Cuillin in colour, particularly in the shade, but when in sunlight the Black Cuillin can appear grey to brown in colour. The main ridge forms a narrow crest, with steep cliffs and scree slopes. The ridge is about 14 km long (measured from Gars-behinn in the south to Sgùrr nan Gillean in the northeast), and curves in an irregular semi-circle around Loch Coruisk, which lies at the heart of the range. The highest point of the Cuillin, and of the Isle of Skye, is Sgùrr Alasdair in the Black Cuillin at 992 m (3,255 ft). The Red Cuillin are mainly composed
Geology of Skye Part of the magma chambers for the volcanoes are exposed at the surface as major intrusions of gabbro and granite. These coarse-grained igneous rocks are relatively resistant to erosion and now form the Cuillin hills. The Black Cuillin are formed of gabbro, which erodes to form the characteristically jagged outlines, although this is in large part due to the many minor intrusions, such as dykes and cone sheets that cut the gabbro. The Red Hills are formed of granite and have a more rounded topography. All pre-Quaternary rock types on the island are affected by a major swarm of dykes,