ARTIFICIAL DUNES. 591 
coast-row has drifted over the inland ranges, which, as was no- 
ticed in the description of these dunes on a former page, were 
protected by a surface of different composition, and the sand 
has thus been raised to a height which it could not have 
reached upon level ground. This elevation has enabled it to 
advance upon and overwhelm woods, which, upon a plain, 
would have checked its progress, and, in one instance, a forest 
of many hundred acres of tall pines was destroyed by the drifts 
between 1804 and 1827. 
Control of Dunes by Man. 
There are three principal modes in which the industry of 
man is brought to bear upon the dunes. First, the creation of 
them, at points where, from changes in the currents or other 
causes, new encroachments of the sea are threatened ; second, 
the maintenance and protection of them where they have 
been naturally formed; and third, the removal of the inner 
rows where the belt is so broad that no danger is to be appre- 
hended from the loss of them. 
In describing the natural formation of dunes, it was said that 
they began with an accumulation of sand around some vegeta- 
ble or other accidental obstruction to the drifting of the par- 
ticles. A high, perpendicular cliff, which deadens the wind 
altogether, prevents all accumulation of sand; but, up to a cer- 
tain point, the higher and broader the obstruction, the more 
sand will heap up in front of it, and the more will that which 
falls behind it be protected from drifting farther. This familiar 
observation has taught the inhabitants of the coast that an arti- 
ficial wall or dike will, in many situations, give rise to a broad 
belt of dunes. Thus a sand dike or wail, of three or four miles 
in length, thrown in 1610 across the Koegras, a tide-washed flat 
between the Zuiderzee and the North Sea, has occasioned the 
formation of rows of dunes a mile in breadth, and thus excluded 
the sea altogether from the Koegras. A similar dike, called 
the Zijperzeedijk, has produced another scarcely less extensive 
belt in the course of two centuries. 
