the two. -So, in 1881, when Konshin first saw the Usboi, he also took it for the old path of the Ainu (1886, 38o), but on further examination he concluded that while the depression in which the Usboi is eroded had served as a strait to unite the expanded Aral and Caspian seas, it had never served as the path of overflow from the Aral to the Caspian, and that the river-like channel along the axis of the depression was the work of local wet-weather streams (1886, 427-431); but it should be noted that one reason for this conclusion was the deductive belief that the Aral could not have had a water supply sufficient for ovérflow after the climate had become so dry as to cause the Caspian to shrink below the Aral level (1886, 428).
Some ten years later (1895) Konshin reversed this earlier opinion, and treated the Usboi as the channel carved by the Aral overflow outlet. He still maintained, however, that the Ainu had never flowed directly into the Usboi, and in evidence of this he pointed out that there was no channel leading from the Ainu to the head of the Usboi ; that the Sary-Kainish depression lay between the two, and that the Usboi channel was decidedly smaller than that of the Amu to-day. More than one writer notes the absence of canals and ruins along the Usboi, and concludes that the river which eroded the channel must therefore have been salt and unattractive to settlement. This conclusion unfortunately begs the important question of the existence of a house-building and canal-cutting human population at the time the Usboi was formed. No independent proof of man's existence at that time and in that place has yet been found. In this connection the levels at some critical points may be introduced. Bala Ishein, 336 feet (72 meters) above the Caspian, is at the divide between the Aral and the Caspian districts ; the Usboi is eroded on the gentle slope southwest from the divide ; no channel occurs on the northeast slope. Sary-Kaunish is the naine of some salt lakes in the bottom of a depression north of Bala Ishem, 5o feet (15 meters) below the Caspian, whose separation from the Aral of to-day may be due to the growth of the great Amu delta between the two basins. Walther quotes various other altitudes (1898,2I2). As the Amu now enters the Aral alone, the former waters of the Sary-Kamish depression have been evaporated almost to dryness, thus repeating the case of the Colorado River at the head of the Gulf of California. The Usboi channel must have lengthened southwestward as the Caspian retreated, thus producing features similar to those well known in the Bonneville basin of Utah. It is pertinent to quote in this connection Seunenofs observation that the plain bordering the Caspian southeast of Krasnovodsk appears to be the remains of spacious deltas formed by large rivers which for manÿ centuries here entered the sea from the east (1888, 292). Konshin (1887, 237) notes that Caspian shells are abundant on the desert plain for 125 miles (20o kin.) east of the present shore and up to nearly 200 feet (6o meters) above the present level ; but they are not mentioned in association with the shorelines of the Ungus. Obruchef gives similar statements (189o, 246).
There seems to have been comparatively little discussion of the relation of the Quaternary Aralo-Caspian in Turkestan to the climatic changes of the. glacial period. Sjögren (1888) explains the expansion of the sea by the greater volume of water received from the glaciated area of northern Russia, and suggests that as far as