52 
EXPLORATIONS IN TURKESTAN. 
to its head, about 6 miles distant. While crossing the headwater col, as well as 
while descending the opposing longitudinal stream of Duruigar Valley southeast- 
ward, we passed a number of Kurd encampments. The valley was well inclosed 
at the col by the steep mountain walls, where great triangular sheets of limestone 
rose between successive lateral consequent ravines. The floor of the col, smoothly 
worn on the shales of the \-alley syncline at an altitude of nearly 7,000 feet, seemed 
to belong to the earlier cycle of erosion; the opposing longitudinal streams have 
intrenched their competing valleys so as to leave terraces of the older floor on either 
side, as in fig. 29. We camped on the further stream, about 10 miles from its 
head, and went up on the terraces in the afternoon. 
THE TERRACES OF DURUIGAR VALLEY. 
Successive cj'cles or impulses of valley deepening in the eastward extension of 
the s)nclinal valley were shown here more clearly than near Namali. The southern 
anticlinal range, now called the Telli Dagh, showed unmistakable graded slopes 
beveling the inclined limestone strata far up toward the crest of the range, as in 
fig. 30 ; remnants of sloping terraces occurred on the shales at less altitude ; then 
came the chief terrace, below which the present valley floor is eroded along the axis 
Fig. 30. — Two-mile profile of Terraces in the Duruigar Valley, loolung east. 
of the shale syncline. The period in which the upper limestone slopes were beveled 
and graded must have been the longest of those here shown ; the later periods pro- 
duced graded slopes onl)- in the weak shales. It may be noted, however, that, by 
whatever process the terraces were produced, their record of terracing impulses is 
probably incomplete, for the reason that each long-lasting period of wide-valley 
erosion must have obliterated the work of earlier, shorter periods. In the ideal 
case of eight impulses to deeper erosion and terracing, shown in fig. 31, the records of 
only three are preserved to-day. In such cases it is only the successively smaller and 
smaller maxima of the whole series of impulses that make themselves known, as is 
well shown in the beach lines made by successive storms of decreasing intensity ; 
for example, in the so-called "curbs" of tile great Chesil bank of southern England. 
The four valley floors in the Kopet Dagh must not, therefore, be taken to imply that 
there have been only four periods of renewed erosion ; there may have been many 
more. 
It is difficult to detennine the cause of the terraces by which the ^•alle^•s in the 
Kopet Dagh are ornamented. Terraces may result from certain changes of climate on 
a stationarj' land mass ; or from uplifts of the land in an unchanged climate ; or from 
