THE FRESH-WATER LOCHS OF SCOTLAND. 



203 



practically uniform from the surface to the bottom at a depth of 1010 

 feet, the surface temperature being 41-9, while that at the bottom was 

 41'8, a range of only 0'l, and on October 23 of the same year the varia- 

 tion was from 50 0> 2 at the surface to 43-0 at the bottom in 1000 feet, a 

 range of 7-2. The temperature at the depth of 1000 feet has generally 

 been regarded as fairly constant at about 42-0 all the year round, with 

 a variation of about 0- 2, and this higher record of 43'0 may be due to 

 the increased amount of water draining into the loch during the wet 

 summer of 1903. The highest surface temperature recorded was one 



FIG. 36. FALLS OF MORAR. 



(Photograph by Mr. T. N. Johnston, M.B., C.M., F.R.S.E.) 



of 59-2 on June 30, 1902, off Bracora, the air temperature at the time 

 being 62-8, with a moderate westerly breeze. This gives a total range 

 of 17-4 between the highest surface and the lowest bottom temperature 

 recorded. 



Deposits. The deposits covering the floor of Loch Morar are mostly 

 dark brown in colour, which becomes almost black in the deeper parts. 

 A sample from 1000 feet was dark brown when wet, and greyish-black 

 when dry, containing about 50 per cent, of black vegetable matter, 

 about 10 per cent, of mineral particles (quartz, mica, hornblende, &c.), 

 with a mean diameter of 0-15 millimetre, and about 40 per cent, of 

 amorphous clayey matter, with many fine Diatoms and a few fragments 



