Early Theories of Tor Formation

Early Antiquarian Theories

The first documented account of tor formation appears to date back to 1754 and William Borlase's Observations of the Antiquities, History and Monuments of the County of Cornwall. Inspired by Stukeley's work on druidic history in particular Stonehenge, Borlase proposed that tors were in fact artificial features and were set up by the druids as temples. The Logan Stone near Land's End, the Cheesewring near Liskeard and at Carnbrea Hill near Redruth were thus considered to be the rock temples of the British druids. Borlase's ideas were later extended by Watson (1773) and Rooke (1783, 1789, 1796) who said that the gritstone tors of Derbyshire and Yorkshire had a similar origin.

These authors produced novel ideas to explain some of the weird features found in the tor group at Brimham Rocks. Borlase himself wrote 18 pages of careful description and discussion on the formation of rock basins. Encouraged initially by more casual writers who suggested that they were intended to hold the blood of sacrificial victims, he later presented a less controversial idea suggesting that they were used for acts of lustration! By analogy with the primitive practice of walking through the severed parts of a sacrifice, he supposed that when a body was passed through the artificial holes or passages in the rock it acquired 'a kind of holiness and became more acceptable to the gods'. At Brimham, horizontal tubular cavities 10 metres long were called 'oracular' stones by Rooke who viewed them as having been drilled by the druids to deliver oracles to a superstitious congregation. The cubic nature of many tors also fuelled Borlase's argument as the cube was used as a symbol for the druidic god Mercury.

Although it is now generally regarded that these early theories were rather fantastic, it was not until the establishment of geology as a discipline, the foundation of the London Geological Society, and a paper produced by MacCulloch in 1814 The Granite Tors of Cornwall that ideas of tors as artificial features were slowly dismissed. MacCulloch put the geologists' attitude somewhat brutally in his paper saying 'not only indeed have idle curiosity and ignorant speculation busied themselves in accounting for phenomena which many of the vulgar have deemed little less than miraculous, but learned antiquarians have tortured their inventions and have constructed religious systems for the purpose of explaining these very simple and intelligible natural appearances'.

In his discussion of rock basins MacCulloch regarded them as being entirely natural. The roundness of the basins, the delicate balance of the rocking stones, the slender pedestals of the idol rocks and the holes and passages of fantastic shape result from processes of decay and disintegration working on rocks with varying degrees of resistance.

After MacCulloch there followed a period of some conflict between the two theories (one natural, the other artificial). Drake (1859) undoubtedly made the last stand for the antiquarians, but druids had by this time been taken over by the Romantic Movement and the Welsh Eisteddfod and were no longer reconcilable with modern scientific reasoning.

Early Geological Theories

Following the stand made by MacCulloch, Phillips (1853) and Mackintosh (1865) were the next workers to make a contribution to the geological understanding of tors. They viewed tors as being relict coastal features and so represented periods of higher sea levels. Mackintosh made a superficial comparison between the tor Lover's Leap at Brimham Rocks and coastal stacks and came to the conclusion that tors were probably fossil coastal landforms. In the absence of shingle, Mackintosh used boulder clay (till) as proof that the foot of many tors was surrounded by marine sediment. It later became obvious however that boulder clay was of glacial origin and that the tors of Brimham Rocks did not occur on a horizontal plane (in other words a wave-cut platform) but were structurally guided.

Following the dismissal of tors as stacks, other theorists viewed tors as being the products of wind erosion. Notable amongst these were Ramsey (1872) and Hull (1880), and there were still adherents to this theory despite overwhelming evidence against it as late as 1948 (Versey). Hull claimed convincingly that tors had suffered wind erosion by comparing them with features found in the semi-arid climate of Egypt. He also proposed that the climate in late-glacial times would have been favourable for this type of erosion. The main argument against wind erosion came with wind tunnel experiments which showed that suspension of sand-sized material could not occur above 2 metres from the ground. Thus it was impossible to use wind erosion as an agent which could be responsible for the sculturing of features found at heights of around 10 metres.

It was during this time that the forerunners of the now most widely accepted theory of tor formation, namely deep chemical weathering, was considered. The idea of differential weathering can be rightly accredited to de la Beche (1851) and Jones (1859). de la Beche's ideas were later supported by Geikie (1882) and Dawkins (1901) in a discussion of a paper written by Sandeman. However, Dawkins' ideas did not receive the attention of the Geological Society in London and because it was widely accepted that the rotten granite (kaolin) on Dartmoor had a pneumatolytic origin discussion of deep chemical weathering was put on the back-burner until Linton's general discussion of tors in 1955.