il, a kind of coarse
reed grass is annually sown on the dunes, which forms a tough sod, and
prevents the sand from being blown away.

The dunes form a natural barrier to the progress of the sea; but these,
of themselves, are insufficient to accomplish the purpose; for in the
highest tides the waters sweep through the openings or valleys between
the sand-hills. Immense dikes and sea-walls are erected to complete the
security of the country from the invasions of the ocean. The embankments
which protect the islands of Zealand are over three hundred miles in
length in the aggregate, and involve an annual expense of two millions
of guilders--more than eight hundred thousand dollars--in repairs.

"The great dike of West Kappel is there," said the pilot to Captain
Kendall, as he pointed to the land on the northern shore of the estuary.

"I don't see anything," replied Paul.

"There is nothing particular to see on this side of the dike,"
interposed Professor Stoute, laughing at the astonishment of the
captain. "What did you expect to see?"

"I hardly know. I have heard so much about the dikes of Holland, that I
expected to see a big thing when I came across one of them," added Paul.

"They are a big thing; but really there is very little to see."

"But what is a dike, sir?" asked Paul, curiously. "I never supposed it
was anything more than a mud wall."

"It is nothing more than that, only it is on a very large scale, and it
must be constructed with the nicest care; for the lives and property of
the people depend upon its security. When they are going to build a
dike, the first consideration, as in putting up a heavy building, is the
foundation. I suppose you have seen a railroad built through a marsh, or
other soft place."

"Yes, sir; the railroad at Brockway went over the head of the bay, where
the bottom was very soft. As fast as they put in gravel for the road,
the mud squashed up on each side, making a ridge almost as high as the
road itself. They built a heavy stone wharf at Brockway, the year before
we sailed, and the weight of it lifted up the bottom of the shallow bay
a hundred feet from it, so that boats get aground there now at half
tide."

"That is the idea exactly: The foundation is not solid; and that is
often the chief difficulty in building a dike. The immense weight of the
material of which it is constructed crowds the earth out from under it,
and it sinks down faster than they can build it. In such p