of the southern and western slopes are short and many, flowing
directly to the Bristol Channel and the Irish Sea; but the no less
numerous streams of the eastern slopes gather themselves into three
river systems, and reach the sea as the Dee, the Severn and the Wye.
The mountain group of _North Wales_ is the largest and loftiest; its
scenery resembles that of the Scottish Highlands because of the
juxtaposition of ancient Palaeozoic rocks--Cambrian and Ordovician,
often altered into slate--and contemporaneous volcanic outbursts and
igneous intrusions. Here rises the peak of Snowdon (3560 ft.), the
culminating point of South Britain, and near it half a dozen summits
exceed 3000 ft., while Cader Idris, farther south, though slightly
lower, presents a singularly imposing outline. The mild winter climate
has fringed the coast with seaside resorts, the rugged heights attract
tourists in summer, and the vast masses of slate have given rise to
the largest slate quarries in the world. The heavy rainfall of the
upper valleys unfits them for agriculture, and the farms are poor.
There are several lakes: that of Bala being the largest, except the
old lake of Vyrnwy, reconstituted artificially to store the rainfall
for the water-supply of Liverpool, 68 m. distant. The Vyrnwy is
tributary to the Severn; but north of it the streams gather into the
Dee, and flow eventually northward. _Mid Wales_ is built up, for the
most part, of Silurian or Ordovician rocks, practically free from
igneous intrusions except in the south-west. There the resistance of a
series of igneous dykes gives prominence to the Pembroke peninsula, in
which the fine fjord-like harbour of Milford Haven lies far out
towards the Atlantic. The coast north of Pembroke and Merioneth has
been worked into the grand sweep of Cardigan Bay, its surface carved
into gently rounded hills, green with rich grass, which sweep downward
into wide rounded valleys. Plinlimmon (2468 ft.) is the highest of the
hills, and forms a sort of hydrographic centre for the group, as from
its eastern base the Severn and the Wye take their rise--the former
describing a wide curve to east and south, the latter forming a chord
to the arc in its southward course. Mid Wales is mainly a pastoral
country, and very thinly peopled. A group of artificial lakes, one of
them exceeded in area only by Windermere, has been formed in the
valley