EXAMPLES OF TERRACES. 267
a valley filling of gravel and are of small size. In many places they number but one, although farther north, around Turbat-i-Haideri, and among the mountains south of Meshed, two was the usual number. Most of the valleys in which the terraces were found drain either to the Heri Rud or to the Khaf playa, or at least belong to the systems of which the river and the playa are the final gathering-grounds. If the tributaries all reached the main streams it would be fair to infer that the diminutive terraces of the branches might be the reflection of the large terraces of the trunks, and were possibly due to a cause acting at some distant point downstream. Inasmuch, however, as many of the branches never reach the trunks at any time, and as some of them are separated from the trunks by ungraded stretches over which the influence of a downstream displacement would not be felt, it becomes almost necessary to refer these minor terraces to some local cause. If this is done, crustal movements are out of the question, since an impossible complexity and conformity with the minor surface features would be required. The only other possible explanation seems to be climatic change.
THE TERRACES ON THE BORDERS OF THE DASHT-I-LIIT.
Along the borders of the Dasht-i-Lut, where the streams run with greater
strength than they do among the gravel-clogged uplands, there is again a considera-
ble development of terraces. In the valley of Haji Hussein Beg, a day's journey
northwest of Birjand on the road to Tun, there are four good terraces of the old familiar type, gravel, more or less cemented by calcite, above, and rock below (fig. 16o). These terraces are highest along the steeper part of the stream's course, and die out
Fig. 1 60.—Terraces in the Valley of Haji Hussein Beg in the as it approaches the smooth salt
playa of Mehemetabad. Therefore they can not be due to any change in the playa whereby it became a lake. Indeed such a change would be impossible, since if the water of the playa rose ever so little it would overflow to the Dasht-i-Lut, and the playa could not be permanently covered with water unless the whole of Central Persia were converted into a vast lake. The terraces of Haji Hussein Beg may be due to warping which, for some peculiar reason, assumed such a form as to produce the same number and sort of terraces here in this detached locality which it had produced at approximately the same time in a score of other distant places. Or these terraces may be due to climatic changes, in which case their likeness to those of other regions is a necessary part of the theory.
From Mehemetabad nearly to Bajistan, 35 miles north of Tun, there are no good series of terraces, and the scenery is much like that of the mountains to the east—gravel fans, buried mountains, and valleys with a single or occasionally a double terrace. At Bajistan three small valleys come together, each of which has one terrace cut in stratified gravel and brown silt. The town lies on what seems to be an older terrace, which has been half-buried by the later deposit of gravel, in