Iranian Upland, let us say, and the Great Lowland, becomes altogether subordinate. Tibet, with its attendant Himalaya, Pamirs, Karakoram, Hindu Kush, and Tianshan—call them together the Tibetan Heights—has no parallel on Earth for combined height and area, or, in a single word, for massiveness. When the Sahara shall be crossed and recrossed daily by the traffic of civilisation, it is probable that Tibet, the 'roof of the world,' will still deflect round its flanks and widely separate the overland routes into China and India, thus giving a special significance to the North-west Frontiers of those two countries.
North of Tibet, a considerable part of which has a continental drainage, and is, therefore, included within the Heartland, spreads the Mongolian Upland, also largely of the Heartland. This Mongolian Upland is of a much lower elevation than Tibet, and is in fact comparable in point of level with the Iranian Upland. Two natural ways come over the arid surface of Mongolia to drop down into the fertile lowland of China; the one through the Province of Kansu, round the north-eastern corner of Tibet, to the great city of Sinan, of a million inhabitants; the other directly south-eastward from Lake Baikal to
