THE HIGHLAND BORDER ROCKS OF THE ABERFOYLE DISTRICT. 
177 
Report for 1893 states that though these rocks had been mapped for many miles, no 
clue as to their age had yet been obtained. During that year Mr J. R. Dakyns in 
the Aberfoyle district and Mr George Barrow in Forfarshire and Kincardineshire had 
noted the occurrence of graphitic schists associated with cherts and green igneous 
rocks. Mr Peach detected Radiolaria in some of the cherts. Messrs Peach and 
Horne were struck with the close resemblance in lithological characters and general 
sequence of these Border Rocks with the Lower Silurian Series in the Southern 
Uplands of Scotland. “The association of a zone of green basic eruptive rock with 
the graphitic schist and red and black radiolaria-bearing cherts, so exactly a counter- 
part of the Arenig succession in the South of Scotland, affords a strong presumption 
that Lower Silurian rocks are included along the Highland Border.” * 
In the Aberfoyle area Mr Dakyns noted that the zone of black shales and cherts 
was associated with bands of greywacke, sandstones, and hornblende schists. It is 
further stated that “ these strata along their northern margin are apparently (but 
perhaps deceptively) overlain by a group of massive greywackes, sometimes pebbly, 
with occasional bands of purple slate.” t 
The exposures in Forfarshire and Kincardineshire were described more fully by 
Mr Barrow in a paper contributed to the Geological Society of London in 1903,J and 
again in the Proceedings of the Geologists Association for the year 1912. He 
arranges the rocks in two divisions : 1. The Jasper and Green Rock Series ; 2. The 
Margie Series, resting unconformably upon the former. He holds that everywhere 
these Highland Border Rocks are separated from the rocks to the north by a plane 
of overthrust, and that while in the Highland Rocks all traces of clastic micas have 
disappeared, in the Border Rocks the original sedimentary micas can still be detected 
under the microscope. 
It is understood that Mr Barrow now regards these Highland Border Rocks as 
pre-Cambrian in age though younger than the Highland Schists. § 
The Annual Report of the Geological Survey for 1895 || gives a brief account of 
Mr Clough’s work along the belt between Aberfoyle and Loch Lomond. It states 
that “ notwithstanding his detailed mapping we are still unable to form a definite 
conclusion as to the structure of this difficult piece of ground.” With some hesita- 
tion Mr Clough inclined to the belief that there are indications of a strati- 
graphical break between the black shales and cherts- and what are termed “ the 
Aberfoyle Grits,” which apparently include grits associated with the Border Rocks 
as well as what are now called Leny Grits. It is even suggested in the Report that 
“the Aberfoyle Grits” might be grouped with the shales and cherts as probably of 
Lower Silurian age, though it is admitted that this would only shift the difficulty 
* Annual Report Geol. Survey for 1893, p. 266. f Ibid. 
\ Barrow, “ On the Occurrence of Silurian (?) Rocks in Forfarshire and Kincardineshire along the Eastern 
Border of the Highlands,” Quart. Journ. Geol. Soc., vol. lvii, p. 328, 1901. 
§ Gregory, “ Problems of the South-western Highlands,” Trans. Geol. Soc. Glasgow, vol. xiv, pt. 1, p. 15, 1910, 
|| Ann. Rep. Geol. Survey for 1895, p. 26, 
