304 W. Maynard Sutchings — Rutile in Fireclays. 



VI. — EuTiLE IN Fireclays — Eeply to Major-General MacMahon. 

 By "W. Maynaed Hutchings, Esq. 



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 inter- 

 pretations 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 claj's and allied shales, and what has taken place in 

 slates ; and passages in my previous paper make this still more 

 evident. I fully hold that slates, such as I refer to, have undergone 

 metamorphism of very "dynamic" nature. And I hold that the 

 beginnings of the same thing went on in the clays and shales, but 

 in a so much less degree that I think General McMahon would fully 

 admit it. 



All I claim for the clays is summed up in the sentence at bottom 

 of p. 316 (July Number of last year), where I speak of "the joint 

 action of pressure, warmth, and mineral solutions " as the probable 

 condition of the changes I believe to have taken place. It was only, 

 I think, in replying to Dr. Irving that I used the word " dynamic " 

 at all in connexion with the clays and shales of the Coal-measures. 

 It may be that it is a wrong expression in that combination. 



" Dynamic " and " Metaraorphic " are dangerous words, perhaps, 

 as they are used so variously by those we look to for light and 

 leading that we hardly know how to use them safely at all. 



Such changes as I believe to have taken place in fireclaj's would 

 not, I assume, be brought about unless the chemical action had been 

 intensified by warmth and pressure. That they have been under 

 conditions capable of producing the pressure and warmth is hardly 

 to be doubted. 



What are we to call the effects of these things, as distinguished 

 from any ordinary surface-weathering due to simple chemical action ? 

 Would " pressure-metamorphism " be allowed to include them ? 

 Where does simple chemical action end and " metamorphism " 

 begin ? 



I at once admit what General MacMahon says as to absence of 

 direct chemical evidence for my views. It is, very unfortunately, a 

 fact that lack of chemical work is felt throughout a great deal of 

 the petrological study that is going on. We have many workers 

 with the microscope, but very few workers with the balance. 



In the present instance, however, the nature of the material is 

 such that I do not think the most devoted analyst could obtain very 

 much solid evidence. 



The " pestle and mortar " business was not so violent as General 



