212 Peter Macnair — Altered Clastic Rocks 



upper argillaceous series marked b. In the section accompanying 

 his map of Scotland, Sir A. Geikie shows the upper arenaceous 

 series as also being seen on the sharp folds of the upper Ben 

 Lawers strata, but this I have not been able to satisfactorily deter- 

 mine. Passing now to the south-east over the crest of the mountain, 

 we come upon the sericite schist with its bands of quart zite, the 

 lower member of our upper argillaceous series. This rock I have 

 already described. It forms the whole of the top of Ben Lawers, 

 where some very fine sections showing its extreme corrugation may 

 be seen, the precipice on the south-west front being specially worthy 

 of notice. It will be seen from the section that the whole of these 

 beds dip to the north-west at greatly varying angles. Proceeding 

 down the south side of the hill, this rock may be traced for a con- 

 siderable distance, when it passes into the mica-schists and quartz- 

 schists of the middle arenaceous group. At its base, and intercalated 

 amongst the latter rocks, we come upon the Loch Tay limestone 

 zone, which passes underneath the mountain with a north-west dip. 

 Traced eastwards, it is seen to be cut off by a powerful fault at 

 Pernan ; and westwards it is found to enter Glen Dochert at Killin. 

 The limestone here is similar to what we have already described, 

 the two principal kinds being the pure limestone and its argillaceous 

 or micaceous variety. Crossing the loch, the bottom of the latter is 

 seen to be formed by the members of the middle arenaceous zone, 

 underlying the Loch Tay limestone. On crossing to the south side 

 of the loch, the structure and succession of the rocks is here made 

 somewhat complex by the presence of the powerful fault already 

 mentioned, which has been carefully traced by the officers of the 

 Geological Survey. The fault enters the loch to the east of 

 Ardeonaig, crossing and emerging again on the north side at Pernan. 

 In the Ardeonaig limestone quarry, near Dall, the limestone is again 

 met with at a slight level above the loch. This is shown on the 

 section immediately to the north of the fault. From this point the 

 limestone runs westwards to the head of Glen Ogle, and southwards 

 clown Glen Beich towards Loch Earn. The downthrow side of the 

 fault is to the north-west, so that in following the section further 

 south, an outlier of the Loch Tay limestone zone is met with on Meal 

 Na Creig. Capping that mountain, and occupying the position as 

 shown on the section, passing over the crest of the mountain and 

 descending its southern side, we again cross the lower members of 

 the middle arenaceous zone, with their characteristic mica and quartz 

 schists. Still further to the south of the section, the latter rocks are 

 seen to merge downwards in Glen Turret into the pebbly grits, 

 gi-eywackes, and quartzites of the lower arenaceous zone, which in 

 turn are succeeded by a narrow band of clay-slates belonging to the 

 lower argillaceous zone. 



X. Section across Craig Na Challeich to Loch Earn. 



Passing now to another section, about eight miles to the west 

 of that already given, and extending from Craig Na Challeich above 

 Killin to the south side of Loch Earn, we find in it a similar 



