THE FRESH- WATER LOCHS OF SCOTLAND. 385 



The volume of water contained in Loch Ness is estimated at 263,000 

 millions of cubic feet, or 1| cubic miles. In no other Scottish loch does 

 the bulk of water amount to a cubic mile, in fact Loch Ness contains 

 about three times as much water as the two lochs which most nearly 

 approach it in this respect, viz. Loch Lomond with 92,800 million cubic 

 feet, and Loch Morar with 81,500 million cubic feet. The largest 

 volume of water recorded by Dr. Mill among the lakes of the Cumber- 

 land district is only 12,250 million cubic feet. As far as we are aware, 

 the volume of water contained in the large lakes of Ireland has not yet 

 been carefully worked out, but, taking Loch Neagh, for instance, which 

 is said to cover an area of 153 square miles (or seven times greater than 

 the area of Loch Ness), and to have a maximum depth of only 48 feet, 

 a rough calculation will show that the bulk of water in Loch Neagh 

 must be less than that in Loch Ness. It seems quite possible, therefore, 

 that Loch Ness may be the largest body of fresh water, not only in 

 Great Britain, but in the United Kingdom. 



Correlated with the enormous volume of water in Loch Ness is the 

 high value of the mean depth, which works out at 433 feet for the entire 

 loch. This far exceeds that of Loch Morar, viz. 284 feet, which comes 

 next in this respect. The mean depth of Loch Ness is equal to 5 7 '4 per 

 cent, of the maximum depth a higher percentage than has been 

 observed in any other large deep loch, the nearest approach to it being 

 in the case of Loch Avich, with a maximum depth of 188 feet and a 

 mean depth of 98 feet, the percentage being 52'4. It is true that in 

 some shallow flat-bottomed basins the percentage of mean depth to 

 maximum depth exceeds that in Loch Ness; as, for instance, Loch 

 Watten in Caithness (70 per cent.), and Loch Bruadale in Lewis (74 

 per cent.), but the maximum depths are here only 12 feet and 6 feet 

 respectively. Except for Lochs Ness and Avich, in all the deep Scottish 

 lochs, i.e. those having depths exceeding 100 feet, the mean depth is less 

 than one-half of the maximum depth, the percentage varying from 19'4 

 in Loch Shiel, and 19-5 in Loch Lomond, to 49-4 in Loch Lungard, 

 and 49-6 in Loch Suainaval (Lewis). 



It has been stated that the surface of Loch Ness stands about 52 

 feet above mean sea-level, so that by far the greater portion of its floor 

 falls below the level of the sea. 



An inspection of the bathymetrical map of Loch Ness shows (1) the 

 comparative simplicity of the basin ; (2) the steep shore-slope throughout 

 the greater part of the loch ; and (3) the large area of the lake-floor 

 covered by very deep water. The 100-feet, 200-feet, 300-feet, 400-feet, 

 and 500-feet contours are continuous, and only the 600-feet and 700-feet 

 contours are interrupted by a shoaling opposite the entrance of the 

 river Foyers, probably due to the deposition of material brought down 

 by that river. This shoaling is covered by 515 to 524 feet of water, 

 and both to the north-east and south-west the bottom sinks to depths 

 exceeding 700 feet. BB 



