178 
BATHYMETRICAL SURVEY OF 
Notes on the Geology of the Assynt District. 
By B. N. Peach, LL.D., F.B.S., and J. Horne, LL.D., F.B.S. With 
Geological Map (Plate XLII.). Published by permission of the 
Director of the Geological Survey. 
From a geological point of view, the Assynt district is one of 
the most interesting in the north-west Highlands. The various rock 
formations which enter into the geological structure of the region are 
there splendidly developed, and the evidence in proof of those great 
terrestrial displacements of post-Cambrian date may be studied in 
detail in the mountainous region that runs southward from Glas Bheinn 
by Ben More Assynt and Breabag to the Cromalt Hills. 
Beginning with the Archaean gneisses on map), which may be said 
to form the foundation-stones of that region, they are unquestionably 
older than the succeeding great development of Torridon Sandstone 
and overlying Cambrian strata. On referring to the geological map, 
it will be seen that they occupy a belt of ground from 6 to 9 miles broad, 
extending along the western coast-line between Enard Bay and Stoer, 
thence inland to the base of the grand escarpment of Torridon Sand- 
stone that stretches southwards from Quinag to the Coigach mountains. 
These crystalline gneisses give rise to a type of scenery that is charac- 
teristic of a large part of the western seaboard of Sutherland and Boss, 
which seems to be typical of Archaean areas. Bare rounded knolls and 
bosses of grey gneiss follow each other in endless succession, and in the 
hollows there are numerous pools and lochs occupying rock-basins. The 
whole tract occupied by these crystalline gneisses is singularly destitute 
of drift. The rocky knolls do not rise much above one general level, 
which does not as a rule exceed a few hundred feet in height, save near 
the base of Quinag, Canisp, and Suilven, where the elevation of the old 
gneiss plateau is about 1000 or 1250 feet. 
The Archaean rocks of the Assynt district, west of the great 
escarpment of Torridon Sandstone, consist largely of pyroxene gneisses 
and ultrabasic rocks (pyroxenites and hornblendites), which still show 
in a marked degree their original characters. Their behaviour in the 
field and their appearance under the microscope have led to the 
conclusion that they have affinities with plutonic igneous products. 
All over that district, where the original characters have not been 
effaced by later mechanical stresses, it is possible to trace the imperfect 
separation of the ferro-magnesian from the quartzo-felspathic con- 
stituents, the gradual development of mineral banding, and the net-like 
ramifications of acid veins (pegmatite) in the massive gneiss. Whatever 
be the origin of the mineral banding in these Archaean gneisses, it is 
