Chapter XXI: Part 9: The Geology of the Mongolian Plateau, Inner Mongolia

Throughout the whole of this journey nothing but igneous and metamorphic rocks were encountered. In general it may be stated that this portion of the Mongolian Plateau is formed by an extensive lava-flow (or flows), traversed by dykes of granite and quartz, the last occurring with less frequency than the others. Whether these dykes are of an older date than the basalt it is not easy to say.

Topographically the area beyond the steep ascent of the Han-nor-pa pass consists of very slightly undulating plains of a uniform altitude (about 4,000 feet), bounded or traversed by small ranges of low, rocky, partially grass-covered hills. The extremities of these are frequently joined by almost imperceptible ridges. Sometimes they end in abrupt cliffs, but most often they slope gently into the plain. In the valleys there are usually shallow lagoons of varying sizes; while occasionally permanent streams of clear, sweet water wind through very clayey soil. The soil round the lagoons is also very argillaceous.

The ascent of the Han-nor-pa pass is through basalt of a dark grey colour, not unlike that encountered in Shansi, while in the valley leading up to it various kinds of rock, all igneous, were noticed. Amongst others, we gathered specimens of a red-brown porphyry containing numerous elongated air-holes, besides distinct crystals of felspar and quartz. Specimens of metamorphosed felspar, of light grey basalt, and of a peculiar yellow sandstone, were also gathered. The predominating rock throughout, however, was found to be basalt, and, nearer to Kalgan, trachyte.

Except in the hills and on the ridges of the Plateau, the thick grass-covered surface soil prevented our noting the nature of the sublying rock, but an examination of the outcrops in the hills showed that basalt greatly predominated, while dykes of granite occurred here and there. As we approached Lama Miao the granite increased in proportion till it seemed, sometimes, as if dykes of basalt crossed the general mass of granite. Usually, however, the higher ridges were found to be of granite, while wherever the sublying rock in the lower slopes and valleys was visible it usually turned out to be basalt. At a place named Oola Hutaga some gneiss was noticed, but here also the hills were chiefly of granite and volcanic rock.

At Tabool we noticed some wide veins of quartz running north and south through metamorphic and granitic rocks. This quartz was not noticed elsewhere. Here also some outcrops of muscovitic schist occurred.

It was stated by one of the missionaries that twenty li (about 6 miles) south-west of Hallo Ossa (near Tabool), the Chinese were excavating for coal. This would suggest an outcrop of the coal-bearing sedimentary rocks noticed west of K’uei-hua-ch’êng.

From Tabool south to Kalgan the outcrops showed almost entirely volcanic, with a little granite.