islets,
on one of which, Station Island, is the cave named St Patrick's
Purgatory, a celebrated place of resort for pilgrims and devotees. The
circumference of the lake is about 9 m., and the extent of the island to
which the pilgrims are ferried over is less than 1 acre. The landscape
round Lough Derg is desolate and sombre in the extreme, barren moors and
heathy hills surrounding it on all sides. Salmon, sea-trout and brown
trout afford sport in most of the rivers and loughs, and Glenties for
the Owenea river, and Gweedore for the Clady, in the west; Killybegs for
the Eanymore and Eask, in the south; and Rathmelton and Rosapenna for
the Owencarrow and Leannan, in the north, may be mentioned as centres.
Ballyshannon and Bundoran, in the extreme south, are centres for the
Erne and other waters outside the county.

_Geology._--The dominant feature in the geology of this county is the
north-east and south-west strike forced upon the older rocks during
earth-movements that set in at the close of Silurian times. The
granite that forms characteristically the core of the folds is
probably of the same age as that of Leinster, or may possibly
represent older igneous masses, brought into a general parallelism
during the main epoch of stress. The oldest recognizable series of
rocks is the Dalradian, and its quartzites form the white summits of
Muckish, Errigal and Aghla. The intruding granite, which predominates
in the north-west, has frequently united with the metamorphic series
to form composite gneiss. In the southern mass near Pettigo, once
regarded as Archaean and fundamental, residual "eyes" of the
hornblendic rocks that are associated with the Dalradian series remain
floating, as it were, in the gneiss. North of this, the country is
wilder, consisting largely of mica-schist, through which a grand mass
of unfoliated granite rises at Barnesmore. The course of the
Gweebarra, or Glen Beagh, of the Glendowan mountains, and the Aghla
ridge, have all been determined by the general strike imparted to the
country. At Donegal Bay the Lower Carboniferous sandstone and
limestone come in as a synclinal, and the limestone extends to
Bundoran. Small Carboniferous outliers on the summits of the great
cliff of Slieve League show the former extension of these strata. Bog
iron-ore is raised as a gas-purifier; and talc-schist has been worked
for steatite at Crohy Head. In most parts of the west