94 THE CANADIAN NATURALIST. [Vol. ix. 



true gneiss. And, similarly, if previous observers have placed 

 certain " volcanic " rocks in the same formation with the Sillerj 

 eandstones, we may be certain that they did so intelligently, and 

 that Sir William Logan and his staff ♦vere fully aware of the 

 differences between a crystalline and a fragmentary rock. 



V. Mr. Seiwyn calls attention to two characters not pointed 

 out by Sir W. E. Logan which distinguish the "Volcanic " from 

 the L^vis area on the Riviere du Sud. One of these is the 

 occurrence of fossils in the district north of the river ; but this 

 does not seem to be a new discovery. The other distinction is a 

 peculiar schistose structure in the sandstones of the "Volcanic" 

 group, which is not to be observed among those of the Ldvis 

 formation. It is worthy of note that here we have Mr, Seiwyn 

 himself making use of a lithological peculiarity for separating 

 two different groups of rocks. The absence of fossils from his 

 se3ond or " Volcanic '' division is emphasised by Mr. Seiwyn ; and 

 uo doubt this difference, as compared with the L^vis formation, 

 is a most important one. Still we know that Sir W. E. Logan 

 was aware of this distinction ; so that here again we have, not the 

 announcement of a new fact by Mr. Seiwyn, but simply a new 

 explanation of a certain peculiarity. Sir William accounted for 

 the absence of fossils by metamorphic action ; Mr. Seiwyn would 

 probably attribute it to volcanic interference : the difference is, 

 after all, only in theory. 



Although I have searched very carefully, I have failed to find 

 in Mr. Selwyn's paper any other traces of original observation 

 than those I have enumerated. The first of these items has no 

 bearing upon the mutual relations of Mr. Selwyn's second divi- 

 sion and the L^vis formation ; the fourth cannot be said to be a 

 new observation at all, and thus we have, as the actual basis of 

 fact for Mr. Selwyn's new conclusions, the absence of Potsdam 

 strata from the neighbourhood of the Ldvis formation, the sup- 

 posed unconformity on the River Etchemin and a trifling litho- 

 logical peculiarity among the sandstones of the Riviere du Sud. 

 The supposed unconformity is by far the most important part of 

 this basis ; but we must recollect that Mr. Seiwyn is far from 

 being positive about it, and, further, that the same difficulty 

 occurred to him as regards the contact of the rocks on the 

 northwest edge of the fossiliferous belt. There too, he does not 

 distinguish between an unconformity and a fault, and I believe 

 were this latter point decided it would go far to settling this 

 vexed question of the age of the Quebec group. 



