ACTION OF RIVERS. 5AT 
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 afiluents of rivers of later geographical origin than them- 
selves. 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 Unterlauf, 
or lower course, that they are much less able to transport heavy 
material 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 sand-banks at the 
outlet of most large streams are of tidal, not of fluviatile, accu- 
mulation, or, in lakes and tideless seas, a result of the concur- 
rent action of waves and of wind. 
Large deposits of sand, therefore, must in general be consid- 
ered as of ancient, not of recent formation, and many eminent 
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 channels of the 
Dutch coast.* His general conclusion is, that the rivers of the 
* De Bodem van Nederland, i., pp. 243, 246-377 et segg. See also the ar-— 
guments of Brémontier as to the origin of the dune-sands of Gascony, Annales 
des Ponts et Chaussées, 1833, ler sémestre, pp. 158, 161. Brémontier 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 mctres per running 
m¢tre, which is equal to two hundred and sixty-eight cubic feet to the running 
foot.—Annates des Ponts et. Chaussées, 1842, 2me scmestre, p. 229. These 
computations make the proportion of sand deposited on the coast of Gascony 
three or four times as great as that observed by Andresen on the shores of Jut- 
land. Laval estimates the total quantity of sand annually thrown up on the 
coast of Gascony at 6,000,000 cubic métres, or more than 7,800,000 cubic yards. 
