41. On the broken rocks in the foreground in the crystalline groups, the mosses seem to set themselves consentfully and deliberately to the task of producing the most exquisite harmonies of colour in their power. They will not conceal the form of the rock, but will gather over it in little brown bosses, like small cushions of velvet, made of mixed threads of dark ruby silk and gold, rounded over more subdued films of white and grey, with lightly crisped and curled edges like hoar frost on fallen leaves, and minute clusters of upright orange stalks with pointed caps, and fibres of deep green, and gold, and faint purple passing into black, all woven together, and following with unimaginable fineness of gentle growth the undulation of the stone they cherish, until it is charged with colour so that it can receive no more; and instead of looking rugged, or cold, or stern, or anything that a rock is held to be at heart, it seems to be clothed with a soft dark leopard's skin, embroidered with arabesque of purple and silver.
42. The colour of the white varieties of marble is of exquisite delicacy, owing to the partial translucency of the pure rock; and it has always appeared to me a most wonderful ordinance--one of the most _marked_ pieces of purpose in the creation--that all the variegated kinds should be comparatively opaque, so as to set off the colour on the surface, while the white, which, if it had been opaque, would have looked somewhat coarse, (as for instance common chalk does,) is rendered just translucent enough to give an impression of extreme purity, but not so translucent as to interfere in the least with the distinctness of any forms into which it is wrought. The colours of variegated marbles are also for the most part very beautiful, especially those composed of purple, amber, and green, with white; and there seems something notably attractive to the human mind in the _vague_ and veined labyrinths of their arrangements.
43. I have often had occasion to allude to the apparent connection of brilliancy of colour with vigour of life or purity of substance. This is pre-eminently the case in the mineral kingdom. The perfection with which the particles of any substance unite in crystallization, corresponds in that kingdom to the vital power in organic nature; and it is a universal law, that according to the purity of any substance, and according to the energy of its crystallization, is its beauty or brightness. Pure earths are white when in powder; and the same earths, which are the constituents of clay and sand, form, when crystallized, the emerald, ruby, sapphire, amethyst, and opal.