VALLEYS FILLED UP BY RIVERS. 157 



tive. As its branches descend from Shunnor Fell, Cam Fell, and 

 Whernside, they transport daily and hourly from those elevated sites 

 the materials accumulated by atmospheric agencies and mechanical 

 attrition ; the soil, the stones, the loosened rocks, grain by grain, and 

 piece by piece, move onward with the current, and thus the whole 

 mountain region, by a slow yet not imperceptible progress, is lowered 

 in height, and its wasted spoils swept away for ever. But let us follow 

 this process. Wherever the valley originally presented great inequali- 

 ties, these are constantly diminished by the upfilling of the hollows, 

 and at length the originally rugged chasm is changed by additions and 

 upfillings into the smooth, evenly declining hollow, which, because of 

 that smoothness and uniform declination, is supposed by many to be 

 entirely a valley of denudation. In this process, the lateral action of 

 rains and inundations from the sides of the valley is a very important 

 auxiliary. Any one who contemplates the valleys of the Jura, near 

 Schaffhausen, and sees them in many cases rugged on the sides, and 

 evidently traced by nature in contortion, must be struck by the 

 smooth, even, equally declining plane of their bottom, which cuts 

 the rude precipices of the sides, and clearly indicates a subsequent 

 powerful modification of the original roughness of the chasm. Still 

 more abundant is the deposit of sediment as the stream glides into 

 lower ground. There, above its narrow channel, rise the broad 

 meadows, which, with every fresh inundation, receive a new coat of 

 sediment, and above these swell the real boundaries of the valley, 

 often consisting of water-worn materials, gravel and sand, left there 

 by ancient floods of greater power, flowing at a higher level. As we 

 approach the sea, when the tidal currents meet the freshes, the sus- 

 pension of motion permits a great part of what sediment still remains 

 to discolour the water, to drop on the bed of the river and its alluvial 

 banks. Thus the streams become choked, their channels sinuous, 

 their beds elevated, and the banks which confine the river, heightened 

 both by nature and art, look like the ramparts and terraces of a lofty 

 military road rather than the boundaries of a river giving passage to 

 the drainage of the neighbouring country. 



Taluses and Fans. In the upper basin of the Indus, Mr. Drew * 

 has described some remarkable deposits of sediment, due to the 

 circumstance that the accumulation of the material is more rapid 

 than its removal ; though the like conditions may be observed on a 

 smaller scale in our own Lake district and in all hilly countries. 

 Wherever the rocks become disintegrated, they fall and accumulate 

 taluses, such as may be seen on the south-eastern side of Wast Water, 

 in Cumberland, extending for miles. The materials of a talus partly 

 fallen and partly washed down by the rain generally lie at an angle of 

 about 35. Sometimes they expand downward in a fan shape, having 

 its foot in a valley, and its apex in a steeper tributary ravine, giving 

 the talus a vertical height, which is often 1000 or 2000 feet. Some- 

 times such a mass becomes infiltrated and cemented by calcareous 



1 Quart. Jour. Geol. Soc., vol. xxix. p. 441. 



