Augen Gneiss and Moine Sediments of Ross-shire. 348 
The unsheared hornfels is never found more than a mile from the 
eranite margin. Round the granite the ‘aureole’ is not continuous, 
but is broken at certain places by the intervention of shearing. It 
should also be stated that at the south-west margin of the Carn 
Chuinneag mass and around most of the Inchbae mass the granite is in 
contact with psammitic schists, in which little evidence of contact 
alteration has been detected. 
In the Moine rocks, at a distance of a mile or more from the granite, 
there is great uniformity in the character of the foliation. The 
explanation that suggests itself is that these sediments were soft and 
readily yielded to folding, while free internal movement gave full play 
to the forces of recrystallization by which schists are produced. Some 
parts of the granite mass and many parts of the hornfelsed rocks of 
the aureole were, on the other hand, more resistant to folding, and 
considerable blocks of them moved en masse and retained their original 
structures, while in adjacent portions there was much internal shearing, 
with consequent production of cataclastic structures and development 
of schistosity. 
The hornfels has been sheared decidedly less than the granite, and 
its original characters are in better preservation. The physical 
structure of these rocks seems to give them a remarkable cohesion and 
toughness under the conditions of pressure and folding that occasion 
metamorphism of the ‘regional’ type. This is no doubt due to their 
finely crystalline state, the perfect interlocking of their minerals, 
which, having grown in a solid mass, often enclose one another; and ° 
especially to the development of authigenic new felspar in the 
interstices between the sand-grains, cementing them together into 
a very rigid mass. It seems clear, from the facts known, both in 
Kaster Ross, Ben Vuroch, Knapdale, etc. (see p. 341), that fine hornfelses 
are rocks from which schists are not readily formed. 
Mr. Barrow has advanced the hypothesis’ that the Ben Vuroch 
hornfelses were preserved because they were sheltered behind a large 
resistant mass of granite. But at Carn Chuinneag the facts show 
clearly that the hornfels is a much more resistant rock than the 
granite; moreover, hornfelses occur on all sides of the granite, not 
only on the north-west, which was the lee side, but also on the south- 
east, from which the pressures came. 
It is obvious that the sediments and horntfelses were solid when 
they were sheared and converted into mica schists, and the phenomena 
observable at the junction of granite and hornfels render it equally 
clear that the igneous rocks also were thor oughly crystallized before 
the movements began. If the hornfels at the junction is quite free 
from foliation—a rare condition—the granite also shows its igneous 
structures well; but if the hornfels has passed into a mica schist the 
igneous rock is always gneissose. This is especially noticeable in the 
fine granite veins that penetrate the schists; they cut the bedding 
clearly in the banded hornfelses, and in the mica schists they have 
a foliation that corresponds with that of the schists and often crosses 
the veins from side to side. 
1 «The Geology of the Country round Blair Atholl, Pitlochry, and Aberfeldy” : 
Mem. Geol. Surv., 1905, p. 93. 
