I9II.] STEVEXSOX— FORMATION OF COAL BEDS. 587 



thick and the underlying peat, though showing some change, still 

 retains its peaty character and is a passage from the lignite of the 

 border to the peat now worked in the open valley. One is left to 

 conclude that the deposit is continuous from the border to the uncov- 

 ered peat. 



77; f Characteristics of Peat Accuuiiikitions.- — Swamp or marsh 

 accumulations of vegetable matter consist essentially of remains of 

 land plants, including the many water-loving types. Locally, as in 

 the Lebertorfs or Sapropels, one finds freshwater algae and remains 

 of mollusks, while in many swamp peats the exuviae of insects 

 abound, often associated with land mollusks. Some of the older 

 books refer to marine peat. ]\Iacculloch°'^ mentioned a peat found 

 in Scotland, which was composed of Zostera marina, and several 

 authors have cited this as a marine peat. But Zostera is the ordi- 

 nary " eel-grass " of estuaries and is a land plant able to endure salt 

 water. Al. Brongniart,**' under the title " Tourbe marine," states 

 that De Candolle saw in the dunes of Holland some peats which burn 

 well and are composed of seaweeds, notably of Fiicns digitatns. 

 He, himself, had seen, opposite the rock of Calvados, some extensive 

 beds of brown material, soft and spongy, which had all the external 

 appearance of peat, but it could be burned only with difficulty. That 

 seaweeds may accumulate on a strand, there to form a considerable 

 deposit, is placed beyond doubt by Potonie's description of such an 

 accumulation on Heligoland, of which he gives a photograph. But 

 such deposits are wholly local and possess no importance. Muck,^'* 

 in the first edition of his work, referred to the occurrence, at several 

 places along the North sea, of peat evidently marine in origin. 

 Samples of the material were sent by him to Friih, who submitted 

 them to microscopic analysis. One consisted almost wholly of de- 

 caying seaweed ; when dried, it burned with small flame and foul 

 odor, but it showed no characteristic of peat. Another, a brown 

 substance washed up on the shore at Blankenberghe, contained no 



"'"J. Macculloch, "A System of Geology," London, 1831, Vol. IL, p. 339. 

 °' Al. Brongniart. " Traite elementaire de mineralogie," Paris, 1807, Vol. 

 II., pp. 41, 46. 



"" F. Muck, "Die Chemie der Steinkohle," 2te Aufl., 1891, p. 164, footnote. 



185 



