GEOLOGICAL HISTORY OF NORTHEASTERN PERSIA. 243
The Jam Basin.—The deposits of the Jam basin south of Zorabad are disclosed in a number of terraces along the Heri Rud and its tributaries. They consist of fine-grained brown silts, neither sand nor clay, but between the two. Most of the silts are reddish-brown in color, others are brown, brownish-purple, or green.
They contain gypsum in thin and very pure transparent layers, which are sometimes so abundant that the ground is white with fragments. Often the strata lie horizontal, but there are many places where warping has taken place. For instance, south of Danidue a terrace 180 feet high consists of a cap of coarse slaty gravel lying unconformably on silts dipping 6° N. The edges of the Jam basin were not seen, and we can not be sure whether the amount of warping increases from the center outward.
An interesting point in regard to the Jam deposits is that as a whole they much
resemble the Moencopie beds which occupy so large an area in the plateau region of the United States (Goldthwait, pp. 203, 205, 21o). Not only is the general character of the two formations similar, but the brilliant color and peculiar form of the cliffs are strikingly alike, while in each case a gravel cap protects the soft underlying silts. Even the terraces present the same appearance, although those of America are structural, while those of Persia are fluviatile.
The Nemeksar Basin.—In the Nemeksar basin, 75 miles south of the Jam River,
many of the phenomena of the Jam basin are repeated. The gravel-capped terraces bordering the playa consist of a soft, fine silt, mostly red, but sometimes slightly green, in which are numerous thin layers of transparent crystalline gypsum. No warping of the silts was here observed, but they were seen only near the center of the basin.
The Chau Bineh Basin.—At Chau Bineh, near Durukh, about 90 miles southeast of Birjand, thick warped clays were noted, purple, red, and green, like those of the Jam basin. They lie unconformably against a mass of ancient volcanic rocks full of serpentine and iron pyrites. The Durukh basin, on the edge of which they lie, is tributary to Sistan.
The Chahak Basin.—This basin and the following one lie on the edge of the main basin of Persia, the Dasht-i-Lut, and would discharge into it if supplied with sufficient water. Yet each possesses its own individuality and is a separate basin with its own "kavir" or salt plaÿa occupying the lowest portion. The basin of
Chahak lies two days' journey, 4o or 5o miles, northwest of Birjand, on the road to Tun. Around the playa at the bottom of the basin the waves of a former lake, have cut bluffs of considerable height. For the most part these are composed of a hard clay shale, partly green and partly red, which usually lies horizontal, although in somé places it is much folded. Three or four miles northwest of the village of Chahak the bluffs, about roo feet high, are capped with lava and disclose the following section, beginning from the top :
Dark volcanic trap 20
Green clay shale 40
Pink shale IO
Yellow clay shale 5
Green clay shale 20