PHYSIOGRAPHY OF EASTERN PERSIA. 
231 
is sometimes called the Helmund basin, from the main river, but a better name is 
the Sistan basin, from the lake and swamp into which all the rivers would finally 
discharge if they did not drj- up on the way. The main portion of this report is 
concenied with the Sistan basin, but certain features of the Persian basin will also 
be described, and there will be frequent occasions to refer to Iran as a whole, and 
also to Turan or Turkestan, as the region farther north is termed. 
The border region between the basins of Persia and Sistan is important becau.se 
it represents a line of earth movements extending north and south across the 
middle of Iran transverse to the main orographic lines. West of this line the 
Persian basin was uplifted, while to the east the Sistan basin, together with that of 
the Heri Rud, was depressed. The region of maximum depression forms a long 
north-and-south strip, the Afghan depression, in which are grouped a number of 
Pamirs 
Fig. 152. — Sketch map of the double basin of Iran. 
notable physiographic phenomena. At the north the low mountains, close to what 
is now the boundar)- between Persia and Afghanistan, afford a ready pa.ssage between 
the deserts of the south and those of the north. Elsewhere, for more than 1,500 
miles from the Pamirs to the Anneniau plateau, a giant wall of mountains separates 
Iran and Turan. Here, however (A, fig. 152), the low, rounded mountains aflTord 
an easy passage which has been utilized by anny after anny, from the time of 
Alexander through the dajs of Timur and Jenghis Khan to the present century-, 
when Russia sees in it her easiest road to the south. Here, too, the Heri Rud 
breaks through the main mountain range and emerges upon the desert of Trans- 
caspia, the only instance where a river escapes from the basin of Iran. South of 
the Heri Rud the east-and-west ranges of Afghan mountains come to a sudden end, 
while those that front them on the Persian side run in the opposite direction nearly 
north and south. Between the opposing mountains lies the "Nemeksar" or "salt 
