THE HIGHLAND BORDER ROCKS OF THE ABEREOYLE DISTRICT. 
199 
igneous structure is in part preserved (Plate IV, fig. 4). The lath-shaped felspars 
show also an apparent flow structure, which may, however, be due to movement. 
Like the sheared pillow lavas of Argyllshire,* too, the rocks are very rich in chlorite 
and carbonates. These textural and mineralogical peculiarities lead us to conclude 
that the chlorite schists represent effusive spilites, just as the hornblende schists are 
the equivalents of intrusive diabases and gabbros. 
Intervening between the above calc-chlorite schists and the hornblende schists 
of the Corrie Burn section there is a belt of muscovite-chlorite schists. These may 
be readily recognised in the field from the development of silvery micas on the 
foliation planes. They are traversed by an anastomosing network of veins of 
ferruginous dolomite, and in all probability represent a zone in which the calc- 
chlorite schists have undergone subsequent shearing. 
Schists of Sedimentary Origin. 
As will be seen from the accompanying map, the metamorphosed sediments occur 
as an interrupted band along the northern margin of the hornblende schist complex. 
In the western part of the area they are found also within the belt occupied by the 
latter. The best and most continuous section is exposed by the roadside just 
beyond the course of the Old Loch Katrine aqueduct. 
The sediments, like the associated igneous rocks, have undergone almost com- 
plete reconstruction. The dominating type perhaps is a black or dark-coloured, 
heavy crystalline quartz schist, consisting of a granulitic aggregate of quartz, iron 
oxides, and muscovite (Plate IV, fig. 5). The muscovite and iron oxides are often 
almost completely confined to definite layers, and the rocks take on a banded 
texture, lighter-coloured quartzose laminae alternating with darker bands. Corru- 
gated folding is well seen on weathered surfaces. 
The quartz schists sometimes contain partially digested fragments of chert, and 
pass occasionally into brecciated cherts showing little trace of reconstruction. It is 
clear, therefore, that they represent metamorphosed highly siliceous sediments. We 
may note, however, that they are often so rich in iron ores as to suggest that they 
have been derived, not from the muddy cherts which overlie the local spilites, but 
from a zone of iron cherts, probably at a lower horizon. Such iron cherts are well 
developed as interbedded layers in the spilites between Craigeven Bay and Garron 
Point on the Kincardineshire coast. 
Careful search was made for minerals indicative of contact metamorphism. 
Biotite occasionally accompanies the muscovite, but it is not of the type found in 
contact-altered rocks. Not infrequently, however, knots, the mineralogical character 
of which is uncertain, make their appearance, and in two slides they are seen to 
contain relics of garnet. The knots, as a rule, have been compressed into flattened 
* Mem. Geol. Survey : Geology of Knapdale, etc., p. 88, 1911. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART I (NO. 9). 
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