THE FRESH- WATER LOCHS OF SCOTLAND. 
427 
(5) Broivn Sand. 
To four samples of sediment dredged in 30 feet near the west coast 
of Urquhart bay we give the name of Brown Sand. One of the samples 
has the following composition : — ■ 
Minerals (69 per cent.), angular, mean diameter 0‘2 mm., mostly 
made up of quartz, coloured reddish by a coating of iron oxide. 
Decomposed mica, hornblende, and plagioclase are also represented. 
The sand contains a few small fragments of rocks, 1 to 3 millimetres in 
diameter. 
Fine washings (31 per cent.), composed of vegetable matter (4-4 
per cent.) and fine mineral particles (26-6 per cent.). There is no clayey 
matter. 
Chemical Composition. 
Total silica 
77*62 
Ferric oxide . . . 
3*60 
Alumina 
5*20 
Lime 
5-88 
Magnesia 
2-20 
Loss on ignition 
4*40 
98-90 
The alumina, lime, 
and magnesia are most likely due to the mica 
and hornblende, whilst the defect of ITO per cent, might represent the 
alkalies. 
Conclusion. 
Loch Ness includes two deep basins separated by a barrier formed by 
the delta of the Foyers river. The muds from the south-western or 
Invermoriston basin contain a large amount of vegetable or peaty 
matter, brought down the lake probably by the rivers Tarff and Oich, 
with mineral particles coming from the disintegration of the rocks, 
transported by the streams. Small concretions of peroxide of iron and 
dioxide of manganese were dredged at one station. The muds often 
gave the characteristic reaction of manganese. On the slopes the muds 
are sandy, and of a red-brown colour, due to the presence of oxide of 
iron. 
The muds from the north-eastern or Urquhart basin contain far 
less vegetable matter than those from the south-western basin, which 
may be due to the Foyers barrier retaining the vegetable matter in 
the upper basin. In the north-eastern basin the vegetable matter 
increases with the depth, which is contrary to what is observed in the 
south-western basin. Off Urquhart bay the contour-lines approach 
each other very closely, and the vegetable matter brought down the lake 
by the river Enrick is carried towards the deeper part of the basin. 
Great differences are observed in the muds from the slopes on the two 
sides of the loch. On the north-western slope we find especially a red 
