China in the different geological periods. — At the close of the Primary period, the greatest portion of China emerged, save the South-Western.
During the whole of the Primary period and the first part of the Secondary period, China remained under water. It then emerged definitively. Subsequently came foldings and dislocations, which evolved hollows like that of Sungaria, or emerged in peaks like those of the Altaï mountains, T'ien-shau, K'uenlun, Nan-shan and Tibet.
Several of these summits, the K'uenlun and Nan-shan for instance, were formerly very high, but erosion has greatly lessened them. Of the sedimentary coating that covered the high summits, there remain but fragments in the less elevated parts, as in the South-Western portion of China.
After the first half of the Secondary period, the geological constitution of China was nearly completed. No trace is to be found of jura-limestone and chalk formations, such as were formed elsewhere at the end of the Secondary period.
During the Tertiary and Quaternary period, China, now completely ont of water, underwent but modifications of its surface, and developed no new rocks.
Formation of coal and sand-stone. — At the close of the Primary period, immense deposits of coal formed along the coasts of Eurasia and Gundwana, in the place now occupied by Yunnan, Kweichow, Honan, Shensi and Shansi.
Great lakes occupied a portion of Eastern China from the Secondary period. When these disappeared, they left behind a thick bed of rocks deposited in their depths; to these rocks has been given the name of sand-stone, so abundant still in many places of China, and particularly in Szechw'an and throughout the whole of Southern China.
Modifications wrought on the surface. — At the same time the mountain-tops were attacked by glaciers, winds, frosts and torrents, and the debris borne away: lakes were filled, the gentler hills became plains, islands like Shantung were joined together, and there were deposited in the North those thick layers of yellow and fertile earth, called lœss, which we shall have more than once occasion to speak about.
Volcanic Action and Eruptions. — Volcanic action does not seem to have been intense. There remain traces of it however in the neighbourhood of Nanking, in the North of Peking, in some regions of Mongolia and in Tibet.
The cruptive rocks play a more important part. These rocks, the principal of which are porphyry and granite, were spread over a great part of China. The mountains of Fokien, for instance, are mostly composed of porphyry.
Present geological action. — This work of geological formation still goes on at the present day, and is more especially to be seen at the mouths of the great rivers where new lands, called deltas, are continually forming.
Predominant Rocks of the Chinese soil. — From what has been said upon the geological formation of China, it is easy to account for the rocks that predominate. For the most part the strata are either Primary or Secondary. The Azoic strata are scarcely represented, covered over as they are by the others. Coal takes up a large place, and loess covers a vast portion of Northern China, extending from Kansu to Shantung and Kiangsu.
A peculiar kind of limestone, known as China limestone, and formed before the coal-beds, is found all over China. Its thickness is at times 10,000 ft. and sometimes more. It is the rock the most widely diffused throughout China.
New modifications wrought on the surface of China. — It may be said in general, that the surface of China slopes from West to East, the highest peaks being found in Tibet and the vast low-lying plains in the East. This slope is moreover
