Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/298

 frequently the latter. I shall, however, for the sake of brevity in the following descriptions, distinguish all those rocks, in the composition of which these three ingredients are found, however disproportionate they may be to each other, by the general name of granite. I feel the more warranted in doing so, from what Mr. Jameson has said in the definition he gives of granite. “ The parts,” he says, “ vary in quantity, so that sometimes one, sometimes the other, and frequently two of them, predominate. Felspar is generally the predominating; as mica is the least considerable ingredient of the rock. In some varieties the quartz is wanting; in others the mica; and these have received particular names. Such distinctions, however, are useless.” But I considered it necessary to give this previous explanation of the peculiarity of their structure, as the mere term granite would convey to most mineralogists, an erroneous idea of the true nature of the rocks I now allude to. I shall also, for the sake of brevity, occasion. ally distinguish those rocks in which hornblende forms a predominating ingredient by the general name of sienitic rocks. It would, be an endless task to give separate names to the various compounds met with in the Malvern hills, although they certainly have different external appearances; and were I to attempt to do so, I should perhaps be making distinctions, which their origin does not warrant, as all the varieties comprehended in the same class have probably been produced under similar circumstances. But in the present state of geological science, and more especially when the great imperfection of the nomenclature of rocks is considered, it would be well if geologists made a practice of describing the simple minerals of which a rock is composed, wherever they can be distinguished, instead of giving specific names without any explanation of the nature of the