een inches wide on top, securely anchored by iron bolts to the stone wall.
.
It is not probable that any water will ever pass over the crest of the
main dam, except in case of a break at the large reservoir higher up
the stream. Great care was taken in building the down-stream face wall
of the dam for any such possible emergency. Should this happen a large
quantity oi water would enter the structure, owing to the inclined beds
of the face stone and the flat slope of the wall, which water would
seek its discharge through the interstices purposely left in the nearly
vertical portion of the lower wall. To prevent the consequent
hydrostatic pressure, which would accumulate at the base of the dam to
perhaps twenty pounds to the square inch, from forcing out the lower
face, the wall was carefully built and tied with iron rods.
There
are 55,000 cubic yards of material in this structure, weighing about
85,000 tons ; the hydrostatic pressure, with the water-line
ninety-five feet above datum, against a vertical plane of that height
across the canon at the dam site will be 21,745 tons. The dam is built
V-shaped, with the vertex of the angle of 1650 pointing up
stream. This mode of construction adds somewhat to the stability of the
structure. The cost was $151,521.44. The rather peculiar construction
of this dam was due to the following causes :
The
stone cliffs in the vicinity are composed of an exceedingly hard
granite with poor cleavage, but with great numbers of short cross
seams, making it most costly to quarry stone of large dimensions.
No limestone existing in the vicinity, the cost of transporting lime was so great as to prevent its use.
On
the side of the mountain, at the distance of about one mile, there was
a large pile of loose stone, too irregular in shape to be used in
wall-building, but of good quality for an embankment. It was found to
be cheaper to build a tramway to this stone and haul it to the work
