﻿THE ISLAX ANTICLINE. 



[vol. Ixxii, 



perfect isoclinal folding, that characterize the Moine Gneisses ;■ 

 Iron, a study of the maps, the speaker felt that there was a pos- 

 sibility of the original rocks, from which the more massive types- 

 of felspathic Moine Gneiss were formed, being found in this part 

 of Islay,. and this was the cause of his visit to the area. He had 

 now little doubt that these sandstones are the rocks in question. 

 They are practically free from any trace of crystallization, present 

 all the characters that the unaltered representatives of the Moine 

 Gneiss should possess, and the Bowmore area shows that they are on 

 the fine margin of the Quartzite and, so far as the folding will allow 

 us to see, they are between the limestone and the Quartzite : that 

 is, they are in the position assigned to them in the speaker's paper 

 published by the Society. Far from being of any great thickness, 

 they were probably quite a thin group originally. Islay is thus- 

 one of the most encouraging areas in the Highlands for further 

 examination, and is worth mapping with the minutest detail. 



Dr. B. N. Peach, in the following written communication to 

 the Secretary, stated that, while making criticisms, he would wish 

 at the same time to state that he considered the view put forth by 

 the Author — that the dolomitic ' Fucoid '-like beds are not the 

 highest rocks in the Islay succession, as held by the Geological 

 Survey, but are in turn overlain by the main quartzite, the Jura 

 Slates, the Scarba Conglomerate, and Port Ellen Phyllites, in 

 upward sequence — to be worthy of the closest consideration, 

 although he felt that the Author had not brought forward sufficient 

 evidence to establish thoroughly his contention. If this could be 

 done, many difficulties left unsolved by the Geological Survey 

 would be cleared up : — 



' The important feature in the paper is the evidence which the Author 

 adduces to prove a further extension of the anticlinal arrangement of the 

 strata in Islay, east of the Loch Skerrols Thrust. This structure, in a modi- 

 fied form, was previously recognized by the Geological Survey. In the 

 Memoir on ' The Geology of Islay,' it was shown that tha Islay limestones, 

 black slates, and phyllites form the core of a compound anticline extending 

 from the Mull of O'a north-eastwards to Kiels, near Portaskaig. It was also 

 pointed out that, between Loch Finlaggan and Port a' Chotain in Northern 

 Islay, the strata, including five subzones, ranging from the Portaskaig Con- 

 glomerate up to the Fucoidal Beds with massive bands of dolomite, are 

 arranged in a compound arch. 



' In his paper the Author contends that the dolomitic group, which resembles 

 the Fucoid Beds of Cambrian age in Sutherland and Boss, is not the highest 

 member of the sequence in Northern Islay, but is overlain by an upper quartzite 

 on the eastern and western limbs of the compound arch. On the eastern limb 

 this upper quartzite runs from Budh a' Mhail to Bonahaven, on the western limb 

 from Budh a' Bholsa to Loch Skerrols in the south. He also holds that there 

 is an ascending sequence from his upper or main quartzite of Islay, Jura, and 

 Scarba, to the black slates of Scarba, Lunga, and Easdale. 



' I submit the following criticisms on these oijinions : — 



' 1 . In proof of the superposition of the upper or main quartzite on the east 

 limb of the compound arch in Northern Islay, the Author states that, west of 

 Budh a' Mhail, the dolomitic group appears as an inlier with gentle anticlinal 

 dips passing- below the upper quartzite of Budh a' Mhail and Port a' Chotain. 

 In my opinion, the evidence shows that the. dolomitic group does not there 

 form an inlier, and that the Port a' Chotain quartzite underlies the dolomitic 

 group. The horizon of the latter quartzite is proved by the occurrence in it 



