PRESIDENT S ADDRESS. 



if not Archaean, series of rocks, principallj' composed of volcanic 

 materials, and among them some doubtful felsites. 



It will therefore be evident how great a disturbance of our 

 ideas would be the result of the general acceptance of Dr. 

 Geikie's contention, as developed in his paper read to the 

 Geological Society last Spring, that the views held by the 

 last Director-General, Sir Alexander Eamsay, are, after all, 

 correct, and that there is no break of geological continuity such 

 as would justify us in separating any of the older strata from 

 the Cambrian system. Taking the St. David's district. Dr. 

 Geikie considers that there is a continuous series of mixed vol- 

 canic and ordinary sediments with lava flows, from the earliest 

 beds exposed to the upper members of the Cambrian system. 

 Afterwards the whole conformable series was thrown up into an 

 isoclinal fold with a general inclination to the north-west, during 

 which process there has been considerable foliation developed. 

 After this a great mass of granite rose through the south-east 

 side, throwing out dykes and tongues of quartz-felsites. During 

 this stage the various tuffs and shales have been changed in 

 character, and have become in many parts finely crystalline in 

 structure. Finally dykes of diabase have risen through the 

 granite, but invade the other series of rocks. 



It is evident that, between this account and the hypothesis 

 of a Pre-Cambrian formation, there is no compromise possible. 

 Dr. Geikie adduces an instance of contact metamorphism due to 

 the Granite, which, on the other hand. Dr. Hicks denies, and 

 points out especially the absence of such phenomena. To 

 account for the rarity of such, it is asserted, in reply, 

 that the amount of change in a rock, due to the contact of 

 granite, varies very greatly according to its nature. A section 

 which I have exhibited to the Society is a case in point : the 

 granite has invaded a rather fine grit, and naturally there is 

 but little scope for metamorphic action, and, in point of fact, 

 very little has taken x^lace. That the granite is intrusive here 

 is nevertheless proved by the fact that at the junction line 

 there is a decided arrangement of the quartz and felspar 



