P. MACNAIR ON ROCKS OF HIGHLAND PERTHSHIRE. 17I 
remarks upon this group :—“ In this section, though the beds dip at 
much higher angles, the relation of the formations is still the same 
as on the Gareloch. The mica-slates dipping south are covered by 
an upper group of blue and green clay-slates and greywackes. The 
two formations also appear to be conformable, and the direction of 
the beds varies little from east and west by compass.” 
The next section is in Perthshire, namely at Callander and the 
Pass of Leny. Here again a similar series of rocks to that seen in 
the Ben Lomond section is described, but with this important 
difference, that they are now seen all to dip inwards upon the mountain 
chain. A detailed account is given in his paper, with exceedingly 
accurate measurements of the dip, of the beds of clay-slate, grits, 
greywackes, limestones and mica-schists of Callander, the Pass of Leny, 
and Ben Ledi, and they are all shown to dip towards the north-west 
at greatly varying angles. With regard to this reversal of the dip he 
makes the following remarks ;—“ The first general impression is that 
there is here a continuous series of beds dipping regularly to the 
north, the one below the other; in that case the greywackes to the 
south would be the lowest and oldest deposit, followed by clay-slate, 
and this by mica-slate, as the upper and newest formation. This 
is, of course, exactly the opposite order from that noted in the 
former sections, and cannot therefore be adopted without some con¬ 
sideration.” 
The next localities with which Nicol deals are those of Comrie, 
Strathearn, Loch Earn, Loch Tay, Dunkeld, and Blairgowrie. It is 
entirely unnecessary that we should here enter into a detailed account 
of his description of these sections. It will be sufficient for our 
purpose merely to indicate their larger features, and to show how this 
influenced his conclusion regarding the structure of the southern 
Crampians. At Comrie he notes the occurrence of greywackes and 
clay-slates exposed in the gorge of the Lednock, and gives their dip 
as averaging about 70 deg. north, 10 deg. west. He, however, after¬ 
wards refers these divisional planes to foliation, and not to planes of 
deposition, and he also believed that there is an uncomformity 
between the clay-slates and mica-schists at this point. At Dunkeld 
and Blairgowrie he shows that the clay-slates and greyw^ackes dip 
towards the north-west, and thus apparently under the main mass of 
the Crampians, which dip they retain onwards through the eastern 
Crampians to Stonehaven. 
Passing now to a consideration of the general relationship of the 
clay-slates and mica-schists along the margin of the Highlands, as seen 
in these sections just described, he shows that in Bute and the 
Careloch both the clay-slates and mica-schists dip to the south-east 
and are evidently perfectly conformable. At Loch Lomond he shows 
