§ 5. Where, however, these same rocks exist in more favorable positions, that is to say, in gentler banks and at lower elevations, they form a ground for the most luxuriant vegetation; and the valleys of Savoy owe to them some of their loveliest solitudes,--exquisitely rich pastures, interspersed with arable and orchard land, and shaded by groves of walnut and cherry. Scenes of this kind, and of that just described, so singularly opposed, and apparently brought together as foils to each other, are, however, peculiar to certain beds of the slaty coherents, which are both vast in elevation, and easy of destruction. In Wales and Scotland, the same groups of rocks possess far greater hardness, while they attain less elevation; and the result is a totally different aspect of scenery. The severity of the climate, and the comparative durableness of the rock, forbid the rich vegetation; but the exposed summits, though barren, are not subject to laws of destruction so rapid and fearful as in Switzerland; and the natural color of the rock is oftener developed in the purples and greys which, mingled with the heather, form the principal elements of the deep and beautiful distant blue of the British hills. Their gentler mountain streams also permit the beds of rock to remain in firm, though fantastic, forms along their banks, and the gradual action of the cascades and eddies upon the slaty cleavage produces many pieces of foreground scenery to which higher hills can present no parallel. Of these peculiar conditions we shall have to speak at length in another place.
5. Adaptation to architecture and the fine arts.
§ 6. As far as regards ministry to the purposes of man, the slaty coherents are of somewhat more value than the slaty crystallines. Most of them can be used in the same way for rough buildings, while they furnish finer plates or sheets for roofing. It would be difficult, perhaps, to estimate the exact importance of their educational influence in the form of drawing-slate. For sculpture they are, of course, altogether unfit, but I believe certain finer conditions of them are employed for a dark ground in Florentine mosaic.
§ 7. It remains only to be noticed, that the direction of the lamination (or separation into small folio) is, in these rocks, not always, nor even often indicative of the true direction of their larger beds. It is not, however, necessary for the reader to enter into questions of such complicated nature as those which belong to the study of slaty cleavage; and only a few points, which I could not pass over, are noted in the Appendix; but it is necessary to observe here, that all rocks, however constituted, or however disposed, have certain ways of breaking in one direction rather than another, and separating themselves into blocks by means of smooth cracks or fissures, technically called joints, which often influence their forms more than either the position of their beds, or their slaty lamination; and always are conspicuous in their weathered masses. Of these, however, as it would be wearisome to enter into more detail at present, I rather choose to speak incidentally, as we meet with examples of their results in the scenery we have to study more particularly.