552 Bryce — Age of the Arran Granites. 



trees referred to are the only instance of Carboniferous trees pre- 

 serving both their original outline and position and their internal 

 structure. 



IV. — On the Age of the Arean Granites. By Dr. J. Bryce, 



M.A., F.G.S. 



THE author began by stating that all the extraordinary phenomena 

 of the geology of Arran arose from the abnormal position of the 

 Granitic nucleus of the north end of the island, which, instead of 

 forming an anticlinal axis, as is usually the case, had broken through 

 the slate band close to its outer edge, within a few yards of the Old 

 Eed Sandstone. Within the area of this nucleus are two granites — a 

 fine and a coarse — and beyond the limits of the nucleus, two separate 

 granite tracts — ^both of the fine-grained variety — one at the outer 

 edge of the Old Eed, and the other amid slates and limestones 

 abounding in fossils. The chief question of interest now in regard 

 to the geology of Arran lay in the age of these granites, and the re- 

 lative position of the two rocks forming the granite nucleus. Dr. 

 Bryce explained that Glen lorsa, instead of being occupied by the 

 fine variety, as was supposed, exhibits only the coarser kind, while 

 the fine granite occupies the heights on either side, and forms the 

 surface over all the higher interior parts of the nucleus ; and, on the 

 south-east of the area, it runs out against the slate, into which it 

 sends veins in the same manner as the coarser kind does on the 

 flanks of Goatfell. He had come to the conclusion that this finer 

 variety was the later of the two, and overlaid the coarser kind, 

 while the two outlying granites of Ploverfield and Craigdhu were 

 of the same age as the fine variety of the nucleus. He adverted to 

 the singular fact that while granite fragments were absent from the 

 Arran conglomerate, small lumps of the Craigdhu granite had been 

 injected into the adjoining conglomerate — probably in a plastic state 

 — quite an exceptional case in the geology of Arran. 



Professor Eamsay said that since he first knew the island of Arran, 

 his opinions regarding it, in some respects, had been considerably 

 altered. Since the publication of his book, now long out of print, some 

 things which were there stated in regard to the special Geological 

 features of certain parts of Arran, he certainly did not now consider 

 correct. If he were to write about the granite formation of Arran in 

 particular, there was scarcely a word in that book that he would re- 

 peat ; he would withdraw every word he had previously said. And 

 if he were now to express his opinion on the granite of Arran, he 

 believed he would be regarded as so heretical by Dr. Bryce and 

 others on the platform, that he thought, for the sake of the harmony 

 of the meeting, the less he said on the subject now the better. 



Professor Ansted expressed his opinion that the granite deposits in 

 Arran were not erupted rocks, and said that the evidence in very 

 many cases of granites not having been erupted in the ordinary 

 sense of the word, was so great as to be entirely incontrovertible. 

 There was no such thing as eruptive granite, properly speaking. 



