The recent paper by A. Holmes on “A Mineralogical Classification of Igneous Rocks” is an attempt to settle a matter which English-speaking petrologists ought to have tackled long ago. There seems, however, to be a disposition, on the part of British geologists especially, to leave the matter alone in the fond belief that some “natural” system of classification will presently be revealed to us whereby all our taxonomic doubts and difficulties will be dispelled. Nothing can be more unreasonable. The philosophic treatment of a subject must follow, not precede, the preparatory work of discriminating, sorting, and docketing; and the sharper the discrimination, the more thorough and orderly the sorting and docketing, the easier to make the philosophic digest. Hitherto petrographers have not discriminated well; we have not done our sorting in a methodical way; we have tied on labels in the most haphazard fashion; our house is in a state of dreadful confusion. It is true that through all the disorder we have caught fascinating glimpses of regularities and relationships; of connexion between this and that; but the deplorable fact appears that we are unable to test or verify any hypothesis, or to take a single confident step towards the philosophic treatment of our subject, until we put our house in order. We have got to do our sorting and docketing all over again, and do it methodically, and then only can we begin to look for the philosophy of the matter.