 The Black Cuillin , which are mainly composed of basalt and gabbro , include twelve Munros and provide some of the most dramatic and challenging mountain terrain in Scotland . The ascent of Sgùrr a ' Ghreadaidh is one of the longest rock climbs in Britain and the Inaccessible Pinnacle is the only peak in Scotland that requires technical climbing skills to reach the summit . These hills make demands of the hill walker that exceed any others found in Scotland and a full traverse of the Cuillin ridge may take 15 – 20 hours . The Red Hills ( Gaelic : Am Binnean Dearg ) to the south are also known as the Red Cuillin . They are mainly composed of granite that has weathered into more rounded hills with many long scree slopes on their flanks . The highest point of these hills is Glamaig , one of only two Corbetts on Skye . 
