ACTION OF EIVERS. 527 



tion — the number of torrents emptying directly into the sea is 

 mucli less than it was at earlier periods. The formation ol 

 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, 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 Unterlaiif, or lower 

 course, that they are much less able to transport heavy material 

 than at earlier epochs. The shme deposited by rivers at their 

 junction with the sea, is usually found to be composed of ma- 

 terial too finely ground and too Kght 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, accumulation, 

 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 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 

 Netherlands " move sand only by a very slow displacement of 

 sand-banks, and do not carry it with them as a suspended or 

 floating material." The sands of the German Ocean he holds 



*De Bodem van Mderland, i., pp. 243, 246-377, et seq. See also the argu- 

 ments of Bremontier as to the origin of the dune sands of Gascony, Annates 

 des Fonts et Chaussees, 1833, ler semestre, pp. 158, 161. Bremontier estimates 

 the sand annually thrown up on that coast at five cubic toises and two feet to 

 the running toise {uM 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 

 mfitre, which is equal to two hundred and sixty-eight cubic feet to the running 

 foot.— Annates des Fonts et Chaussees, 1843, 2me semestre, 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 

 Jutland. Laval estimates the total quantity of sand annually thrown up on 

 the coast of Gascony at 6,000,000 cubic metres, or more than 7,800,000 cubic 

 yards. 



