38 EXPLORATIONS IN TURKESTAN. 
indicating a progressive diniinntion of size. A continuous decrease from the 
larger Pliocene to the diminishing Quaternar>- area is inferred by this observer and 
explained by dr}-ing winds and by uplift of the eastern part of the plain, where the 
surface is now 2,000 feet above sea-level. Obruchcf also describes the Quateniar)- 
Aralo-Caspian as the direct successor of the Pliocene sea, the decrease of area being 
ascribed to uplift on the east (1890, 25). Neither of these obser\-ers gives explicit 
recognition to the idea that the Quaternar)- sea resulted from the expansion of a 
smaller early-Quaternar}- sea, to which the waters had shrunk from their great 
Pliocene extension. 
The Aralo-Caspian is marked by Konshin, in the article just refened to, as 
reaching, at the beginning of the Quaternar)-, eastward to the present ends of the 
Murg-ab and Tejen rivers, and southward to the base of the mountains at Kizil- 
Arvat ; farther west it connected with the Caspian basin by the Balkhan gateway ; 
to the northwest it spread be)-ond the present Aral ; to the northeast it had a 
well-defined boundar)' south of the Anui River. Here a higher northeastern part 
of the Kara-Kum, underlaid by Pliocene and older strata, breaks off in a dissected, 
south-facing escarpment, the Ungus, which Obruchef ascribes to a fault (1890, 250), 
and along the base of which Konshin describes shorelines (1887, 238), probably 
contemporaneous with those at Krasnovodsk and Jebel. The floor of the depression 
south of the Ungus is stated by Lessar to be 44.6 meters below the Caspian (1889, 7 14). 
This escarpment and the shorelines along its base are features toward which future 
obser\'ation might well be directed, with the hope of deciphering the histoiT of the 
sea in greater detail. If I understand Konshin's description, the dissection of the 
Pliocene strata in the escarpment must have taken place before the shorelines were 
made at its base. It might, therefore, here be possible to recognize the time interval 
that obsen'ations elsewhere lead us to suppose elapsed between extensions of the 
Pliocene and the Quaternar}- Aralo-Caspian Sea, and perhaps to decipher the pre- 
sumably complicated histor}- of the Quaternary- sea itself 
In the late Quaternary-, the sea was reduced to lower and lower levels, and the 
Caspian and the Aral were thus separated, except for a water passage or channel, the 
Usboi, which passes along the southeastern base of the Ust-xnt and through the 
Balkhan gateway. There has been much discussion regarding the nature and origin 
of this channel. As it has the form of a river channel, and as the Anui is the only 
large ri\-er in the region, the Usboi has been repeatedly said to be the former course 
of the Amu. For example, Sievers (1873) describes the Usboi as a channel so well 
preser\'ed that it seems to have been only lately abandoned ; it is about 65 feet deep, 
two-thirds of a mile wide, eroded in the unconsolidated deposits of the steppe or in 
the firmer Miocene beds on the border of the Ust-urt. The channel has man}- bends ; 
it often divides, .so as to include islands, but there are no branch channels entering 
it. Other obsers-ers have noted that the gentle southwestward descent of the 
channel is broken by the sills of rapids at several points, from wliich it may be 
inferred that the stream by which the channel was eroded did not endure long. 
The Amu being a large river not far distant, its former connection with the Usboi 
seems to ha\-e been assumed without waiting to trace an actual connection between 
