File:The Quarterly journal of the Geological Society of London (12645856563).jpg

194
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