THE FRESH-WATER LOCHS OF SCOTLAND. 
235 
One of the most remarkable geological features of the Loch Maree 
district is the evidence relating to the topography of the primeval land 
surface on which the Torridonian sediments were laid down. Between 
the head of Loch Maree and Strath na Sheallag, where the overlying red 
sandstone has been partly removed by denudation, it is possible to trace 
the direction of the old valleys and the orientation of the ancient 
peaks. On the eastern slope of Ben Slioch, near Glen Fhasaigh, the 
observer may climb one of these hills, which rises to a height of 
about 2000 feet in the midst of the Torridon Sandstone, and trace the 
alternation of breccia and sandstone filling the ancient valley. Similar 
evidence is obtained further north in the mountainous region near the 
head of Glen na Muic. Where these deeply-eroded valleys are pre- 
served, breccias of local origin frequently appear at the base of the 
Torridon Sandstone. In the Loch Maree district this formation has 
been subdivided into three groups : a lower, consisting of epidotic grits, 
dark and grey shales, with calcareous bands and red sandstones; a 
middle, composed of a great thickness of false-bedded grits and sand- 
stones with scattered pebbles; an upper, comprising chocolate-coloured 
sandstones, micaceous flags, with dark shales and calcareous bands. 
The members of the lower group are well displayed in the district near 
Talladale and Slattadale, on the south-west shore of Loch Maree ; those 
of the middle group are typically developed in the mountains round 
Loch Torridon, from which district this system takes its name, while 
the upper group appears in the islands north of Gruinard. Throughout 
this region this formation {t on map) reaches a vast thickness, for on 
the shores of Loch Torridon it rises on Liathach from the sea-level to 
a height of over 3000 feet. In the mountains between Slioch and An 
Teallach these sandstones have a gentle dip towards the south-east ; 
in the Torridon district they are nearly horizontal, while further south 
they form a low arch. 
As indicated in our previous notes on the geology of the Assynt 
district, the Torridon Sandstone is separated from the overlying 
quartzites by an unconformability, which in some parts of the Loch 
Maree area is not so prominent as in Assynt. On An Teallach in 
the Dundonnell forest and southwards towards Mullach Coire Mhic 
Fhearchair, the Cambrian quartzites are inclined at a higher angle 
to the south-east than the Torridon Sandstone. In the area lying to 
the west of the post-Cambrian displacements we find at various localities 
the normal Cambrian sequence in ascending order — 1, the basal 
quartzites (a} on map); 2, the pipe-rock {a^) ; 3, the Fucoid beds (a^). 
This sequence is displayed in the Dundonnell forest, on the western 
slope of Ben a’ Vuinie near Kinlochewe, on the west declivity of Meall 
a’ Ghuibhais south of Loch Maree, and on Beinn Eighe. Within these 
limits the Fucoid beds have yielded at several localities well-preserved 
trilobites and other organic remains of Lower Cambrian age. The 
