56 
BATHYMETRICAL SURVEY OF 
end comparatively deep water, maximum 17 feet, was found, sej^arated from 
the main body of deep water by lesser depths, maximum 11 feet. The 
area covered by less than 10 feet of water is about 35 acres, that covered by 
more than 29 feet of water is about 13 acres, while that covered by water 
between 10 and 20 feet in depth is about 50 acres, or one-half of the entire 
lake-floor. 
Loch Braigh Horrisdale (see Plate XVIII.). — Loch Braigh Horrisdale 
(or Horisdel) lies about 4 miles to the north-west of Loch a’ Ghobhainn, 
and little more than a mile from the head of Loch Shieldaig, the south- 
eastern extension of Loch Gairloch ; but its outflow is carried by a stream 
2 miles in length, entering Loch Gairloch farther to the west. The loch 
is irregular in outline, somewhat in the form of a triangle, with the apex 
pointing in an easterly direction, and with the base-line protruding towards 
the centre of the triangle. Measured along the axis of maximum depth 
from north to south, the length exceeds three-quarters of a mile, the 
maximum breadth being one-third of a mile. The superficial area is about 
91 acres, and the area draining directly into the loch is about 8 square 
miles, but since it receives the overflow from Loch a’ Bhealaich and Loch 
a’ Ghobhainn, the total drainage area exceeds 14 square miles. The 
maximum depth of 51 feet was observed in two places in a central position. 
The volume of water is estimated at 62 million cubic feet, and the mean 
depth at 18 feet. The loch was surveyed on August 6, 1902, but the 
elevation of the lake-surface above the sea could not be determined ; 
when levelled by the officers of the Ordnance Survey on June 23, 1870, 
the elevation was found to be 302’3 feet above sea-level. 
Loch Braigh Horrisdale is, on the whole, shallow, since 83 per cent, of 
the lake-floor is covered by less than 25 feet of water, and 44 per cent, by 
less than 10 feet of water. The lines of soundings all indicate a regular 
and gentle slope from the shores towards the centre ; but there is a slight 
shoaling of the water at the entrance of the inflowing river, which isolates 
a small 20-feet basin to the south from the main basin to the north. The 
deeper water lies in the north-eastern portion of the loch, where there is 
a small 50-feet area, based on two soundings in 50 feet and two soundings 
in 51 feet; and it is curious to note that the two 50-feet soundings are 
within the two deeper ones, indicating a slight rise of the bottom in the 
deepest part of the loch. The area covered by less than 25 feet of water 
is about 75 acres, while that covered by more than 25 feet of water is about 
16 acres. 
Temperature Observations . — The following series of temperatures was 
taken in the deepest part of the loch at 6 p.m. on the date of the survey : — 
Surface ... 
10 feet ... 
20 „ ... 
40 „ ... 
50 
55°*1 Fahr. 
54°'9 „ 
54°-8 „ 
53°-8 „ 
53°-2 „ 
