128 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 4, 



I could not find the limestone which, in Mr. Buist's map, is placed 

 at Rattray ; but the spot where he has marked it is in the Old Red 

 Sandstone. I had not time to visit the limestone between Blair 

 Gowrie and Cluny, but the strike of the beds in the neighbourhood 

 left me little doubt of their lying in the Old Red Sandstone. The 

 position of the clay-slate on the Tay is so nearly the same as that 

 just described, as not to require a figure. It covers a breadth of 

 about four miles from Dunkeld to Birnan Hill, at which latter spot it 

 is largely quarried, and supplies an excellent roofing-slate. The beds 

 dip N.W. towards the mica-schist at about 60°, and they meet the 

 Old Red Sandstone without any trap appearing between them ; yet 

 the trap-dyke probably runs below the surface, and has produced the 

 apparent anomaly of clay-slate dipping N.W., meeting, on its 

 southern edge. Old Red Sandstone dipping S.E., the two thus 

 appearing to form an anticlinal axis. 



The next valley to be mentioned is Strath Earn ; but the abun- 

 dance of drift in the valley prevented me from getting a complete 

 section. The clay-slate is not two miles wide, and is very highly 

 incUned ; on the north side of Comrie, where it meets the mica- 

 schist, it dips N. 85°. 



Thus far we have only met with the lower formation of dark clay- 

 slate ; but in the sections to the westward, which are next to be de- 

 scribed, the upper green slate comes also into view. 



Eig. 2.— Section of the Valley between Aberfoyle and Loch Chon. 



N.V^. Side of Loch Chon. Loch Ard. Aberfoyle. S.E. 



Mica- schist, 



Green slate. 



Clay- slate. 



Trap. 



Old Red Sand- 

 stone, with calca- 

 reous beds, L. 



Fig. 2 is a section of the beds seen in the valley between Aberfoyle 

 and Loch Chon. The Old Red Sandstone is separated from the 

 clay-slate by a great dyke of greenstone-trap ^ of a mile wide, on 

 which the Inn of Aberfoyle stands, and which crosses the valley and 

 enters the hills on both sides, running about E. 20° N. The lowest 

 part of Old Red Sandstone is a dark brown grit, perhaps between 

 200 and 300 feet thick ; on this rests a bed of limestone, marked 

 L L in the section, associated with thick beds of quartz-rock with 

 partings of steatite, surmounted by a great thickness of coarse ferru- 

 ginous conglomerate many hundred feet thick, with pebbles larger 

 than cannon-balls. All the beds of the Old Red Sandstone dip about 

 S. 20 E. 40°. Owing to the upper part of the quarry having lately 

 fallen in, I was unable to see the thickness of the calcareous beds. 



The north side of the trap is overlaid by the dark clay-slate, dip- 

 ping N. 20 W. 80°., which forms a band a mile and a half wide, on 

 the northern side of which is a large quarry of excellent roofing- 



