THE FRESH- WATER LOCHS OF SCOTLAND. 
147 
south-west end, and has laid down a large delta, which is covered by 
vegetation, thus contrasting with the other lake-shores, which are but 
scantily clothed with vegetation. The Black burn, entering near the 
middle of the southern shore, has not formed a delta, as it runs down a 
rocky steep slope. The maximum depth is 256 feet, while the mean 
depth is estimated at over 116 feet, and the volume of water at 2771 
millions of cubic feet. The ratio of maximum depth to length is 46, and 
of mean depth to length 101; these figures show the relatively great 
depth of the basin, for in Loch Morar, the deepest of all British lakes 
(1017 feet), the ratio of maximum depth to length is 61, and of mean 
depth to length 217, while the Lake of Geneva is 230 times longer than 
deep. 
The basin is simple in conformation, the shores sloping on all sides to 
the deepest part of the loch, which is centrally placed. At the south-west 
end the 50-feet and 100-feet contours are sinuous, due to the deposition of 
material brought down by the burns. The mud from the deepest part is 
black and peaty. The approximate areas between the contour-lines drawn 
in at equal intervals, and the percentages to the total ^area, are as 
follows ; — 1 
Feet. 
Acres. 
Per cent. 
Oto 50 
170 
31-1 ] 
50 „ 100 
96 
17*5 
100 „ 150 
69 
12-5 
150 „ 200 
91 
16-5 
200 „ 250 
113 
20-7 
Over 250 
10 
1-7 
549 
100-0 
These figures indicate the flat-bottomed character of the basin, the zone 
between 200 and 250 feet being larger than any of the three preceding 
shallower zones. 
The loch was surveyed on July 8, 1905, but the elevation could not be 
determined from bench-mark ; from spot-levels it was estimated to be 
about 1308 feet above the sea, and on the Ordnance Survey map the 
elevation of 1309*8 feet is given, though the date when levelled is not 
indicated. The surface of the water was 1*2 feet below the large stone at 
the south-east corner of the pier at His Majesty’s boathouse. The water 
was then very low — about 2 feet below the ordinary level — and might rise 
4 or 5 feet above ordinary level, the range being about 7 feet. 
Temperature Observations . — At noon on the date of the survey the 
temperature of the surface water was 58°*2, and at 7 p.m. serial tempera- 
tures gave the following results : — 
Surface ... 
50 feet . . . 
100 „ ... 
56°-l Fahr. 
47°*2 „ 
44°*3 „ 
43°-0 „ 
