DRAINING OF THE LAKE OF HAAELEM. 407 



where used to bind and compact the mass together. This opera- 

 tion was completed in 1848, and three steam-pumps were then 

 employed for five years in discharging the water. The whole 

 enterprise was conducted at the expense of the stat , and in 1853 



islands seems incredible, aud has sometimes been treated as a fable, but no 

 geographical fact is better established. Kohl (Insebi und Marschcn Sc7deswi[/- 

 Ilolsteins, iii., p. 309) reminds us that Pliny mentions among the wonders of 

 Germany the floating islands, covered with trees, which met the Roman 

 tieets at the mouths of the Elbe and the Weser. Our author speaks also of 

 having visited, in the territory of Bremen, floating moors, bearing not only 

 houses but whole villages. At low stages of the water these moors rest upon 

 a bed of sand, but are raised from six to ten feet by the high water of spring, 

 and remain afloat until, in the course of the summer, the water beneath is 

 exhausted by evaporation and drainage, when they sink down upon the sand 

 again. 



Staring explains, in an interesting way, the whole growth, formation and 

 functions of floating fens or bogs, in his very valuable work, Be Bodem van 

 Nederland, i. , pp. 36-43. The substance of his account is as follows : The 

 first condition for the growth of the plants which compose the substance of 

 turf and the surface of the fens, is stillness of the water. Hence they are not 

 found in running streams, nor in pools so large as to be subject to frequent 

 agitation by the wind. For example, not a single plant grew in the open part 

 of the Lake of Haarlem, and fens cease to form in all pools as soon as, by the 

 cutting of the turf for fuel or other purposes, their area is sufliciently enlarged 

 to be much acted on by wind. When still water above a yard deep is left 

 undisturbed, aquatic plants of various genera, such as Xuphar, Nymphaea, 

 Limnanthemum, Stratiotes, Polygonum, and Potamogeton, fill the botton with 

 roots and cover the surface with leaves. Many of the plants die every year, 

 and prepare at the bottom a soil fit for the growth of a higher order of vege- 

 tation, Phragmites, Acorus, Sparganium, Rumex, Lythrum, Pedicularis, 

 Spiraea, Polystichum, Comarum, Caltha, etc., etc. In the course of twenty oi 

 thirty years the muddy bottom is filled with roots of aquatic and marsh plants, 

 which are lighter than water, and if the depth is great enough to give room 

 for detaching this vegetable network, a couple of yards for example, it rises 

 to the surface, bearing with it, of course, the soil formed above it by decay 

 of stems and leaves. New genera now appear upon the mass, such as Carex, 

 Menyanthes, and others, and soon thickly cover it. The turf has now acquired 

 a thickness of from two to four feet, and is called in Grouingen, lad ; in Fries- 

 land, til, Ulland, or drijftil ; in Overijssel, drag ; and in Holland, rietzod. 

 It floats about as driven by the wind, gradually increasing in thickness by the 

 decay of its annual crops of vegetation, and in about half a century reaches 

 the bottom and becomes fixed. If it has not been invaded in the meantime by 

 men or cattle, trees and arborescent plants, Alnus, Salix, Myrica, etc., appear, 

 and these contribute to hasten the attachment of the turf to the bottom, both 

 iby their weight and by sending their roots quite through into the ground. 



This is the regular method employed by nature for the gradual filling up of 



