42 
BATHYMETKICAL SUEVEY OF 
This series shows a total range of temperature amounting to about 7°, 
the greatest fall observed being one of about 3° between 75 and 100 feet. 
Fionn Loch (see Plate XVII.). — The Fionn Loch, a large irregular 
sheet of water, lies less than 3 miles to the north-east of Loch Maree. 
It is a good trout loch, and contains also Salmo ferox, but the fishing 
is strictly preserved. The lower portion does not lie in a well-marked glen, 
though round the upper end rise some precipitous and high mountains. 
There are many large islands, and almost everywhere around the shores, 
and in places at some considerable distance from shore, large rocks and 
boulders rise above the surface of the water. The head of the Fionn 
Loch is practically continuous with the Dubh Loch, which are separated 
from each other only by an artificial causeway built on a sandbank. When 
the water is high this causeway is flooded, though under ordinary circum- 
stances the difference of level is about a foot. The matter was the subject 
of litigation in 1877, the Lord Ordinary deciding that the lochs were one, 
but the House of Lords reversed this decision. In this place the two 
lochs are treated separately. 
The general trend of the Fionn Loch is from south-east to north-west, 
its total length being 5| miles ; it varies greatly in width, the maximum 
breadth being about Ij miles, the mean breadth of the entire loch being 
nearly two-thirds of a mile. Its waters cover an area of about 2250 acres, 
or over 3| square miles, and it drains directly an area of nearly 15 squate 
miles, but since it receives the outflow from the Dubh Loch, Lochan 
Beannach, and Loch na Moine Buige, its total drainage area is about 26| 
square miles. The maximum depth of 144 feet was observed in two 
places: (1) near the south-eastern end, and (2) in the central part of 
the loch opposite the entrance of the stream bearing the outflow from 
Lochan Beannach. The volume of water contained in the loch is 
estimated at 5667 millions of cubic feet, and the mean depth at 57| feet. 
The Fionn Loch was surveyed on August 4 to 8, 1902, but the elevation 
of the lake-surface could not be determined by levelling, owing to the 
inability of the surveyors to find bench-marks after prolonged search ; 
when visited by the Ordnance Survey officers on September 2, 1870, the 
elevation was found to be 5 58 ‘6 feet above the sea. The keeper stated 
that the water may rise 5 feet and fall about 2 feet from the level on 
the date of the survey. The bottom of the Fionn Loch is most irregular, 
and the contour-lines in most places extremely sinuous in character ; the 
north-western end is filled with boulders, which often rise out of com- 
paratively deep water in an astonishing manner. The main 50-feet basin 
is nearly 4 miles in length, approaching quite close to the south-eastern 
end, and extending between the islands called Eilean Fraoch and Eilean 
nan Corr-scriach. A second 50-feet basin runs in a north and south 
direction, along the centre of the large arm thrown out in a northerly 
direction towards the foot of the loch, extending to the west of Eilean nan 
