THE FRESH-WATER LOCHS OF SCOTLAND. 
275 
This series shows a range of temperature from surface to bottom 
amounting to 9° Fahr. The upper 20 feet of water was practically of 
uniform temperature, followed by a fall of 1°'8 between 20 and 30 feet, 
but the greatest fall observed was one of 3°*6 between 60 and 75 feet. 
Loch Achilty (see Plate LXI.). — Loch Achilty is a small but deep 
loch in Torrachilty wood, near Strathpeffer, containing char. In outline 
it is somewhat elliptical, with the long axis trending north-east and 
south-west. It is about 1500 yards in length, by 700 yards in maxi- 
mum breadth, the mean breadth being 450 yards. Its waters cover an 
area of about 147 acres (or nearly a quarter of a square mile), and it 
drains an area exceeding 2 square miles. The maximum depth of 
119 feet was observed about 250 yards from the western shore. The 
volume of water is estimated at 332 million cubic feet, and the mean 
depth at 51J feet. The floor of Loch Achilty is irregular. The 10-feet 
contour follows approximately the outline of the loch, in many places 
approaching very close to the shore, but the deeper contours are all 
sinuous in character, and there are two small basins exceeding 100 feet 
in depth, the larger and deeper towards the western shore, and the 
smaller, based on a sounding of 112 feet, near the centre of the loch. 
Deep soundings were recorded in some positions near shore, while in 
other positions comparatively shallow soundings were taken some 
distance offshore. A longitudinal section along the axis of maximum 
depth is shown in section C-D on the map. The areas between the 
consecutive contour-lines, and the percentages to the total area of the 
loch, are as follows : — 
0 to 25 feet 
41 acres 
28*0 per cent. 
25 „ 50 ,, 
28 „ 
19-2 
50 ,, 75 ,, 
39 „ 
26*2 „ 
75 „ 100 „ 
30 ,, 
20*2 „ 
Over 100 ,, 
9 „ 
6-4 „ 
147 ,, 100 0 
This table shows a smaller area, and therefore an average steeper 
slope, between 25 and 50 feet, than in the deeper water. The loch was 
surveyed on August 20 and 21, 1902, when the elevation of the lake- 
surface was found to be 98*5 feet above the sea, so that the 100-feet 
contours show approximately the two small portions of the lake-floor 
which lie below the level of the sea. 
Temperature Observations . — In the following table are given the 
results of three series of temperatures taken in Loch Achilty by Mr. 
Clark in 1901, along with a series taken in 1902 at the time of the 
survey : — 
