P. MACNAIR ON ROCKS OF HIGHLAND PERTHSHIRE. l8l 
were there made to appear as if they were older than the schists of 
the interior. Taking this marginal group of arenaceous and argilla¬ 
ceous rocks as a whole we are still inclined to think that in Perth¬ 
shire we find these rocks in their normal position, and that there is 
there a perfectly conformable upward succession as shown in the 
tables already referred to, prepared by Sir A. Geikie and ourselves. 
Towards the north-east of the mountain chain, as in Perthshire, the 
north-west dip of the beds of phyllites, slates, grits, and greywackes 
indicates that these rocks form the southern limb of a deep synclinal 
trough. Traced inwards towards the north-west, they are seen 
to pass upwards into the quartz and mica-schists and limestones of 
Loch Tay and Ben Lawers, which rise to form the northern limb 
of the syncline. From a comparison of the dips it seems that the 
southern limb of the syncline formed by the phyllites and grits abut¬ 
ting against the great fault is much steeper than the northern limb, 
and, so far as we can see at present, it seems to us that in tracing this 
southern limb from north-east to south-west across the mountain 
chain it gradually becomes steeper and steeper till it folds over and 
eventually, in the Firth of Clyde and Cowal district, is made to appear 
as if it overlay the higher group of quartz-schists and limestones which 
it really underlies, as seen in Perthshire. 
Within this zone of phyllites and grits whose relationships we 
have just been discussing occur certain beds showing a much less 
altered appearance than others. As we have already seen. Sir A. 
Geikie, in his Government Reports, mentions their occurrence at 
Aberfoyle, Callander, and in the river Esk, Kincardineshire. The beds 
in the latter locality containing radiolaria have a general appearance 
which seems to link them with the Arenig rocks of the Southern 
Uplands. From this he concludes that amongst this belt of grits and 
phyllites, which evidently belong to the crystalline rocks of the High¬ 
lands, there has been interposed a group of younger rocks, probably 
of Lower Silurian age, the most continuous section of these younger 
rocks being that seen in the Keltie Water, at Callander. We have 
long been acquainted with this section, but can see no reason for 
separating these rocks out from amongst the grits and phyllites with 
which they are evidently interbedded. The following may be taken 
as the general structure, succession, and lithological characters of the 
rocks seen at Callander, the Pass of Leny, and the Keltie Water. 
Immediately to the north of the line of fault, and exposed in Kilma- 
hog quarry and the bed of the Keltie, are a series of beds of graphitic 
shale, with lenticular bands of limestone, for which the quarry was 
originally worked, and which are seen to dip at angles of 50 degrees to 
the north-west. To the north of these less altered beds a series of 
purple shales with phyllites and beds of grit and greywacke occur, 
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