THE FRESH-WATER LOCHS OF SCOTLAND. 
255 
Depth in feet. 
Loch Dubh. 
July 12, 1902, 
3 p.ni. 
Loch Dubh. 
March 28, 1903. 
° Dahr. 
° Fahr. 
0 
59-0 
41-0 
10 
59-0 
16 
58-9 
20 
56 0 
25 
53-7 
35 
51-5 
50 
47T 
41 -0 
75 
44T 
41 0 
100 
43-6 
40-9 
150 
43-5 
40-9 
The series taken in March calls for no discussion, but the series 
taken in July is remarkable for the low temperature of the deep water 
at this season of the year, and for the great range of temperature from 
surface to bottom. Compared with the temperatures recorded in Loch 
Shiel a week earlier in the same month, we find the temperature in 
Loch Dubh l°-7 lower at the bottom in 150 feet than in Loch Shiel in 
420 feet, and in Loch Morar (the deepest of all Scottish lochs), ten days 
earlier in the same month, a temperature equal to that at the bottom 
of Loch Dubh was recorded only after descending to a depth of 250 
feet. The extreme range of temperature shown by the series in Loch 
Dubh amounts to 15°-5, while the series taken in Loch Shiel shows a 
range of only 12°, and the series in Loch Morar shows a range of only 
13°, from surface to bottom. The extraordinary temperature conditions 
observed in Loch Dubh may probably be accounted for (1) by the great 
depth of the loch compared with other lochs of similar area ; (2) by the 
small extent of its drainage area, so that very little rain-water enters 
the loch ; and (3) by the small area of the loch and the steepness of the 
surrounding hills reducing the mixing effect of the wind to a minimum. 
Lochs Mama and na Creige Duibhe doubtless formed at no distant 
date one sheet of water, which was gradually separated into two portions 
by the deposition of material brought down by the Allt Dearg. This 
is evidenced by the fact that locally the name Mama is applied to 
both divisions, but in this place that name is restricted to the western 
basin, the name na Creige Duibhe being applied to the larger and 
deeper eastern basin. The connecting stream is about 60 yards in 
length, with a depth of 7 to 8 feet, the fall from Loch na Creige Duibhe 
to Loch Mama being less than a foot. The tract of alluvium separating 
the two lochs was about 2| feet above the water of Loch Mama, and 
the keeper stated that he had often seen it flooded when the lochs were 
high. The hills along the northern and southern shores of the lochs 
rise steeply up to heights exceeding 1000 feet, approaching 2000 feet 
along the northern shores, down the sides of which a few torrents rusli 
