406 THE TERTIARY BASALT-PLATEAUX OF N.W. EUROPE. [May 1 896. 



also a graphic picture of the features of the ancient lands now only- 

 represented by these "Western Isles. "We see, by the traces of old 

 river-courses, their former connexion with the mainland, and are 

 able to realize the enormous work which subaerial and marine 

 denudation have effected over this great area of the north-west. 



Prof. Sollas remarked that, in listening to this important con- 

 tribution, he had been greatly impressed with the uniformity in 

 character of the rocks belonging to the great Gaelic-Icelandic pro- 

 vince. The granophyre on the table from St. Kilda was so precisely 

 similar to the granophyre of Mourne and Carlingford that, without 

 labels, it would be impossible to distinguish the rock in hand- 

 specimens. It was theretore the less surprising to find that the 

 same order of extrusion was maintained in places so far apart 

 as Carlingford and St. Kilda. No deduction in favour of a regular 

 order of differentiation from basic to acid igneous products could, 

 however, be drawn from this province ; and now less than ever, 

 since Sir Archibald Geikie had pointed out that granophyres were 

 among the most recent igneous rocks in Iceland. The speaker 

 welcomed the confirmation which Mr. Harker had afforded of 

 observations previously made at Barnavave. The constancy in 

 direction of dykes over wide areas stood in direct relation to the 

 constancy in direction of the thrusts which prevailed over Europe- 

 Asia during the Tertiary period. In Ireland, as Sir A. Geikie had 

 already shown, the dykes ran from S.E. to K"W., and this direction 

 closely corresponded to that of normals to the axes of the folds : the 

 change in direction of the dykes in Iceland was of great interest, 

 and might furnish evidence of the direction of the concealed folds of 

 that island, which had in all probability been subject to thrusts 

 coming from the south and west. 



Mr. W. "W. Watts remarked that at the time this paper was being 

 read Prof. Cole was probably communicating one on the rhyolites of 

 Antrim at the Royal Dublin Society. "Were there no rhyolitic lavas 

 on the Scottish side of this great province ? The reported difference 

 between pre-granophyre and post-granophyre dykes, if substantiated, 

 would be of great value in Ireland as well as in Scotland. He did 

 not quite understand what connexion there was between the old 

 river of Canna and that of Eigg, if one was overflowed by pitch- 

 stone and the other by plateau-basalt. He referred to „the work of 

 Prof. Iddings on the composite dykes of the Electric Peak. 



Dr. Du Biche Preller wished to ask the Author, with reference 

 to the third section of the paper, what was the material immediately 

 underlying the two alternations of conglomerate at the eastern end 

 of Canna. Assuming the conglomerate to be fluviatile, one would 

 expect it to rest on sand, which, whether loose or hardened to sand- 

 stone, should be of a certain depth, the more so as the conglomerate 

 was in each case as much as 100 feet in thickness. 



The Author thanked the Fellows for their cordial reception of 

 his paper, and briefly replied to the questions that had been put by 

 the previous speakers. 



