THE FRESH- WATER LOCHS OF SCOTLAND. 233 



when dry, and when wet plastic and creamy, not unlike cocoa and milk 

 of a pink brown colour. The material is made up of probably 90 per 

 cent, of clayey matter with minute mineral particles less than O05 mm. 

 in diameter, the remaining 10 per cent, consisting of mineral particles 

 with a mean diameter of 0'15 mm. Quartz is the principal mineral 

 species, but small grains of pink microcline-felspar are very abundant, 

 and it is apparently to this mineral that the pink colour of the deposit 

 is due; the microcline shows cross-hatching, and is much kaolinized. 

 The washed mineral grains have a decided pink tinge, which is, how- 

 ever, much more pronounced in the fine washings. Besides quartz and 

 felspar, white and brown mica, hornblende, garnet, and magnetite were 

 observed. There is little or no vegetable matter. 



The particulars regarding the lochs in this basin are collected 

 together in the table on p. 232 for convenience of reference and com- 

 parison. From this table it will be seen that in the fourteen lochs under 

 consideration, which cover an area of nearly 15 square miles, nearly 

 2500 soundings were taken, or an average of 167 soundings per square 

 mile of surface. The aggregate volume of water contained in the lochs 

 is estimated at 44,500 millions of cubic feet, and the area draining 

 into them is 185J square miles, or 12J times the area of the lochs. 



NOTES ON THE GEOLOGY OF THE LOCH MAREE DISTRICT. 



By B. N. PEACH, LL.D., F.R.S., and J. HORNE, LL.D., F.R.S. With 

 Geological Map (Plate LI.). Published by permission of the 

 Director of the Geological Survey. 



The Loch Maree district presents features of special geological 

 importance relating to the subdivisions of the Archaean rocks, to the 

 topography of the old pre-Torridoniaii land surface, and to the series 

 of terrestrial movements which affected the north-west Highlands in 

 post-Cambrian time. Throughout the mountainous region, stretching 

 north to Dundonnell forest and south to Achnashellach and Glen 

 Shieldaig, excellent sections are to be found showing the geological 

 structure of that region. 



The Archaean rocks (gi on map), lying to the west of the great post- 

 Cambrian displacements, occur mainly in the north-west of the area, 

 where they form a broad tract of mountainous ground between Loch 

 na Sheallag and Loch Maree, and westwards by Torrisdale to Gairloch. 

 There is also an important development of them on both sides of Loch 

 Torridon above Loch Shieldaig, and they likewise appear as inliers, 

 surrounded by Torridon Sandstone, as, for instance, on the southern 

 slope of Beinn Dearg north of Liathach. Within the territory affected 



