THE FRE8H- 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 Torridoniaii 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 Fh'asaigh, 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 Dundomiell 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 1 on map); 2, the pipe-rock (a 2 ); 3, the Fucoid beds (a 3 ). 

 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 



