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 Katrine 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 inean diameter being about 0T5 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 OT mm., but principally made up of 
amorphous clayey matter with vegetable matter, and many minute 
mineral particles less than O' 05 mm. in diameter. There were a few 
