Sec. 11. The first, that these crystalline rocks being, as we saw above, generally the oldest and highest, it is from them that other soils of various kinds must be derived; and they were therefore made a kind of storehouse, from which, wherever they were found, all kinds of treasures could be developed necessary for the service of man and other living creatures. Thus the granite of Mont Blanc is a crystalline rock composed of four substances; and in these four substances are contained the elements of nearly all kinds of sandstone and clay, together with potash, magnesia, and the metals of iron and manganese. Wherever the smallest portion of this rock occurs, a certain quantity of each of these substances may be derived from it, and the plants and animals which require them sustained in health. The second reason appears to be that rocks composed in this manner are capable of more interesting variety in form than any others; and as they were continually to be exposed to sight in the high ranges, they were so prepared as to be always as interesting and beautiful as possible. And divisible into two classes, Compact Crystallines and Slaty Crystallines. Sec. 12. These crystalline or spotted rocks we must again separate into two great classes, according to the arrangement, in them, of the particles of a substance called mica. It is not present in all of them; but when it occurs, it is usually in large quantities, and a notable source of character. It varies in color, occurring white, brown, green, red, and black; and in aspect, from shining plates to small dark grains, even these grains being seen, under a magnifier, to be composed of little plates, like pieces of exceedingly thin glass; but with this great difference from glass, that, whether large or small, the plates will not easily break _across_, but are elastic, and capable of being bent into a considerable curve; only if pressed with a knife upon the edge, they will separate into any number of thinner plates, more and more elastic and flexible according to their thinness, and these again into others still finer; there seeming to be no limit to the possible subdivision but the coarseness of the instrument employed. [Illustration: FIG. 3.]