THE FRESH-WATER LOCHS OF SCOTLAND. 
41 
of cubic feet, and the mean dej^tb at 103| feet. Locb na Sheallag was 
surveyed on August 13 and 14, 1902, when the elevation of the lake-surface 
was determined, by levelling from bench-mark, as being 277‘7 feet above 
the sea ; when visited by the officers of the Ordnance Survey on October 
22, 1868, the elevation was found to be 279*3 feet above sea-level. The 
keeper stated that the water might rise 6 feet above, and fall half a foot 
below, the level on the date of the survey ; a line of drift was observed 
51 feet above the surface of the water. 
The main body of Loch na Sheallag forms a simple basin, the deeper 
water occuj^ying the wide south-eastern portion, while the water shoals 
gradually as the loch narrows in outline towards the north-west. The 
lower very narrow portion of the loch, for a distance of about a mile from 
the north-west end, is less than 50 feet in depth, except for a small subsi- 
diary basin situated about a quarter of a mile from the outflow, in which 
depths of 52 to 56 feet were recorded. The slope of the bottom is thus 
in striking contrast at the two ends of the loch, for while a depth of 100 
feet may be found about 250 feet off the south-eastern end, where the 
Abhuinn Srath na Sealga flows in, one must proceed more than a mile 
from the oj^posite end, where the Gruinard river flows out, before en- 
countering depths exceeding 100 feet. The 100-feet basin is nearly 2| 
miles in length, and the main 200-feet basin is over three-quarters of a 
mile in length, with an isolated sounding of 201 feet separated from the 
main basin by an interval of one-third of a mile, in which the greatest 
depth observed was 191 feet. An inspection of the map shows that the 
deeper part of the loch is distinctly flat-bottomed in character, and this is 
borne out by the following table, giving the areas between the consecutive 
contour-lines drawn in at equal intervals, and the percentages to the total 
area of the loch, from which it will be seen that the area between 150 and 
200 feet is larger than that between 100 and 150 feet: — 
Feet. Acres. Per cent. 
Oto 50 
229 
26-2 
50 „ 100 
207 
23-6 
100 „ 150 
186 
21-2 
150 „ 200 
202 
234 
Over 200 
... 
52 
5-9 
876 
100-0 
Temperature Observations . — The surface temperatures taken in Loch 
na Sheallag on August 13 and 14, 1902, showed very little variation, 
while a series taken beneath the surface in the deepest part of the loch 
gave the following results : — 
Surface 55°-0 Fahr. 
30 feet 53°-0 „ 
50 53°-0 „ 
75 51°-4 „ 
100 48°-5 „ 
180 47°-9 „ 
