GRANITE, in natural history, a distinct genus of stones, composed of separate and very large concretions rudely compacted together; of great hardness, giving fire with steel, not fermenting with acids, and slowly and imperfectly calcineable in a great fire.
Of this genus there are three species: 1. The hard white granite, with black spots, commonly called moor-stone. This is a very valuable kind, consisting of a beautiful congeries of very variously constructed and differently coloured particles, not diffused among or running into one another, but each pure and distinct, though firmly adhering to whichever of the others it comes in contact with, and forming a very firm mass. It is much used in London for the steps of public buildings, and on other occasions where great strength and hardness are required. 2. The hard red granite variegated with black and white, and common in Egypt and Arabia. 3. The pale whitish granite, variegated with black and yellow. This is sometimes found in strata, but more frequently in loose nodules, and is used for paving the streets.
Some of these kinds of stones are found in almost every country, and in many places they are found of immense bigness. The largest mass of this kind in the known world, lying as an unconnected stone, is found near the Cape of Good Hope in Africa, and of which we have the following description in the Philosophical Transactions, vol. 68. p. 102, given by Mr Anderson in a letter to Sir John Pringle. "The stone is so remarkable, that it is called by the people here the Tower of Babel, and by some the Pearl Diamond. It either takes the last name from a place near which it is situated, or it gives name to the tract of cultivated land called the Pearl. It lies upon the top of a ridge of low hills, beyond a large plain, at
Granite. the distance of about thirty miles from the Cape Town; beyond which, at a little distance, is a range of hills of a much greater height. It is of an oblong shape, and lies north and south. The south end is highest; the east and west sides are steep and high; but the top is rounded, and slopes away gradually to the north end, so that you can ascend it by that way, and enjoy a most extensive prospect of the whole country. I could not precisely determine its circumference, but it took us above half an hour to walk round it; and by making every allowance for the rugged way, and stopping a little, I think the most moderate computation must make it exceed half a mile. The same difficulty occurred with respect to knowing its height: but I think, that, at the south end, it is nearly equal to half its length: or, were I to compare it to an object you are acquainted with, I should say it equalled the dome of St Paul's church.
"I am uncertain whether it ought to be considered as the top of the hill, or a detached stone, because there is no positive proof of either, unless we were to dig about its base; but it would certainly impress every beholder, at first sight, with the idea of its being one stone, not only from its figure, but because it is really one solid uniform mass from top to bottom, without any interruption; which is contrary to the general character of the high hills of this country, they being commonly divided, or composed of different strata, at least if we may judge from the rows of plants or shrubs which grow on the sides of the steepest, and, as I suppose, are produced from the small quantity of earth interposed between them. It has indeed a few fissures, or rather impressions, which do not reach deeper than four or five feet; and near its north end a stratum of a more compact stone runs across, which is not above twelve or fourteen inches thick, with its surface divided into little squares, or oblongs, disposed obliquely. This stratum is perpendicular; but whether it cuts the other to its base, or is superficial, I cannot determine. Its surface is also so smooth, that it does not appear to have formerly been joined to, or separated from, any other part by violence, as is the case with many other large fragments; but enjoys the exact situation where it was originally placed, and has undergone little change from being exposed for so many successive ages to the calcining power of a very hot climate."—A part of this stone being examined by Sir William Hamilton, he determined it to be a granite, and of the same nature with the tops of some of the Alps; and supposes both of them to have been elevated by volcanic explosions.