It is about half way cut
through the solid granite rock, which in that part furnishes a natural
wall. My friend had watched its progress, and gave me many interesting
details of the engineering processes employed: among others, the
tremendous application of steam and gunpowder. An engine bored holes
in the rock fifteen feet deep and twelve inches in diameter; and these
were so placed, and in such numbers, that at a single blast 170 tons
of granite were blown into the air--an operation hardly conceivable.
This canal leaves the town in a westerly direction--being, at its
outset, about a quarter of a mile from the Merrimac, but gradually
approximating for a quarter of a mile, until it touches and unites
with that river. Between the two, is one of the prettiest of public
walks, ten feet wide, having rows of trees on each side, and
terminating in a point; being the end of a splendid granite wall, at
its base thirty feet thick, and tapering to half the thickness,
dividing the natural from the artificial stream. Here we come to a
point of great interest: on the right is an artificial dam across the
river, with two sharp lines at an angle of sixty-seven degrees, the
point meeting the stream, thus stopping the waters, and insuring a
supply for the reservoir, while it forms a cascade of about twenty
feet.
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