THE FRESH-WATER LOCHS OF SCOTLAND. 247 



lying 3 miles to the south. The stream which brings the drainage of the 

 whole central valley of Unst has various names the Burn of Caldback 

 where it leaves Loch Watlee, the Burn of Mailand in its middle course, 

 and the Burn of Baliaster where it enters the loch. On the date of the 

 survey (August 4, 1903) the surface-level was 5'75 feet above the sea. 



The surface temperature in the main loch was 56'4 Fahr., and in the 

 eastern branch 56'3. 



Loch of Snarravoe (see Plate CV.) is in the southern part of Unst. It 

 is a narrowly triangular loch, broadest in the south, its axis running 

 north-east to south-west. Both shores of the loch are steep grassy slopes, 

 the west lower and cultivated, the east rising nearly 200 feet above the 

 loch, and strewn in its lower part with myriads of stones. The largest 

 burn is that coming in at the north-east end from the Loch of Stourhoull, 

 half a mile higher up the valley. Some torrents entering on the east 

 have spread out wide deltas of stones. There is a sparse fringe of reeds 

 along the west shore. The Burn of Snarravoe flows out at the south- 

 west corner, and winds through a flat meadow a quarter of a mile north- 

 westwards into Snarra Voe. There is hardly any beach, and no rock was 

 seen at the margin of the loch. The upper end is sandy, with some large 

 boulders. Loch Snarravoe is over half a mile long, and a quarter of a 

 mile broad at the extreme south. The superficial area is about 53 acres, 

 the volume of water 27 millions of cubic feet, and the drainage area 

 three-quarters of a square mile. The basin is simple, the 10-feet contour 

 closely following the shore. In the centre the depth is only 1 2 feet ; 

 northwards it deepens slightly to 15 feet; to the south, and close to the 

 west shore, is a small area over 20 feet in depth, with the maximum 

 of 29 feet. The surface is very little above sea-level ; on the date of the 

 survey (August 6, 1903) it was at its lowest, 5*3 feet ; the Ordnance Survey 

 found the level on November 10, 1876, to be 5'6 feet above the sea. 



The temperature of the water was almost uniform throughout 



Surface 55-2 Fahr. 



10 feet 55-l 



25 55-l 



From the following table it will be seen that in the thirty-one lochs 

 under consideration 1707 soundings were taken, and that the aggregate area 

 of the water surface is nearly 5J square miles, so that the average number 

 of soundings per square mile of surface is 318. The aggregate volume of 

 water contained in the lochs is estimated at 1416 millions of cubic feet. 

 The area drained by these lochs is nearly 52 square miles, or about 9 J times 

 the area of the lochs. 



