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 Mail and 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. 
