Walking in the United Kingdom the scrambling suddenly becomes much more serious. In Britain, the term "mountaineering" tends to be reserved for technical climbing on mountains, or for serious domestic hillwalking, especially in winter, with additional equipment such as ice axe and crampons, or for routes requiring rock-climbing skills and a rope, such as the traverse of the Cuillin ridge, on the Scottish island of Skye. The British Mountaineering Council provides more information on this topic. Navigation and map-reading are essential hillwalking skills on high ground and mountains, due to the variability of British and Irish weather and the risk of rain, low cloud, fog
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