I 70 TRANSACTIONS-PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
and schists. How thoroughly the true structure of the southern 
Grampians escaped their notice, and how much they were under the 
influence of this preconceived succession, will be better understood 
when we come to consider NicoPs paper, which was published 
shortly afterwards. Mention may here simply be made of the paper by 
Harkness^ on the structure of the Southern Highlands, as it follows 
much the same lines as that of Murchison and Geikie, adopting 
as he did their theory of succession. In all his sections, including 
those from Callander to Loch Earn, from Loch Earn to Loch Tay, 
from Loch Tay to Glenlyon, and from Dunkeld to Blair-Atholl and 
Ben-y-Ghloe, he recognises the same succession of quartzites and 
limestones, overlaid by a great series of schists. 
We now proceed to examine the famous paper of James Nicol,’^ 
published in 1863, on the Geological Structure of the Southern Gram¬ 
pians. Geikie, Murchison, and Harkness, as we have already seen, 
had published their papers, which were based on a hypothetical 
succession supposed to have been discovered in the north-west of 
Sutherlandshire. Nicol, however, was free and untrammelled by 
any such theory, if we except, perhaps, a tendency towards the 
Wernerian doctrine of the succession of the crystalline rocks. At 
the outset of his paper, he states the object of it, which was to examine 
the relations to each other of each of the three great formations,— 
the clay-slate, the mica-slate, and the gneiss,—which, with some 
subordinate groups, such as quartz-rock and the chlorite series of 
Macculloch, had hitherto been regarded as composing the chief 
stratified masses in the Scottish Highlands. NicoPs method was 
to begin at the south-west end of the Grampians, and, proceeding 
towards the north-east, he made a series of sections at different points 
across the Highlands from the verge where they abut against the Old 
Red Sandstone, explaining their principal mineral and stratigraphical 
features, and comparing with one another the results arrived at in the 
various sections. He first of all notes the position of the clay-slates 
in the Island of Bute, showing that they dip towards the south-east 
at angles varying from 20 deg. to 60 deg., and appear to be overlaid 
by the mica-schists of the interior. In his next section, that of 
Loch Long and the Gareloch, he notes a similar dip of the clay-slates 
towards the south-east at Roseneath at an angle of 40 deg., these in 
their turn being conformably overlaid by the mica-schists and grey- 
wackes. 
Passing now still further towards the east, the next locality 
which he describes is that from Ben Lomond to Balloch. In this 
section he again notes the occurrence of the clay-slates, greywackes, 
and mica-schists, the whole series being apparently conformable, and 
dipping at high angles towards the south-east. He makes the following 
