352 
CHANGES PRODUCED BY MAN. 
changes in the face of nature. The reduction 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 tens bv 
domestic cattle, deprived the surface of cohesion and consist¬ 
ence, 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 watercourses on one side, 
and exposing the coast to erosion by the sea upon the other. 
c. Geographical Influence of such Operations. 
The changes which human action has produced within 
twenty centuries in the Netherlands and the neighboring prov¬ 
inces, are certainly of no small geographical importance, con¬ 
sidered simply as a direct question of loss and gain of territory. 
They have also 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 has been very sensibly modified by the operations I 
have described, and on this coast, at least, man has acted 
almost as powerfully on the physical geography of the sea as 
on that of the land. 
