544 SAND-BANKS.' 



in the magnitude of tlie particles carried off from tlie beach by 

 it, and, of course, every storm in a landward direction adds sen- 

 sibly to the accumulation upon the shore. 



ScmdrBanhs. 



Although dunes, properly so called, are found only on dry land 

 and above ordinary high-water mark, and owe their elevation 

 and structure to the action of the wind, yet, upon many shelving 

 coasts, accumulations of sand much resembhng dunes are formed 

 under water at some distance from the shore by the oscillations 

 of the waves, and are well known by the name of sand-banks. 

 They are usually rather ridges than banks, of moderate iachna- 

 tion, and with the steepest slope seawards,* and their form differs 

 little from that of dunes except in this last particular and in 

 being lower and more continuous. Upon the western coast of 

 the island of Am rum, for example, there are three rows of such 

 banks, the summits of which are at a distance of perhaps a couple 

 of miles from each other ; so that, including the width of the 

 banks themselves, the spaces between them, and the breadth of 

 the zone of dunes upon the land, the belt of moving sands on 

 that coast is probably not less than eight miles wide. 



Under ordinary circumstances, sand-banks are always rolling 

 landwards, and they compose the magazine from which the ma- 

 terial for the dunes is derived.t The dunes, in fact, are but 

 aquatic sand-banks transferred to dry land. The laws of their 

 formation are closely analogous, because the action of the two 

 fluids, by which they are respectively accumulated and built up, 



* KoKL, Inseln und Marschen ScTilesicig Hblsteins, ii., p. 33. From a draw- 

 ing in Andkesen, Om Klitformationen, p. 24, it would appear that on the 

 Schleswig coast the surf -formed banks have the steepest slope landwards, 

 those farther from the shore, as stated in the text. 



f Sand-banks sometimes connect themselves with the coast at both ends, 

 and thus cut off a portion of the sea. In this case, as well as when salt water 

 is enclosed by sea-dikes, the water thus separated from the ocean gradually 

 becomes fresh, or at least brackish. The Haffs, or large expanses of fresh 

 water in Eastern Prussia — which are divided from the Baltic by narrow sand- 

 banks called Nehnmgen, or, at sheltered points of the coast, by fluviatile de- 

 posits called Werders — all have one or more open passages, through whicli 

 the water of the rivers that supply them at last finds its way to the sea. 



