ANlflYEKSARY ADDRESS OF THE PRESIDENT. 8l 



Canada. 



I proceed next to notice, very briefly, the metamorphic rocks of 

 Canada. Our fellow-workers on the American continent regard the 

 Ottawa group as the base of the Laurentian series. Of this I was 

 not able to examine a typical area, and will therefore merely state 

 that the specimens which I saw were generally coarse granitoid 

 gneisses, resembling, in their absence of definite characteristics, some 

 of the oldest rocks of Britain, and those which appear to be the most 

 ancient in the Alps. The next group, however, to which in certain 

 areas the name of the Grenville group has been given, and to which 

 I believe the majority of the rocks, which I saw in the field, belong, 

 like the second series of the Alps, presents us with a more definite 

 foliation and with indications of stratification. The gneisses commonly 

 vary from moderately coarse-grained to fine-grained ; they are fre- 

 quently " banded," zones distinctly micaceous (or hornblendic) alter- 

 nating with those mainly quartzo-felspathic, and varying from mere 



Sterry Hu.nt (chiefly after Gastaldi). 



Central gneiss =(2 and b. 



Pietre verdi. 



Newer gneiss and schistic and d. 



Upper lustrous schists ==/ (and px'obably more than here described). 



It must be remembered that these three groupings extend over a much wider 

 area than that to which mine applies. Still a general correspondence will be 

 observed. With one exception, a similar lithological succession may be noted 

 in all. This is the Pietre verdi group of Himt, or the three groups of Von 

 Hauer which I hare bracketed as being probably only subordinate members of 

 one group and so its equivalent. The Fietrc verdi group obviously intervenes 

 between {b) and (c) of my tabulation. I do not dispute its existence ; but in tlie 

 district of which I have been speaking, it is often wanting and, if ever present, is 

 only imperfectly represented. I have examined specimens of it ; but as it is 

 several years since I visited the i-egions where it is considered to be best de- 

 veloped, I prefer to limit my arrangement as above. I will, however, remark that 

 the group, as at present defined, requires much curtailment. We are told 

 (Hunt, " Geol. History of Serpentines," Trans. R. S. Canada, vol. i. p. 154) that 

 it received its name from " the frequent pi-esence therein of serpentine, diorite, 

 diabase, and related rocks of a greenish colour." It is, however, obvious that, 

 if we use the terms diorite and diabase in their strict sense, and serpentine in 

 that to which niost petrologists will now agree with me in restricting it, these 

 rocks, as being of igneous origin, cannot be used in defining a chronological 

 series unless we can prove that they are contemporaneous with it (a point 

 with which Dr. Hunt does not seem to concern himself). Seeing, then, that in 

 all probability many of them (as being coarse-grained rocks) are most probablv 

 intrusive, the Pietre verdi group may have to be greatly reduced in volume, and 

 may prove to be one rather of local occurrence than of general significance. I 

 may add that this is not the only case where the greatest possible confusion is 

 produced (both in books and maps) by not distinguishing rocks certainly of 

 igneous from those presumably of sedimentary origin. I am well aware that 

 in a district like the Alps this cannot always be done ; but in many cases it is 

 perfectly possible, and to lump together these rocks of dissimilar origin fear- 

 fully increases the confusion and the difficulties which beset the student. I 

 could name more than one author on the subject of this address whose writings 

 I liave occasionally felt inclined to treat as a certain student did his manuscript 

 of Persius, when he threw it to the other side of his room with the exclamation 

 " If you do not desire to be understood, you do not deserve to be read." 



