Croagh Gorm and Blue Stack Mountains lie north and west of Barnesmore Gap and above Lough Eske, reaching nearly to Glenties, Lough Eske being about 30 miles east of Slieve League. The coast eastwards from Slieve League becomes suddenly low, and the formation changes to carboniferous limestone, which occupies a broad belt round Donegal Bay. The Blue Stack group is about 7 miles across.
Blue Stack (2,219 ft.) lies above Lough Eske and is granite, although the Lough itself lies in the limestone. About Lough Belshade, which lies north of Lough Eske, about half-way up the east side of Blue Stack, the granite is precipitous, and one bold bluff west of this lake (Belshade), with a sort of little cave in its face, may be taken in the ascent of the mountain. Most of the granite portions of the range are rounded, flowing, gently contoured, barren slopes of bare rock, sometimes at low elevations becoming steep and difficult. The ascent of Blue Stack from Lough Eske should on no account be missed. The lake is about 10 miles round, and most beautifully situated at the southern base of a bold mass of rugged, desolate granitic bosses and cliffs, cleft by a few fairly steep ravines. In direct contrast to this sombre scene is the west shore of the lake, which is girt with timber, chiefly natural. Ardnamona is the nearest portion of this sylvan scene to the mountain base, and the whole basin is admirably sheltered by the surrounding mountains from the violent storms which of late years have been more destructive than ever.
From the road above Ardnamona, looking down over it upon Lough Eske and its solemn background, the view is perfect. It is a sort of compact Killarney, which the eye and mind will long feast upon.
North-west of Blue Stack, a couple of miles from it, lies Lavagh More (2,211 ft.), a fine upstanding lump of turf-covered schists. Schists and sandstones constitute the greater part of these hills. From Lavagh More, descending southwards, by a series of lakes, the head of the Shrule River is reached, in a valley with a precipitous northern side, which gives difficult bits of crag work. In this valley at the northern end lies a waterfall known as the Grey Mare's Tail.
The Blue Stack Mountains are best explored from Donegal on the south or Glenties on the west, in both of which places there are comfortable inns. It is best to drive to the head of Lough Eske, and it is a fine walk from that, including most of the tops, down to Martin's Bridge, 3 miles from Glenties, over Blue Stack, Lavagh More, and Silver Hill.
In the mountainous district around Glenties other excursions are available. A walk to be recommended is from Barnesmore Gap (drive of 7 miles from Donegal) across the Croagh Gorm and Blue Stack summits to Glenties. Barnesmore Gap should by all means be visited. The mountains on either side rise 1,500 to 1,700 ft., not quite precipitously, but with bluffs, heavy boulders, and steep rocky faces. Cæsar Otway gives a highly-coloured description of this impressive scene. Another way to explore the group is to follow up the course of the Reelan water through a peculiarly secluded and remote valley. From Glenties to Ardara is about 4 miles, and the latter village is a capital halting place. Fishing and fowling can be had. The road from Ardara to Carrick, about 10 miles, passes up the wild, grand gorge of Glen Gesh by a zigzag road, reminding one of some of the Swiss ascents. For the sake of the varied scenery obtained by these doublings it is almost preferable to stick to the road till near the summit. On the south side of this glen it is bounded by a range known as Altnadewon or Croaghnagcaragh (Reek, 'hill of the thicket'). A steep rock face extends from the main road at the 'nock of the Ballagh,' or Pass, which forms a wide amphitheatre on the north face of the highest point of this range (1,652 ft.) For some distance it is by no means easy to scale this declivity.
Towards the southern verge of the county the coast is low and flat, but the bold precipitous face of Ben Bulben looks highly attractive.
Before leaving Donegal it will be well to mention one useful hint. The Ordnance maps of this county show 100-ft. contours, which are of the utmost advantage upon any excursion, as the height of any point attained by the pedestrian may be fixed within a hundred feet. Very few other parts of Ireland are thus favoured.
The Ben Bulben Range lies in the northern part of Sligo and Leitrim; a most conspicuous object in the landscape viewed from Slieve League across Donegal Bay. The shapely escarpment of the nearest point looks, indeed, as if it belonged to Donegal, which is 7 miles away. This portion consists of Cloughcorragh (2,007 ft.) and Ben Whiskin (1,666 ft.)