490 
ENCROACHMENTS OF THE SEA. 
out of tlie reacli of causes wliicli might bring it back to its 
former position. 
Although, then, the eastern shore of the German Ocean 
here and there advances into the sea, it in general retreats 
before it, and but for the protection afforded it by natural 
arrangements seconded by the art and industry of man, whole 
provinces would soon be engulfed by the waters. This pro¬ 
tection consists in an almost unbroken chain of sand banks and 
dunes, extending from the northernmost point of Jutland to 
the Elbe, a distance of not much less than three hundred miles, 
and from the Elbe again, though with more frequent and w T ider 
interruptions, to the Atlantic borders of France and Spain.* 
So long as the dunes are maintained by nature or by human 
art, they serve, like any other embankment or dike, as a partial 
or a complete protection against the encroachments of the sea; 
and on the other hand, when their drifts are not checked by 
natural processes, or by the industry of man, they become a 
cause of as certain, if not of as sudden, destruction as the 
ocean itself whose advance they retard. 
Encroachments of the Sea . 
The eastward progress of the sea on the Danish and Nether¬ 
landish coast, and on certain shores of the Atlantic, depends so 
much on local geological structure, on the force and direction 
of tidal and other marine currents, on the volume and rapidity 
of coast rivers, on the contingencies of the weather and on 
other varying circumstances, that no general rate can be as¬ 
signed to it. 
* 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 Kehrungen, or, at sheltered points of 
the coast, by fluviatile deposits called Werders—all have one or more open 
passages, through which the water of the rivers that supply them at last 
finds its way to the sea. 
