22 BATHYMETRICAL SURVEY OF 



From the table on previous page it will be seen that in the thirteen 

 lochs over 3800 soundings were taken, and that the aggregate area of 

 water-surface is about 17 square miles, so that the average number of 

 soundings per square mile is 225. The aggregate volume of water 

 contained in the lochs is estimated at 36,543 millions of cubic feet. The 

 area drained by these lochs is about 228 square miles, or about 13 times 

 the area of the lochs. 



Deposits. As a general rule, the materials forming the deposits in 

 these fresh-water lochs become finer grained the further from the shore 

 and the deeper the water. Off the mouths of rivers and burns there is 

 frequently a considerable accumulation of gravel and fine sand, extend- 

 ing for some distance into the lake and occasionally reaching rather 

 deep water. Large stones, gravel, and sand are usually found all round 

 the shores within the limits of wave-action. The height and length of 

 the waves, and the depth to which wave-action extends, depend on the 

 size and depth of the loch. 



The central parts of the lochs are occupied by a fine impalpable mud, 

 which is found in its most characteristic form in the greater depths far 

 from shore ; it is usually of a light or dark brown colour, and sometimes 

 there are indications of different-coloured layers. The usual mineral 

 species are quartz, felspars, black and white mica, amphibole, pyroxene, 

 magnetite, garnets, &c. Chemical analysis showed that these fine muds 

 contained no appreciable calcareous matter, but traces of sulphuretted 

 hydrogen were always present. The loss on ignition after drying at 

 90 C., due to organic matter and combined water, varied from 13 to 

 26 per cent. Diatoms were observed in nearly all the samples, and 

 vegetable fibre was usually present in greater or less abundance. 



The samples from the deepest part of Loch Ka.trine were brownish, 

 fine-grained homogeneous muds, with glittering mica-flakes, consisting 

 principally (50 to 70 per cent.) of angular mineral particles exceeding 

 0-05 mm. in diameter, the mean diameter being about 0-15 mm., with 

 clayey and vegetable matter, and many minute mineral particles less 

 than 0'05 mm. in diameter. A few diatoms were observed, and one 

 sample, after drying at 90 C., gave 19' 91 per cent, loss on ignition. 



The mud from the deepest part of Loch Achray was of a grey-brown 

 colour, containing much vegetable and clayey matter, the mineral 

 particles exceeding 0'05 mm. in diameter making up probably 30 or 40 

 per cent, of the whole deposit. Some fine diatoms were observed, and 

 the loss on ignition, after drying at 90 C., amounted to 12'84 per cent. 



The mud from a depth of 102 feet in Loch Vennachar was yellowish- 

 brown in colour, containing about 20 per cent, of mineral particles 

 with a mean diameter of O'l mm., but principally made up of 

 amorphous clayey matter with vegetable matter, and many minute 

 mineral particles less than 0'05 mm. in diameter. There were a few 



