V. The geology and physical geography of Chinese Tibet, and its relations to the mountain system of south-eastern Asia, from observations made during the Percy Sladen expedition, 1922

1. The mountainous highlands of south-western China, Chinese Tibet and north­-eastern Burma, consist of a high platform which projects southward from the Tibetan tableland. That platform lies along the foundations of the ancient Indo-Malayan mountains and athwart the eastern end of the Himalaya. It appears, on examination of a map, to have caused the eastern continuation of the Alpine-Himalayan Systems to have been diverted southward as the Burma and Malay Arcs. Further to the north­ east the tableland of east central Asia ends abruptly above the lowlands of eastern China. Its eastern front forms the Great Khingan Mountains, which have been regarded by the late Prince Kropotkin (1904, p. 333) as the continuation of the Himalaya. This view of the eastern prolongation of the Himalaya into central China has been also adopted by Archibald Little (1905, map opposite p. 19, and p. 209). The whole geography of south-western China and the adjacent lands is dominated by the inter­ action of mountain movements belonging to two far-distant periods. The older moun­tains, the Indo-Malayan, belong to the Hercynian group of earth movements, which happened toward the end of the Paleozoic Era. The younger mountain system, the Himalayan, is Kainozoic, and though its uplifts happened at intervals from Upper Eocene to Pliocene, its movements culminated in the Middle .Kainozoic, and were probably most important in the Oligocene and Miocene. The mountain plan of south­ eastern Asia has been considered as a combination of the mountain lines of Eurasia, which trend from W. and E., with the border chains of the Pacific, which cross at high angles the eastern end of the Asiatic mountains. The history of the Indian Ocean is incomplete, until it be known what was happening on its north-eastern side synchronous with the movements which made the rift-valleys of East Africa. Chinese Tibet is one of the critical areas for the solution of these problems, for it is opposite the eastern end of the Himalaya. This country has also attracted attention from the parallelism of the three great rivers which cross it.