THE FRESH- WATER LOCHS OF SCOTLAND. 91 



in outline, somewhat resembling the capital letter Y, a promontory of 

 land projecting into the loch from the eastern shore opposite the inlet 

 on the western shore which leads to the outflow. The length of the loch 

 from north-east to south-west in a straight line is about half a mile, but 

 a line following the axis of deep water would be considerably over half 

 a mile in length. The maximum breadth is about one-third of a mile, 

 and the mean breadth about one-seventh of a mile. Its waters cover 

 an area of about 43 acres, and it drains an area twenty times greater, 

 or about 1J square miles. About 60 soundings were taken in Lochan 

 Breaclaich, the maximum depth observed being 41 feet. The volume of 

 water is estimated at 26,619,000 cubic feet, and the mean depth at 14 

 feet, or 34 per cent, of the maximum depth. The length of the loch is 

 64 times the maximum depth, and 187 times the mean depth. The 

 bottom of the loch is fairly regular, sinking, to the north and south of 

 the promontory referred to, into two basins with depths exceeding 25 

 feet, occupying the arms, as it were, of the letter Y, while the shank of 

 the letter, leading to the outflow, is occupied by shallower water. Of 

 the two deep basins the northern one is the larger and deeper, the 

 maximum depth of 41 feet having been found approximately in the 

 centre of this basin, but towards the north-western shore, while the 

 southern basin is based upon soundings of 32 and 26 feet. The 10-feet 

 basin is a continuous area extending from close to the north-eastern end 

 to near the south-western end, and occupying the greater portion of the 

 loch. The area of the lake-floor covered by less than 10 feet of water is 

 over 19 acres, or 45 per cent, of the total area of the loch, while that 

 covered by more than 10 feet of water is nearly 24 acres, or 55 per cent. 

 Lochan Breaclaich was surveyed on June 16, 1903, but the elevation of 

 its surface above the sea could not be determined. 



Temperature Observations. The temperature of the surface water 

 on commencing the survey at 2 p.m. on June 16, 1903, was 57 0- Fahr. 

 Serial temperatures taken in the deepest part of the loch gave the 

 following results : 



It will be observed that the range of temperature from surface to 

 bottom amounted to 9-5, and that the fall of temperature between the 

 depths of 10 and 15 feet amounted to 6-2. 



Lochan na Lairige (see Plate XXVII.). Lochan na Lairige lies 

 to the west of Ben Lawers and flows into Loch Tay by the Allt a' 

 Mhoirneas, which enters the loch nearly opposite the entrance of the 



