552 MESSRS. HILL & EYNASTON ON KENTALLENITE [Aug. I9OO, 



a lamprophyre-sill, while the mass exposed in Brannie Burn has 

 been invaded by a later intrusion of a granite closely resembling 

 that of Ben Bhuidhe. This granitic intrusion is well seen in a 

 tributary burn flowing into the Brannie from the flanks of Ben 

 Bhuidhe, and granite is exposed in the bed of the burn for a distance 

 of 170 yards. There can be no doubt of its intrusive character, the 

 rock being distinctly fine-grained at its contact with the kentallenite, 

 and gradually becoming coarser as one proceeds farther into the 

 mass. Veins also of the granite are seen to penetrate the kental- 

 lenite. The actual outline of the intrusion cannot be determined, 

 as, on either side of the burn, it is hidden by morainic material. 



Again, a lamprophyre-sill, which must be referred to the same 

 group as that cutting the Allt-an-Sithein kentallenite, and occurs 

 on the northern flanks of Ben Bhuidhe, is seen to be distinctly 

 veined by the granite, close to the main mass of which it is exposed, 

 while the microscope shows that distinct contact-alteration has taken 

 place. A section taken close to the contact with the granite-vein 

 shows that the lamprophyre now consists essentially of small scales 

 of contact-brown mica and water-clear pla°doclase [8467]. Slightly 

 farther from the vein [8468] there are still signs of contact-action, 

 while the original crystals and c^stalline aggregates of the horn- 

 blende of the lamprophyre may be seen. Mr. Teall, who has kindly 

 examined these slides, remarks that ' these specimens seem to 

 remove all doubt as to the contact-metamorphism of the lampro- 

 phyres." We have therefore clear examples of a lamprophyre cutting 

 kentallenite, and of a lamprophyre being in its turn cut by granite, 

 while a granite of similar type again cuts kentallenite. This, then, 

 will give us the sequence — kentallenite, lamprophyre, granite, in order 

 of intrusion. Tn other words, this evidence shows that in the Ben- 

 Blmidhe area, more acid material followed the intrusion of basic. 

 This conclusion is borne out by the fact that both the kentallenite- 

 masses of this area are traversed by a band or vein of felspathic 

 material, representing the more acid portion of the underlying 

 reservoir. Whether this process was continuous or not, we have no 

 means of determining in respect to the general area under considera- 

 tion ; locally, however, the phenomenon of acid veins in the basic 

 rocks shows that this was not always progressively continuous. 



It is very probable, moreover, that basic material may still have 

 existed and have been intruded, during the later phases of intrusive 

 activity ; since in certain other of our Argyllshire centres we find 

 sills, belonging to the camptonite-group, cutting the larger granite- 

 masses, and moreover, in the Ben-Cruachan area, we find basic dykes 

 allied to basalt, cutting the latest and most acid portion of the 

 granite. From the single case of a lamprophyre being veined by 

 granite in the Ben- Bhuidhe region, we are hardly justified in conclud- 

 ing that all the lamprophyres are older than the granite. It may 

 well be, judging from the evidence of other areas, that some are older, 

 while others again are younger. 



It is interesting, however, in this connexion to note that our 

 conclusion, that in the main, acid material followed basic, is strongly 



