The word 'tor' is also used in southern Wales, particularly on the rocky coastlines such as the Vale of Glamorgan and the Gower peninsula; on the Gower one of the sandy beaches near Oxwich Bay is called "Tor Bay" because the beach is framed by a huge outcrop of carboniferous limestone. Tor (Cornish tor, Old Welsh twrr, Scots Gaelic tòrr, meaning tower[1]) is notable for being one among a mere handful of Celtic loan-words to be borrowed into vernacular English prior to the modern era - such borrowings are mainly words of a geographic or topographical nature, also including crag and Avon ("river"). This origin of the word and the very fact it has survived hints at the places' special meaning to the Celtic peoples, often being centres of ritual and beliefs in the mystic and spiritual - a belief which in some cases carries on to today.[citation needed]

Tors are composed usually of granite or metamorphic rocks. Tors can also be found around any previously erupted volcanoes (although Devonian and Carboniferous outcrops are also found), though occasionally of other hard rocks such as quartzite, and are the result of millions of years of weathering. In prehistoric times, when the land was covered in forest, rain water seeped into the ground and gradually weathered the bedrock through its natural cracks, or joints. Once the land became exposed, the weathering was accelerated, particularly during the Ice age when freezing water expanded in the cracks. The result can be seen today in dramatic rock formations.

Weathering has also given rise to circular "rock basins'" formed by the accumulation of water and the repeated freezing and thawing - a fine example is to be found at Kes Tor on Dartmoor.

As the weathering of the tors continues, the rock is broken down into ever smaller sizes. Many hillsides are covered with loose rocks, known as clitter, which have provided ready building materials for thousands of years. Eventually the granite is weathered down to a level equivalent to sandy gravel, known as growan, which consists of individual crystals.

The most distinctive granite landform in temperate countries is the tor and in tropical regions, the inselbergs. Both suggest the removal of material by solifluction and hence lead to the opinion that tors and inselbergs are relict features.