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, ix. 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 
