450 
MR. D. SHARPE ON THE ARRANGEMENT OF THE FOLIATION AND 
arches along which the foliation is perpendicular. In fact it is not always possible 
to distinguish the central axis of the arches, as the slight inclination and numerous 
waves of the foliation are most confusing to the observer near the crown of the arch. 
In some places the correspondence between the central axis of the foliation and the 
watershed of the district will be an assistance, but in many cases the axis of the arch 
of foliation will be most easily ascertained by dividing the distance between the two 
vertical boundaries. For .these reasons, in describing the geographical arrangement 
of the foliation and cleavage through the Highlands, I shall point out in most detail 
the lines on which their planes are perpendicular. 
On the Map which accompanies this paper, the direction of the vertical planes is 
marked by double lines as far as I observed them or find them recorded ; these are 
continued in double lines of dots to show the supposed continuation of the observed 
portions : the central axes are indicated by a single thick line, continued by dots in 
the same manner over the unobserved portions of country : the fainter single lines 
represent the strike of the foliation over the intervening spaces, the lines being 
closest where the dip is the steepest. Similar lines are used both for the foliation of 
the gneiss and schist, and for the cleavage of the slates, the colours on the Map in- 
dicating the rock being a sufficient distinction. It must be understood that this 
map is but a first rough attempt to lay down in a geographical form a set of pheno- 
mena which few observers have thought worth recording*, and which require long 
and patient examination before it can be completed. 
Commencing on the south of the Highlands, the first perpendicular line will be 
found about four miles north of the Highland border, following a direction not quite 
uniform, but on the whole about N. 60° E., and running partly through clay slate 
and partly through mica schist, as follows ; on the east side of Loch Lomond the 
cleavage of the slate is perpendicular at the farm of Cashel, half-way between 
Rowardennan and Balmaha, striking N. 30° E. I did not trace the course of this 
line to the west coast, but proceeding eastward, I observed it between Loch Chon 
and Loch Ard striking N. 65° E., and again a few hundred yards above the foot of 
Loch Ketterin striking N. 45° E., in both cases through slate. There are obviously 
some faults in this district which have broken the line and thrown its eastern end to 
the southAvard. In Strath Earn the boundary of the slate trends someAvhat south- 
ward of its previous course ; but this has not altered the direction of the perpendicular 
plane, which runs N. 60° E, through the mica schist one and a half mile south of St. 
Fillan’s. The line follows nearly the same direction through Perthshire without 
further disturbance, running N. 45° E. through the clay slate on the north side of 
* Macculloch often mentions the strike of the gneiss in his “ Western Isles,” but rarely gives the dip. A 
few observations on the point occur in Nicol’s useful Guide to the Geology of Scotland. The only consecutive 
series of observations which I have met with, are laid down on the geological maps of Sutherland and Banffshire 
by the late Mr. Cunningham, published in the forty-sixth and fifty-seventh numbers of the Journal of the 
Highland Society for September 1839 and June 1842 : these have been of great service to me. 
