THE FRESH- WATER LOCHS OF SCOTLAND. 41 



of cubic feet, and the mean depth at 103J feet. Loch na Sheallag was 

 surveyed on August 13 and 14, 1902, when the elevation of the lake-surface 

 was determined, by levelling from bench-mark, as being 277'7 feet above 

 the sea ; when visited by the officers of the Ordnance Survey on October 

 2ii. I>I.N, the elevation was found to be 279*3 feet above sea-level. The 

 keeper stated that the water might rise 6 feet above, and fall half a foot 

 below, the level on the date of the survey ; a line of drift was observed 

 5J feet above the surface of the water. 



The main body of Loch na Sheallag forms a simple basin, the deeper 

 water occupying the wide south-eastern portion, while the water shoals 

 gradually as the loch narrows in outline towards the north-west. The 

 lower very narrow portion of the loch, for a distance of about a mile from 

 the north-west end, is less than 50 feet in depth, except for a small subsi- 

 diary basin situated about a quarter of a mile from the outflow, in which 

 depths of 52 to 56 feet were recorded. The slope of the bottom is thus 

 in striking contrast at the two ends of the loch, for while a depth of 100 

 feet may be found about 250 feet off the south-eastern end, where the 

 Abhuinn Srath na Sealga flows in, one must proceed more than a mile 

 from the opposite end, where the Gruinard river flows out, before en- 

 countering depths exceeding 100 feet. The 100-feet basin is nearly 2f 

 miles in length, and the main 200-feet basin is over three-quarters of a 

 mile in length, with an isolated sounding of 201 feet separated from the 

 main basin by an interval of one-third of a mile, in which the greatest 

 depth observed was 191 feet. An inspection of the map shows that the 

 deeper part of the loch is distinctly flat-bottomed in character, and this is 

 borne out by the following table, giving the areas between the consecutive 

 contour-lines drawn in at equal intervals, and the percentages to the total 

 area of the loch, from which it will be seen that the area between 150 and 

 200 feet is larger than that between 100 and 150 feet : 



Feet. Acres. Per cent. 



Oto 50 229 ... 26-2 



50 100 207 ... 23-6 



100 150 186 ... 21-2 



150 200 202 ... 23-1 



Over 200 52 ... 5-9 



876 100-0 



Temperature Observations. The surface temperatures taken in Loch 

 na Sheallag on August 13 and 14, 1902, showed very little variation, 

 while a series taken beneath the surface in the deepest part of the loch 

 gave the following results : 



Surface 55-0 Fahr. 



30 feet 53-0 



50 53-0 



75 51-4 



100 48-5 



180 , 47-9 



