TERRACED VALLEYS. 
53 
Fig. 3 1 . — Scheme of Terrace Development. 
the interaction of these two causes. The slope that would lead, in the present altitude 
of the mountains, from the high-level floor of the Serani Valley through the former 
floor of the Firuza gorge to the plains, seems rather steep for a graded valley, its 
fill being about 4,000 feet in 20 miles ; yet it does not seem impossible that under a 
climate even drier than that of to-day such a grade might have been developed and 
maintained by a stream of small volume and abundant load, after which a moister 
climate would pennit \alley erosion to a greater depth. On the other hand, it is 
manifest that uplifts of the mountain mass, whereby the streams were periodically 
accelerated, would result in terraces of a depth 
proportionate to the amount of uplift, and of a 
breadth proportionate to the interval of time 
between uplifts. The choice between these two 
possible explanations is not advisedly made by 
following a preference for one or the other, but 
rather by means of some crHx\, which contra- 
dicts one explanation and supports the other. This crux may perhaps be found on 
further exploration, if the terraced valleys are found to interlock in such fashion 
that no simple movement of uplift could ha\-e accelerated all the terracing streams, 
as is believed by Mr. Huntington to be the case for the Tian Shan valleys. Our 
few days in the Kopet Dagh did not enable us to apply this test there. 
We continued southeastward on June 4 along the Duruigar \"alle^•. It soon 
widened ; the Telli Dagh, on the south, becoming a broad anticline with moderate 
dips, and the Kara Ilikhi, as the continuation of the Giluli range is called, on the 
north, seeming to be cut oflf b>- faults. In the wide \-alle\- thus fonned the shales 
have been broadh- planed and covered with from 50 to 150 feet of gravel in con- 
tinuation with the chief terrace seen on the preceding afternoon. A patch of higher 
terrace, associated with a beveled limestone slope behind it, was seen on the side of 
the Kara Ilikhi range. The modem xalley is cut about 300 feet beneath the main 
terrace, and here has gained a width of half a mile at an altitude of about 4,800 feet. 
Leaving the valle\-, we crossed the gravelly terrace plain eastward, and after 
about 3 miles descended to the Russian frontier post, Gaudan (about 4,440 feet 
altitude), on the great Meshed-Askhabad road, which had crossed the terrace plain 
somewhat to the southeast of our trail. The main anticline of the Kopet Dagh 
here breaks down in some manner, but is soon replaced by the Suru-nuizdar 
anticline, an open but crooked vallej- separating the two. The bend of this \alle\- 
into the vSuru-muzdar anticline seemed to give opportunity of seeing the basal 
members of the heavy mountain-making limestones, but we had no time to leave 
the road to search for them. The head of the valley is gnawing southward into 
the broad, gra\el-covered terrace. The road follows northward along the valley, 
which is manifestly enough guided by an oblique fault as it opens on the plains ; 
for here we had the eastern dips of the heavy limestones overlaid with the shales 
of the main anticline on our left, and a bold scarp of the same limestones in the 
obliquely breached Suru-muzdar anticline on our right. Farther on the shales were 
be\eled in smooth, graded slopes, co\-ered with 100 or 200 feet of cobbles and 
