Correspondence, 177 



these memoirs," he says, " apparently representing in some measure 

 the views entertained by the Geological Survey of Great Britain, 

 decided the writer in at once protesting, etc." It is as well to 

 assure Mr. D. Forbes and your readers that the Geological Survey is 

 no way to be identified with opinions expressed in '-extra-oiScial" 

 communications ; for these the writers themselves are alone respon- 

 sible. 



If I do not misunderstand Mr. D. Forbes, his opinion seems to 

 be that a profound knowledge of chemistry and mineralogy 

 is necessary to the geologist who would attempt the investiga- 

 tion of metamorphic phenomena ; that, in short, if he be neither a 

 practised chemist nor mineralogist, his purely geological observa- 

 tions go for little or nothing. Every one, indeed, is aware that the 

 subject of metamorphism has for many years occupied the attention 

 of able chemists and mineralogists ; and it is never denied that 

 without their aid the geologist cannot hope to do much towards 

 clearing away the many difficulties by which the subject is sur- 

 rounded. It is not doubted that the question of metamorphism is 

 one which can only be settled by the zealous co-operation of the 

 various sciences involved. But if it be true that these sciences are 

 all equally concerned in this matter, then it follows that there must 

 be different kinds of evidence, viz., chemical, mineralogical, and 

 geological evidence ; and three classes of investigators, — -chemists, 

 mineralogists, and geologists. It is quite possible, indeed, that an 

 individual observer may combine in himself a fair knowledge of the 

 three sciences, but highl}'- improbable that he shall be equally good 

 as a chemist, mineralogist, and geologist. One of the three studies 

 is sure to exert a preponderating influence upon his mind, so as in 

 some measure to prevent absolute impartiality in his investigations. 

 According as his bent is chemical, mineralogical, or geological, he 

 will prefer a particular line of evidence. It is vain to hope for an 

 "admirable Crichton," who shall.be at once a profound chemist, 

 mineralogist, and geologist, with a mind so equally balanced that he 

 shall be able to accord to each kind of evidence its proper place and 

 value. All that we can expect is, that each labourer, be he chemist 

 or geologist, shall honestly state his convictions as deduced from 

 data, for the study of which he has had a special training. Cases 

 of metamorphism, which the unassisted geologist never could have 

 discovered for himself, have been detected by chemists and mine- 

 ralogists. On the other hand, it is no less true that the metamorphic 

 origin of certain rocks is capable of being proved by evidence purely 

 geological. Nor can it be denied that there are instances where 

 both the work of the laboratory and the labours of the field observer 

 are equally necessary before the metamorphic origin of some rocks 

 can be decided upon. If eminent chemists and mineralogists, who 

 are sometimes "not much at home" in geology, have, nevertheless, 

 contributed largely to our knowledge of metamorphic phenomena, 

 it can scarcely be presumption if a geologist believes that he, too, 

 although confessedly not versed in chemistry, may yet be able to 

 see something of the subject, by viewing it from his own peculiar 

 VOL. rv. — NO. XXXIV. 12 



