P. MACNAIR ON ROCKS OF HIGHLAND PERTHSHIRE. 179 
along the marginal Highlands of Kincardineshire by a microscopic 
examination of their micas. In the slates and phyllites belonging to 
the crystalline rocks of the Highlands the micas show evidence^ of 
re-crystallisation, while in the unaltered band of supposed Siluiian 
age they still retain their original clastic appearance. Referring in 
the same Report to the work of Mr. Clough at Callander, Sir A. 
Geikie says they are still unable to come to any conclusion which 
will enable them to separate out the presumably Lower Silurian rocks 
from the phyllites and grits of the marginal Highlands, for similar 
reasons to those which we have already cited in our extracts from 
last year’s Report. 
Last summer we had an opportunity of re-examining these rocks 
at the following localities,—Bridge of Cally, Hunkeld, Callander, 
Aberfoyle, and Dunoon,—for the purpose of seeing how far these 
later views of the Survey could be maintained. We think that there 
can be no doubt that the whole of this marginal belt of grits, grey- 
wackes, and slates, extending from Stonehaven on the north-east to 
the Firth of Clyde on the south-west, belongs to the same group 
of rocks. The dominant north-east and south-west strike of the 
rocks forming the southern Grampians is one of their most character¬ 
istic features. Local variations in the strike undoubtedly occur, 
but, when we consider the extreme plication and twisting to which 
these rocks have been subjected, this is not to be wondered at. 
A comparison of the lithological characters of the rocks at different 
localities along the margin of the Highlands also points to their all 
belonging to the same group or horizon, though at some points they 
show evidence of more extreme metamorphism than at others. Thus 
at Bridge of Cally, Dunkeld, and Callander they appear to be less 
altered than at Dunoon and elsewhere on the Firth of Clyde, where 
the slates pass into true phyllites and the grits become more 
mineralised. We also think there can be no doubt, from what we 
have seen, that the grits, slates, and phyllites are conformably 
interstratified with each other, and belong to one stratigraphical 
group. At Dunkeld and Birnam, in the quarries, this interbedding 
of the arenaceous and argillaceous types is well seen. To the north 
they pass upwards into the arenaceous group, as seen to the north 
of the Loch of the Lows, while to the south, as at Forneth, this 
areno-argillaceous zone passes downwards into beds of pure grit. 
Again, at Callander and Aberfoyle a similar lithological succession 
may be seen, namely, shales with bands of grit passing both up¬ 
wards and downwards into pure grits. 
We now pass on to consider briefly the structure of this marginal 
belt of grits, greywackes, and phyllites, and the problem of their 
relationship to the more crystalline rocks. In Perthshire and the 
