'91 1-] STEVENSON— FORMATION OF COAL BEDS. 589 



deposits, which are, practically all of them, freshwater, marine 

 marshes being unimportant economically. Lesquereux, in 1845, rec- 

 ognized two general types of bogs, which he termed supraaquatic or 

 emerged and infraaquatic or submerged, the former being above 

 the waterline and the other at or below it. The prevailing classifi- 

 cation in Germany recognizes the Hochmoor, equivalent to the 

 Heathermoors of Scotland, and, in great part, to the supraaquatic 

 of Lesquereux ; the Wiesenmoor, Griinlandsmoor, Niedermoor, or 

 Rasenmoor, equivalent to the bogmeadows of other lands ; and the 

 Waldmoor or forested bog. These are the Lyngmose, Svampmose, 

 Hoermose ; the Kjaermose, Engmose ; and the Skovmose of the 

 Danish authors. A similar division is that of Hochmoor, Flach- 

 moor and Zwischenmoor, these being the terms employed by Potonie 

 and some recent authors. 



Potonie"" has described a great moor in east Prussia on the delta 

 of the Memel and Xemonien rivers, which shows the relations of 

 the several types. Going eastward from the shore, one finds first 

 the mud, which on the border is held by water lilies and other plants, 

 referred to as " landmakers " because they are outposts. Higher 

 plants, especially canes, occupy water areas, behind which there 

 develops a meadow Flachmoor of sedges, where frequent floodings 

 prevent growth of trees. Beyond that, foresting begins, and one 

 reaches a moor of black alder, several kilometers broad. The sur- 

 face is occupied by swamp plants, such as Iris, SiiDii, sedges, which 

 endure well the periodical floodings of this zone. If the area were 

 one of gradual subsidence, equal to the accumulation, the condition 

 would continue for a long period. The surface rises gently and one 

 comes to another flora, accustomed to somewhat drier soil, with 

 alders, hops and nettles. Thus far, one has followed the Flachmoor 

 or Xiedermoor ; but at a little distance beyond, swamp birches are 

 seen among the alders. The latter soon disappear and the birch 

 zone is reached, beyond which is a zone of forest with Piiiiis sylves- 

 tris and Picea cxcelsa. These form the Zwischenmoor or Waldmoor. 



In this passage zone, the peat has risen so high that the surface 

 is drv ; the forest is here, but as one advances the trees become 



^''' H. Potonie, " Die Entstehung," etc., pp. 35-40. 



187 



