THE ORIGIN OF GRANITE TORS ON DARTMOOR, DEVONSHIRE

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Abstract
Summary: The Dartmoor tors and associated clitters were formed by the action of frost and solifluction acting recurrently throughout Pleistocene times. Incoherent granite, in situ , is sometimes the product of frost shattering along crystal and cleavage boundaries, but usually it is granite that has been partially kaolinized by pneumatolytic processes. The intermittent occurrence of decayed granite often facilitated the formation of valleys, so that it is generally found in valley bottoms and is never found around the tors, which have formed in resistant, well-jointed granites. Where decayed granite occurs on ridges tors are absent, though rounded core-stones are occasionally exposed by erosion. Tors are not found on ridges underlain by the mechanically weak, close jointed “blue granites”. Post-glacial atmospheric weathering, predominantly chemical, has induced variable degrees of rounding in basically angular landforms, but some large partially rounded tor masses were formed by frost weathering on favourable structures.

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