CONSTRUCTION OF DIKES. 413 
the estuaries of the great rivers, and it is not impossible that 
the double character they possess as a security against mari- 
time floods and as a military rampart, led to their adoption 
upon those islands before similar constructions had been attemp- 
ted upon the mainland. 
At some points of the coast, various contrivances, such as 
piers, piles, and, in fact, obstructions of all sorts to the ebb of 
the current, are employed to facilitate the deposit of slime, 
before a regular enclosure is commenced. Usually, however, 
the first step is to build low and cheap embankments, extend- 
ing from an older dike, or from high ground, around the parcel 
of flat intended to be secured. These are called summer dikes. 
They are erected when a sufficient extent of ground to repay 
the cost has been elevated enough to be covered with coarse 
vegetation fit for pasturage. They serve both to secure the 
ground from overflow by the ordinary flood-tides of mild 
weather, and to retain the slime deposited by very high water, 
which would otherwise be partly carried off by the retreating 
ebb. The elevation of the soil goes on slowly after this; but 
when it has at last been sufficiently enriched, and raised high 
enough to justify the necessary outlay, permanent dikes are 
constructed by which the water is excluded at all seasons. 
These embankments are constructed of sand from the coast- 
dunes or from sand-banks, and of earth from the mainland or 
from flats outside the dikes, bound and strengthened by 
fascines, and provided with sluices, which are generally 
founded on piles and of very expensive construction, for drain- 
age at low water. The outward slope of the sea-dikes is gentle, 
experience having shown that this form is least exposed to in- 
jury both from the waves and from floating ice, and the most 
modern dikes are even more moderate in the inclination of the 
seaward scarp than the older ones.* The crown of the dike, 
however, for the last three or four feet of its height, is much 
steeper, being intended rather as a protection against the spray 
* The inclination varies from one foot rise in four of base to one foot in 
fourteen.—KOHL, iii., p. 210. 
