circle, and consequently well
designed to resist pressure. The dam is built of rubble masonry in
hydraulic mortar, and cost L80,556.

The Stony Creek lower reservoir dam of the Geelong water supply, Fig. 16,
colony of Victoria, is interesting as being constructed of concrete, in
the proportion of 1 to 81/2. Its erection occupied eighteen months, and
cost about L18,000. It is curved in plan to a radius of 300 ft., and the
greatest depth or head of water is 52 ft. 4 in. The width at the crest is
only 2 ft. 8 in., although surmounted by a heavy coping of bluestone 3
ft. 3 in. broad and 1 ft. 9 in. deep. There being no facility for making
a by-wash at the side, the center of the dam is dished to form a weir 30
ft. long. There are both outlet and scour pipes, and valves of 2 ft.
diameter, and the capacity of the reservoir is 143,145,834 gallons.

The Paramatta dam, in New South Wales, built of masonry in hydraulic
mortar, is another instance of a dam built on the curve, and which has
resisted a flood of water 4 ft. in depth over the crest; and in the case
of a dam of about 40 ft. high across the river Wyre, in connection with
the Lancaster Water Works, made of cement concrete in proportion of 4 to
1, there has, according to Mr. Mansergh, frequently been a depth of 5 ft.
of flow over it. This dam is built to a radius of 80 ft. only, and as it
measures 100 ft. along the crest, must include about the fifth of a
circle.

There now remain only two other examples of masonry dams, the first being
that in connection with the Liverpool water supply, and known as the
Vyrnwy dam, Fig. 17, this being thrown across a stream of that name in
North Wales. It is now under construction, and when completed will
impound an area of 1,115 acres.

The dam will be 1,255 ft. long, and formed of Cyclopean rubble set in
cement mortar, and the interstices or spaces between the large masses of
stone, which are rough hewn and not squared, are filled with cement
concrete. The proportion of the cement mortar is 21/2 to 1. These masses of
stone weigh from two to eight tons each, and it is expected that the wall
will be of a most solid description, as great care is being taken to fill
up all spaces. The face next to the water is cemented. The area of the
cross section shown on the diagram, which is at one of the deepest
points, is 8,972 square feet, and the height from foundation to flood
level is 129 ft., the breadth at the base being 117 ft. 9 in.

Th