Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/376

 pointed to the metamorphic character of granite ; and in some parts of Corsica this was still more plainly shown than in Devonshire.

Mr. W. W. Smyth agreed that the disintegration of granite was mainly due to the causes pointed out by the author. He did not, however, regard them as entirely resulting from subaerial denudation acting on a surface of uniform quality. There was probably a difference in the proportions of the constituent parts in the granite, some parts in the same quarry being soft while others were of extreme hardness. These softer parts were easily removed, while the harder parts were left. The question was, whether this difference was the result of the original deposition or of subsequent segregation. Even where china clay resulted from the decomposition of the rock, some of the nodules of harder granite occurred.

Prof. Brayley remarked that the subject of the spheroidal structure of some of the crystalline rocks was of much importance in geological physics. He believed he had been the first to call attention (Phil. Mag. 1830) to the connexion of rock-basins with that structure as existing in granite. The phenomena at Karn Bre in Cornwall were much the same as on Dartmoor, and resulted, originally, from the concealed spheroidal structure of the rock, or rather from what he might term a spheroidal tension. In Mount- Sorrel syenite and Northumberland basalt the same was to be traced ; and Rowley Rag exhibited the effect of the spheroidal tension, as developed by weathering, in the most perfect manner.

Mr. Scott stated that in the granite district near Dublin isolated blocks, deeply weathered, like the tors described in the paper, were met with. The granite itself contains masses of a harder nature than the surrounding rock, which are usually enveloped in a coating of black mica. In the stratified granites of Donegal and Argyllshire such a structure had never been noticed by him.

2. Notes on Apparent Lithodomous Perforations in North-west Lancashire. By D. Mackintosh, Esq., F.G.S.

[Abridged.]

The author, after referring to the discovery of perforations in limestone rocks, at various altitudes above the sea, by Mr. Pengelly in Devonshire and Mr. Darbishire in North Wales, proceeded to describe the character and mode of occurrence of those he lately observed near the shores of Morecambe Bay. They were stated to be most numerous in the neighbourhood of Great Urswick, at altitudes of between 200 and 300 feet ; but after a persevering search he found them on the eastern or Grange side of Hampsfell up to 667 feet above the sea. " They occur in limestone rocks of varying structure. . . . They have been excavated irrespectively of any hardness or softness of the rock, and of any susceptibility to decay in one part of the rock more than another. Their circumference runs continuously through portions of rock of varying composition," and the holes often run into and through fossils.