GRANITE is considered as the foun dation rock of the globe, or that upon which all secondary rocks repose. From its great relative depth, it is not often met with, except in Alpine situations, where it presents the appearance of hav ing broken through the more superficial strata of the earth, the beds of other rocks in the vicinity rising towards it at increasing angles of elevation as they ap proach it. It is composed of three mi nerals, viz., quartz, feldspar, and mica, which are more or less perfectly crystal lized and closely united together.
The three constituents of granite are as under, taking their mean : Granite has been divided into several sub-species, or varieties ; of these, the following are the most important : Common granite, in which the three ordinary constituents above-mentioned occur in nearly equal proportions ; the feldspar may be white, red, or gray. Porphyritic granite, in which large erys tats of feldspar are disseminated through a common granite, whose ingredients are fine grained. Graphic granite, which consists of feldspar in broad laminte, penetrated perpendicularly with long imperfect crystals of quartz, whose trans verse angular sections bear some resem blance to certain letters, especially to those of Oriental languages. Sienite or sienitic granite, in which hornblende, either wholly or in part, supplies the place of mica. Takky or granite (the protogine of the French), in which talc or chlorite takes the place of the mica. Feldspathic granite, in which feld spar is the principal ingredient.
The aspect of granitic mountains is extremely diverse, depending, in part, upon the nature of its stratification, and the degree of disintegration it has under gone. Where the beds are nearly hori zontal, or where the granite, from the preponderance of feldspar, is soft and disintegrating, the summits are rounded and heavy. Where hard and soft granite are intermixed in the same mountain, the softer granite is disintegrated, fin d falls away, leaving the harder blocks and masses piled in confusion upon each other, like an immense mass of ruins.
Where it is bard, and the beds are nearly vertical, it forms lofty pyramidal peaks or aiguilles, like the Aiguille de Due and others, in the neighborhood of Mont Blanc.
Granite forms some of the most lofty of the mountain-chains of the eastern continent. In Europe, the central part of the principal monntain-ranges is of this rock—as in Scandinavia, the Alps, the Pyrenees, and the Carpathian moun tains. In Asia, granite forms a consi derable part of the Uralian and Altaic ranges of mountains ; and it appears, also, to compose the principal mountains that have been examined in Africa ; whereas, in the western hemisphere, it has never been observed rising to such great elevations, or composing such ex tensive chains. It is, nevertheless, very abundantly distributed,over the northern parts of the American continent, as in Labrador, the Canadas, and the New England States. In New Hampshire, it is the predominating rock of the White Mountains, in which it attains the eleva tion of more than 6000 feet. In the Andes, it has been observed at the height of 11,000, but is here generally covered by an immense mass of matter, ejected by ancient and recent eruptions.
Granite very frequently forms veins shooting up into the superincumbent rocks, which seems to indicate that it has existed below in a state of fusion, the heat of which has softened and parted the upper rocks, and forced up the granite, in a melted state, into these fissures.
Granite abounds in crystallized earthy minerals ; and these occur, for the most i part, in those masses of it existing in veins. Of these minerals, beryl, garnet, and tourmaline, are the most abundant. It is not•rich in metallic ores, though it contains the principal mines of tin, as well as small quantities of copper, iron, tungsten, bismuth, silver, columbium, and molybdenum.
Granite supplies durable materials for architecture and for decoration. It va ries much in hardness, as well as in co lor; accordingly, there is room for much care and taste in its selection.