424 
BATHYMETRICAL SURVEY OF 
(1) Dark Grey Mud. 
The eleven samples of this mud are homogeneous and coherent when 
dry. A typical sample from 740 feet, opposite Urquhart bay, has the 
following mineralogical composition : — 
Minerals (25 per cent.), mean diameter OH millimetre. Of these 
particles quartz is the most abundant, often coloured red by a coating of 
iron oxide. Orthoclase, chloritic minerals, and limonite are also present. 
FDie washings (75 per cent.), composed of vegetable matter (15*89 
per cent.) and clayey matter with fine mineral particles and limonitic 
matter (59*11 per cent.). 
Chemical Composition. 
Total Silica . . . 
Ferric oxide ... 
Alumina 
Lime 
Magnesia 
Loss on ignition 
99*90 
12*27 
9*38 
tr. 
tr. 
15*89 
The high percentage of silica is due to the great proportion of quartz. 
The alumina is due to the presence of felspar and clayey matter. The 
defect 0*10 per cent, is probably due to the fact that the alkalies have 
not been estimated. 
(2) F errugineous Mud. 
This type of sediment is limited to the part of the Invermoriston 
deep basin opposite Horseshoe craig. One of the samples was found 
after examination to be composed of : — 
Minerals (29 per cent.), essentially represented by ferrugineous 
grains, which are accompanied by quartz, orthoclase, chlorite, and 
hornblende. These mineral particles are angular, and have a mean 
diameter of 0*12 millimetre. 
Fine washings (71 per cent.), composed of vegetable matter (18*46 
per cent.), and fine minerals (52*54 per cent.) belonging to the species 
mentioned above. 
Total silica 
Chemical Composition. 
37-44 
Ferric oxide ... 
24*48 
Alumina 
15*12 
Lime 
2*16 
Magnesia 
1*80 
Loss on ignition 
18*46 
99*46 
The defect 0*54 per cent, is to be sought for in the alkalies. 
