Vol. 62.] STKUCTURE OF THE SGtTRR OE EIGG. 67 



that date is as clear here as elsewhere. It includes the removal of 

 the greater part of the then existing mass of Eigg, leaving the 

 valley exalted to a summit-ridge. It includes perhaps the separation 

 of this island from Oigh-sgeir (Hyskeir), 18 miles to the west, now 

 divided by a sea 40 to 50 fathoms deep. On the lava-flow hypothesis 

 it certainly includes the cutting back of the coast of Eigg for miles, 

 until the cliffs truncated the valley at an altitude of more than 

 500 feet above the present sea-level. 1 If the pitchstone of the 

 8gurr of Eigg is an intrusive sheet, this dilemma vanishes with the 

 other difficulties which have been pointed out above ; and, in its 

 erosion as in other respects, Eigg is brought into correlation with 

 other parts of the region to which it belongs. 



EXPLANATION OF PLATES III & IV. 



Plate III. 



The Sgurr of Eigg, from a photograph by Mr. A. S. Reid. 

 See key, fig. 3, p. 46. 



Plate IV. 



Bidein Boidheach, Isle of Eigg, from a photograph by Mr. A. S. Eeid. 

 See key, fig. 4, p. 53. 



Discussion. 



The President said he was sure that, from the sentimental point 

 of view, the feeling of the Fellows was one of regret that doubts 

 should be cast upon an explanation of phenomena which had long 

 been dear to all geologists. 



Sir Archibald Gelkie said that, owing to the lateness of the 

 hour, it was not possible for him to criticize the paper in detail, 

 but he hoped to have an opportunity of doing so after it had been 

 published. He would have been glad to go over the ground with 

 the Author and discuss the points in dispute on the spot, but ho 

 only heard of the Author's views late in the summer, when it was 

 no longer possible for him to return to the Western Isles. None 

 of the points raised in the paper seemed to the speaker to be 

 incapable of explanation in accordance with the interpretation of 

 the Scuir which he had himself proposed many years ago. It 

 appeared to him that the Author had very greatly exaggerated the 

 proportion of sills among the plateau-basalts. It was difficult to 

 conceive the physical possibility of these basalts being invaded by 

 such a multitude of intrusive sheets, and yet that they should show 

 so little visible sign of disturbance. That there were true sills in the 

 district was well known, but the Author seemed to have somehow 

 come to the conclusion that every columnar sheet must be a sill. 



1 Reckoned from the sea-level at the epoch of the great erosion, the 

 -altitude would doubtless be considerably greater. 



F2 



