496 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 11, 



a few rainless seasons ; and Sir F. Goldsmid's party in 1872 found 

 that it had entirely disappeared, with the exception of two small 

 pools*. 



Slopes of Gravel on the margins of Desert Plains. — The margins 

 of the desert plains have already been described as stony. They 

 usually consist of a long slope composed of gravel and boulders, and 

 with a surface -inclination of from 1° to 3°. Such slopes often ex- 

 tend for a distance of from 5 to 10 miles from the base of the hills 

 bounding the plains, the difference in level between the top and 

 bottom of the incline being frequently from 1000 to 2000 feet, or 

 even more. What proportion of this thickness consists of detritus it 

 is impossible to say ; but the depth of the deposit must be great, 

 because hills of solid rock but rarely emerge from it. The greater 

 part of such slopes consists of sand and pebbles, the latter more or 

 less angular, and mixed with large blocks, all derived from the 

 adjacent hills. There is, so far as I know, nothing like a beach- 

 deposit in any case. Fragments 2 to 3 feet in diameter are not 

 uncommon, even at a distance of a mile or two from the base of the 

 hills ; but I only observed them near places where small streams 

 issue from the higher ranges. At such spots the gravel deposits 

 are naturally very often raised into a fan-shaped slope. Such 

 a phenomenon is common enough in all countries ; and so are stony 

 slopes at the bases of steep hills ; but the peculiarity of these slopes 

 in Persia consists in their great breadth and in the enormous mass 

 of detrital deposits which they contain. 



Slopes of Detritus in Valleys. — From many of the desert plains of 

 Persia valleys of great width extend far into the more hilly regions. 

 These valleys have, along their sides, precisely such long slopes of 

 gravel as I have just described. The presence of a stream in the 

 middle of the valley is by no means constant ; but occasionally small 

 rivulets coming from the side run for miles along the slopes without 

 descending to the bottom of the valley, and are finally absorbed by 

 the soil, if not exhausted by being diverted for irrigation. 



Instances of Gravel Slopes. — It is as well to describe briefly a few 

 instances f of these remarkable gravel slopes, in order to show their 

 nature. One of the most striking cases noticed was near the town 

 of Bam, in South-east Persia. The town is built at a point where a 

 broad and very straight valley coming from the west-north-west 

 opens on to the desert which stretches to the north of Narmanshir. 

 From the town, which is about 3600 feetj above the sea, a very 

 gradual gravel slope leads to the desert plain, the elevation of which 

 near its margin is probably between 2000 and 2500 feet. The 



* Goksha Lake, near Erivan, in the Transcaucasian province of Russia, is 

 another example of a freshwater lake without an outlet ; and there is a small 

 example of the same kind at Dastarjan, west of Shiraz. 



t I hope that the detailed geological observations made during my journey 

 through Persia will hereafter be published by the Indian Government, and I 

 must refer to them for further details of these formations. 



I The heights given are chiefly from aneroid readings, and are consequently 

 only approximate. The height of Bam is from Major St. John's boiling-point 

 observations. 



