The rocks that immediately overlie the granite are gneiss, mica-slate, quartz-rock, and limestone. They all partake of the crystalline structure, and all, except the last, possess the same ingredients, and assume interchangeably the same aspect. Of gneiss there are three varieties, each composed of feldspar, quartz, and mica, and distinguished by the size and form of the crystals that constitute the mass. This rock, consisting in all cases of thin lenticular plates, has a ribbon-like appearance, and, according to the predominance of one of the parts, becomes glandular, slaty, or aggregate. Mica-slate consists of quartz and mica—the latter predominating—and feldspar frequently entering as an adjunct. Quartz-rock, as the term implies, is formed of the pure siliceous matter, nearly homogeneous in many instances—but scales of mica are often present—and feldspar not always absent. The limestone, again, differs from all the above in the excess of the calcareous element, while, along with talc, steatite, actynolite, asbestus, and other simple minerals, mica, quartz, and feldspar are likewise to be numbered among the imbedded crystals. These rocks, over the entire surface of the globe, are of one family, and generally associated. They are always the lowest of the stratified series, and follow in the order now described. They are essentially one and the same in their constituent mineral qualities—different in the form and proportions in which they are aggregated—and geographically connected with the granite in their distribution. Thus these crystalline rocks not only constitute the floor of our earth, but have in all probability supplied the materials under whose plutonic agency, when fused and molten, the massive pavement was raised above the waters and tempered into its present consistency.