180 BATHYMETRICAL SURVEY OF 



Loch Olavat (see Plate LXIX.). Loch Olavat, one of two lochs of the 

 same name, is situated nearly in the middle of the island, lying part on 

 each side of the main road, but nearer the south ford than the north one ; 

 the other Loch Olavat lies close to the north ford and is tidal. It is 

 extremely irregular in form, but is longest from north-west to south-east, 

 in which line it measures about If miles. In area it is the largest loch 

 surveyed in the island, measuring fully 140 acres, but is inferior in 

 length to both Loch Heonravay and Loch Langavat. Its greatest breadth 

 is half a mile, and mean breadth one-seventh of a mile. It is the 

 shallowest of the lochs, being only 12 feet in greatest depth, and 4 feet in 

 mean depth. The volume, 26 millions of cubic feet, is equal to that of 

 Loch Heouravay and about half that of Loch Langavat. When surveyed 

 on July 1, 1904, the height of the surface above sea-level was 16*0 feet. 

 It is chiefly fed by surface drainage from the boggy moor around, and by 

 small burns from many adjoining lochs. The outflow is controlled by a 

 sluice in connection with a corn mill some quarter of a mile to the south. 

 The area drained is considerable (2| square miles). Bock shows almost 

 everywhere round the shores, but is in many places covered with great 

 numbers of angular stones. The bottom of the loch is pretty regular, with 

 no abrupt deepenings, probably indicating that the silt is spread out and 

 levelled by the waves around and between the boulders and islands. 

 The temperature at the surface and at 10 feet was 59'2 Fahr. 



Loch Langavat (see Plate LXVI1L). Loch Langavat is a long, 

 straight, and extremely narrow loch, running nearly east and west, close to 

 the south shore of the island, and east of the road. It is the longest loch 

 in Benbecula, being 24 miles long, but only a quarter of a mile in maximum 

 breadth, and less than one-tenth of a mile in mean breadth. The shores 

 are rock, forming low cliffs in the central and eastern parts. Towards the 

 west the north shore for nearly a mile is of stones and peat. Several 

 narrow inlets go off from the south shore, and there are many islands, all 

 narrow and running east and west. The maximum depth, 34 feet, is equal 

 to that of Loch na Deighe fo Dheas, and less than that of the other lochs 

 except Loch Olavat, but the mean depth, 8 feet, slightly exceeds that of 

 Loch Heouravay. The superficial area, about 124 acres, is only inferior to 

 that of Loch Olavat, while in volume (44 millions of cubic feet) the loch 

 is by far the largest in Benbecula. The loch is fed only by small burns 

 from many little lochs and by local drainage, and has its outflow to the 

 east into Loch a' Laip, through Oban Uaine. The area drained is only 1 

 square mile. When surveyed on July 4, 1904, the surface was 15'95 feet 

 above sea-level. Narrow as it is throughout, Loch Langavat is divided 

 into two nearly equal parts by a canal-like strait, one-third of a mile long 

 and only 5 feet deep. West of this it is on the whole very shallow, with 

 one small depression of 20 feet in the broadest part. East from the strait 

 it is relatively deep throughout, the deepest part of the main loch (30 feet) 



