THE FRESH-WATER LOCHS OF SCOTLAND. 227 



west to east, where the maximum depth of 7 feet is found. The mean 

 depth is 4 feet, the area about 149 acres, and the volume 28 millions of 

 cubic feet. The drainage area is. about a square mile. The outflow is 

 by Mill burn, a quarter of a mile long, issuing from the south-west corner 

 of the loch. The surface was 13-9 feet above sea-level on August 17, 

 1903, and the surface temperature was 58'5 Fahr. 



Loch of Swannay (see Plate XCIIL). The Loch of Swannay (or 

 Swona, or S wanna) is a large loch of elliptical form, in the extreme north 

 of Pomona, at Costa head. It is surrounded by moorland, in part 

 cultivated. The shores are paved with flat stones. Under Costa hill 

 are ranges of crags. The Muckle Holm island is stony, and there are 

 many stony shoals, especially south of the island, and along the west 

 shore. The length is 2 miles, and the greatest breadth two-thirds of 

 a mile. Around the Muckle Holm the bottom is irregular and shoaly. 

 South of the island is a considerable flat of 8 feet deep. North of the 

 island is a large flat-bottomed basin, gradually deepening from 12 feet 

 to 16 feet near the north end. The mean depth is 9J feet, the area about 

 603 acres, or nearly one square mile, and the volume 242 millions of 

 cubic feet. The drainage area is fully 5 square miles. A small burn 

 enters at the southern end, and the Swannay. burn flows out at the north- 

 west corner, over a dam with a sluice, which is now disused. There is 

 rock in the stream at the outflow. The bottom is visible to a depth of 

 8 or 10 feet, and is stony, with little or no deposit of mud. The surface 

 was 134'55 feet above sea-level on August 31,' 1906. The temperature 

 at the surface was 57-7 Fahr., at 15 feet 57'0. 



Loch of Boardhouse (see Plate XCIII.). The Loch of Boardhouse, 

 which, in accordance with the Orcadian custom of naming a loch in- 

 differently from any conspicuous feature in its neighbourhood, also receives 

 the appellations Loch of Birsay, Loch of Twatt, Loch of Kirbuster, Barony 

 Loch, and perhaps yet others, is a large and broad loch in the parish of 

 Birsay, about half a mile east of the village of that name. It lies amid 

 fields gently sloping up from the shore, with patches of moorland. Ravie 

 hill, on the south-west, and Kirbuster hill on the north-east, are heather- 

 topped hills of no great elevation. The shores are stony, and so shallow 

 that they are difficult to approach in a boat the grass slopes come quite 

 to the water's edge, with hardly any beach. The only rock seen was at 

 the original outflow. The length is 2 miles, and the greatest breadth 

 near the eastern end two-thirds of a mile. The bottom is flat, and 

 gradually deepens from 5 feet at the north-west end to the maximum 

 depth of 9 feet close to the east end. The mean depth is 6 feet, the area 

 nearly a square mile, and the volume 150 millions of cubic feet. The 

 drainage area is 1 3 \ square miles. The Kirbuster burn, a fair-sized river, 

 enters at the east end. From the north-west corner the Birsay burn flows 



