180 
BATHYMETRICAL SURVEY OF 
Loch Olavat (see Plate LXIX.j. — Locli 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 1| miles. In area it is the largest loch 
surveyed in the island, measuring fully 140 acres, but is inferior in 
length .to both Loch Heouravay 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*6 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 (21 square miles). Rock 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 o9°*2 Fahr. 
Loch Langavat (see Plate LXVIll.). — 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 21 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 canaldike 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) 
