94 
BATHYMETRICAL SURVEY OF 
Loch Giorra (see Plate XXVII.). — Loch Giorra (or Girre) trends 
almost east and west ; there is a slight bend near the middle of the loch, 
the eastern half trending north-west and south-east. It is over four- 
fifths of a mile in length, with a maximum breadth of over a quarter 
of a mile, the mean breadth being about one-sixth of a mile, or 20 per 
cent, of the length. Its waters cover an area of about 88 J acres, or 
less than one-seventh of a square mile, and it drains directly an area of 
over square miles, but, since it receives the outflow from Loch 
Daimh, its total drainage area is over 10| square miles — an area 78 
times greater than the area of the loch. Fifty-five soundings were taken 
in Loch Giorra, the maximum depth observed being 49 feet. The 
volume of water is estimated at 83,686,000 cubic feet, and the mean 
depth at nearly 22 feet, or 44 per cent, of the maximum depth. The 
length of the loch is 88 times the maximum depth, and 200 times the 
mean depth. 
The floor of Loch Giorra is rather irregular. The deepest part is in 
the western half, the maximum depth of 49 feet having been observed 
about one-sixth of a mile from the west end. The 25-feet basin in this 
part of the loch is about two-fifths of a mile in length, and towards the 
east end there is a second 25-feet basin about one-fifth of a mile in 
length, in which the maximum depth is 40 feet. These two basins are 
separated by a remarkable rise of the bottom, on which depths of 15 
and 18 feet were recorded, surrounded on all sides by deeper water. The 
area of the lake-floor covered by less than 20 feet of water is nearly 
43 acres, or over 48 per cent, of the total area of the loch ; that covered 
by water between 20 and 40 feet in depth is nearly 38 acres, or about 
42 J per cent. ; while that covered by more than 40 feet of water is 
over 8 acres, or over 9 per cent. Loch Giorra was surveyed on the same 
day as Loch Daimh (May 26, 1903); its elevation above the sea could 
not be determined. 
T emperature Ohservations. — A series of temperatures taken in the 
deepest part of the loch gave the following results : — 
Surface ... 
10 feet ... 
25 ,, .. 
45 ,, 
50° 0 Fahr. 
48° -0 ,, 
46° -8 „ 
46° O ,, 
A comparison of these temperatures with those taken in Loch Daimh 
later in the day shows that, while the surface temperature in each loch 
was nearly identical, the temperature of the water beneath the surface 
was lower in the deeper loch : thus at 10 feet the temperature in Loch 
Daimh was 1°'0 lower than in Loch Giorra, at 25 feet it was 2°*8 lower, 
and at 50 feet it was 2°*5 lower than at 45 feet in Loch Giorra. 
Loch Bhac (see Plate XXVIII.). — Loch Bhac (Bhaic, or Vach) lies 
to the north of Loch Tummel, and flows by the Allt Bhaic into the river 
