THE FRESH- WATER LOCHS OF SCOTLAND. 89 



Temperature Observations. The temperature of the surface water on 

 commencing the survey at 9 a.m. on June 12, 1903, was 59-0 Fahr. 

 Later in the day serial temperatures were taken in the deepest part 

 of the loch, with the following results: 



Surface 60 i)Fahr. 



10 feet 59 -0 ,, 



15 ,, 55-3 ,, 



20 49'2 



' 49'0 >. 



45 ,, 48-0 



55 ,, ... ... ... ... ... ... ... 47'5 ,, 



The range in the temperature of the water from surface to bottom was 

 thus 12 0> 5 ; between the surface and a depth of 10 feet the fall was only 

 1, but between the depths pf 10 and 20 feet the fall of temperature 

 amounted to nearly 10 3-7 between 10 and 15 feet, and 6'l between 

 15 and 20 feet. These readings are all higher than those taken in Lochs 

 Kennard and Derculich about a fortnight earlier in the season. 



Loch Broom (see Plate XXVII.). Loch Broom, a fine trout loch, 

 but strictly preserved, lies to the east of the river Tummel, into which 

 it flows by the Lochbroom burn to the north of Ballinluig, before the 

 river Tummel joins the river Tay. It is nearly three-quarters of a mile 

 in length, and over one-third of a mile in maximum breadth, the mean 

 breadth being nearly one-fifth of a mile. Its waters cover an area of 

 about 86 acres, or over one-eighth of a square mile, and it drains an 

 area of 3J square miles an area 26 times greater than the area of the 

 loch. Over 60 soundings were taken in Loch Broom, the maximum 

 depth observed being 9 feet. The volume of water contained in the loch 

 is estimated at 18,813,000 cubic feet, and the mean depth at 5 feet, or 

 56 per cent, of the maximum depth. The length of the loch is 422 times 

 the maximum depth, and 757 times the mean depth. 



Loch Broom is very shallow, being simply a large bog-hole, or 

 depression in the moorland, with shores of yellow sandy debris covered 

 by peat, and all heather clad. The outflow is over a dam about 5 feet 

 high, so that the greater part of the loch must be artificial. Where the 

 depth is less than 5 feet the bog-bean is everywhere seen, and there are 

 numerous islets some of peat, others chiefly of bog-bean on several of 

 which gulls nest. The deeper water (over 5 feet) lies to the east and 

 north of the islets, the maximum depth of 9 feet having been observed 

 in several places towards the eastern shore ; along the western shore and 

 around the islets the bottom is covered by less than 5 feet of water, but 

 at the outflow, where the waters of the loch pass into Lochbroom burn, 

 two soundings of 5 feet were taken. The area of the lake-floor covered 

 by less than 5 feet of water is about 38 acres, or 44 per cent, of the 

 entire area of the loch, while that covered by more than 5 feet of water 



