ASIA -The continent of Asia, which has an area generally estimated at about 17,250,000 square miles, occupies nearly one-third of the land surface of the globe. The most pro minent feature in the physical structure of this vast area is the great system of mountains and plateaus which extends across it from west to east. This system is much contracted in the region of the Pamirs, which practically divide it into two parts, the eastern part, however, being much more extensive than the western. To the west of the Pamirs, the system is again contracted in the Armen ian Knot where meet the Pontus and Taurus ranges, which enclose between them the plateau of Asia Minor. This plateau has a height varying from 2,000 feet in the west to about 6,000 feet in the east. The Taurus mountains, on the south of the plateau, rise in places to over 10,000 feet, but the Pontus range on the north is somewhat lower and more irregular. To the east of the Armenian Knot, where Mount Ararat is over 17,000 feet above sea-level, the fold ranges of Asia again diverge to enclose the plateau of Iran. In the north are the Elburz Mountains which curve round the southern extremity of the Caspian Sea and are continued through the high lands of North Afghanistan eastwards to the Pamirs, while to the south the Kurdistan Highlands, the Zagros Mountains, the South Persian ranges, and the Sulaiman Mountains extend from Armenia to the Hindu Kush and the Pamirs. These various ranges differ greatly in height. Mount Demavend, in the Elburz, is over 18,000 feet, while in the Hindu Kush the peaks rise to over 25,000 feet. In the southern loop the mountains are lower, but everywhere present considerable barriers to communication. The plateau of Iran, which has an average height of about 3,000 feet, contains two basins of inland drainage, that of Iran in Persia and that of Seistan in Afghanistan. To the north of the plateaus of Asia Minor and Iran, and of the mountain ranges which border them, is a region of relative depression, occupied by the Black Sea, the valley of the Kura, and the Caspian. This region is bounded on the north by the Caucasus, which are continued by the Kopet Dagh, east of the Caspian, to the highlands of North Afghanistan. The Caucasus
and the Kopet Dagh form, on the west of the Pamirs, the northern boundary of the Asiatic mountain system.
East of the Pamirs, which consist of a series of high valleys separated by still loftier mountain ranges, the same distribution of land forms is continued but on a much more extensive scale. The plateau of Tibet, much of which has an elevation ranging from 14,000 to 17,000 feet, is buttressed on the south by the greatest mountain range in the world, the Himalayas, in which the passes are from 17,000 to 19,000 feet above sea-level. The Himalayan fold is continued southwards in the Naga and Arakan Yoma hills of Burma and the Andaman and Nicobar Islands, and then eastwards through Sumatra and Java. To the east of this fold, other ranges running southwards, apparently from the Tibetan plateau, separate the various river systems of Indo-China from one another. On the north the Tibetan plateau is bordered by the Kwen-lun Mountains. About latitude 100°E. these bifurcate, one branch running eastwards into China as the Tsin-ling Mountains, and the other running north-east as the Inshan and Khingan Mountains. To the north of these various ranges the area of relative depression is represented by the basin of the Tarim in the west, and by the Mongolian plateau, with the desert of Gobi, in the east. The folded Tian Shan enclose the Tarim basin on the north, while further east the Mongolian plateau is bordered by a series of ancient highlands which include the Altai, the Sayan, and the Yablonoi and Stanovoi Mountains. These present a steep escarpment to the Siberian Lowlands, and form, to the east of the Pamirs, the northern limit of the Asiatic mountain system. On the south-east the Inshan and Khingan ranges overlook the lowlands of North China and Manchuria, while to the south of the Tsin-ling Mountains lies the ancient massif of South China. Both in Manchuria and in South China the hills have been formed by the fracturing of an ancient land mass.