﻿152 



MR. E. BATTERSBY BAILEY 02f 



[vol. lxxii, 



in the Geological Survey Memoir on Islay, where, however, it is 

 interpreted as a local inversion. 



Jura. — A full statement of my observations in Jura has been 

 published in the Geological Survey Memoir on Knapdale, Jura, and 

 North Kintvre. Of this a short resume is given below. 



The following succession has been recognized in the Islay Quart- 

 zite as developed in Jura, where, unfortunately, the base of the 

 formation is not exposed. The sequence is stated in descending 

 order : — 



Scarba Conglomeratic Group. 



Jura Slates — black above, grey below. 



Non-Vitreous Pebbly Quartzite with seams of Black Slate. 

 Non- Vitreous Pebbly Quartzite with. Flags, except in the south. 

 Vitreous Pebbly Quartzite (Pebbly Quartzite, North Islay). 

 Vitreous Fine-Grained Quartzite (Upper Fine-Grained Quartzite, 

 North Islay). 



As indicated in PI. XII, two important faults pass northwards 

 across the Sound of Islay into Jura : the more westerly merely 

 touches the western shore of Jura ; the more easterly — the Beinn 

 Bhan Fault of Islay — runs inland for a short distance. The 

 position of these two faults in the coastal cliffs is indicated by 

 pronounced shattering. Between the two faults one meets with 

 an upward succession from the Vitreous Fine-Grained Quartzite 

 into the Vitreous Pebbly Quartzite — in fact, the same sequence 

 exactly as one encounters along the northern shore of Islay west 

 of the anticlinal axis. 



The Beinn Bhan Fault has not been followed in the inland part 

 of its course, Avhere, indeed, exposures are rather unsatisfactory. 

 It probably joins its western neighbour on re-emerging upon the 

 coast, for there is great shattering of the quartzite at the place 

 where the two faults are mapped as coming together ; while no 

 marked shatter-belt is seen in the coast-sections farther north. 



The Vitreous Pebbly Quartzite seen west of the fault — or, 

 at any rate, a rock of identical character — continues northwards 

 along the coast to the mouth of the loch that almost divides Jura 

 into two. After the interruption due to this loch, the group is 

 seen again for some 3 miles, when it passes below the sea, to 

 reappear once more in Scarba. 



Dipping off the Vitreous Pebbly Quartzite comes the most 

 characteristic division of the Islay Quartzite as developed in Jura — 

 namely, the Non-Vitreous Pebbly Quartzite with Flags. It is an 

 immensely thick group, and in the south consists almost uninter- 

 ruptedly of pebbly quartzite, which, in a northerly direction, is 

 increasingly split up by cleaved grey sandy shales (or mudstones) 

 and flags, more or less evenly distributed throughout. In some 

 cases, as Dr. Peach has pointed out, the flags are crowded with 

 worm-casts. 



The next group, the Non- Vitreous Pebbly Quartzite with seams 

 of Black Slate, has only been differentiated in the north of Jura, 



