Vol. 58.] TO THE PHYSICAL GEOGRAPHY OF THEIR AGE, 199 
* 
XIII. Breccras in Perstra.! 
Probably more than half the surface in the Persian upland is 
covered by breccia, gravel, sand, or loam (of recent origin, geologically 
speaking), the thickness of which is so great that no other formation 
can be seen for hundreds of square miles. The elevated plains or 
broad valleys, surrounded by mountains of moderate height, are 
covered in the central part with a fine pale-coloured loam—probably 
leess, and thus of subaérial origin, though lacustrine deposits exist 
in places. But from the foot of the hills, a fringe of breccia 
extends over this on either side, for a distance of 3 or 4 miles 
and sometimes more, its surface sloping at a very low angle, usually 
from 1° to 4°. 
A very brief description of the district near Baghin may suffice 
as an example. Here the valley-plain, some 5500 feet above the 
sea-level, is about 13 miles in width, and runs in an east-to-west 
direction, between hills which rise on either side from 1500 to 2000 
feet above it. On the northern side the breccia-fringe extends for 
about 3 miles, the angle of its upper slope being less than 2° ; 
on the southern is a similar fringe, + to 5 miles wide, its in- 
clination being a little under 1°;”? and between these is the flat 
central plain (lcess) about 6 miles across. 
The climate of the Persian plateau is one of extremes. At 
Teheran (lat. 35° 41' N.), about 3700 feet above the sea, the mean 
temperature of January is 39°6° Fahr., of July 79°3°, of the year 
60°3° ; at Ispahan (lat. 32° 38’), altitude 5020 feet, it is, for 
January 31°6°, for July 82°, for the year 59:4°. In the region of 
the breccias, some 2000 feet or so higher above the sea, the annual 
temperature would be about 6° lower, and the winter-temperature 
affected to at least the same amount, and perhaps yet more. The 
rainfall alsois small—probably not more than 10 inches (it is 10°4 
at Teheran), and on the hills most of this descends as snow. The 
same type of climate—extremes of heat and cold, with a limited 
rainfall—prevails in a large part of Central Asia from Persia to 
Eastern Tibet, in which simiiar formations are frequent. They 
occur also in parts of the mountains of Northern Hindustan.? 
It may be well to mention that the ‘alluvial fans’ produced by 
‘mud-avalanches, which are such conspicuous features in many 
’ This description is founded on Dr. W. T. Blanford’s account of the 
‘ Geology of Eastern Persia’ vol. ii (1876) p. 465, and Quart. Journ. Geol. Soc. 
vol. xxix (1873) p. 495; and I have to thank him for kind information which 
has allowed me to make one or two verbal changes. I have also referred to 
eta by E. Tietze, Verhandl. der k.-k, Geol. Reichsanst. 1874-77, esp. 1875, 
D- LOU, 
ae Eyen this low slope would give a thickness of about 450 feet near the 
hills. At Teheran, however, as Dr. Blanford informs me, the slope of débris 
which extends from the town to the base of the Elburz, a distance of about 
10 miles, shows a difference in level of 3500 feet, and at Kashan, about 150 miles 
to the south, where the slope is of about the same breadth, he found this to be 
2250 feet. 
2 
* See ‘The Making of a Frontier’ by Col. A. Durand, chapters i & ii, for an 
excellent description of breccia-slopes and alluvial fans. 
