380 STUDIES FOR STUDENTS 



are due to arrest of motion, whether partial or total, in the transporting agent, 

 we can easily understand that the rainfall on the Persian hills may suffice to wash 

 down as far as the sides of the valleys those fragments which, by chemical agency 

 or the action of frost, are loosened from the hill-sides; but when once the momen- 

 tum given by the steepness of the incline is at an end, the quantity of water drained 

 from the surface is insufficient to transport the debris to a lower level; all that 

 it can do is to leave the detritus in a long slope, the surface of which is arranged 

 by the wash of rain.^ 



These views receive further support from the observations of Med- 

 licott and Blanford on the relations to the rainfall of the piedmont 

 gravels which face the south slopes of the Himalayas. In this con- 

 nection they state : 



Bhdbar is the slope of gravel along the foot of the Himalayas. Compared 

 with the slopes in the dry regions of Central Asia, Tibet, Turkestan, Persia, etc., 

 the gi-avel deposits at the foot of the great Indian ranges are insignificant, the 

 difference in height between the top and bottom of the slope nowhere exceeding 



1,000 feet This difference is probably partly due to the much greater 



rainfall in India, and to streams being consequently able to carry away a much 

 larger proportion of the detritus washed from the surface of the hills, partly also 

 to the circumstance that the rocks in the lower regions of the hills are not sub- 

 jected to the loosening effects of frost. 



The bhdbar slope of gravel along the foot of the Himalayas, although evidently 

 of comparatively recent formation, has frequently, to the eastward, been cut into 

 terraces by the streams from the hills. This is a necessary consequence of the 

 streams cutting deeper channels in the rocks of the hilly ground. It is curious 

 to note, however, that to the westward the bhdbar is being raised instead of being 

 cut through by streams. The difference is not improbably due to the much greater 

 rainfall to the eastward, and to the streams being consequently able to carry 

 away the gravel as they cut back their bed in the rock, whereas weaker streams 

 are prevented from cutting back their channels by their inability to wash away 

 the gravel they have already deposited. It may be, too, that from local causes the 

 gravels to the westward are more easily percolated by water and therefore streams, 

 instead of carrying away the bhdbar deposits, sink into them; but, judging from 

 the enormous development of the gravel slopes in regions of small rainfall, it is 

 more probable that the first hypothesis is correct.^ 



In conclusion on this topic it is to be pointed out and emphasized 

 that the climatic significance of gravel deposits on piedmont slopes is 

 precisely opposite in character to the same when found on the delta 

 plain. Climatic inferences cannot therefore be safely made unless, 



1 Loc. ciL, p. 498. 



2 Medlicott and Blanford, Geology of India (1879), Part I, pp. 403, 412, 413. 



