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Encyclopedia Britannica - Main :: TOO-TUM |
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TRANSCASPIAN REGION , a Russian territory on the E. of the Caspian, bounded S. by Khorasan and Afghanistan, N. by the Russian province of Uralsk, N.E. by Khiva and Bokhara and S.E. by Afghan Turkestan. Area, 212,545 sq. in. Some of the most interesting problems of geography, such as those relating to the changes in the course of the Jaxartes (Syr-darya) and the Oxus (Amu-darya), and the supposed periodical disappearance of Lake Aral, are connected with the Transcaspian deserts; and it is herethat we must look for a clue to the physical changes which transformed the Euro-Asiatic Mediterraneanthe Aral-Caspian and Pontic basininto a series of separate seas, and desiccated them, powerfully influencing the distribution of floras and faunas, and' centuries ago compelling the inhabitants of Western and Central Asia to enter upon their great migrations. But down to a comparatively recent
(P. A. K.; J. T. BE.) Turkomans, were almost a terra incognita. A mountain chain, comparable in length to the Alps, separates the deserts of the Transcaspian from the highlands of Khorasan. It begins in the Krasnovodsk peninsula of the Caspian, under the names of Kuryanyn-kary and Great Balkans, whose masses of granite and other crystalline rock reach an altitude of some 5350 ft: Farther south-east they are continued in the Little Balkans (2000 ft.) and the Kopepet-dagh or Kopet-dagh. The latter rises steep and rugged above the flat deserts over a stretch of 600 m. In structure it is homologous with the Caucasus chain; it appears as an outer wall
the 'south-east and is a tributary of the Murghab. On the other side of this valley the Alla-dagh (Aladagh) and the Binalund border-ranges (9000 to 11,000 ft.) fringe the edge of the Khorasan plateau. Descending towards the steppe with steep stony slopes, the mountain barrier of the Kopet-dagh rises to heights of 60009000 ft. to the east of Kyzyl-arvat, while the passes which lead from the Turkoman deserts to the valleys of Khorasan are seldom as low as 3500, and usually rise to 5000, 6000 and even 8500 ft., and in most cases are very difficult. It is pierced by only one wide opening, that between the Great and Little Balkans, through which the sea, which once covered the steppe, maintained connexion with the Caspian. While the Alla-dagh and Binalund border-ranges are chiefly composed of crystalline rocks and metamorphic slates, overlain by Devonian deposits, a series of more recent
wall
The loess terrace, called Atok (" mountain base "), to to 20 M. in width, is very fertile; but it will produce nothing without irrigation, and the streams flowing from the Kopet-dagh are few and. scanty. The winds which impinge upon the northern slope of the mountains have been deprived of all their moisture in crossing the Kara-kumthe Black Sands of the Turkoman desert; and even such rain as falls on the Kopet-dagh (IOj in. at Kyzyl-arvat) too often reaches the soil in the shape of light showers which do not penetrate it, so that the average relative humidity is only 56 as compared with 62 at even so dry a place as Krasnovodsk. Still, at those places where the mountain streams run closer to one another, as at Geok-tepe, Askhabad, Lutfabad and Kaaka, the villages are more populous, and the houses are surrounded by gardens, every square yard and every tree of which is nourished by irrigation. North of this narrow strip of irrigated land begins the desertthe Kara-kumwhich extends from the mountains of Khorasan to Lake Aral and the plateau of Ust-Urt, and from the Caspian to the Amu-darya, interrupted only by the oases of Mery and Tejon. But the terrible shifting sands, blown into barkhans, or elongated hills, sometimes 50 and 6o ft. in height, are accumulated chiefly in the west, where the country has more recently emerged from the sea. Farther east the barkhans are more stable. Large areas amidst the sands are occupied by takyrs, or flat surfaces paved with clay, which, as a rule, is hard but becomes almost impassable after heavy rains. In these takyrs the Turkomans dig ditches, draining into a kind of cistern, where the water of the spring rains can be preserved for a few months. Wells also are sunk, and the water is found in them at depths of to to 5o, or occasionally too ft. and more. All is not desert in the strict sense; in spring there is for the most part a carpet of grass.The vegetation of the Kara-kum cannot be described as poor. The typical representative of the sandy deserts of Asia, the saksaul (Anabasis ammodendron), has been almost destroyed within the last hundred years, and occurs only sporadically, but the borders of the spaces covered with saline clay are brightened by forests of tamarisk, which are inhabited by great numbers of the desert warbler
The Uzboi.A feature distinctive of the Turkoman desert is the very numerous shors, or elongated depressions, the lower portion of which are mostly occupied with moist sand. They are obviously the relics of brackish lakes, and, like the lakes of the Kirghiz steppes, they often follow one another in quick
' On the original Russian map of the Transcaspian, drawn
P. M. Lessar and Svintsov,2 went to show that the Uzboi is no river-bed at all, and that no river has ever discharged its waters in that direction. The existence of an extensive lacustrine depression, now represented by the small Sary-kamysh lakes, was proved, and it was evident that this depression, having a length of more than 130 m., a width of 70 m., and a depth of 28o ft. below the present level of Lake Aral, would have to be filled by the Amu before its waters could advance farther to the south-west. The sill of this basin being only 28 ft. below the present level of Lake Aral, this latter could not be made to disappear, nor even be notably reduced in size, by the Amu flowing south-west from Urgenj. A more careful exploration of the Uzboi has shown that, while the deposits in the Sary-kamysh depression, and the Aral shells they contain, bear unmistakable testimony to the fact of the basin having once been fed by the Amu-darya, no such traces are found along the Uzboi below the Sary-kamysh depression ;$ On the contrary, shells of molluscs still inhabiting the Caspian are found in numbers all along it, and the supposed old bed has all the characteristics of a series of lakes which continued to subsist along the foothills of the Ust-Urt plateau, while the Caspian was slowly receding westwards during the post-Pliocene period. On rare occasions only did the waters of the Sarykamysh, when raised by inundations above the sill just mentioned, send their surplus into the Uzboi. It appears most probable that in the 16,1 century the Sary-kamysh was confounded with a gulf of the Caspian;' and this gives much plausibility to Konshin's suppositio.a caat the changes in the lower course of the Amu (which n~ geo'egist would venture to ascribe to man, if they were to mean the alternative discharge of the Amu into the Caspian and Lake Arai) merely meant that by means of appropriate dams the Amu was made to flow in the 13th16th centuries alternately into Lake Aral and into the Sa -kamysh.The ancient texts (of Pliny, Strube', Ptolemy
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