ch convey the
water to Birmingham). The water flows into the tower through several
large openings on all sides, and its entrance into the aqueduct is
controlled by hydraulic machinery.

Bending to our oars again we follow the curves of the lake for about
three miles, with the railway running close to the water's edge. It was
laid by the engineers to assist them in this great undertaking. Then we
come in sight of the Pen-y-gareg wall. This was built in the same manner
as the first dam, though slightly different in design. At regular
intervals all along the top, we see square openings like windows in an
old castle. They are to admit light and air into a narrow passage left
in the heart of the dam and stretching from end to end. It is only six
and a half feet high and two and a half wide, so that two people,
however obliging they might be, would have a difficulty in letting each
other pass if they met half-way. But it is not a public passage, being
only constructed for the purpose of admitting workmen to the valve
tower, which regulates the flow of water into the lower reservoir.

Some mile and a half farther on we come to the third and last dam on the
Elan River. It is called the Craig Goch, and is the tallest of them all,
rising one hundred and thirty-five feet from the river-bed. In order to
build it a tunnel was driven through the hills on one side to carry the
water past, the stream being guided into this tunnel by means of a
concrete wall built a short distance from the scene of operations. The
dam is built on a curve, the bow being towards the reservoir. It carries
on its summit a handsome stone bridge with a public roadway less than
ten feet wide between the parapets. To stand on this bridge and watch
the flood water flow between its arches, to fall with a roar like
thunder on its way to the lower reservoir, is very impressive. It is
said that at times the water passes over the crest of the dam in a
cascade eighteen to twenty inches deep. Thus the water is held back
among the mountains in three huge steps, much as the water in a canal is
banked up by the locks. On the river Claerwen three similar dams are
being built.

While this work was going forward, another army of engineers was
preparing the road to Birmingham. Hills had to be tunnelled through,
valleys and rivers crossed by bridges, while syphons were used for
passing under small streams and similar obstructions. One of the tunnels
was no less than four an