THE FRESH-WATER LOCHS OF SCOTLAND. 



255 





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 rush 



