300 THE BASIN OF EASTERN PERSIA AND SISTAN. 
Extinct lakes are a feature of many of the chief playas of the Iran basin. At 
Mashkel, south-southeast of Sistan, in the continuation of the Afj^han depression, 
the plaj'a seems to be surrounded by terraces in the same way as the playa of Khaf, 
so far as can be judged from the brief notes of MacGregor (pp. 128, 129, 134) and 
others. Farther to the east, in the center of northern Bahichistan, tlie Lora Hamun, 
as described by Vredenburg (pp. 210-21 1), "is now a large playa entirely dry most 
of the time. In it are islands of lava rising to a height of 50 feet, more or less. 
They are surrounded and even covered by pale-yellow silt of just the same sort as 
that which forms the floor of the playa. The lower portion of these mud deposits, 
though ravined by the rain, still presents a terraced outline, and denudation has 
exposed sections in which strings of angular pebbles from the tuffs of the hills rest 
iipon strata of the buff-colored mud. It is quite evident that this mud, washed down 
in former times by rivers, was deposited in the still water of a lake, just as the 
deposit of the same nature which co\-ers the dried-up floor. Moreover, as they are 
found at all heights along the slopes of the hill, it shows that these were at that 
time entirely submerged ; further, that a large sheet of water then existed whose 
surface rose to a height of 50 feet or more above the floor of the dried-up lake, and 
that the Lora Hamun covered a surface three or four times as extensive as the plain 
which now bears that name." 
In the same connection Vredenburg (p. 210) says that throughout all the 
confusion of the volcanic mountains, interrupted drainage, and smooth playas of 
northern Baluchistan "there are some curiously regular features. Such are the 
long lines of terraces formed by the conglomerates (/. <?., gravels) stretching over 
wide areas. It frequently happens that the traveler following the narrow camel- 
track beaten out of the stone-strewn 'dasht' (i. e., naked gravel slopes), along what 
seems an interminable plain, suddenly finds himself on the edge of an escarpment 
and sees another plain below him some 30 or 40 feet lower. This lower ground 
may again slope gently down to another step-like escarpment, and there may be thus 
three or four of these superposed terraces. If the country had been more thoroughly 
examined it would have been found probably that these lines of terraces fonn 
concentric belts surrounding at a distance some of the larger lake basins. They 
admit of only one explanation — they represent ancient shorelines of great lakes, 
which now have either dried up entirely or are reduced to insignificant shallow 
marshes or salt swamps." It is not impossible that these gravel terraces of Vreden- 
burg are of fluviatile rather than lacustrine origin, and resemble those which I have 
described along the Bendan stream, for example. Nevertheless, the facts stated in 
regard to these and to the Lora Hamun are enough to show that the phenomena of 
Sistan are not isolated, but form part of a record of changes which have affected all 
the neighboring regions. 
SUMMARY. 
On the basis of the facts and conclusions set forth in the preceding review of 
Sistan and of the confirmatory' evidence from surroimding districts, we are prepared 
to sum up the history of this part of Eastern Persia during recent geological times. 
Changes of climate have been the keynote of that historj', although there has been 
