482 ME. J. B. HILL ON PL0GKES3IVE METaMORPHISM [Aug. 1 899, 



calcareous sericite-schist is seen in the Eas a Ghaill burn near Socach. 

 These micaceous beds of the Ardrishaig Series, which in the Loch 

 Pyne area have a width of outcrop of about 6 miles, narrow a little 

 north of Inveraray to under 4 miles. Still farther north-east, 

 about 4 miles south of Dalmally, the breadth of outcrop is only 

 2^ miles ; here, however, the great compound fold before spoken of 

 begins. By the time it has swept back to its normal position at 

 Socach it is represented by a width of about ^ mile. Prom Socach 

 the Ardrishaig beds sweep round the flank of Beinn Laoigh into 

 Perthshire, and have been traced as calcareous sericite-schists into 

 the heart of the Central Highlands, where they appear in such a 

 metamorphoeed condition that their sedimentary character has often 

 been entirely destroyed, and they have been sometimes mistaken for 

 igneous rocks. 



Here, then, within a distance of about 6 miles, one is able to 

 follow rocks little removed from the condition of clay-slates into 

 highly crystalline rocks of the normal Central Highland type. 

 Purther, the sections from rocks of the least altered to rocks of the 

 most altered character can be continuously followed without a 

 break. 



Having now dealt with the Ardrishaig division of the group, I 

 will proceed to describe the changes that occur in the next division 

 of the series, which I have for convenience called the Loch Awe 

 Series. As previously pointed out, the Ardrishaig phyllites are 

 succeeded uninterruptedly by : — 



Limestones, 1 



Black slates, I Loch Awe Series. 



Grits and quartzites. J 



In following the Loch Awe beds round the great compound fold, 

 we find corresponding changes in them proportionate to the amount 

 of alteration in the Ardrishaig phyllites that underlie them ; or, in 

 other words, where the Ardrishaig phyllites are found in an un- 

 altered condition the Loch Awe beds preserve a similar character. 

 Where the Ardrishaig phyllites have been most altered and rendered 

 coarsely crystalline, as at Socach, a similar change has been seen in 

 the Loch Awe Series, into which they pass upward. 



Limestone. — The first member of the series to be dealt with is the 

 limestone. Beginning, as before, in the least altered district on the 

 south side of the Pass of Brander, we find the Ardrishaig phyllites 

 passing up into limestone associated with more or less black slate. 

 These beds are well seen in the country extending from Tervin to 

 Lochan-na-Cuaig. As they approach the Pass of Brander, however, 

 they become curiously altered. Epidote at first appears sufficiently 

 in the limestone to colour the rock in places ; but on approaching the 

 Pass of Brander, between Tervin and Lochan-na-Cuaig, an abnormal 

 amount of epidote is developed, and the rock assumes a curious 

 banded appearance, with colours varying from purple to yellow and 

 green, yellow and green bands being the commonest. It must be re- 

 collected that the limestone is not pure ; it is often associated with a 



