Correspondence — Pro/". T. G.Bonney — Major- Gen. MeMahon. 89 



I do not lay claim to any great originality for my little sketch, 

 but, in fact, I did not derive ray ideas from Dr. Irving's paper. 



3, Pump Court, Temple, E.G. Horace W. Monckton. 



REPLY TO ME. A. SOMERVAIL. 



Sir, — I owe an apology to Mr. Somervail for plucking a leaf 

 from bis coronet of laurels. It is the simple truth that the paper 

 which he cites had not in any way impressed itself on my mind, 

 and thus (as the index for the last volume was not then published) 

 escaped recollection. While making this atonement, I will take 

 the opportunity of explaining to him why I use that plainness of 

 speech to which he evidently objects. If he is right in his principal 

 hypothesis about the rocks of the Lizard, I am so hopelessly wrong 

 that I must begin my petrological studies de novo. The one or the 

 other of us, so to say, is ignorant of the very grammar of the 

 language. Now, as it happens, I have given, for nearly twenty 

 years, more attention to petrology than to any other branch of 

 geologj' ; twice or thrice every year I have visited districts which 

 were known to be instructive, making often long journeys in order 

 to study some critical question. I have examined many of the 

 most interesting localities on the Continent of Europe, a few also 

 in Canada. I have formed a very large collection of rock specimens 

 and microscopic slides, to the study of which I have devoted such 

 leisure as I can command. Now in Mr. Somervail's writings no 

 evidence appears of either wide experience or knowledge of the 

 microscope, both of which are necessary for theorizing on difficult 

 problems in petrology ; indeed, of the latter, not so long since, he 

 admitted his ignorance. Of course I know that many of these 

 problems are yet unsolved; I make no claim to infallibility; I am 

 well aware that notwithstanding all my pains I have not escaped 

 the fate of workers in a progressive science, and have to modify or 

 even abandon conclusions which at one time seemed most accordant 

 with facts, but some of Mr. Somervail's hypotheses appear to me 

 irreconcilable with facts and inductions which, not only I, but also 

 petrologists of greater repute, accept almost as axioms. To me he 

 appears to occupy the position in which I should have placed myself 

 had I signalized ray entrance in the "fifth form" at school by 

 publishing " adversaria " on a trilogy of ^schylus. 



T. G. BONNEY. 



DYNAMO-METAMORPHISM. 

 Sir, — M. Spring's valuable experiments have had a very stimulat- 

 ing effect on many minds ; so much so that his experiments are 

 sometimes quoted in proof of positions very much in advance of 

 those taken by M. Spring himself. Thus Mr. Barker in his letter 

 on the subject of dynamo-metamorphism in your last issue, after 

 remarking that " the practical verification " of " the direct correla- 

 tion of mechanical and chemical energy " " rests on such experiments 



