6 EXPLORATIONS IN TURKESTAN.
Along the base of the southern mountains stretches a chain of narrow oases at the mouths of the mountain valleys ; there are other very narrow strips along the larger river courses, and more extensive areas inclosed between the projecting spurs of the eastern mountains ; all the rest of the basin has become the prey of the moving sands, which are still very slowly but surely invading the oases. The boundary is sharply defined ; within it is high cultivation ; beyond it is a sea of
waves of sand.
As they extend eastward the southern mountains increase in height, till both they and the great spurs of the Tian Shan, giant snow and ice covered crests and peaks, dominate the oases which are the offspring of their waters. It is on these mountains of snow and ice that the life of the whole region is and has been from a remote period absolutely dependent.
This life is also limited by another factor—itself a result of the desiccation—the moving sands. For, other things remaining equal, while the shrinkage of the water areas can continue only till equilibrium between supply and evaporation is reached, and while there might be also cyclical periods of revivifying afflux, these compensations are offset in the oases by the slow but steadily overwhelming progress of the sands.
The progressive desiccation of Turkestan is shown by direct observations during the past century, by artificial landmarks, by historical statements, and by natural records. The Aibughir Gulf of the Aral was 133 kilometers long and 3,500 square kilometers in area in 1842, and dry land in 1872.
The volume of the Syr Darya has diminished greatly, as shown by the remains of old irrigating canals along, its whole lower course, which are now too high to receive water. The statements of Arabian writers show that, within recent historical times, there was a far more numerous population than the country could support now, when all available water is utilized. Old water-level lines occur at various heights up to 225 feet above the Aral.
The progress is not uniform, but is broken by periods of temporarily increased precipitation. Dorandt measured in 1874-75 a fall of 7o mm. in the year in the Aral Sea. Schultz, in comparing his surveys of 188o with earlier maps, found a lowering of the level of 38 cm. in nine years. On the other hand, Berg, in 1901, comparing the gage established by Tillo, found the level 121 cm. higher than in 1874. He calculates the total rise between 1882 and 1901 to be at least 3 meters, or 178 mm. yearly.
Judging from our observations and from those of others, especially of the Arabian writers and of the later Russian explorers, it would seem that the country has long been an interior region, dependent for its life mainly on the snows and glaciers of the mountains ; that there have been within the present geological period great fluctuations in the amount of water derived from the mountains, as recorded in high and low shorelines of the seas and in the strata containing living forms left by different expansions of the united waters of the Aral and Caspian, and that man already existed within the region during at least the last great maximum