trenailed strongly together, and is
filled with ballast, to the very top.
The upper slope is covered with
five inch pine plank, jointed and
perfectly tight; the lower With five
and three inch hemlock plank.—
The crest, terminating at the sluice,
near the middle of the overfall, is
level, and covered entirely with
stone eight feet in length, and
strongly secured with iron straps
and bolts. The sluice, sixty feet
in length, is covered in the same
manner, and is about twenty inches
lower than the wings. The walls
of the Lock are 170 feet in length,
its chamber 101 feet by 28 1-3 feet
in the clear, with a single lift; the
west wall serves as the eastern
abutment of the Dam—it is 28 feet
thick at the base, graduated to 25
at the top. The head and east walls
are of corresponding strength.—
Both are built wholly of granite.
The face courses hammered, bed
and joint, rabbitted, and laid in ce-
ment, and the rabbit filled with
cement The floor of the Lock is
constructed of timber fifteen inches
deep, and covered with five inch
pine plank, tongued and grooved,
with an additional flooring of five
inch hard wood plank, commencing
at the head of the Lock and ex-
tending fourteen feet. The main
gates of the Lock, and /guard gates
of the Canals, are of white oak from
the Chesapeake, and the wicket
gates of cast iron. The large stone
piers above the Dam, for the pro-
tection of the Lock and abutments,
are each 30 feet square on the base,
graduated to 25 feet on the top, and
about 34 feet high, and built of
granite, clamped and strapped with
iron.

The Canals on each side of tbe
river are 50 feet wide in the clear,
carrying 10 feet of water from tbe
level of the top of the dam. The
walls are 22 feet bigh, 7 1-2 feet
thick at the base, and 5 feet at the
top. They are finished as far as, and
including, the guard gates. The
gates are of great strength, built of
heavy oak timber, and in the most
substantial manner, revolving in
stone coins, with which stone and
sheet-piling is connected, extending
across and 25 feet into each bank,
and driven 10 feet below the bottom
of the Canals.

' The walls on the banks of the
river, above and below the Dam,
extending about 500 feet, are of the
same height as the Canal walls,
and 8 feet thick at the base. On
the upper side of the Dam is a
sheet of timber-piling, tongued and
grooved, and either resting on the
bare ledge, or driven as far as they
could be made to penetrate into the
solid bed which covers a portion of
its surface, and is connected with
the piling which passes under and
across the Lock into the east hank,
and also with that which is driven
in the west bank of the river.—
Above this, and extending to the
top of the Dam, so as to cover the
entire planking of the upper slope,
is a mass of gravel from 20 to 30
feet deep.

2,500,000 feet of timber and about
25 tons of iron have been used in
constructing the Dam, and about

75,000 tons of ballast have been de-
posited in it.

The Lock, Piers, River and Mill
walls, with the Canal walls, ex-
tending to and including tbe guard
gates, contain about 800,000 cubic
feet of stone.

During the progress of the work,
and especially while the course of
the river was contracted to a space
of 17 feet wide by 24 deep (a time
peculiarly favorable for forming an
estimate, and rarely offered in a
stream of this magnitude) repeated
observations were made upon the
velocity of the current, and at no
time was there found a less quanti-
ty than 2,500 cubic feet per second.
It is proper to add that the seasons
of 1836 and 1837, were both re-