Or 
CHANGES PRODUCED BY MAN. 49 
changes in the face of nature. The destruction of the forests 
around the sources and along the valleys of the rivers by man 
gave them a more torrential character. The felling of the 
trees, and the extirpation of the shrubbery upon the fens by 
domestic cattle, deprived the surface of its cohesion and con- 
sistence, and the cutting of peat for fuel opened cavities in it, 
which, filling at once with water, rapidly extended themselves 
by abrasion of their borders, and finally enlarged to pools, 
lakes, and gulfs, like the Lake of Haarlem and the northern 
part of the Zuiderzee. The cutting of the wood and the depas- 
turing of the grasses upon the sand-dunes converted them from 
solid bulwarks against the ocean to loose accumulations of 
dust, which every sea-breeze drove farther landward, burying, 
perhaps, fertile soil and choking up water-courses on one side, 
and exposing the coast to erosion by the sea upon the other. 
Geographical Effect of Physical Improvements im _ the 
Netherlands. 
The changes which human action has produced within 
twenty centuries in the Netherlands and the neighboring 
provinces, are certainly of no small geographical importance, 
considered simply as a direct question of loss and gain of terri- 
tory. They have also, as we shall see hereafter, undoubtedly 
been attended with some climatic consequences, they have 
exercised a great influence on the spontaneous animal and 
vegetable life of this region, and they cannot have failed to 
produce effects upon tidal and other oceanic currents, the 
range of which may be very extensive. The force of the 
tidal wave, the height to which it rises, the direction of its 
currents, and, in fact, all the phenomena which characterize it, 
as well as all the effects it produces, depend as much upon the 
configuration of the coast it washes, and the depth of water, 
and form of bottom near the shore, as upon the attraction 
which occasions it. Every one of the terrestrial conditions 
which affect the character of tidal and other marine currents 
