178 
PROFESSOR T. J. JEHU AND DR ROBERT CAMPBELL ON 
further north, “for we should still have to find somewhere a southern line of 
demarcation for the schistose rocks of the Highlands.” 
The same difficulty in separating the presumably Lower Silurian belt from the 
grits and slates of the Highland Series was found by Mr Clough in the mapping of 
the exposures in the Callander district.* 
The results of the survey of the Highland Border Rocks, from Loch Lomond to 
Callander by Messrs Dakyns and Clough are shown on the Geological Survey map 
(scale one-inch to a mile), Sheet 38. The provisional correlation of these rocks with 
the Lower Silurian rocks of the Southern Uplands by Messrs Peach and Horne led 
to their being marked on the Survey maps as doubtfully Silurian. The doubt arose 
from the fact that the evidence then obtained was not regarded as sufficient to prove 
the correlation. The junction between the Border Rocks and the Leny Grits to the 
north is marked by a discontinuous line indicating an uncertain boundary. - ]; Similar 
discontinuous lines are shown on the map separating various members of the High- 
land Border Group and running in the direction of the strike of the rocks. 
A strip of rocks in North Glen Sannox, Arran, has been mapped and described by 
Mr W. Gunn as “ Arenig ” (?). This strip is shown on the Geological Survey map 
(scale one-inch to a mile), Sheet 21, and the description is given in the Survey 
Memoir on “The Geology of North Arran, South Bute, and the Cumbraes” (1903). 
The group consists of igneous rocks, both volcanic and intrusive, associated with 
black shales and thin bands of chert. In the neighbourhood of Scalpsie Bay in 
Bute exposures of epidiorite passing into hornblende schist and of serpentine are 
recorded as representing intrusions probably of Arenig age. 
In a paper, entitled “ The Lower Old Red Sandstone Rocks of the Balmaha-Aber- 
foyle Region,” communicated to the Edinburgh Geological Society in 1902, | Mr 
Alex. Du Toit discusses the origin of the gabbro-serpentine-dolomite complex which 
occurs along the line of the Highland Boundary Fault and the jaspery zone which 
can be traced along a branch of that fault further north-west. The gabbro- 
serpentine-dolomite belt is regarded as being made up of crystalline igneous, pyro- 
clastic, and sedimentary material, much altered by dolomitisation and silicification. 
The serpentine and gabbro originally formed part of a plutonic mass earlier than 
the Lower Old Red Sandstone. The jasper belt has undergone a similar series of 
changes, the original serpentine having been changed into a sheared rock, in which 
carbonates and silicates of lime and magnesia predominated, and subsequently the 
calcareous matter was replaced by silica stained with ferric oxide. 
Mr Peter Macnair in his volumes on The Geology and Scenery of the 
Grampians (1908) maintains that the Highland Border Rocks form an integral part 
of the Highland Schist Series, and he places the group at the base of that series. § 
* Ann. Rep. Geol. Survey for 1896, p. 28. f For Dr Clough’s views on this boundary line see p. 209. 
t Trans. Edin. Geol. Soc., vol. viii, pt. 3, p. 315, 1905. 
§ The Geology and Scenery of the Grampians, vol. i, pp. 41 and 194, 1908. 
