iii which cleaved rocks are to be found. 1 We may therefore infer, that the Lower Silurian rocks of North Wales, the Devonian and Carboniferous slates of Devon and Cornwall, and those of the Lower Car boniferous age of the South of Ireland have been subjected to denudation on a large scale. Results of Cleavage on the structure of the Rocks. The direction of the planes of cleavage is indepen dent of that of the planes of bedding ; and we, there fore, have these planes intersecting each other at various angles, or accidentally coinciding. In general, however, the tendency of the rock to split along the planes of cleavage predominates, so that a slab of slate is equally strong throughout, though crossing several divisional layers of original stratification. This is the case in all good roofing slates, in which we may frequently observe the layers of bedding crossing the surface in a series of parallel bands indi cated by faint shades of colour, or slight differences of texture. At the same time, it has been fre quently observed, that amongst strata composed of various materials, such as sandstone and slate in alternate bands, the cleavage planes take different directions in the different beds, depending on the amount of resistance the materials have been able to offer to the lateral forces. 1 Professor Ramsay, Descrip. Catalogue of Rock Specimens M. P.G. p. 122 (1858).