THE FRESH- WATER LOCHS OF SCOTLAND. 157 



southern shore. The areas between the consecutive contour-lines, and 

 the percentages to the total area of the loch, are as follows : 



to 25 feet 109 acres 68 '3 per cent. 



25 50 45 28-0 



Over 50 , 6 . 3'7 



160 , 100-0 



Loch Crocach was surveyed on September 17, 1902, but the elevation 

 of the lake-surface above the sea could not be determined ; the elevation 

 must be between 350 and 370 feet above sea-level. The boatman stated 

 that the water might rise 2 feet above, and fall 3 feet below, the level 

 on the date of the survey. 



Temperature Observations. Temperature observations showed a 

 greater variation than was observed in the larger and deeper Loch 

 Assynt, as will be seen from the following serial taken at 2.30 p.m. on 

 September 17, 1902: 



Surface 537 Fahr 



40 feet 53 2 



70 ;, 50-8 ,, 



This series shows a range of 3, the greatest fall of temperature 

 occurring in deep water below 40 feet. 



Loch an Tuirc (see Plate XXXVII.). Loch an Tuirc is situated 

 about two miles north-east of Loch Inver, and over a mile to the west 

 of Loch Beannach. It receives the outflow from Loch Crocach, and 

 flows by the Uidh nan Caorach into Loch an Aite Mhoir, thence 

 through three other small lochs into Loch Roe. The ground around the 

 loch is low, the greatest elevation being one of 400 feet to the north-west 

 of the loch. Islands are not so numerous in this loch as in the neigh- 

 bouring Lochs Beannach and Crocach; weeds are very abundant in 

 some parts of the loch. Loch an Tuirc trends north-east and south- 

 west, and is irregular in outline and conformation. There is a con- 

 striction near the centre of the loch, which cuts the deeper water into 

 two portions, and the loch narrows gradually towards the outflow at the 

 south-west end. It is about four-fifths of a mile (or about 1400 yards) 

 in length, with a maximum breadth of one-fifth of a mile (or over 300 

 yards), the mean breadth being one-tenth of a mile. Its waters cover 

 an area of about 53 acres, and it drains directly an area of about 1J 

 square miles, but, since it receives the outflow from Loch Crocach, its 

 total drainage area is nearly 3 square miles. Nearly 100 soundings 

 were taken, the maximum depth observed being 39 feet. The volume of 

 water is estimated at about 24,787,000 cubic feet, and the mean depth 

 at 10 \ feet. The portion of the loch to the north-east of the central 



