THE FRESH- WATER LOCHS OF SCOTLAND. 257 
intervals, and the percentages to the total area of the loch, are as 
follows : — 
0 to 25 feet 
21 -2 acres 
58 T per cent. 
25 ,, 50 ,, 
6-9 „ 
19-0 
50 „ 75 „ 
5-1 „ 
14*1 
Over 75 ,, 
3-2 „ 
8-8 
36-4 „ 
100-0 
Temperature Observations.- 
—The surface 
temperature observed in 
Loch na Creige Duibhe on the date of the 
survey was 57°-4, in the 
stream between the two lochs 
57°T, and in 
Loch Mama 56°-5. The 
following serial temperatures 
were taken in 
the deepest part of Loch 
na Creige Duibhe at 4.45 p.m 
. on July 11, 
1902: — 
Surface ... 
57°-4Fahr. 
10 feet ... 
57°-4 „ 
‘20 „ 
57°-4 „ 
30 ,, 
53°-0 „ 
50 „ 
50° -8 ,, 
75 „ 
49°-2 ,, 
90 ., 
48°-8 ,, 
This series shows a constant temperature down to 20 feet, then a 
fall of 4°-4 between 20 and 30 feet, and a further fall of 2°*2 between 
30 and 50 feet, the extreme range of temperature from surface to bottom 
being 8°' 6. 
The details regarding the lochs in the Shiel, Ailort, and nan Uamh 
basins are collected together in the table on p. 258 for convenience of 
reference and comparison. From this table it will be seen that in the 
six lochs under consideration nearly 1200 soundings were taken, and 
that the aggregate area of the water-surface is over 8J square miles, so 
that the average number of soundings per square mile of surface is 139. 
The aggregate volume of water contained in the lochs is estimated at 
about 29,000 millions of cubic feet. The area drained by these lochs 
is nearly 100 square miles, or 11| times the area of the lochs. 
Geology of the Loch Shiel Catchment Basin . — Though the basin of 
Loch Shiel has not been surveyed by the Geological Survey, we under- 
stand that certain members of the staff have examined the rock cuttings 
on the line of railway between Loch Eil and Kinlochailort. The rocks 
exposed in these cuttings consist of muscovite-biotite gneiss and flaggy 
mica-schists, which are included in the Moine series of crystalline 
schists by the Geological Survey. The general strike of these strata 
is north-east and south-west, so that in all likelihood they are continued 
to the south-west along both sides of Loch Shiel. This conclusion is 
supported by the fact that on the lofty watershed between Loch Shiel 
s 
