The granite of Killiney is one of those igneous rocks, and the appearances which we detect in that interesting locality afford satisfactory evidence of its mode of formation. When we descend to the shore by the stairs, a little to the east of the Obelisk, we find ourselves in a little way bounded by perpendicular rocks. These rocks are of two kinds--granite, and a schistoze or slaty rock, of a bluish colour, which we may term mica-schist. We then observe that the mica-schist rests on its edges, on a pavement of granite, and also reclines against that rock. The junction of the two rocks may be seen with the utmost perspicuity; and there is no blending of their characters, even where they are in absolute contact. We may next observe a ledge of rock partly covered by the waves, and extending in nearly a north and south course along the shore. This is a granite vein of many feet in breadth, and several hundred yards in length, and may easily be traced for a considerable distance. This granite vein is bounded on both sides by mica-schist; and, what is still more important, we may follow the vein till it is lost in the general mass of granite of the hill. When we now remember that the water-formed rock (the mica-schist) is standing on edge, a suspicion arises that the granite is a fire-produced rock, and has been the agent of this elevation, and the large wall of granite may have been intruded in a molten state between the beds of mica-schist. If it be objected that the granite vein is merely a portion of the strata of mica-schist, and was like them deposited from water, an inspection will dissipate this illusion; for we observe that the great vein running parallel to the strata gives off a smaller vein at right angles to the direction of the strata. On examining this smaller vein, which may be seen a little to the north of the stairs, all doubts respecting its nature or origin are very soon removed. We are surprised to find that this vein contains fragments of the mica-schist. We may therefore conclude from this that originally fissures were produced in the schist, and these fissures were filled up by molten granite, which entangled fragments of the mica-schist which fell from the sides of the fissure. It is scarcely necessary to add, that we know of no agent capable of melting granite but heat.