214 Peter Macnair — Altered Clastic Rocks 



drawn out into ovates, and in the case of extreme shearing have 

 been reduced to a mere line or streak. Seen under the microscope, 

 these greywaekes present a finely fragmental structure with 

 occasional crystals of felspar disseminated through the mass. 

 Passing down the mountain-side, we cross the middle arenaceous 

 group, which as usual is composed of massive beds of quartz-schist, 

 often becoming highly garnetiferous. Near the level of the road which 

 passes along the north side of Loch Tay, we come upon the Loch 

 Tay limestone zone, with its massive beds of limestone and 

 calcareous mica-schist ; followed eastwards it is found to pass under 

 the base of the Ben Lawers group ; westwards it skirts the base of 

 Sron Clachan in a bold escarpment, and thence stretches to the west 

 through Glen Dochert. The sill of altered basic rocks upon which 

 the limestone rests may be well seen on the road leading to Killin 

 Pier. Here the limestone is shown resting immediately upon the 

 sheared basic rock, and evidence of the extreme alteration of the 

 limestone is to be found in the hardened bands of that rock found 

 running along the lines of contact. It is not our intention here, 

 however, to enter into a detailed description of these associated 

 igneous rocks, but merely to mention their occurrence in connection 

 with the clastic series. 



Following the line of section and crossing the head of Loch Tay, 

 the lower members of the middle arenaceous group are exposed, lying 

 below the limestone zone, and folded over in an anticlinal axis. 

 They are well seen at the falls of Dochert near the head of the village 

 of Killin, where they are still found dipping to the north-west. 

 Passing up the burn at the back of Auchmore House, the quartz- 

 schists are found to become flatter and flatter till they roll over and 

 dip to the south-east. Near the base of Ben Leathan and at the head 

 of the burn, we again come upon the Loch Tay limestone zone, now 

 dipping to the south-east at a very gentle angle, and capped to the 

 top of Ben Leathan with the upper members of the middle arenaceous 

 group. A transverse section of the latter mountain is well exposed in 

 the deep pass of Glen Ogle ; all the beds seen on the higher sides 

 of that glen to the top of Ben Leathan belong to the upper members 

 of the middle arenaceous zone, and are mainly, as usual, composed of 

 massive beds of quartz-schists, with occasional bands of grit and 

 conglomerate. From the head of the Auchmore burn to the old 

 Killin junction at the head of Glen Ogle, the Loch Tay limestone 

 skirts the base of Ben Leathan ; down Glen Ogle the quartz-schists 

 and limestone are seen to undulate gently to the south-east, the 

 latter being well exposed in the quarry at Dalveich on the northern 

 shore of Loch Earn. In Glen Ogle several very fine sections 

 of the limestone resting upon the sheared basic rocks are to be 

 seen ; one, in particular, about a quarter of a mile north of the Glen 

 Ogle toll-house, exhibits all the phenomena before described as seen 

 on Loch Tay at Killin Pier. On the south side of Loch Earn, the 

 massive beds of grit and conglomerate belonging to the lower 

 arenaceous group are well seen on the sides of Ben Vorlich, where 

 our section is supposed to terminate. 



