There is also a long tunnel which was part of the Cheddar Valley Line but is now used for pedestrians and cyclists. Within the tunnel the central surface has been paved with tarmac but it is unlit except for a central guide line of small guide lamps. The north half of the tunnel is brick lined, but about midway it reverts to unlined rock for the southern half, marking a change in the underlying geology from sandstone to limestone. This is the best hill in Somerset! Crook Peak has been important as a landmark and boundary from very early times, and the origins of the name are unclear. The local parish council state that 'Crook' comes from the Old English 'Cruc' meaning 'peak' or 'pointed hill'. 'Shute' is a contraction of "schute" which meant slope in the Middle Ages. This ecology of the site is varied. There are ancient and secondary semi-natural broadleaved woodland, however the majority is unimproved calcareous grassland with calcareous grassland and acidic dry dwarf-shrub heath. Four of the calcareous grassland communities and two of the woodland types have a restricted distribution in Britain, as does the calcareous grassland/acidic dry dwarf-shrub heath. These support species, four of which are considered nationally rare while seven of the plant species present are considered notable. Plants of interest include the nationally rare Cheddar pink ("Dianthus gratianopolitanus"), bedstraw ("Galium fleurotii"), dwarf sedge ("Carex humilis") and dwarf mouse-ear ("Cerastium pumilum"). Rose Wood and King's Wood are ancient woodland sites. King's Wood has coppiced hazel and nationally important small leaved lime. The nationally rare purple gromwell ("Lithospermum purpurocaeruleum") occurs at Rose Wood. Shute Shelve Hill, which is formed of Carboniferous Limestone laid down in the Dinantian period about 350 million years ago, rises to above sea level. It is an anticline with younger limestones on the lower slopes. Black Rock Limestone is exposed at several sites but is commonly covered by Burrington Oolite. Picken's Hole at the southern end of Crook Peak is considered to be of importance because of its clear, well-stratified sequence of deposits and faunas, all dating from within the Devensian. The cave is below the plateau and above the valley floor.