1668. Among the primitive rocks of the globe, whose period of creation is considered by geologists as antecedent to that of organic beings, is that of granite, whose use in architecture seems to bid defiance to time itself. The term granite appears to be a corruption of the Latin word geranites, used by Pliny to denote a particular species of stone. Tour- nefbrt, the naturalist, in the Account of his Voyage to the Levant in 1699, is the first of modern writers who uses the name. The word seems to have been applied by antiquaries to every granular stone susceptible of use in architecture or sculpture, in which vague sense it was used by mineralogists, until about fifty years since, when true granite was classed as a particular mountain rock. Its constituent parts are concretions of felspar, quartz, and mica, intimately joined together, but without any basis or ground. These parts are variable in quantity, so that sometimes one, sometimes the other, and frequently two of them, predominate over the third. The felspar, however, generally predominates, as mica is the least considerable ingredient of the rock. In some varieties the quartz is wanting, in others the mica ; but where these peculiarities occur, the granites must be considered as varieties, not as distinct species.

1669. The constituent parts differ in their magnitude, alternating from large to small and very fine granular. The colour, moreover, is very variable, depending principally on the predominating ingredient, — the felspar, the quartz, and the mica having usually a grey colour. The felspar is mostly white, inclining to grey and yellow, sometimes red, and even also milk white, sometimes flesh-red ; rarely grey, yellow, or green. The quartz is usually grey, seldom milk-white, and always translucent. The mica is usually grey, and sometimes nearly black. The felspar in granite has usually a vitreous lustre, and of perfectly foliated fracture ; yet in some varieties it passes into earthy, with the loss of its hardness and lustre ; in other words, it has passed into porcelain earth. The appearance in question is sometimes produced by the weathering of the felspar, and sometimes it appears to be in its original state. When pyrites arc found in the veins which traverse granite, the vicinous felspar and mica are converted into a species of steatitical matter by the action of the sulphuric acid formed during the decomposition of the pyrites. The mica also is liable to decomposition from exposure to the atmosphere, but the quartz never alters. In Cornwall, there is a con¬siderable portion of the granite in which earthy felspar is found.

1670. Granite is not decomposed by acids, and is only imperfectly and slowly calculable in a great heat Those species which contain much white felspar, and only a small portion of quartz, like the greater part of the granites of Cornwall and Devonshire, are liable to decomposition much sooner than many of the Scotch granites, in which the quartz is more abundant, and equally disseminated. In the selection of the Cornish and Devon granites, those are to be preferred which are raised in the largest blocks and are easiest worked, which, for common purposes, answer well enough, such as for paving-stones and the like; but harder granite must be sought for than Devonshire or Cornwall produces, where the construction is of importance ; for the masses in these counties are mostly in a condition of rapid disintegration and decay, which seems chiefly attributable to their containing a large portion of potass. The Naval Hospital of Plymouth is built of a granite whose parts appear to have been well selected. It was erected upwards of seventy years since, and, except in the columns of the colonnades, does not exhibit symptoms of decay. In these, on their more exposed sides, the disintegration of the felspar has commenced, and lichens have already attached their roots to some parts of the surfaces.

1671. The grey granite, or moorstone as it is called in Cornwall, is got out in blocks by splitting it with a number of wedges applied to notches pooled in the surface of the stone about four inches apart The pool holes are sunk with the point of a pick, much in the same way as other hard quarry stones are split. The harder the moorstone the nearer it can be split to the scantling required. All granite may be wrought, and, indeed, is wrought into mouldings by means of pointed tools of various weights and sizes; but it is first roughed out by means of heavy hammers, whose shape is formed by two acute angled triangles, joined base to base by a rectangle between them, thus . Red granite, sometimes yellowish, and generally interspersed with black mica, is found in Devonshire, and indeed at Mount Edgcumbe there are fine tables of it equal to the finest oriental granite, and it is found also in other parts of England; but for hardness, and in works where durability is indispensable, the granite from Aberdeen and Dundee is to be preferred by the architect These take an admirable polish, and are superior to all others which the island produces. Of these the red generally is harder than the grey sorts, but more difficult to work. The Peterhead, from the vicinity of Aberdeen, is perhaps the best, and it is, more- over, in appearance, the most beautiful which Scotland affords; indeed, in point of beauty, it is only surpassed by the oriental granites.

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