
aaa as oe ) 
Parr II. Sucr. ii. § 3.] RIVER DEPOSITS. * Ga 
4 Aevel ground at the base of the slope the water, abruptly checked in its 
_ velocity, at once drops its coarser sediment, which gathers in a fan- 
shaped pile or cone (“cone de déjection”), with the apex pointing up 
_ the water-course. Huge accumulations of boulders and shingle may 
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thus be seen at the foot of such torrents,—the water flowing through 
_ them often in several channels which re-unite in the plain beyond. 
From the deposits of small streams every gradation of size may be 




















































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-Fie, 117.—-Triputary ToRRENT SENDING A ConE oF DETRITUS INTO A VALLEY (B.). 
traced up to huge fans many miles in diameter and several hundred 
feet thick, such as occur in the upper basin of the Indus! and 
_ on the flanks of the Rocky Mountains,’ and other ranges in North 
America (Fig. 118). 
(6) In River-beds.—This is characteristically shown by the 
accumulation of a bed of sand or shingle at the concave side of each 
sharp bend of a river course. While the main current is making a 
‘Sweep round the opposite bank, the water lingers along the inner 
side of the curve and drops there its freight of loose detritus, which, 
when laid bare in dry weather, forms the familiar sand-bank or 
shingle beach. Again, when a river, well supplied with sediment, 
leaves mountainous ground where its course has been rapid, and 
enters a region of level plain, it begins to drop its burden on its bed, 
which is thereby heightened, till it may actually rise above the level 
__ | For an interesting account of the alluvial deposits of this region, see Drew, 
Q. J. Geol. Soc. xxix. p. 441. 
_ 2 See Dutton’s “High Plateaux of Utah.” Hayden’s “Reports of the U.S. 
Geological and Geographical Surveys of the Territories,” 

