178 BATHYMETRICAL SURVEY OF 



casual inspection satisfies us that they can be of no great depth. The 

 selection of the lochs to be surveyed was determined by the presence of 

 boats, which were found only on some half-dozen of the larger lochs. 



Loch Heouravay (see Plate LXVIII.). Loch Heouravay is a loch of 

 extremely irregular form, lying close to the sea- shore on the east side of 

 * the island, where Loch Uskavagh cuts so deeply into the interior of the 

 land. It drains into Heouravay bay, an inlet from Loch Uskavagh, by a 

 stream a few yards in length. We were told that there was formerly a 

 mill on this stream and that the surface of the loch was kept at a higher 

 level by a dam with a sluice. When that was the case Loch Heouravay 

 might be a single loch ; the removal of the dam has divided it into five 

 distinct little lochs, differing slightly in level, and connected by very short 

 streams which fall only a few inches. The surroundings are rough moor- 

 land, the shores of rock, overlain in places by gravel and boulders. There 

 is rock close by the outflow. 



The length, in a straight line between the most distant points, is lj 

 miles, following the middle line of the loch If miles. The greatest 

 breadth is 1 a quarter of a mile, the mean breadth one-twelfth of a mile. The 

 greatest depth in the largest western basin of the loch is 25 feet ; the 

 maximum for the whole loch is in the smaller second basin, south of the 

 first, where there is a depth of 41 feet close to the shore; the third basin, 

 south of the second, has a depth of 1(3 feet; and the fourth and fifth 

 basins are only 5 and 6 feet deep. The mean depth of the whole loch is 

 about 7 feet. The superficial area is about 80 acres, and the contents 26 

 millions of cubic feet. The drainage area is nearly 2 square miles, and 

 includes many small lochs. 



The surface of the lowest basin was 8'3 feet above sea-level, the upper- 

 most basin 9-6, and the largest fall, between first and second basins, 9 

 inches. The temperatures in the deepest basin on June 29, 1904, were 



Surface 60-0 Fahr. 



15 feet 59-0 



25 56-6 



40 55-6 



Loch nan Auscot (see Plate LXVIII.). Loch nan Auscot is a very small, 

 roughly triangular loch, situated between Loch Heouravay and Loch 

 Hermidale. Its long axis runs north and south ; it is broadest towards the 

 south and narrows northwards to a point near Loch Hermidale into which 

 it drains by a very short stream. The shores are entirely of rock. It is 

 a quarter of a mile long, one-tenth of a mile in greatest breadth, and one- 

 twentieth of a mile in mean breadth. Relatively it is the deepest loch 

 surveyed in Benbecula, the maximum depth being 39 feet, and the mean 

 depth 17 feet. The area of the surface is only about 8 acres, and it 

 receives only surface drainage. The surface level was 13'0 feet above the sea. 

 The basin is quite simple, with deep water (of over 35 feet) in a straight 



