THEORY OF FORMATION.—When we examine a piece of granite, nothing appears less likely, to a common observer, than that it was once in a molten state through the action of fire, and that its crystalline structure was assumed in process of cooling. Now, the fact of its crystallization, the beautiful and perfect arrangement of its parts, the impress of the one crystal upon the other reciprocally communicating their respective shapes to each other, and the compact, agglutinated state of the whole, is regarded as the strongest proof of the igneous origin of this remarkable rock. Granite is not a mere congeries of parts, which, after being separately formed, was somehow brought together and united; but it is certain that the quartz, at least, was fluid when it was molded on the feldspar. In some granites, the impressions of the substances on one another are observed in a different order, and the quartz gives its form to the feldspar. The ingredients of granite were therefore fluid when mixed; and this fluidity was not the effect of solution in a menstruum, as in that case one kind of crystal does not impress another, but each retains its own peculiar shape; and the conclusion is, that they crystallized from a state of simple fluidity, such as, of all known causes, heat alone is able to produce. This is the account given in the Huttonian theory, as expressed nearly in the words of Playfair, which, along with the position of veins, the disruption of superincumbent strata, and other phenomena, has resulted in the universally received admission of the Plutonic character of this class of rocks. Dr. Macculloch has extended the principle, and has satisfactorily proved, that granite is but one term in the series of igneous products, the passages from which are distinctly traceable into granitoid syenite, and syenitic greenstone, and thence into greenstone, basalt, and lava. Professor Forchhammer considers granite, when melted, as one simple compound, and which only on cooling becomes separated into the different minerals that compose it. Granite, wherever it is found, is inferior to every other rock; and as it composes many of the greatest mountain chains, it has the pre-eminence of being elevated the highest into the atmosphere and sunk the deepest under the surface, of all the mineral constituents of the globe to which our researches extend. The associated primary rocks in this upland region overlie the granite, and possess a distinctly stratified structure. They are not now in their original position. They have been tilted up, traversed, and interlaced by the granite while in fusion, and have been altered greatly in their texture and qualities by their contact with the heated mass. Hence they are called METAMORPHIC ROCKS, because of the change to which they have been subjected.