Farther south, in the Chinese provinces of Shansi and Shensi, the geological succession is similar in some respects to that of the Siberian Palaeozoic plateau, but the sequence is more complete.
Excluding the territory to which the name of Mongolia is geographically applied, but which is included in the provinces of Shansi and Chihli, Mongolia is divided into inner and outer divisions.
They are widely distributed throughout China Proper, but those of the province of Shansi appear to be the richest.
After passing Lanchow-fu, the capital of this province, the river takes an immense sweep to the north and north-east, until it encounters the rugged barrier ranges that here run north and south through the provinces of Shansi and Chihli.
By these ranges it is forced due south for 500 m., forming the boundary between the provinces of Shansi and Shensi, until it finds an outlet eastwards at Tung Kwan - a pass which for centuries has been renowned as the gate of Asia, being indeed the sole commercial passage between central China and the West.