Some of these islands approach entirely, or in part, to the nature of that of Rugen. This island of Seeland, on that side which is called Hedding, has a promontory composed of strata of _chalk_ with its flints. The island of Moen (or Mona), on the south of the latter, has a similar promontory near Maglebye and Mandemark; and the island of Bornholm, the easternmost of those belonging to Denmark, contains strata of _coal_, covered by others of _sandstone_. Phenomena like these, evident symptoms of the most violent catastrophes at the bottom of the ancient sea, proceeding, as I think I have clearly shewn, 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 dispersed 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 nature as the neighbouring continent, but have been since extended by _marsches_[380]. 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 become fertile by manure, of which there has been no deficiency, 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 consisting of _moor_, but its head of land, which extends on the south as far as Mornum, is composed entirely of _marsch_, and is bordered with _dunes_ towards the open sea, because, the sediments of the rivers not reaching any farther, the _sea-sand_ impelled against it by the waves remains 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 may be passed over on foot; and there are found on it gravel and blocks of _granite_. But on the same side of Fora there is a great extent of _marsch_, beginning from St Laurencius. Among the islands consisting entirely of _marsch_ and surrounded with dikes, the most considerable are Pellworm and Nord Strand; and among the Halligs, or those inhabited without dikes, the chief are Olant, Nord-marsh, Langne, Groode, and Hooge.