240 TIIK liASIN OF EASTERN PERSIA AND SISTAN. 
below (fig. 155). The whole series has been much folded along the edge, but appears 
to lie more nearly in its original position out toward the center of the basin. 
The known facts in regard to Zorabad are too few to warrant any hard and fast 
conclusions as to its liistory. The most probable lupothesis is that in early Tertiary 
times apparently a body of shales was deposited under what were presumably marine 
conditions. At length the water retired and heavy conglomerates and sandstones 
were deposited either subaerially or in very shallow water of fluctuating depth. 
Toward the close, or perhaps during the progress of this deposition, earth-movements 
were in progress which dimini.shed the size of the basin and uplifted its sides, as is 
shown by the crumpling of the strata along the edge. Eventually the northern 
border was raised so high that the Hcri Rud was checked and the basin was con- 
verted into a lake where clayey marls were deposited. It is proljable that these 
movements were contemporaneous with those which uplifted the alluvial deposits 
southeast of Seraklis and inaugurated the present cycle of erosion, for the cutting 
of the gorge at Pul-i-Khatun must have proceeded pari passu with the draining of 
the lake which now ensued. After the lake had disappeared the lacustrine deposits 
were covered with the subaerial gravels which are so common in arid regions. 
To-day the deepening of the gorge of the Heri Rud has permitted the dissection 
of both the clays and the gravels. The most notable fact in regard to Zorabad is 
that we have here on a small scale the same phenomenon which will presently be 
described in other basins of Persia, and which seems to have taken place in some of 
the basins of Turkestan. The area of deposition along the edges of the basin is 
continually in process of folding, and tlie folding progresses gradually inward. 
THE AFGHAN DEPRESSION SOUTH OF THE RUSSO-AFGHAN BOUNDARY. 
On the southern rim of the Zorabad Ixisin the fieri Rud enters the ancient lake 
bed through a deep gorge cut in Cretaceous limestone and probably of nearly the 
same age as the corresponding gorge of Pul-i-Khatun on the north side. Upstream 
the river flows through a broad open valley, which is in realit\- another large basin 
extending northwest for 60 miles past Turbat-i-Sheikh Jam. The innnediate 
river valley is bounded by the broad terraces cut in gravel and in an underlying 
deposit of unconsolidated silts. The silts are sliglitly warped and are truncated by 
the terraces. They will l:)e described later. Opposite the southeastern corner of the 
Jam basin, and offset to the south from it, just as the mountain ranges on the two 
sides of the Heri Rud are offset from one another, lies the basin of Herat, Inroad at 
first, but gradually contracting into the stupendous gorge of the upper river. The 
Jam-Herat basin is bordered on the south by low hills, cliiefl)- of sandstone, I;e>ond 
which the smooth, white sheet of the " Nemeksar," or playa of Khaf, and the smaller 
sheets of its neighbors fill the bottom of a depression which is chiefly remarkaljle 
for the large number of half-buried momitains which rise on every hand like islands 
in an archipelago. It seems as though a once mountainous region had been depressed 
to form a hollow, in which the mountains still stand as of old, although some have 
been buried in detritus to the waist, others to the neck, and some are doubtless 
wholly hidden. 
