POSTGLACIAL, &>c, DEPOSITS OF CONTINENT. 479 



West Friesland of 10 to 15 feet, and is covered in like manner 

 with marine clay and silt, yet its bottom -layers are abundantly 

 charged with stools and trunks of trees. The phenomena, as 

 described by Arends and Grisebach, would appear thus to be 

 closely paralleled by the peat-beds of the Lincolnshire Fens. In 

 the interior of the Low Countries we find peat-bogs with buried 

 trees, 1 which, as they are followed to the lower-lying tracts and 

 the coast, are overlaid by recent marine deposits, while under- 

 neath this upper peat occurs, at a variable depth of from 10 to 

 40 feet, an older peat with intercalated marine silt and clay. 

 Grisebach is of opinion that the Ztor^-peat, like the so-called 

 forest-bogs, was formed upon the land, and that it gradually 

 became covered with marine alluvium during continual en- 

 croachments by the sea. High-tide floods would cover it here 

 and there with mud and silt, upon the surface of which, when 

 the waters had retired, marshy vegetation would spring up 

 anew until another high flood overspread the low coast-lands as 

 before with a fresh deposit of silt, upon which the plants would 

 again encroach until the next irruption ensued, and a third layer 

 of silt was formed — the land of course slowly subsiding the 

 while. All these changes were effected long before the dawn of 

 history, and the marshes and peat winch now overlie the Darg 

 or bottom-peat were already in existence in the time of the 

 Eomans, as is rendered evident beyond dispute by the appear- 

 ance of Eoman structures resting upon the most recent alluvial 

 deposits of the land. 



Peat with the stools and roots of trees is well known to occur 

 at and below the sea-level at many points on the Belgian coast 

 and the French shores of the Channel. The peat of the Flemish 

 coast, which occurs between high- and low-water mark, has been 

 described by M. Debray, 2 and according to him it shows the fol- 

 lowing succession : — 



1 In East Friesland these bogs contain trunks of oak and pine 50 to 60 feet 

 long, and 2 to 3 feet thick. The trees lie from north-west to south-east, and are 

 said to bear the marks of axes and fire.— S. von Waltershausen. 



" Bull. Soc. des Sciences de Lille, t. xi. 1872 ; Ann. Soc. Xmj. des Sciences de 

 Lille, 1870-74, pp. 19, 84 ; Bull. Soc. Geol. France, Ser. 3. t. ii. p. 46. 



