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 l-8 between 20 and 30 feet, 

 but the greatest fall observed was one of 3 0< 6 between 60 and 75 feet. 



Loch Achilty (see Plate LXL). 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 51 J 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 : 



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 : 



