Every one is aware that rocks are formed in two very different ways, they may be produced either from the decayed materials of older rocks, carried down to the sea or lakes by the rivers, and subsequently consolidated by various processes, which geologists have explained, or they may be formed by the solidifying of liquid matter poured forth through some volcanic aperture from the deeper parts of the earth. The first kind of rocks are disposed in layers, beds, or strata, by the return of water, and hence are called stratified, and also aqueous or water-formed; the second, being liquid matters which have become hard from cooling, are called igneous, or fire-produced rocks. As volcanoes are at present confined to particular regions of the earth, some may imagine that such igneous rocks should only be found in volcanic regions. This, however, is a mistaken supposition, for geology assures us that igneous rocks are to be found in every mountain range. The mode of reasoning which they follow is equally simple and convincing. If we visit Howth, for example, we find many of the strata resting on their edges, or variously twisted. At the Killerys in the west of Ireland we find strata composed of rolled pebbles, elevated to a very considerable angle. It is impossible that strata of loose sand or gravel would have been originally deposited in such inclined positions, and we know of no natural power which would elevate them but that of the igneous agency, producing either a violent earthquake, or a long-continued upward pressure. This opinion is much strengthened, when we find in every country, whether volcanic or not, a series of rocks which appear to have been violently inserted among the strata, and which we can prove were once in a state of intense heat and fusion, like the lavas from a modern volcano.