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106
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DAMS.
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The
dam was built in 1872 to the height of seventy-two feet, as shown by
the sketch, being a timber crib formed of unhewn cedar and tamarack
logs, notched and firmly bolted together, and solidly filled with loose
stones of small size. A skin of pine planking, spiked to the
water-face, forms a water-tight lining. During the years 1875 and 1876
the dam was increased to the height of ninety-six and one-fourth feet
above datum line (one hundred feet extreme height) by filling in a
stone embankment on the lower side of the old structure, faced with
heavy walls
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of
dry rubble stone of large size. The down-stream face wall is fifteen to
eighteen feet thick at the bottom, diminÂishing to six or eight feet at
the top. Most of the face stones in this wall are of good size,
weighing from three-fourths to four and one-half tons, and there are
many of equal weight in the backing.
The
lower portion of the wall is seventeen and one-half feet high, with a
batter of fifteen per cent. It is built of heavy stone, with ranged
horizontal beds and with the face stone tied to the backing by long
iron ties.
The
upper portion of the wall is built with a slope of forty-five degrees,
and the face stones are bedded on an angle of twenty-two and one-half
degrees, thus dividing
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