ce of the land was skimmed off, just as workmen in the city
dig away a hill. It was so in Holland; and you must understand that the
bottom of these peat-beds forms the land now improved as gardens and
farms.

"These depressions of the surface were filled with water. The first
thing to be done is to shut out the ocean and its tributaries--all those
rivers of which I have been speaking, that form a network of canals all
over the country. For this purpose a dike is built on the border of the
land to be enclosed. Take, for example, the Island of Ysselmonde,--the
land next south of us,--and Holland really consists of nothing but
islands formed by the rivers and the natural and artificial canals. It
will, therefore, be a correct specimen of the system of dikes and
ditches throughout the country, though some of the sections are subject
to greater or less difficulty in the drainage, owing to various causes,
which will be explained.

"When the dike around Ysselmonde is finished, the country is protected
from inundation from without. Sometimes in winter the river may be
blocked with ice, which stops the passage of the water. All the ice from
the Rhine and Meuse must pass through these rivers on their way to the
sea, and, being stopped in a narrow place, it forms a dam. In 1799 a
large portion of Holland was threatened with total destruction, on
account of one of these blockades. Behind the dam the water rose seven
feet in one hour, overflowing the dikes, and breaking through them. This
danger is incurred every winter; but disaster is generally warded off by
the vigilance of the dike-keepers.

"We will suppose that the dike we have built around Ysselmonde protects
it from the exterior water; but as the water in the Maas, at high tide,
or even at low tide, is above the surface of the polders, they cannot be
drained by the ordinary ditches; and it is necessary to remove the water
by mechanical means. For this purpose windmills are erected on the
dike,--as you see them in every direction,--many of which work
water-wheels, pumps being but seldom used. The apparatus for removing
the water is of several kinds, including a scoop-wheel, the screw of
Archimedes, and the inclined scoop-wheel. The water is not lifted to any
considerable height by these instruments.

"When the height to which the water is to be raised is too great to be
accomplished by the agency of one machine, a series of them is
introduced. Supposing the land in the mi