THE FRESH-WATER LOCHS OF SCOTLAND. 



31 



mile from the head of Scourie bay, but at an elevation of nearly 50 feet 

 above the sea. The loch trends almost east and west, and is nearly a mile 

 in length, with a maximum breadth of a third of a mile, its waters covering 

 an area of about 111 acres, or one-sixth of a square mile. The maximum 

 depth of 121 feet was observed approximately near the middle of the loch, 

 but rather nearer the west than the east end. The volume of water is 

 estimated at 270 million cubic feet, and the mean depth at 55i feet. The 

 loch was surveyed on September 8, 1902, when the elevation of the lake- 

 surface was found to be 48*5 feet above the sea, so that the 50-feet contour- 

 line on the map shows approximately the area of the bottom which falls 

 below the sea-level. 



Loch a' Bhaid Daraich forms a simple flat-bottomed basin, with no 

 indication of any pronounced irregularity. The contour-lines coincide 

 approximately with the outline of the loch, having here and there a 

 slightly sinuous character, and there are in places steep off-shore slopes, 

 as, for instance, off the northern shore towards the west end, where a 

 sounding in 45 feet was taken about 40 feet from shore a gradient ex- 

 ceeding 1 in 1. The following table gives the approximate areas between 

 the consecutive contour-lines drawn in at equal intervals of 25 feet, and 

 the percentages to the total area of the loch : 



Oto 25 

 25 50 



50,, 75 

 75 100 

 Over 100 



Acres. 

 26 

 29 

 19 

 22 

 15 



111 



Per cent. 

 23-3 

 26-2 

 17-6 

 19-5 

 13-4 



100-0 



These figures show that Loch a' Bhaid Daraich departs from the usual 

 rule of decreasing area with increasing depth, for in each of the zones 

 between 25 and 50 feet, and again between 75 and 100 feet, the area is 

 greater than in shallower water. 



Temperature Observations. A series of temperatures taken at 2 p.m. on 

 the date of the survey, in the deepest part of the loch, gave the following 

 results : 



Surface 



20 feet 



40 



42-5 



45 



50 



60 

 ICO 

 110 



57-2 Fahr. 



57'l 



56 C -1 



54-8 



52-0 



50-8 



50-0 



48-9 



48-6 



These observations show a range of temperature throughout the body 

 of water amounting to 8 -'6, the greatest fall being observed between 42J 

 and 45 feet, viz. a fall of 2-8 in the interval of 2J feet of depth a decrease 

 exceeding \ per foot. 



