y,
excavations were made for the foundations. When the wall had been raised
to a height of thirty feet, with two large culverts or openings left in
its lower part for the great water-pipes to pass through, the stream was
again turned into its old course, through these openings, and the next
part of the dam was begun. Thus in three sections the water-wall rose
till a height of one hundred and twenty-two feet was reached, stretching
six hundred feet at the top, to the sloping walls of the valley. As this
dam will have to hold back five hundred acres of water, containing 7800
million gallons of water, its base has been made as wide as its height.
The wall tapers to the top and is perpendicular towards the reservoir.
It is formed of large blocks of granite called 'plums,' set in strong
cement, and weighing many tons each. Over the top, when the reservoir is
full, the flood water pours like a small Niagara. If we could launch a
boat on the glittering surface of the reservoir, from the top of this
dam, we should have to row for four and a half delightful miles, between
the overshadowing sides of the valley, before we reached the next
principal dam, at a place called Pen-y-gareg--so huge are these cups of
water in Birmingham's service. On the way we should pass under the
arches of a stone bridge, thirteen feet wide, stretching from side to
side of the artificial lake. The archways spring from the top of a
submerged dam, forty feet below the surface. And this was built because
Birmingham, seventy-three miles away, is six hundred feet above the
level of the sea. In constructing the long water-hill from the Welsh
mountains down to the famous Warwickshire city, it was deemed necessary
that the upper end should be one hundred and seventy feet higher than
the lower end. Now at the point where the first dam was erected, the
river-bed is only one hundred feet higher than the land on which
Birmingham stands. Therefore, the starting point for the water was made
farther up the valley at a spot seven hundred and seventy feet above
sea-level (thus giving the necessary fall of one hundred and seventy
feet), and just below that spot the sunken dam of which we have spoken
was built across to hold back enough water when the main bulk had been
used.

As our boat glides onward from under the shadow of the arch, we see near
the eastern shore a strongly built stone tower. This stands over the
mouth of the aqueduct (as the huge pipes are called whi