254 BATHYMETRICAL SURVEY OF 



under half a mile, its maximum breadth one-sixth of a mile, and its 

 mean breadth one-tenth of a mile. Its waters cover an area of about 32 

 acres, and it drains an area eight times greater, or about 262 acres. 

 Sixty-five soundings were taken, and the maximum depth observed was 

 153 feet, which bears the ratio to the length of the loch of 1 to 15. 

 This low ratio is only equalled by the little loch on Eilean Subhainn 

 in Loch Maree, and the loch which most nearly approaches it is Loch 

 Fender in the Tay basin, in which the ratio is as 1 to 22, followed by 

 Loch Dhugaill, near Kishorn, in which the ratio is as 1 to 27. Among 

 the larger Scottish lochs, the nearest approach is found in Loch Treig, 

 with a ratio of depth to length of 1 to 62. The volume of water 

 contained in the loch is estimated at 86,956,000 cubic feet, and the mean 

 depth at nearly 63 feet, or 41 per cent, of the maximum depth. The 

 loch was surveyed on July 12, 1902; the elevation of the lake-surface 

 above the sea was found, by levelling from bench-marks, to be 103-0 

 feet ; when visited by the Ordnance Survey officers on August 6, 1869, 

 the elevation was 103*3 feet above sea-level. No drift-marks were seen, 

 but the keeper stated that the annual range in level was about 9 inches. 

 Loch Dubh is very simple in conformation, the contour-lines follow- 

 ing approximately the shore-line. Near the north-west end there is a 

 slight rise of the bottom, as shown in section A-B on the map, but 

 otherwise the lake-floor slopes down regularly to the deepest part, 

 which lies towards the north-eastern shore. The maximum depth of 

 153 feet was observed at a distance of about 120 feet from this shore, 

 giving a slope of 59 ; the height of the hill immediately adjoining is 

 240 feet, and the slope 35, hence the slope from the top of the hill to 

 the bottom of the loch is one of 45. The areas between the consecutive 

 contour-lines drawn in at equal intervals, and the percentages to the 

 total area of the loch, are as follows : 



Oto 50 feet 14 '8 acres 407 per cent. 



50,, 100 ,, 8-9 30-9 



100,, 150 ,, 7-6 26-5 



Over 150 , 0'5 . 1-9 



31-8 . 100-0 



Temperature Observations. A most interesting series of temperatures 

 was taken in Loch Dubh at the time of the survey, as given in the first 

 column of the following table. The loch was revisited in March, 1903, 

 when the water was found to be uniform in temperature from surface 

 to bottom, as given in the second column of the table 



