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 IV in section) is the most easterly of the great 



