THE FRESH- WATER LOCHS OF SCOTLAND. 257 



intervals, and the percentages to the total area of the loch, are as 



follows : 



to 25 feet 21 '2 acres 58 '1 per cent. 



25 50 ,, 6-9 19-0 



50,, 75 5-1 14-1 



Over 75 , 3-2 , 8 '8 



36-4 , 100-0 



Temperature Observations. The surface temperature observed in 

 Loch na Creige Duibhe on the date of the survey was 57'4, in the 

 stream between the two lochs 57'l, and in Loch Mama 56'5. The 

 following serial temperatures were taken in the deepest part of Loch 

 na Creige Duibhe at 4.45 p.m. on July 11, 1902 : 



Surface 57'4 Fahr. 



10 feet 57'4 



20 ,, 57'4 



30 ,, 53-0 



50 ,, 50'8 ,, 



75 49-2 



90 ., - 48'S 



This series shows a constant temperature down to 20 feet, then a 

 fall of 4-4 between 20 and 30 feet, and a further fall of 2-2 between 

 30 and 50 feet, the extreme range of temperature from surface to bottom 

 being 8-6. 



The details regarding the lochs in the Shiel, Ailort, and nan Uamh 

 basins are collected together in the table on p. 258 for convenience of 

 reference and comparison. From this table it will be seen that in the 

 six lochs under consideration nearly 1200 soundings were taken, and 

 that the aggregate area of the water-surface is over 8J square miles, so 

 that the average number of soundings per square mile of surface is 139. 

 The aggregate volume of water contained in the lochs is estimated at 

 about 29,000 millions of cubic feet. The area drained by these lochs 

 is nearly 100 square miles, or 11 J times the area of the lochs. 



Geology of the Loch Shiel Catchment Basin. Though the basin of 

 Loch Shiel has not been surveyed by the Geological Survey, we under- 

 stand that certain members of the staff have examined the rock cuttings 

 on the line of railway between Loch Eil and Kinlochailort. The rocks 

 exposed in these cuttings consist of muscovite-biotite gneiss and flaggy 

 mica-schists, which are included in the Moine series of crystalline 

 schists by the Geological Survey. The general strike of these strata 

 is north-east and south-west, so that in all likelihood they are continued 

 to the south-west along both sides of Loch Shiel. This conclusion is 

 supported by the fact that on the lofty watershed between Loch Shiel 



