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).
Cuillin the summits had no recorded name prior to this period, although names for corries and other features were in existence. Many of the summits are thus named after early climbers such as John MacKenzie (Sgùrr MhicChoinnich), Alexander Nicolson (Sgùrr Alasdair), and Norman Collie (Sgúrr Thormaid). The Cuillin now consists of two estates divided by Glen Sligachan. The hills on the west side of Glen Sligachan (the Black Cuillin) remained the property of Clan MacLeod despite the long history of conflict between them and Clan MacDonald. The earliest formal record of MacLeod ownership was in a land grant from the Crown