554 



DESTRUCTION OF ISLANDS. 



[Ch. XXI. 



parts of the rich and populous isthmus, a low tract which 

 stretched on the north of Lake Flevo, between Staveren in 

 Friesland and Medemblick in Holland, till at length a breach 

 was completed about the year 1282, and afterwards widened. 

 Great destruction of land took place when the sea first broke 

 in, and many towns were swept away ; but there was after- 

 wards a reaction to a certain extent, large tracts, at first 



submerged, having been gradually redeemed. 



The 



new 



straits south of Staveren are more than half the width of 



■ 



hose of Dover, but are very shallow, the greatest depth not 

 exceeding two or three fathoms. The new bay is of a some- 



t 



what circular form, and between thirty and forty miles in 

 diameter. How much of this space may formerly have been 

 occupied by Lake Flevo is unknown. (See map, fig. 55.) 



Destruction of islands. — A series of islands stretching from 

 Texel to the mouths of the Weser and Elbe are probably the 



last relics of a tract once continuous. They have greatly 



diminished in size, and have lost about a third of their num- 

 ber, since the time of Pliny; for that naturalist counted 

 twenty-three islands between the Texel and the Eider, in 

 Schleswig-Holstein, whereas there are now only sixteen, in- 

 cluding Heligoland and Neuwerk."* The island of Heligoland, 

 at the mouth of the Elbe, consists of a rock of red marl of the 

 new red sandstone formation (or keuper of the Germans), and 

 is bounded by perpendicular red cliffs, above 200 feet high. 

 (See fig. 56.) Although, according to some accounts, it has 

 been greatly reduced in size since the year 800, M. Wiebel 

 assures us, that the ancient map by Meyer cannot be depended 

 upon, and that the island, according to the description still 

 extant by Adam of Bremen, w r as not much larger than now, 

 in the time of Charlemagne. On comparing the map made 

 in the year 1793 by the Danish engineer Wessel, the average 

 encroachment of the sea on the cliffs, between that period 

 and 1848 (or about half a century), amounted to about three 

 feet a year for the whole circumference of the island. f Ac- 

 cording to some authorities, Sandy Island (see a, fig. 56), now 

 separated from Heligoland by a navigable channel, formed, 



* Von Hoff, vol. i. p. 364. 



t Quart. Journ. Geo]. Sue. vol. iv. p. 32; Memoirs. 













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