364 ON ALLUVIAL FORMATIONS. 



these labours, the islands were so considerably enlarged 

 in size, and the intervals between them so much raised, 

 that, at low water, it was possible to pass on foot from 

 one to the other. The extent of these marsches was so 

 great on the coast of Sleswigh alone, that they were di- 

 vided into three provinces, two of which comprehended 

 the islands, and the third comprised the marsches conti- 

 guous to the coast ; and the same works were carried on 

 upon the marsches of the coast of Holstein. 



But the grounds thus gained from the sand-banks 

 were very insecure ; these people, though they had in- 

 habited them more than ten centuries, had not yet un- 

 derstood the possibility of that combination of fatal cir- 

 cumstances above described, against which their dikes 

 formed but a very feeble rampart ; the North Sea, by 

 the extraordinary elevations of its level, being much 

 more formidable in this respect than the ocean, where 

 the changes of absolute level are much less considerable. 

 I shall give an abridged account of the particulars ex- 

 tracted by M. Hartz from the chronicle of Dankwerth, 

 relative to the great catastrophes which these marsches 

 successively underwent, previously to the time when ex- 

 perience led to the means necessary for their security. 



In 1075, the island of Nord Strand, then contiguous 

 to the coast, particularly experienced the effect of that 

 unusual combination of destructive causes ; the sea pass- 

 ing over its dike, and forming within it large excava- 

 tions like lakes. In 1114 and 1158, considerable parts 

 of Eyderstede were carried away ; and in 1204, the part 

 called Sudhever in the marsch of Uthholm was destroyed. 

 All these catastrophes were fatal to many of the marsch 

 settlers ; but in 1&16, the sea having risen so high that 



