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■■■■■I 224 ON THE ORIGIN, MATERIALS, COMPOSITION, known materials. In the intermediate cases, it has produced gneiss and hornblende schist, or micaceous schist; differences similarly resulting from a nearly common action on materials differently apportioned. And further, as far as the aqueous or chemical rocks contain the minerals of granite, or the original ma terials not in the simple forms of clay and sand, they are indebted for them to that very igneous source, however circuitously and remotely. Thus the laws and the materials have been, throughout, simple, and, consequently, the constancy of these variations could not have been otherwise. I have already shown that the rocks themselves are all connected in leading ana logies, or resemblances, throughout the whole series, and are, virtually, reducible to a few, instead of pre senting that great variety which is popularly imagined. The merely simple rocks require no remarks; as their resemblance through the whole series, is such that we often cannot distinguish them, except by position. Now, with respect to the difficulties supposed to consist in their alternation, I have equally shown that this has been regulated by one leading law, and that what remains may be accounted for by the operation of another, equally simple. Hence the results ought to be simple; and this they actually are, when justly viewed. The separation of clay and sand, in conse quence of their different powers of gravitating in water, is the leading law; and its modified effects are the binary, but differently proportioned mixtures which exist. This also applies to the mixtures of an tecedent minerals found in the strata. The case of limestone from organic bodies is too obvious to re quire repetition. The second law, is the influence of heat in changing the characters of different simple deposits, or of differently compounded ones, whether