spelling on its signage, despite advice from the Welsh Language Commissioner and from Park officers, who favoured 'Cadair'. The local dialect form is also seen in the name of the local secondary school, Ysgol y Gader. The name of the mountain is typically spelt Cadair Idris on current maps. The summit of the mountain is known as Penygader ("top of the chair/stronghold"). Ascent There are three main trails that lead to the top of Cadair Idris. The summit, which is covered in scree, is marked by a trig point. There is also a low-standing stone shelter with a roof. Pony Path The Pony Path (Welsh: Llwybr Pilin Pwn), which begins in the north from either Dolgellau or the Mawddach estuary, is the easiest but the longest of the main trails. Its length from the mountain's base is with a climb. Fox's Path The Fox's Path (Welsh: Llwybr Madyn),This is the most direct way to the summit as the trail leads straight up the northern face. The ascent involves a climb up a cliff-scree face. However, this part of the Fox's Path has been heavily eroded in recent years making the descent dangerous. Minffordd Path The Minffordd Path (Welsh: Llwybr Minffordd) starts on the southern side of the mountain near the glacial Tal-y-llyn Lake. Hikers using this ascent climb past Llyn Cau and along the rim of Craig Cau (rockwall) to Penygadair. Its length is and involves two climbs of over . Geology Cadair Idris is formed from a complexly fractured and folded pile of both sedimentary rocks and igneous rocks of Ordovician age. They comprise the mudstones and siltstones of the Ceiswyn Formation which form much of the southern part of the mountain, together with the varied rocks of the underlying Aran Volcanic Group. The steep cliffs rising above Llyn Cau to the north are formed from hard-wearing basalts and tuffs of the Pen y Gadair Volcanic Formation whilst those on the south side are acid tuffs of the Craig Cau Formation. The imposing cliffs which characterise the north side of the mountain are formed from a microgranite intruded into the Ty'r Gawen mudstones. In common with the rest of Snowdonia, the faulting and folding of this rock succession took place during the Caledonian Orogeny. The crater-like shape of Cwm Cau has given rise to the occasional mistaken claim that Cadair Idris is an extinct volcano (though as noted above,