THE HIGHLAND BORDER ROCKS OF THE ABERFOYLE DISTRICT. 
179 
Professor J. W. Gregory in a Presidential Address to the Geological Society of 
Glasgow, 1910, on “The Problems of the South-Western Highlands,” discusses the 
age, origin, and relations of the Border Rocks. While admitting the uncertainty 
that prevails, he puts forward the view that “ they are either the uppermost part of 
the series which includes the Aberfoyle slates and grits, or a younger series, 
separated from the Aberfoyle Series by a still doubtful unconformity and by the 
absence of cherts from the Aberfoyle Series.” * 
Some of the bedded rocks of this marginal belt are so little altered that it was 
expected that a careful search would eventually result in the discovery of fossils, and 
so shed fresh light on the question of their age. This expectation was fulfilled, and 
in 1911 Dr Campbell recorded the presence of brachiopods, phyllocarid crustaceans, 
and worm-like tubes in cherty shales and jaspers which he found associated with 
spilitic lavas at Stonehaven immediately south of the Highland Boundary Fault.! 
In the following year a somewhat similar suite of fossils was found by Dr Jehu 
in cherty beds belonging to the Border Rocks near Aberfoyle, but here the belt lies 
on the north-west side of the Highland Boundary Fault. + Subsequently a grapto- 
litic form was recognised amongst the collection of fossils obtained at Aberfoyle, and 
a description of that form by Miss Gertrude Elles is given in a paper by Dr Jehu 
on “ The Highland Border Series, near Aberfoyle,” which appeared in the Geological 
Magazine in 1914. These discoveries at Stonehaven and Aberfoyle afforded strong 
evidence for the Upper Cambrian or Lower Ordovician age of the Black Shale and 
Chert Series. 
III. General Account of the Stratigraphy of the Highland Border Rocks. 
The Highland Border Rocks in the Aberfoyle district emerge from under a 
covering of Upper Old Red Sandstone due north of Gualann, and extend in a north- 
easterly direction for seven miles to a distance of a mile north-east of the village of 
Aberfoyle. They form a belt of narrow but varying width between the Lower Old 
Red Sandstone on the south-east and the Leny Grits on the north-west. The belt 
is widest near Gualann, where the width exposed is about half a mile ; as traced 
north-eastwards it narrows, until between Arndrum and Dungarrow it is reduced 
to little over 100 yards, after which it swells out to from 300 to 400 yards, narrowing 
a little again as we approach the village, where it is lost under alluvium. North-east 
of Aberfoyle the belt is extremely narrow (under 100 yards), and it disappears just 
beyond the old limestone quarry above Upper Dounans. 
The junction with the Leny Grits appears to be everywhere a line of dislocation ; 
that with the main area of the Lower Old Red Sandstone is again a fault — the High- 
land Boundary Fault — but in the western part of the belt, beds belonging to that 
formation have been faulted down to the north-west of the main boundary. 
* Trans Geol. Soc. Glasgow, vol. xiv, pt. 1, p. 16, 1910. 
f Geol. Mag., dec. v, vol. viii, p. 63, 1911 ; Trans. Roy. Soc. Edin., vol. xlviii, pt. 4, No. 34, p. 927, 1913. 
1 Nature , vol. lxxxix, p. 347, 1912 ; Rep. Brit. Assoc., p. 463, 1912. 
