Page:A Treatise on Geology, volume 2.djvu/98

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If our knowledge of the true composition of many of the old rocks of fusion were perfect, we might propose for them a scale of classification parallel to that which Mr. Scrope has given for volcanic rocks. Of such a scale the following would appear to be the elements:—

Rocks in which the characteristic and most abundant mineral, felspar, is not at all or but slightly mixed with hornblende, augite, or their conveners, hypersthene, diallage, &c.

Rocks in which felspar is mixed in nearly equal proportion with hornblende or augite, or their conveners, hypersthene, diallage, &c.