Notes on Dartmoor

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Abstract
The geology of Dartmoor has already furnished material for a somewhat extensive literature; but, as many points in connexion with this region are still in dispute, the discussion of the subject cannot be considered as finally closed. The view advocated by De la Beche was that the granite of Dartmoor was intrusive in the adjoining sedimentary rocks, and that the metamorphism exhibited by the Culm and Devonian beds for a certain distance round the margin of the granite was due to the contact-action of the heated eruptive rock. Quite recently, however, this view has been challenged by Mr. W. A. E. Ussher, F.G.S., of the Geological Survey, and it is alleged by this observer that “the genesis of the Devon and Cornish granites .... resulted from the metamorphism in situ of pre-existing rocks of pre-Devonian age, which had in a rigid state exercised an obstructive influence on the N. and S. movements, and had thereby produced great mechanical effects on the surrounding strata prior to the alteration of the latter” (p. 219). The result of this dynamic action is spoken of as ‘fusion’ (pp. 207, 217); the “fusion and subsequent consolidation would appear to have been effected in situ ” (p. 217), and “the consolidation of the granite in its present aspect may therefore be regarded as post-Carboniferous, or possibly coeval with the later stages of Carboniferous deposition” (p. 218). If I understand Mr. Ussher aright, the north-and-south movement did not set up any material metamorphic change in the Culm and

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