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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



slates at Comrie, and proving that it too is cleavage and not stratifi- 

 cation. The position of the other planes is less definite from their 

 curvature, but they seem on the whole to dip S.E., and the large 

 rock-masses in some of the neighbouring hills appear also to dip 

 in that direction. The subjoined figure (fig. 7) may give some 

 imperfect idea of the contortions in the beds in one part of these 

 quarries. The borders, represented as seen in the quarry, are nearly 

 in the line of cleavage. 



Fig. 7. — Contortions in Slate, Aberuchil Quarry. 



On the whole, therefore, I conclude that the chief division -planes 

 seen in the slates near Comrie are those of cleavage, and not of 

 deposition. The dip of this cleavage is predominantly N. 10° "W., 

 and the direction W. 10° S. to E. 10° N., and thus oblique to the 

 general course of the slate on the south flank of the Grampians. 

 The strike of the beds, as marked by the other division-planes, 

 N. 30° W., with a S.W., or more rarely N.E. dip, is still less conform- 

 able to the usual course of the slates. This deviation may perhaps 

 be caused by the intrusion of the Glen Lednock syenite, though, as 

 stated, it appears to have exercised no very marked influence on the 

 position of the slates *. 



12. Mica-slate of Loch Earn. — The relation of the clay-slate to the 

 mica-slate formation is not very clearly shown in any of the sections 

 I examined in Strath Earn. Mica-slate appears near St. Eillans 

 Church, but soon again gives place, higher in the valley, to clay- 

 slate and greywacke. This mica- slate, as already noted, besides a 

 very distinct foliation, much twisted and contorted, as is common 

 in mica-slate, shows also other division-planes parallel to the bed- 

 ding of the clay-slates. Mica-slate predominates along the north 

 bank of Loch Earn, but the rocks are much concealed by wood and 

 vegetation, and the strata greatly disturbed, probably by intrusive 

 greenstones. So irregular are the beds, that at first it seems almost 

 impossible to discover any dominant dip or direction. On further 

 examination, however, the direction E. 22° IN", comes out as the 

 average result of the whole; or, excluding a few dips nearly at 

 right angles to the others, a mean direction of E. 40° N., with a 



* The strike of these beds is thus parallel to that of the gneiss on the N.W. 

 coast of Ross and Sutherland, which it has been supposed to characterize as an 

 older group ; but see my paper, Quart. Journ. Geol. Soc. vol. xvii. p. 110. 



