some of its bedrock is volcanic in origin). This theory was discounted as early as 1872, when Charles Kingsley commented in his book Town Geology: The natural bowl-shaped depression to which the name of chair has been attached, was formed by a cirque glacier during multiple ice ages when snow and ice accumulated on these slopes partly through avalanching. The glacier was up to a square kilometre in size surrounded on three sides by steep cliffs the highest being the headwall. The chair of Cadair Idris is this bowl-shaped hollow in the bedrock formed by the movement of glacial ice across the floor of the hollow, abrading it and the lip over which it then flowed. There are several tear-drop shaped knolls above the edge of Llyn Cau, each of which is a roche moutonnée formed by the abrasive action of the moving ice. The two highest lakes are Llyn Cau and Llyn y Gader; the latter is thought to have a maximum depth of about . Much of the area around Cadair Idris was designated a National Nature Reserve in 1957, and is home to Arctic–alpine plants such as purple saxifrage and dwarf willow. Myths, legends and popular culture There are numerous legends about Cadair Idris. Some nearby lakes are supposed to be bottomless, and anyone who sleeps on its slopes alone will supposedly awaken either a madman or a poet. This tradition (of sleeping on the summit of the mountain) apparently stems from bardic traditions, where bards would sleep on the mountain in hope of inspiration. Although the mountain's name is typically taken to refer to the mythological giant Idris, who was said to have been skilled in poetry, astronomy and philosophy, it has sometimes been mistranslated as Arthur's Seat, in reference to King Arthur (and to the hill of the same name in Edinburgh), an idea used by author Susan Cooper in her book The Grey King. However, this translation is mistaken and there is no etymological or traditional connection between Idris and Arthur. In Welsh mythology, Cadair Idris is also said to be one of the hunting grounds of Gwyn ap Nudd and his Cŵn Annwn. The howling of these huge dogs foretold death to anyone who heard them, the pack sweeping up that person's soul and herding it into the underworld. The mountain is mentioned several times and is used as a backdrop to the