THE BASIN REGION OF IRAN.
Before proceeding to a more detailed study of the influence of an arid climate upon the physiography of Eastern Persia, I shall describe the main features of the mountain rim and of the diversified basin which it incloses. Among geographical writers it is customary to speak of Persia, Afghanistan, and Baluchistan as composing the plateau of Iran. It is well to use the name Iran for the portion of the three countries included within the mountain border, but the term " plateau" is misleading. The region is essentially a basin, not a plateau. From the central knot of the Pamirs, a genuine plateau, two mountain passes diverge westward. One, the more northerly, runs west by south under the name of Hindu Kush, and then, as the Paropamisus, turns directly westward and traverses Northern Afghanistan. From a height of 25,000 feet in the Pamirs it descends until in Western Afghanistan the highest peaks rise but 5,000 or 6,000 feet above the sea, and the main range is traversed from south to north by the Heri Rud, the river of Herat. Westward in Persia the Mountains incline to the north, and in Kopet Dagh and the mountains of Khorasan reach an altitude of Io,000 feet. Then, inclining once more to the south, they take the name of Elburz, south of the Caspian Sea, and rise to an extreme height of 19,40o feet in Deinavend. Lastly, still at tremendous heights, the range swings to the northwest and loses itself in a second mountain knot, the plateau of Armenia. The other mountain mass starts from the Pamir as part of the Hindu Kush, but soon diverges to the south, and running south-southwest traverses the eastern part of Afghanistan and Baluchistan under the naine of the Suliman Mountains, rising often to heights of 12,000 feet. As it approaches the Arabian Sea it turns westward, and at decreasing heights follows the seacoast until Persia is reached. Here, as in the corresponding portion of the northern range, the mountains are but 5,000 or 6,000 feet high. Farther west in Persia, however, the mountains soon regain their height, and swinging to the northwest run straight through the center of the country at heights from 8,000 to 14,000 feet, and finally in the highlands of Armenia coalesce with the northern of the two mountain chains which start from Hindu Kush. Between these two chains, and completely inclosed by them, lies the basin region of Iran, which is roughly shaped like a segment of a circle, 1,200 miles long from east to west, and 600 miles broad. This region, most of which is absolute desert, contains an area of over 500,000 square miles, and is as large as the twenty of the United States which lie east of the Mississippi River and north of Tennessee and North Carolina ; or, to compare it with a region where physiographic conditions are more similar, as large as the five semi-arid states of Colorado, Utah, Nevada, Arizona, and New Mexico.
THE TWO BASINS OF IRAN.
The basin region of Iran contains two chief basins divided into many smaller basins (fig. 152). The largest basin, embracing about three-fifths of all Iran, lies wholly in Persia and may properly be called the Persian basin. The other chief basin, embracing the greater part of the remaining two-fifths of Iran, about 200,000 square miles, contains parts of Persia, Afghanistan, and Baluchistan. It