﻿part 2] 



THE ISLAy ANTICLINE. 



,157 



(3 Ji) Scarba Transition .Group. 



East of the Conglomeratic Group in Scarba lies a thick suc- 

 cession of interbedded black slates, quartzites, and limestones. 

 The black slates, which are 'of Easdale type, are the dominant 

 members of the ' group. The interbedded quartzites are often 

 pebbly, and resemble the quartzite of the adjoining Conglomeratic 

 Croup. The yielding nature of the slates has permitted the 

 development of much obvious crumpling. 



There is scarcely room for doubt that the mixed : slate and 

 quartzite group of Eastern Scarba represents a Transition Group 

 connecting the Islay Quartzite with the Easdale Slates. The 

 relation of this Transition Group to the Port Ellen Phyllites and 

 the Laphroaig and Ardmore Quartzites cannot definitely be settled, 

 owing to lack of exposure ; but it seems probable that the two sets 

 of rock's are roughly equivalent, as one would expect from their 

 relations to the Scarba .Conglomeratic Group. Such an inter- 

 pretation is in keeping with the growing importance of black slate 

 in the Jura Slate Group wliieh followed northwards : in the south 

 of Islay the Jura Slates are mainly grey, whereas in the north of 

 Jura-they are entirely black. ' ' - 



■ - • • (Si) Easdale Slates. 



The Easdale Slates which build up Luing and its associated 

 islands are carbonaceous, v quite black, and 'very pyritous. Quartzose 

 intercalations are rare, but thin black limestones common. , ;, 

 A As might be expected from their composition, the Easdale Slates 

 are thrown into numberless small-scale folds., 



(. .> . (4) Rocks of Degnish and Shuna. 



The schists of Degnish and Shuna probably belong to the Loch 

 Awe rather than to the Islay region. They are dealt with in the 

 present paper, so as not to leave a gap between the district here 

 described and that already discussed in the Journal of this Society 

 ' (vol. 'lxix, 1913) under the title of the Loch Awe Syncline. 



v . (4 a) Degnish Limestone. 



Dr. Peach has traced a very well-characterized dark sandy lime- 

 stone through Degnish and Shuna into Keis an-t-Sruith — an island 

 off Craignish Point. Much of the limestone is mottled with round 

 i aggregates of dark calcite, in large crystals, embedded in a sandy 

 calcareous matrix. 



Dr. Peach describes a narrow belt of Easdale Slates as generally 

 "recognizable in Degnish and Shuna, separating the limestone from 

 the adjacent Ardrishaig Phyllites : in this I think that he has 

 been mistaken. After careful re-examination I consider that the 

 rocks in contact with the limestone are members of the Ardrishaig 

 Group, that the junction is a normal sedimentary one, and that no 

 Easdale Slates occur anywhere in Degnish or Shuna. 

 Q. J. G. S. No. 286. w 



