78 BATHYMETRICAL SURVEY OF 



A series of temperatures beneath the surface was taken in the deepest 

 part of the loch on May 17, at 5 p.m., with the following results : 



Surface 43'8 Fahr. 



5 feet 43 -5 



10 43 -4 



20 



30 



50 



100 



125 



150 



200 



250 



43 -3 

 43 2 

 43 -2 

 43 -1 

 42 3 

 42 -1 

 42 -0 

 41 -5 



This series shows a range of 2'3 between the temperature at the 

 surface and that at 250 feet, the greatest fall being one of 0'8 between 

 100 and 125 feet. 



Loch Tummel (see Plate XXIII.). Loch Tummel is situated amid 

 beautiful scenery, rock, wood, and water being combined in such a way 

 as to present pictures of rare loveliness, the crests of Farragon, Meall 

 Tarruinn Chon, and Schiehallion rising to great heights to the south 

 and south-west. It contains large trout and a great many pike. Loch 

 Tummel is two and three-quarter miles in length, with a maximum 

 breadth of half a mile, the mean breadth being a little over one-third 

 of a mile, or 13 per cent, of the length. Its waters cover an area of 

 630 acres, or rather less than one square mile. It drains directly an 

 area of 62J square miles, but since it receives the outflow from Lochs 

 Rannoch, Laidon, Ba, &c., its total drainage-area is about 306 square 

 miles, or 312 times the area of the loch. Nearly 300 soundings were 

 taken in Loch Tummel, the maximum depth observed being 128 feet, or 

 4 feet more than the maximum depth recorded by Mr. Grant- Wilson, 

 who took 123 soundings in 1888. The volume of water contained in the 

 loch is estimated at 1,316,635,000 cubic feet, and the mean depth at 

 48 feet, or 37 \ per cent, of the maximum depth. The length of the 

 loch is 113 times the maximum depth, and 302 times the mean depth. 

 The floor of Loch Tummel is irregular, falling into three deep basins 

 separated by two ridges, the maximum depth on the westerly ridge 

 being 52 feet, and the maximum depth on the easterly ridge being 56 

 feet. The deepest of the three basins is situated near the west end of the 

 loch, the maximum depth of 128 feet occupying a central position in this 

 basin, but a short distance to the south a sounding of 74 feet is recorded 

 in close proximity to a sounding of 127 feet. The 100-feet contour-line 

 in this western basin is almost circular and nearly one-third of a mile in 

 diameter ; about one-fifth of a mile to the east is an isolated sounding 

 of 102 feet, surrounded by shallower water. The central 100-feet basin 

 is oblong in outline and nearly half a mile in length, the maximum 



