SISTAN. 281 
The drinkable quality of the water of Sistan is another of the qualities which 
many writers have deemed remarkable. At times of \'ery high water, perhaps once 
in a dozen years, the lake possesses an outlet to the south which will presently be 
described. The amount of water passing through this, however, is a most minute 
fraction of the tottd which reaches the lake, and as it passes out at the time of high 
water, when the percentage of salt dissolved in the water is least, the amount of salt 
carried by it must be ver\' small compared with the total amount brought in by all 
the tributaries. The amount thus brought to Sistan in a single year, or in a score 
of years, ma}- be insignificant, but it must be large compared with that carried by 
streams in moist countries. Ferrier (pp. 400 ff.) describes the Dasht-i-Margo, through 
which the Helmund flows, as full of salt pools. Bellew (pp. 166, 168, 172, et al.) 
found the soil of the Helmund Valley highly charged with saline matter. In one 
place close to the river, a region some 10 miles long contained several thousand 
pits from which the people extract salt for commercial purposes. On the opposite 
side of Sistan, to the northwest, many of the tributarj' streams are strongly impreg- 
nated with salt. The Shor Rud (Salt River) of Durukh proved so saline that we 
could not drink it. The Gisha stream was drinkable in December, although our 
guide said that in summer, when the brook is reduced to a few pools, not even 
camels can drink the water. In the same way the Bendan stream and the other 
seeping brooklets which I saw along the northwest shore of the lake are all bordered 
by incrustations of .salt ; and lastly, the unconsolidated strata of the bluffs and of 
the lacustrine plain on all sides of Sistan are frequently white with saline matter. 
Clearly the water of the lake is not fresh by reason of any lack of salt in the sur- 
rounding basin. The amount of saline matter brought in each year b}- the streams 
must be large. 
It is possible that the freshness of the lake is due to its occasional overflow. 
If we suppose that a flood occurs ever}' tenth year and carries out of the lake a tenth 
of the water which is that year discharged into it, the nia.ximum salinity of the water 
would be one hundred times that of tlie tributary rivers. Under such conditions 
the water might be apparenth' fresh, although as to this we have no data. It is 
probable that the amount of water escaping from the lake is less than a tenth ever}' 
tenth year, and the salinit}- should be two or three times as great as we have esti- 
mated. Another explanation of the lack of salt is that in comparatively recent 
times the lake stood so much higher than now that it overflowed permanently, and 
was flushed clean. Other lines of evidence, as we shall see, point to this conclusion. 
It is mentioned here to show that while the freshness of the lake proves nothing, 
it is strictly in accordance with the theory which will be considered later. 
THE DELTA OF THE HELMUND. 
The most important part of Sistan from a human standpoint is the arable plains 
which lie outside the central expanses of the lake and swamp. In certain places 
these represent a shore platform cut by the waves when the lake stood higher. 
Elsewhere they represent a portion of the general lake bottom, now laid bare by the 
