large part of Asia, comprising Tibet, Mongolia, Turkestan, and most of Baluchistan, Persia, and Arabia, that is, nearly all the central and southwestern parts of the continent, the region in which the rainfall is deficient, has no drainage to the sea.
Geology. Little is known of the geology of the greater part of Asia. Certain limited regions, such as India, have been studied in detail, but our knowledge of the greater part of the continent has been derived from piecing together the reports of explorers. The great mountain systems consist principally of granites, gneisses, schists, and allied rocks, with, in many cases, the older stratified rooks lying on their flanks. This is the case with the Himalayas, whose uplift is believed to have occurred as late as Tertiary times and with the Tian-shan, Altai, Stanovoi, and the Kuenlun ranges. The Ural Mountains, also, have a metamorphic nucleus. In the Caucasus, in Armenia. the Vindhya range of India, and in Persia, are extinct volcanoes, which have contributed lava and ashes to the building of the mountains, while in the peninsula of Kamchatka, the Japanese Islands, and the East Indies are many active cones. Indeed, this region on the east and southeast of Asia is one of the largest and most active volcanic regions on the earth.
The vast plain of Siberia is floored in succession from east to west with stratified beds, ranging from the oldest to the youngest, with large areas of eruptive and metamorphic rocks. The Desert of Gobi and the Plateau of Tibet are, except for the mountain ranges, floored with Tertiary and Quarternary beds. In China, however, the rocks are much older, consisting of Carboniferous and Jurassic beds, which in the low coast regions underlie great beds of loess with which much of the level country is covered. The western plateaus in Afghanistan, Baluchistan, Persia, and Asia Minor are in the main covered with Tertiary and Quarternary rocks, but in Arabia a large part of the plateau is floored with Jurassic beds. The great depression of northern India, south of the Himalayas, is a Tertiar deposit and a part of a large land area that once extended across the Indian Ocean to South Africa. The peninsula itself is composed of metamorphic and igneous rocks, with here and there areas of Paleozoic beds. Glaciers are found chiefly in the high mountain regions of the Tian-shan, Kuenlun, and Himalaya ranges, in the Tibetan highland, and in the Caucasus. No glaciers are found near the Arctic coast, owing to the deficient precipitation. See Geology, under India; Chinese Empire.
Climate. Asia has a great variety of climate, owing to its range of latitude, altitude, and its relations to the bordering seas. It is in the main a continental climate, with light rainfall, a dry atmosphere, and great extremes of temperature. Near the coasts the climate is modified by the proximity of the sea, but this influence extends but a short distance inland, as the prevailing winds are off the land, except in the south, and even there the contrary is the case only during the prevalence of the monsoons. The whole of northern Asia lies within the range of the prevailing westerly winds of the Northern Hemisphere, in which are found the extensive cyclones and anticyclones which give variability to the weather in temperate latitudes. On the eastern and southeastern coasts, cyclones of the hurricane type originate in the region of the tropical islands, and, pursuing a course at first westerly, under the influence of the trades, gradually turn toward the north and east, often ravaging the coast to some distance inland. In the extreme southern part of Asia occur general storms of hurricane character and local storms of the tornado form.
Temperature. The mean annual temperature in Asia reduced to sea-level, decreases uninterruptedly from about 90° F. at the south to 0° at the north. On the eastern coast the decrease in temperature, with increase in latitude, is somewhat slower than in the interior, but on the whole the isotherms follow the parallels quite closely, especially in the southern half of Asia. The isotherm of 32° crosses eastward from Archangel with a slightly southerly bend, to the mouth of the Amur. On the western side of Asia the temperatures decrease from 72° at Suez to 14° at the northern end of the Ural Mountains. On the eastern coast there is a decrease from 78° in Siam to 10° at Bering Strait. The region of greatest cold is near Verkhoyansk, in Siberia, on the Yana River, but a short distance north of the Arctic Circle, between the meridians of 130° and 140° E.
The average temperatures for January decrease from about 80° at the south of the continent to -55° in the neighborhood of Verkhoyansk, whence there is an increase to -40° on the coast. From Verkhoyansk, the centre of cold, the temperature rises in all directions; westward along the Arctic coast to -4° at the northern end of the Urals, and eastward to -13° at Bering Strait. On the western side of the continent the temperature decreases from 57° at Suez to -4° in the northern Urals. On the eastern coast the temperature decreases from about 80° at the south to -13° at Bering Strait. The isotherms in the northern part of the continent swing far to the south in the interior, showing much lower temperatures there than on the coasts in winter. The isotherm of 32 runs nearly due east from the middle of the Caspian Sea to the middle of the Yellow Sea, showing in this latitude little difference in winter temperatures between the coast and the interior. Throughout the greater part of northern Asia the January temperatures are more than 18° below the normal for those latitudes, and at Verkhoyansk it is -47° below normal, owing to the distance from the sea and its influences.
In July, the highest temperature is on the Arabian and Persian plateaus, where the average is 93°; from this section there is a fall to 82° in southern India, southern Siam, and southern China, and toward the north and east, to 39° throughout most of the Arctic coast. The maximum temperature of the whole continent ranges from 120° in Persia and Arabia, to 75° on the northern coast, and in the northern interior it reaches 100°. The minimum ranges from about 65° in the extreme south, to -58° on the northern coast, but in the neighborhood of Verkhoyansk, in the interior of northeastern Asia, a temperature of 92° below zero has been observed.
Rainfall. In most regions of Asia, except near the Pacific coast and south of the Himalayas, the rainfall is scanty. On the immediate coast of the Arctic Ocean in Siberia, the annual precipitation is under ten inches. Elsewhere in Siberia it is between ten and twenty inches.
