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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 28, 



general deepening of the bed of the river, of the denudation by it of 

 its own alluvium, and also of a change in character of the fan- 

 streams from accumulators to denuders ; and this will now be brought 

 forward. 



First comes what must be a rare case ; for I have met with only 

 one instance of it. High up the Indus valley, on the right bank, 

 close to the Chinese frontier, is a fan which spreads on to the allu- 

 vial flat and has not been cut into by the great river ; its slope is 4°, its 

 radius 1| mile ; in this fan is a gully which originates by the mouth 

 of the ravine from which the fan spreads, and continuing on gets to 

 a depth of 70 feet ; but it dies away altogether as the fan meets 

 the plain. At the time I was there (being summer) the ravine 

 and gully were perfectly dry; but the gully must have been 

 made by the same stream that produced the fan, which therefore 

 had changed from an accumulator to a denuder without the extra- 

 neous .cause of the formation of a cliff, and without any similar 

 change on the part of the main river to which it was tributary. 



Our next set of cases depend on the main river having lowered 

 its bed, having cut through beds of alluvium formed by itself. 

 These, again, with reference to the fans, divide themselves into two 

 kinds : — the first where, though the main stream has become a de- 

 nuder, the fan-stream has remained an accumulator; the second 

 where the fan-stream no longer accumulates material. The sketch, 

 fig. 10, illustrates the former class of cases, and at the same time 



Fig. 10. — Triple Fan (three miles above Tsotu, Changchenmo, Ladakh). 



represents a beautiful instance of the compound fan ; I did not bring 

 it forward before, only because the case is complicated by the cir- 

 cumstances we have now to consider. A careful look at the sketch 

 (which is of a fan in the Changchenmo valley) will enable one to 

 to make out these details : — The dark horizontal shading at a, and 

 that corresponding to it on the left is alluvium of the main stream ; 

 it continues far below as well, but is there hidden by fallen stuff : 



