In the June Number of the GEOLOGICAL MAGAZINE, p. 259, Major-General MacMahon deals with my paper on fireclays, etc., and raises, with much fairness, several objections to some of my interpretations and inferences. Some of the criticisms are exactly what I should expect to be made, and were more or less present in my own mind, so that I can well see how they may arise in the minds of others.

General MacMahon appears to have somewhat overstated my views as to the “dynamic” part of the “Metamorphism” in question, owing to taking all I say as equally applying to slates and clays, which is not the case. Thus, the paragraphs he refers to on p. 168 will, I think, plainly show that I distinguish between what has taken place in clays and allied shales, and what has taken place in slates; and passages in my previous paper make this still more evident.