54 EXPLORATIONS IN TURKESTAN. 
gravels, and now dissected b}- the re\i\ed streams in ravines from 300 to 500 feet 
deep near the mountain base, but shallowing as the graded slopes descended to the 
plains. The return along the road from the frontier to Askhabad, some 30 miles, 
we covered rapidly in carriages. 
The net results of the excursion into the Kopet Dagh, in so far as they bear 
on the work of the expedition, are as follows: A series of changing conditions 
has prompted the streams to tenace their \-alleys at se\'eral le\'els. The sticcessi\'e 
changes in the beha\-ior of the streams indicated by the terraces ha\e probably had 
some recognizable effect in changing the character of the piedmont deposits ; the 
latter changes may possibly be recognized b)' borings and may then be correlated 
with the changes in the mountain valleys. It is ven,- probable that terraces similar 
to the ones that we saw occur in other parts of the range. If the valleys were 
examined at intervals of 30 or 40 miles all around the border of the plains on the 
south and east, it might be possible to connect the dates of the several terraces on 
the west with the history of the Quaternary Aralo-Caspian Sea, and on the east 
with the glacial records of the more lofty ranges. Thus successive piedmont 
deposits could be dated. It is evident, however, that there are many difficulties in 
the solution of such a ])roblem, and that much time and patience would be required 
before a solution could be reached. Yet in no other way does it seem possible to 
decipher the recent history of the piedmont fluviatile deposits. 
THE DESERT PLAINS. 
The railroad journey across the desert plains from Askhabad to Samarkand 
with three days stop at Old Merv, was extremely interesting, even if monotonous. 
The surface was absolutely plain to the eye, except for the dunes, and the dunes 
departed from the plain only as \vind-wa\-es at sea depart from a calm surface. 
Although apparently level, the plain has slope enough to give the Tejen, the 
Murg-ab, and the Amu rapid currents, in which these rivers carry forward a great 
volume of mountain waste. Mushketof (1891) describes this part of the plain as of 
fluviatile origin. Obruchef does the same, adding that the thickness of the river- 
laid layers is only several fathoms (1887 ; 1890, 247). The rivers have great varia- 
tion of \olume. The population of Mer\-, depending entirely on the Murg-ab for 
irrigation, had crops abundant enough in 1891 to export some of the surplus to 
Russia; and in 1892 had but little more than half the ordinary yield (Tarnovski, 
1895). We were fortunate enough to see the Tejen and the ]\Iurg-ab in flood. 
The former had overflowed its channel and spread in a thin sheet for miles over the 
plain. The latter would have spread but for the restraint of dikes at IVIerv. Some 
of its waters had escaped further upstream and came to the railroad, wandering 
across the plain among the dunes, a curious combination of too much and too 
little water supply. The rivers had been still higher a few weeks before our arrival, 
and the Tejen bridge had been carried away, as well as some of the track on the 
plain west of Merv, causing great delay to traffic and especialh- to freight transport. 
By the time of our arrival, June 10, a temporary foot-bridge had been built across 
