ARTIFICIAL DUNES. 
499 
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 apprehended 
from the loss of them. 
Artificial Formation of Dunes . 
In describing the natural formation of dunes, it was said 
that they began with an accumulation of sand around some 
vegetable or other accidental obstruction to the drifting of the 
particles. A high, perpendicular cliff, which deadens the wind 
altogether, prevents all accumulation of sand; but, up to a 
certain 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 
artificial wall or dike will, in many situations, give rise to a 
broad belt of dunes. Thus a sand dike or wall, 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 Zyperzeedyk, has produced another 
scarcely less extensive belt in the course of two centuries. 
A few years since,, the sea was threatening to cut through 
the island of Ameland, and, by encroachment on the southern 
side and the blowing off of the sand from a low flat which con¬ 
nected the two higher parts of the island, it had made such 
progress, that in heavy storms the waves sometimes rolled 
quite across the isthmus. The construction of a breakwater 
and a sand dike have already checked the advance of the sea, 
and a large number of sand hills has been formed, the rapid 
growth of which promises complete future security against 
both wind and wave. Similar effects have been produced by 
