182 
BATHYMETRICAL SURVEY OF 
of Glas Bheinn, we encounter the Glencoul thrust (T in section), the 
first of the series of powerful displacements in the Assynt region. 
Overlying this plane there is a mass of Archaean gneiss, covered un- 
conformably by both divisions of the Cambrian quartzite with their 
characteristic igneous sills. Along the western slope of Glas Bheinn 
the quartzites are inverted, but the sequence can be interpreted by 
means of the subdivisions of the pipe-rock, based on the characters 
of the worm-casts from which that zone derives its name. Eastwards 
we find the Poll an Droighinn thrust (T' in section), and still further 
east, beyond Loch Cuaran, the Ben More thrust (T" in section). By 
means of these displacements, additional slices of the Archaean floor 
with the overlying Cambrian sediments and intrusive sheets have been 
driven westwards like the materials above the Glencoe thrust-plane. 
The visitor to that district may study the relations of the Ben More 
thrust-plane and the materials above and below it on the southern 
slope of that mountain in the Beallach (pass) of Coniveall. A con- 
siderable thickness of Torridon Sandstone there intervenes between the 
Archaean gneiss and the Cambrian quartzites, which does not appear 
in the line of section further north between Quinag and the river 
Cassley. Indeed,' on Ben More Assynt, the double unconformability 
of the Cambrian quartzite on the Torridon Sandstone and the Archaean 
gneiss is well seen. In the deep corries on the south side of Ben More 
Assynt, the observer finds a great development of the Lewisian gneiss 
with its dykes of epidiorite, forming a rocky slope about 1000 feet high, 
which presents many of the characteristic features of the old Archaean 
floor west of Quinag. Eastwards again, towards the river Cassley, 
beyond the Cambrian quartzites, fucoid beds, serpulite grit, and 
limestone, appears the Moine thrust, which brings forward a great 
succession of crystalline schists (Moine schists, M in section), to which 
reference will immediately be made. 
One of the romantic features of the geology of the Assynt region is 
the isolation by denudation of materials overlying the Ben More thrust- 
plane. Two outliers of this nature occur west of Breabag, on Beinn 
nan Cnaimhseag and Beinn an Fhuarain, where slices of Torridon 
Sandstone and basal Cambrian quartzite overlie Cambrian limestone. 
Indeed, in the more southerly mass (see map) a small core of Archaean 
gneiss with an intrusive dyke of epidiorite appears in the midst of the 
younger formations. These outliers clearly point to the original 
westward extension of the materials overlying the Ben More thrust- 
plane having been separated from the main mass east of Breabag by 
prolonged denudation. It is worthy of note that, though the structure 
of the disturbed area in the mountainous region of Assynt is highly 
complicated, still by the zonal mapping of the various rock groups, 
the relations of the displaced materials can be satisfactorily determined. 
The Moine thrust (T^'" in section) is the most easterly of the great 
