until, at length, the masses become separated, as it they had never been connected. Thus they acquire the appearance of piles of masonry, often putting on strange forms, like the Cheese-wring in Cornwall, and producing the well-known rocking stones. Under a further decomposition at the angles, these masses be come a heap of irregular spheroids, which, being often easily removed, roll down the declivities of the hills, forming some of the travelled blocks so often discussed. Among these indications of a peculiar internal struc ture, I have formerly described the exfoliations into spheroidal crusts and schistose laminae, so as to render any further notice of them unnecessary. Decided marks of concretionary arrangement are also found in the occasional orbicular tendency of the component parts; familiar in the well known variety of Corsica, and in “ Tiger granite,” and sometimes marked in a circular distribution, affected by the mica in ordinary granite. They all present analogies to the similar structures occurring in such porphyries as that of Cor sica, in the Traps, and in the products of earths fused by artificial heat; and I need not now repeat their bearing on the igneous origin of these rocks. The last circumstance in the geological character of gi-anite, relates to its distribution in the form of veins; of which there are two distinct kinds. The first lie wholly within the rock, consisting of the same mate rials, under slight differences in the colour and mag nitude of the parts, being also connected with similar variations, of a concretionary appearance, without the venous form. If the exact cause of these is not obvious, they arc connected with that venous struc ture formerly described, which is only detected by the exposure or disintegration of the rock. The next are much more interesting, and constitute