Science is the coordination of fact with fact, fact with principle, and principle with principle. It depends on the rigorous use of words. Neither fact nor principle nor coordination can rise into full consciousness until phrased in unimpeachable terms. Unceasing attention to the use of words therefore represents a principal duty of every scientific investigator. Experience shows how hard it is, in a fluid science like geology, to hold technical words to constant, universally accepted definitions. The causes of this unrest are many: progress in the discovery of facts, progress in coordination, progress in interpretation or theory, and, one must add, the varying subjectivity, if not carelessness, of writers.
Few geological topics are as far-reaching and profoundly important as rock metamorphism. Few have had, and are having, such increase of content, both empirical and theoretical. Invented eighty years ago, the words “metamorphic” and “metamorphism” are almost as old as scientific . . .