south-west along the south-eastern margin of the Hsin-chou plain. The range consists of a massive scarp on the north-west and a dip slope on the south-east, as a result of an extensive fault, running in the same direction as the range. This fault is one of a series, which, as already stated, extend down through Shansi. The next in the series occurs, in the opinion of the author, along the north-western margin of the T’ai-yüan Fu plain, where again the limestone rises in a massive and precipitous scarp; only in this case the downthrow is on the south-eastern side. Considering the general westerly dip of the strata from the Chihli plain to well west of T’ai-yüan Fu, and the merging of the upper rocks of the Shansi formation into the T’ai-yüan plain on its eastern margin, the sudden recurrence of the limestone on the western margin of the same plain can only be explained by the existence of a fault, such as I have just described. Indeed there is no reason why a fault should not occur here, for further south and in an almost direct line with it a similar fault occurs, running in a direction slightly west of south, along the eastern side of the O Shan. In this also the downthrow is on the east. Richthofen, also, came to the conclusion that there was a fault along the north-western margin of this plain.

We put up at Huang-t’u-tsai, the place which gives its name to the Huang-t’u formation, a name given by Bailey Willis to the loess and various other Quaternary deposits of North China.

The following day we continued down a dry stream bed and finally came out upon the T’ai-yüan Fu plain once more.