THE TERRACES OF SISTAN. 293 
THE TERRACES OF SISTAN. 
NORTHWEST SIDE OF THE r,AKE. 
In Sistan lacustrine and fluviatile terraces merge into one another, but cause no 
confusion, as they both tell the same stor)'. Scattered among them and often parallel 
to them are numerous structural terraces, due to the hardness of the gravel among 
the upper and of the green clay among the lower strata. Most careful work is 
needed to avoid confusing them with their neighbors. A fourth class of terraces is 
due to warping. None of these has been detected, but the older lacustrine terrace 
has been warped, and the corresponding stream terraces must have been similarly 
affected. 
The lacustrine terraces agree with those of fluviatile origin ; two are well devel- 
oped, and a third is now in process of formation. They indicate that since the last 
heavy gravels were deposited on the smooth plain which caps the upper terrace 
(fig. 169) the lake has stood at three different levels, at two of which it has cut high 
bluffs in the soft clays or formed large beaches where the shore is less steep. The 
bluffs are best developed on the northwest side of the lake. At Bereng, where there 
has been no warping, the two upper levels are about 15 and 25 feet above the level 
occupied by the lake surface of January', 1904, which was perhaps 5 feet lower than 
the extreme high level of floods. Just north of Bereng all the space between the 
15-foot beach and the present beach is covered with beach material, and the same is 
tnie wherever the shores of the lake are fairly steep. Where the shores are flat, on 
the contrar)-, the two beaches are sharply separated. The 15-foot beach appears to 
be parallel to the present shoreline. The 25-foot beach, on the contrary-, has been 
warped up to a height of 300 feet. At no time, apparently, did the lake level reach 
any great height, for even a rise to the 15-foot level would mean that the lake of 
Sistan must permanently overflow to that of Zirrah, and a rise to 25 feet would cause 
the two lakes to coalesce into one and would invoh'e an immense increase in area. 
The recent histon,- of the lake resolves itself into a few simple changes. At 
the time of the volcanic eruptions of Chaku the lacustrine deposits at tlie northwest 
corner of the Hamun-i-Sistan and along the western side had been uplifted and 
covered with layers of gravel and silt. The gra\-el layers appear to ha\-e numbered 
two before the eruptions began and one during their progress or after their comple- 
tion. When the deposition of gravel came to an end a vast and vev}- smooth gravel 
plain (I, fig. 169) surrounded the Hamun and concealed a series of lacustrine 
deposits, very complete at the north, but worn away by the Bendan stream at the 
south. At Chaku the plain stood several hundred feet higher than the lake, 
although not so high as at present ; at Bereng it stood at the level of to-da}-. When 
matters were in this state the lake stood at the 25-foot level (A, fig. 169), and remained 
there long enough to form bluflfs on all sides of tlie lake. Near Chaku these are 
500 to 600 feet high and are capped with lava ; toward the south the)- gradualh' 
descend till at Bereng they are but 20 or 30 feet high. At Daghaz the bluffs still 
border the lake and are being actively undercut. The)' present an almost perpen- 
dicular cliff 100 feet high. From here northward they gradually retreat, and at 
the same time grow higher, till at Chaku the)- are 3 miles from the water. Where 
