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 0*1 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. 

 Fine 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 ... .'. 62-36 



Ferric oxide 12*27 



Alumina 9'38 



Lime tr. 



Magnesia tr. 



Loss on ignition 15*89 



99-90 



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) Ferrugineous 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. 



Chemical Composition. 



Total silica 3744 



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. 



