ACTION OF RIVERS. 
453 
Meteoric and mechanical influences are still active in the 
reduction of rocks to a fragmentary state; but the quantity of 
sand now transported to the sea seems to be comparatively 
inconsiderable, because—not to speak of the absence of diluvial 
action—the number of torrents emptying directly into the sea 
is much less than it was at earlier periods. The formation of 
alluvial plains in maritime bays, by the sedimentary matter 
brought down from the mountains, has lengthened the flow of 
such streams and converted them very generally into rivers, 
or rather affluents of rivers, much younger than themselves. 
The filling up of the estuaries has so reduced the slope of all 
large and many small rivers, and, consequently, so checked the 
current of what the Germans call their JJnterlauf ,, or lower 
course, that they are much less able to transport heavy ma¬ 
terial than at earlier epochs. The slime deposited by rivers at 
their junction with the sea, is usually found to be composed 
of material too finely ground and too light to be denominated 
sand, and it can be abundantly shown that the sandbanks at 
the outlet of large streams are of tidal, not of fluviatile origin, 
or, in lakes and tideless seas, a result of the concurrent action 
of waves and of wind. 
Large deposits of sand, therefore, must in general be con¬ 
sidered as of ancient, not of recent formation, and many emi¬ 
nent geologists ascribe them to diluvial action. Staring has 
discussed this question very fully, with special reference to the 
sands of the North Sea, the Zuiderzee, and the bays and chan¬ 
nels of the Dutch coast.* His general conclusion is, that the 
* De Bodem van Nederland , i, pp. 243, 246—377, et seqq. See also the 
arguments of Br6montier as to the origin of the dune sands of Gascony, 
Annates des Ponts et Chaussees , 1833, ler semestre, pp. 158, 161. Br6- 
montier estimates the sand annually thrown up on that coast at five cubic 
toises and two feet to the running toise (ubi supra, p. 162), or rather more 
than two hundred and twenty cubic feet to the running foot. Laval, upon 
observations continued through seven years, found the quantity to be 
twenty-five metres per running metre, which is equal to two hundred and 
sixty-eight cubic feet to the running foot.— Annates des Ponts et Chaussees , 
1842, 2me s6mestre, p. 229. These computations make the proportion of 
sand deposited on the coast of Gascony three or four times as great as that 
