44 
BATHYMETRICAL SURVEY OF 
is estimated at 374 million cubic feet, and the mean depth at over 42 feet, 
or nearly one-half of the maximum depth. The Dubh Loch was surveyed 
at the same time as the Fionn Loch, and the elevation of the lake-surface 
was, for the same reason, not determined by levelling. 
The conformation of the Dubh Loch is quite a contrast to that of the 
adjoining Fionn Loch. Except for one or two irregularities of the lake- 
floor, Dubh Loch forms a simple basin, all the contour-lines, though 
showing occasional sinuosities, enclosing continuous areas. A bank 
covered by 2 feet of water occurs in the middle of the loch, about 
300 yards from the south-east end, surrounded by depths exceeding 
20 feet ; farther down, a line of soundings running from south to north, 
towards the entrance of the Allt Bruthach an Easain, showed a rise of the 
bottom from 43 to 38 and 39 feet, sinking again to 51 feet ; still farther 
down, another line of soundings running from south to north showed a 
remarkable rise of the bottom from 65 to 51 and 48 feet, sinking again to 
the deepest recorded sounding (88 feetj, whence the soundings shoaled 
gradually towards the northern shore. The last-mentioned rise is the 
more striking, as it was observed in the deepest part of the loch, and in 
close proximity to the maximum depth. The soundings taken in the wide 
lower portion of the loch are quite regular, the irregularities above 
referred to occurring in the upper half of the loch. The areas between 
the consecutive contour-lines, and the percentages to the total area of the 
loch, are as follows : — 
Feet. 
Acres. 
Per cent. 
0to25 
50 
24-6 
25 „ 50 
78 
38-2 
50 „ 75 
57 
28-2 
Over 75 
18 
9-0 
203 
100-0 
These figures indicate an average slope off-shore much steeper than in 
the deeper water, and an inspection of the map shows that the 25-feet 
contour follows aprroximately the shore line, approaching in some places 
very close to the shore, whereas the 50-feet contour runs, for the greater 
part of its course, at a considerable distance from shore, while the upper 
part of the loch is occupied by water less than 50 feet in dejDth. 
Loclian Beannacli (see Plate XVII.). — Lochan Beannach is a small 
irregular sheet of water lying off the central part of the western shore of 
the Fionn Loch, into which it flows by a stream less than a quarter of a 
mile in length. The loch consists of two distinct portions, and, as it was 
found impossible to get a boat through the passage, the smaller south- 
eastern portion was not surveyed, the soundings being limited to the larger 
western portion, which is of very peculiar form, almost encircling a large 
promontory of land projecting out into the loch from the western shore ; 
the narrow neck of land connecting the promontory and the shore is less 
