Cuillin range. Cracks and fissures in the rock provided pathways for later magma intrusions, leading to dykes of basalt which are commonly seen across Skye. The Red Cuillin also have volcanic origins, being formed from a later intrusion of acidic, granitic rock. This granite was more uniformly eroded by wind and water than the gabbro and basalt, causing the red hills to have smoother outlines. The Cuillin provide classic examples of glacial topography and were the subject of an early published account by James Forbes in 1846 (who had become a fellow of the Royal Society of Edinburgh aged only nineteen).
Rùm Torridonian sandstone and shales resting on Lewisian gneiss. Two of the Cuillin are classified as Corbetts: Askival and Ainshval, (Old Norse for "mountain of the ash trees" and "hill of the strongholds" respectively) and Rùm is the smallest Scottish island to have a summit above . Other hills include Hallival, Trollaval ('mountain of the trolls'), Barkeval, and Sgurr nan Gillean (Gaelic: "peak of the young men") in the Cuillin and Ard Nev, Orval, Sròn an t-Saighdeir and Bloodstone Hill in the west. It is likely that only the higher peaks remained above the Pleistocene ice sheets as nunataks. Hallival and