part 2] THE SOFTH-WEST HIGHLANDS OE SCOTLAND. 115 



if anything, occurs between the Appin and Iltay Nappes in Ard- 

 mucknish. The alternative (illustrated in fig. 5, p. 109) is that 

 the Iltay Nappe has almost or quite pushed aside the Ballachulish 

 Nappe in the Ardmucknish district ; but the evidence for this in- 

 terpretation is reserved for the following section, where it v^dll be 

 shown that black slate and pebbly quartzite of the Iltay Nappe 

 have a south-eastward extension quite out of keeping with the 

 recognized limitations of such rocks in the Ballachulish Nappe. 



In the foregoing argument no attention has been paid to a very 

 confusing feature of Loch-Creran geolog}^ An important fault, 

 known as the Strath- Appin or Pass-of-Brander Fault, crosses the 

 loch at the eastern corner of fig. 6. Its downthrow is to the south- 

 west, as shown by its effect on the distribution of the Old Red 

 Sandstone lavas. Along its course, west of the loch, rock-exposures 

 are altogether wanting in a belt upwards of half a mile wide. 

 North of this obscure tract, they occur again in their usual pro- 

 fusion, but they can be shown to belong almost entirely to the 

 Leven-Schist Group of the Ballappel Foundation. The contrast 

 of character is, however, not nearly so marked as might be desired. 

 The Banded Series of the Leven Schists (p. 104) is very strongly 

 developed beneath the Ballachulish Nappe between the Balla- 

 chulish Grranite and Loch Etive, and is for several miles well seen 

 about the head of Loch Creran. A prevalent rock-type is a grey 

 quartzose schist, passing gradually into non-pebbly impure 

 quartzite, with repeated laminations of black seams. 



It is not surprising that at first this Banded Series was supposed 

 to belong to the same stratigraphical group as the rocks south of 

 the fault, now referred to the Transition Group of the Iltay 

 Succession. The reasons which render such a correlation untenable 

 at the present time are : — 



(1) The frequent pebbly character, the limestone -bands, and the genuine 

 black slates of the Transition Group are wanting in the Banded Series — a 

 contrast which impressed Clough strongly when in conversation he disagreed 

 with the correlation of the two accepted by Peach, Home, Grant Wilson, and 

 myself, during a joint traverse in 1906. 



(2) At the time when we made our joint traverse. Grant Wilson was of 

 opinion that the Banded Series at the head of Loch Creran was merely a local 

 facies of the Ballachulish Slates. It therefore appeared that, to correlate the 

 Transition and Banded Series of Loch Creran, was simply equivalent to corre- 

 lating the Easdale and Ballachulish Slates — a probable enough correlation 

 even to-day (p. 106). When later it was shown that the Ballachulish Slates 

 continue with constant character to the head of Loch Creran, and that the 

 Banded Series belong to the Leven Schists, the whole situation changed, A 

 correlation of the Transition and Banded Series of Loch Creran now involves 

 a correlation of Easdale Slates and Leven Schists within the limits of a single 

 nappe ; and this, with its attendant stratigraphical consequences, seems 

 incredible. 



(3) When we made our correlation, we thought that the outcrop of the 

 Transition Series gave place in toto to that of the Banded Series. I am now 

 in a position to show (next section) that the pebbly-quartzite and black-slate 

 series preserves its individuality in an outcrop which escapes eastwards round 

 the northern end of the Loch-Awe Syncline. 



I 2 



