. Correspondence — Dr. C. Callaway. 527 



ANGLESEY GEOLOGY.— REPLY TO DR. R. D. ROBERTS. 



Sir, — I have just seen, after a prolonged absence from home, Dr. 

 Eoberts' paper in your August Number. 



I do not know whether it is usually considered fair play to ignore 

 tiie memoir in whicli an author has expressed his views with tech- 

 nical accuracy, and to base destructive ci'iticism upon a subsequent 

 paper, written in semi-popular language, in which the topic of the 

 memoir is introduced simply by waj' of illusti-ation. In an elaborate 

 paper, embodying the results of tlie work of several years, whicli 

 was printed in the Journal of the Geological Society (May, 1881), 

 I most emphatically insisted that the altered rocks of Northern 

 Anglesey were on the whole not metamorphic, but /«//pometamorphic. 

 Surely Dr. Eoberts must have seen this memoir. If he had not, he 

 was not qualified to express an opinion upon my views ; if he had, 

 he was not justified in misrepresenting them. 



My papers on " How to work in the Archaean Eocks," which 

 appeared in this Magazine, were written for students rather than 

 for teachers, and the terms employed were sometimes used in a 

 general, rather than a strictly technical, sense. Thus I avoided the 

 term " hypometamorphic " as a refinement unnecessary for my pur- 

 jDOse ; and spoke of " metamorphic " as generally equivalent to 

 '•altered." A critic should have selected the scientific, not the 

 popular, exposition of his author's views. 



Archsean geologists will eagerl}^ look for the evidence upon which 

 Dr. Eoberts affirms that a "passage" occurs between the black 

 shales and the "altered Cambrian," my Pebidian, of Northern 

 Anglesey. I have hammered over almost every patch of " meta- 

 morphic "rock in Great Britain, and have seen something of the 

 older formations in Ireland and North America. I have studied 

 hundreds of sections where eminent authorities had declared that a 

 " passage" existed between unaltered strata and areas of regional 

 metamorphism ; but I cannot recall a single instance in which I was 

 not able to resolve the "passage" into a faulted junction, or some- 

 thing equally inconsistent. In Northern Anglesey, the Pebidian is 

 sometimes, especially near its junction on the south with the black 

 shales, more highly altered than usual, and in places is truly meta- 

 morphic (chlorite-schist) ; so that proof of a true passage would be 

 of great theoretical importance. When Dr. Eoberts publishes this 

 discovery, I trust he will furnish such evidence, microscopic and 

 strati graphical, as will remove the doubt which must necessarily 

 attach to the mere statement that a passage exists. 



Dr. Eoberts does not think that the occurrence of included frag- 

 ments of the " gnarled sei-ies " (which ?) in the Cambrian would 

 place him in a dilemma. In my simplicity, I thought that if B con- 

 tained pebbles derived from A, A must be the older group. Dr. 

 Eoberts, however, has certain " hypotheses " on hand to help him 

 out of his dilemma, though he candidly admits that they are not yet 

 " working." I should think not. C. Callaway. 



Wellington, Salop, 



September 23, 1882. 



