1873.] GEIKIE — GLACIAL PHENOMENA OF OUTER HEBRIDES. 533 



glaciation upon those islands which are furthest removed from the 

 mainland. If these shall be proved not to have been visited by ex- 

 traneous land-ice, then we shall have a known limit to the breadth of 

 the mer de glace. On the other hand, if it should be put beyond 

 all doubt that even the remotest island has been overflowed by the 

 general ice-cap that covered the mainland, then we shall have ad- 

 vanced so far towards forming such an estimate as I have hinted at. 

 In a future paper, I hope to take up this particular point. The 

 present communication is limited to a description of the older glacial 

 phenomena of Lewis. 



II. Lewis- — its physical features. 



Lewis, or the Lews, as it is frequently called, forms the northern 

 portion of that long string of islands which, taken collectively, are 

 generally styled " The Long Island." In the south it is broken 

 and mountainous ; but with this exception, nearly all the rest of the 

 island is low-lying and gently undulating. Immediately south of 

 Stornoway and along the northern shores of Loch Roag, the ground 

 is broken and rocky ; but north of a line drawn between the head 

 of Loch Erisort and Gearaidh nah Aimhne, the whole of the island 

 might be described as one great extended peat-moss, rising gradually 

 from the coasts to an average height, at the watershed, of about 

 400 feet. In many places, however, the rock peers through the 

 peat and heath ; and the ground occasionally reaches an elevation 

 several hundred feet higher. A few such elevations form con- 

 spicuous land-marks in the north of Lewis. The highest point, 

 however, is not much more than 900 feet (Beinn Barabhais) ; but 

 rising, as it does, somewhat abruptly out of an undulating peaty 

 plain, it obtains an importance which it does not otherwise deserve. 

 A rapidly waving line drawn from near the Butt, south-east through 

 Beinn Barabhais to Beinn nan Surrag, marks the watershed of this 

 dreary district. 



From the Butt to Aird Laimisheadar the land opposes to the 

 swell of the Atlantic a long straight line of bold cliffs nowhere 

 penetrated by any considerable inlet ; and the coast-line of the 

 north-east side of the island, between Stornoway and the Butt, 

 although more undulating, and running here and there into capes, 

 presents much the same character. But south of Aird Laimisheadar 

 in the west, and of Stornoway in the east, the land is ever and anon 

 penetrated by long sea-lochs that stretch into the heart of the 

 country, and in one place, at least, nearly succeed in cutting off a 

 large segment from the island — the distance between the heads of 

 Loch Seaforth and Loch Erisort being little more than one mile 

 and a half. 



The south and much smaller part of Lewis, adjoining Harris, differs 

 completely from the north in being almost wholly mountainous. The 

 change from the northern moorlands to this hilly tract is singularly 

 abrupt. The mountains appear to rise quite suddenly out of compara- 

 tively flat and low-lying ground, and have thus, like the smaller hills 

 in the north of the island, an imposing appearance, which is hardly 



