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"From the hill's crest the entire lake bursts at once upon the view ; and a dreary and desolate expanse of water it is, about thirteen miles in circumference containing 2,140 statute acres. The encircling hills are heathy and barren, rising from 400 to 700 feet above the level of the lake. On the north-east, the superfluous waters force their way through a narrow gorge to join the river Foyle. The range of hills on which I stood was in reality the boundary line between the watershed of northern and southern Ulster. Lough Derg itself supplies the head water of the Foyle, while the stream at my feet flowed down to the Erne valley to join the sea at Ballyshannon. The basin of the lake is a huge quarry of the metamorphic rock known as mike slate, or schist, upheaved in ages azoic by some fiery agent, so that the stratification is now almost perpendicular to the surface. It crops up all round the shore, and through the lake into numerous rocky islets and hidden reefs, whose projecting points are sharp as iron spikes, and render the navigation of the lake a matter of great caution."