194 ON ALLUVIAL FORMATIONS. 



of the most violent catastrophes at the bottom of the an- 

 cient sea, proceeding, as I think I have clearly shown, 

 from the subsidence and angular motions of large masses 

 of strata, which must have forced out the interior fluids 

 with, the utmost impetuosity, it is not surprising that so 

 many fragments of the lowermost strata are found dis- 

 persed over this great theatre of ruins. 



I now proceed to the details which I received from 

 M. Hartz ; beginning by a specific designation of the 

 islands dependent on the province of Sleswigh, such as 

 they are at present, belonging to the three classes already 

 defined. To commence from the north ; Fanoe, Rom, 

 Sylt, and Amrom, were originally islands of the same na- 

 ture as the neighbouring continent, but have been since 

 extended by marsches.* The soil of these islands, with 

 its gravel and blocks of primordial stones, was at first 

 barren, as the geest is naturally every where ; but is be- 

 come fertile by manure, of which there has been no de- 

 ficiency, since those grounds have been surrounded with 

 marsch, where the cattle are kept in stables during the 

 winter. In the island of Sylt, there are spaces consist- 

 ing of moor ; but its head of land, which extends on the 

 south as far as Mornum, is composed entirely ofmarsch, 

 and is bordered with dunes towards the open sea, be- 

 cause, the sediments of the rivers not reaching any far- 

 ther, the sea-sand impelled against it by the waves re- 

 mains pure, and is thus raised by the winds in hillocks 

 on the shore. The shallow bottom of the sea, between 

 this island and that of Fora, is of geest : at low water, it 



* By marsch is understood the new land added to the coasts since 

 the last retiring of the water of the globe from the surface of the earth, 

 and is formed by the sediments of rivers, mixed more or less with 

 sand from the bottom of the sea. 3. 



