﻿1861.] HARKNESS HIGHLANDS AND N. IRELAND. 



2G1 



the Loch Tay rocks obtains. To the south of these contorted lime- 

 stones at Mornish, a flaggy trap is seen. These limestones of the 

 north side of Loch Tay are well exhibited for a considerable di- 

 stance along their strike, on the road leading from Killin to Ken- 

 more. They are well seen on their dip in traversing the mountain- 

 road from Loch Tay to Inverwick in Glen Lyon ; and also in the 

 streams which run nearly parallel to this mountain-road, which in- 

 tersect the valleys lying between Ben Lawers on the east, and Meal 

 Girdy on the west. The section which is shown in this traverse 

 between Loch Tay and Glen Lyon, is probably one of the most 

 instructive which can be seen in any part of the Grampians south 

 of the Caledonian Canal. Commencing near the north margin of 

 Loch Tay, we have the thin-bedded limestones with their N.N.W. 

 dips succeeded conformably by gneiss ; but this gneiss becomes 

 much contorted in the neighbourhood of Loch-a-Larich ; still the 

 prevailing aS";N.W. dip is seen. After passing the water-shed, a 

 reversed dip in this gneiss occurs; and these reversed S.S.E. dips 

 are well seen in the rocky course of the brook which has its origin 

 on the N.E. side of Meal Girdy. These gneissose rocks, which are 

 seen in almost constant succession for more than two miles and a 

 half along this stream, have a S.S.E. dip, which averages 45°. 

 Then, as we approach Glen Lyon, we find coming out conformably 

 beneath the gneiss limestones like those of the north side of Loch 

 Tay ; and after passing downwards through the limestones, we find 

 underneath them, and also conformable to them, the thick masses 

 of quartz-rocks which are so extensively developed along the south 

 side of Glen Lyon. After crossing this area in a northern direction 

 to Inverwick, we find the quartz -rocks suddenly disappear, and on 

 their N.W. side we have thin-bedded blackish gneissose rocks with 

 the same S.S.E. dips ; and rocks of this character are well seen in 

 the course of the burn leading from Inverwick to Dall, on the south 

 shores of Loch Rannoch. Reference will subsequently be made to 

 this gneiss when describing the sections which lie N.W. of the 

 zone marked in Sir Roderick Murchison's sketch-map* of the geology 

 of the north of Scotland, as occupied by " quartz-rock and lime- 

 stones." 



§ 5. Section from Dunkeld to Blair Atlwl (fig. 4). — In portions of 

 the Grampians which lie N.E. of the areas already referred to, we 

 have sections which are very nearly allied to those already de- 

 scribed. In many instances, in these north-eastern areas, the rocks 

 are by no means so well exposed as in the districts which have 

 been under previous notice. In the neighbourhood of Dunkeld the 

 relations of the Old Red Sandstone deposits to the metamorphic 

 rocks of the Grampians are well seen, — the former being cut off 

 from the latter by masses of trap, and the metamorphic strata 

 marked by the N.W. dips which distinguish the southern margins 

 of this class of rocks. With reference to lithological character, we 

 have at Dunkeld schistose beds, possessing the nature of clay-slates, 

 as the lowest exposed rocks of the metamorphic series ; and these 

 * Quart. Journ. Geol. Soc, vol. xv. pi. 12. 



