Mountains and irregular groups of highlands occupy the whole interior of the county, and a considerable portion is bog and moorland. Errigal mountain in the north-west attains an elevation of 2466 ft. and commands from its summit a fine view over a considerable portion of the country. In its vicinity, the Derryveagh mountains reach 2240 ft. in Slieve Snaght; Muckish is 2197 ft.; in the south Bluestack reaches 2219 ft.; and in the Innishowen peninsula between Loughs Swilly and Foyle, another Slieve Snaght is 2019 ft. in elevation. At the western extremity of the north coast of Donegal Bay stands Slieve League, whose western flank consists of a mighty cliff, descending almost sheer to the Atlantic, exhibiting beautiful variegated colouring, and reaching an extreme height of 1972 ft. From these details it will appear that the scenery of the highlands and the sea-coast often attain a character of savage and romantic grandeur; whereas the eastern and southern portions are generally less elevated and more fertile, but still possess considerable beauty. A considerable portion of the surface, however, is occupied by bogs, and entirely destitute of timber.
With the exception of the tidal river Foyle, which forms the boundary between this county and Tyrone and Londonderry, the rivers, though numerous, are of small size. The branches of the Foyle which rise in Donegal are the Derg, issuing from Lough Derg, and the Finn, rising in the beautiful little lake of the same name in the highlands, and passing through some of the best cultivated land in the county. The Foyle, augmented by their contributions, and by those of several other branches from the counties Tyrone and Londonderry, proceeds northward, discharging its waters into the southern extremity of Lough Foyle, at the city of Londonderry. It is navigable for vessels of large burden to this place, and thence by lighters of fifty tons as far as Lifford. Boats of fourteen tons can proceed up the Finn river as far as Castlefinn. The fine river Erne flows from Lough Erne through the southern extremity of the county into the southern extremity of Donegal Bay. Its navigation is prevented by a fall of 12 ft., generally called the Salmon Leap, in the neighbourhood of Ballyshannon, and by rapids between Ballyshannon and Belleek, on the confines of Co. Fermanagh. The Gweebarra, the Owenea, and the Eask are the only other streams of any note. Lakes are very numerous in Donegal. The most remarkable, and also the largest, is Lough Derg, comprising within its waters several 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.
