LXXXVII[ ROYAL SOCIETY OF CANADA 



•'MoNTRKAL. !tth Dc'comljer, 1870. 



■My Dear Professor Dana. — I liave Just read your remarks (Am. 

 Journal of 8ci.. vol. xviii.) in reference to what J have ventured to call 

 the volcanic group of the Quebec series of Sir W. Logan. As regards 

 the volcanic question. I should like very much to know what 3'our views 

 on the subject are. and hope at some future time to hear them from your- 

 self personally. In the meantime 1 would make a few explanatory re- 

 marks on the points you refer to in ray paper. You say the evidence of 

 the general volcanic character of the second group is not stated, and the 

 kind of rocks mentioned make a remarkable assemblage to be spoken of 

 as -these volcanic rocks.' This would seem as if I had meant to assert 

 that all the rocks mentioned as constituting the group Avere of volcanic 

 origin. I might certainlj- have made the matter plainer had 1 specified 

 those rocks in the grouj) which there were reasons for supposing to be of 

 volcanic origin. It never occurred to me, however, that in giving a de- 

 scription of a grcHip of strata of mixed volcanic and ordinary sedimentary 

 origin it would be necessary to do so. 



" As regards the evidence of volcanic origin. I can onh' say now that 

 it is of precisely the same kind as that which, in respect of similar lîi'itish 

 strata, has been considered to be conclusive by almost every British geo- 

 logist of note, including De la Bêche. Lj'cll, Sedgewick. Murchison, Jukes, 

 Kamsay, Scrope, and a host of others now living. Further, that these 

 conclusions, first arrived at b}" the most careful and minute geological 

 investigation and mapping of the stratigraphy, have been or are supposed 

 to be entirely contirmed by the comparatively recent microscopical and 

 chemical investigations of these same rocks. 



•'It is now rather more than thirty years since I took an active [)art, 

 under the geologist tirst named, in working out in all their intricate de- 

 tails the great Lower Silurian volcanic series of JSTorth Wales. Since then 

 I have had abundant and world-wide opportunities of studj-ing volcanic 

 formations of all ages, recent. Tertiarj^ Mesozoic and Paheozoic ; and I 

 may say it is on the result of this world-wide geological investigation, and 

 not on the occuri'ence of labradorite or any other parliculai- mineral, that 

 I have come to the conclusion that we have in Canada, as in Britain and 

 elsewliere, good evidence of the existence of volcanic strata, and conse- 

 quently of volcanoes, in Silurian, Cambrian and pre-Cambrian epochs. I 

 am quite awyre that most of the peculiar rocks which, in common with a 

 majoi'ity of British and some American geologists, I hold to be of vol- 

 canic origin have heretofore been generally, and doubtless quite correctly, 

 described simply as crystalline metamorphic rocks ; but this, it seems to 

 me, rloes not refer so much to the question of their origin as it does to 

 their present condition and character. And if Ave carefully study their 

 stratigraphical relations in the field, and their microscopic and physical 

 characters, Ave at once find — at least that has been my experience — that 



