GEOLOGICAL HISTORY OF NORTHEASTERN PERSIA. 237
THE BINALUD RANGE AND THE NEIGHBORING BASINS.
Little is known of the third and fourth divisions of Khorasan. I have seen nothing of the basins and shall not attempt to describe them. The Binalud Mountains, as seen from the north, present somewhat the same youthful appearance as Kopet Dagh, though to a less degree. I was told by Mr. Clemenson, of Meshed, that some of the valleys are as deep and narrow as those of the northern range. Farther south, however, the youthful outlines are lost and the mountains assume a mature appearance. The component rocks also change in character and become largely igneous or of Paleozoic age. It appears that the uplifting of the mountains of Eastern Persia has proceeded gradually from south to north. On the edge of the Dasht-i-Kavir the mountains are mature, farther north in the Binalud range they are young, while still farther north in Kopet Dagh many features are exceedingly young. In Central Asia the saine thing seems to be taking place. Step by step the ranges are gaining in area at the expense of the basins, and the mountainous areas of the central massif of Asia seem to be encroaching northward upon the great plains.
THE AFGHAN DEPRESSION.
The Afghan depression is bounded on the north by the low mountains through which the Heri Rud has cut its way out from the basin of Iran. Gathering its waters from the snowy heights of Hindu Kush, in the most inaccessible portion of northern Afghanistan, the Heri Rud flows westward for 300 miles between towering mountain ranges which gradually decrease in height and finally come to an end at the edge of the Afghan depression. Here the Heri Rud turns abruptly north, and after threading its way through a gorge emerges upon the plain of Transcaspia. There, after receiving the waters of the Keshef Rud from Meshed, it takes the name of Tejen River, and soon loses itself in the swamps and sands of the Turkoman desert.
Where the Heri Rud crosses the mountains, the eastern portion of the northern border of Iran appears to be offset to the south. 'The Paropamisus appears to be the continuation of Kopet Dagh, and the mountains south of Herat the continuation of the Binalud range. The eastern mountains lie roughly 5o miles south of their Persian counterparts. This break between the ranges of Persia and Afghan-
! istan causes the depression through which the Hen Rud escapes to the north.
Little is known of the mountains which border the depression. Those on the west at the end of Kopet Dagh, according to Mushketoff, consist for the most part
0 of Cretaceous limestone, but I saw several large basins and other areas where the
prevailing formations are of Tertiary age. The topography on the whole is mature;
sio it probably corresponds to that which would exist farther west in the neighborhood
of Meshed and Askhabad if no recent uplift had taken place. East of the river the topography is still more mature. Holdich (p. 113), whose opportunities for
observation were extensive, describes the country north of Herat as so mature that,
although the passes rise to a height of 4,800 feet, wagons can be driven across the
mountains in spite of the absence of roads. In the region about 6o miles north of Herat, which Mushketoff erroneously, I think, marks as Triassic, Holdich