﻿158 



ME. E. BATTERSBY BAILEY OS 



[vol. lxxii, 



(16) Ardrishaig Phyllites. 



The Degnish Limestone is followed eastwards, both in Degnish- 

 and in Shuna, by a set of greenish-grey phyllites with many thin 

 intercalations of white limestone, and also, in the eastern part 

 of Shuna, of fine-grained quartzite. Lithological character and 

 geographical position assign these rocks to the Craignish Phvllite 

 Group, which Mr. J. B. Hill 1 several years ago correlated with the 

 Ardrishaig Phyllites of Loch Fyne, on the other side of the Loch 

 Awe Syncline. 



III. Conclusion. 



The object of the present paper has been to give an account of 

 the stratigraphy and structure of the Islay district. The main 

 results are graphically expressed in PI. XII. The map and sections 

 of this plate speak for themselves, but a few words may be useful 

 in regard to the explanations. 



The Raised Beaches of the Loch Gruinart hollow and the lavas 

 of Old Red Sandstone age north of Degnish are altogether later 

 than the rocks dealt with, and are designated by black-and-white 

 symbols. 



The epidiorite- sills have no stratigraphical significance, and are 

 shown in an isolated tablet. 



To the rocks of Shuna and Degnish are assigned a separate 

 index, because it is suspected that they may be resting upon an 

 important thrust, separating them from the Islay succession below. 

 The Degnish Limestone is placed under the Ardrishaig Phyllites, 

 because it is so arranged in fact ; but whether the limestone is 

 older or 3^ounger than the phyllites is an open question. 



The long index at the left-hand side of the plate represents the 

 succession in Islay above the Loch Skerrols Thrust, and also its 

 continuation in the islands on the north. The upper part of the 

 index is split, in order to indicate the probable equivalence of the 

 Port Ellen Phyllites and the Laphroaig and Ardmore Quartzites in 

 the south to the Scarba Transition Group in the north. There is 

 very good reason to believe that the index represents the rocks in 

 their original order of superposition, with the oldest at the bottom. 



The Bowmore Sandstone is given an index to itself, on account 

 of its structural isolation. 



The rocks of the Rhinns of Islay and Colonsay are cut off from 

 the rest of the district by the Loch Gruinart Fault They are 

 shown in a single index, but with the unconformity between the 

 Lower Torridonian sediments and the Lewisian Gneiss quite clearly 

 indicated. 



Finally, it may be pointed out that the Loch Gruinart Fault is 

 probably the Great Glen Fault of the mainland, while the Loch 

 Skerrols Thrust is not unlikely the Moine Thrust of the North- 

 West Highlands (see fig. 3, p. 138). 



1 ' On the Progressive Metamorphism of some Dalradian Sediments in the 

 Reg-ion of Loch Awe ' Q. J. G-. S. vol. lv (1899) p. 479. 



