68 
BATHYMETRICAL SURVEY OF 
soundings run from 2 to 5 feet; the south-western expansion is the 
shallowest, with a maximum depth of 3 feet to the west of the central 
large island (Eilean na Coille), the bottom to the east and south of that 
island being covered by only 1 foot of water. Over 90 per cent, of the 
entire lake-floor is covered by less than 10 feet of water, and less than 
2 per cent, by over 20 feet of water. The surface temperature in the 
eastern expansion at 11 a.m. on April 21, 1902, was 44°*2. 
Loch Rannoch (see Plate XIX.). — Loch Hannoch, one of the larger 
and more important of the lochs in the Tay basin, was the headquarters 
of the Lake Survey for nearly four months, from March 20 to July 10, 
1902, and during that period a great many soundings, as well as 
observations on the temperature of the water, on the biology, and on the 
rise and fall of the surface of the loch, were taken, all the members of 
the staff taking part in the work. The lake trends in an east-and-west 
direction, and is a lovely sheet of water, the hills on both sides, and the 
woods clothing its shores in many places, adding beauty to the scene. 
The famous Black Wood of Hannoch on the south side is of great 
antiquity. The loch contains many small trout, and is famed for large 
Sahno ferox. It is nearly 9J miles in length, considerably over a mile 
in maximum breadth, the mean breadth being about three-quarters of 
a mile, or about 8 per cent, of the length. Its waters cover an area of 
over 4700 acres, or nearly 7^ square miles, and it drains directly an area 
of about 130 square miles, but, since it receives the outflow from Loch 
Ericht, Loch Eigheach, Loch Laidon, Loch Ba, &c., its total drainage 
area is about 243J square miles, or 33 times the area of the loch. 
Over eight hundred soundings were taken in Loch Hannoch, the 
maximum depth observed being 440 feet, or 20 feet deeper than the 
maximum depth recorded by Mr. Grant- Wilson during his survey in 
the year 1888, when he took about 320 soundings. The volume of 
water contained in the loch is estimated at about 34,387,131,000 cubic 
feet, or less than a quarter of a cubic mile, and the mean depth at 1674 
feet, or 38 per cent, of the maximum depth. The length of the loch 
is 116 times the maximum depth, and 306 times the mean depth. The 
loch is widest and deepest in the eastern half, narrowing and shallow- 
ing towards the west on approaching the island Eilean nam Faoileag, 
then deepening again to the west of that island. It consists of one 
large main basin, with two subsidiary small basins over 50 feet in 
depth towards the west end, separated from the main basin by the 
shallow water in the neighbourhood of Eilean nam Faoileag. The 
larger of the two subsidiary basins is about three-quarters of a mile in 
length, stretching from south of the island An t-Eilean Fearna, at the 
entrance of the river Ericht, towards the west end of the loch, and the 
maximum depth recorded in it was 84 feet ; the smaller basin lies 
between the two islands mentioned and towards the northern shore. 
