THE FRESH- WATEK LOCHS OP SCOTLAND. 29 



Temperature Observations. The following serial temperatures, taken at 

 2 p.m. on the date of the survey in the deepest part of the loch, show 

 a range of only 1'2 Fahr. throughout the body of water : 



Surface 57'8 Fahr. 



10 feet 57-2 



20 57-0 



30 56-6 



Loch nam Breac (see Plate X.). Loch nam Breac lies about a mile to 

 the north-west of Loch na Claise Fearna, near the southern shore of Loch 

 Laxford, into which its overflow is carried by the Allt a' Mhuilinn. It is 

 most irregular in outline, with arms projecting in various directions, and 

 with one large and many smaller islands. From north to south it exceeds a 

 mile in length, with a maximum breadth of half a mile, the superficial area 

 being about 142 'acres, or nearly a quarter of a square mile. The maximum 

 depth of 71 feet was recorded in the southern wide portion of the loch. 

 The volume of water is estimated at 172 million cubic feet, and the mean 

 depth at 28 feet. The loch was surveyed on September 9, 1902, but the 

 elevation of the lake-surface above the sea could not be determined. 



Loch nam Breac is extremely irregular in conformation, which is 

 not surprising, considering that the numerous islands and projecting pro- 

 montories give rise to many constrictions in the outline. The bottom 

 sinks in two places below the 50-feet level : (1) in the most southerly 

 expansion of the loch, where there is a basin a quarter of a mile in 

 length, enclosing the maximum depth of the loch (71 feet), three sound- 

 ings having been recorded at that depth near the centre of the expansion ; 

 and (2) to the south-west of the largest island, where there is a smaller 

 basin having a maximum depth of 66 feet. These two 50-feet basins cover 

 an area of about 24 acres, or 17 j^er cent, of the total area of the loch. 

 Besides these two deep basins, there are six isolated small areas in which 

 the depth exceeds 25 feet, based in some cases on single soundings, the 

 largest and deepest lying to the north-east of the largest island, and having 

 a maximum depth of 44 feet. The area of the lake-floor covered by less 

 than 25 feet of water is about 76 acres, or 54 per cent, of the total area. 



Temperature Observations. A series of temperatures taken at 6 p.m. on 

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

 results : 



Surface 57'l Fahr. 



25 feet 57*0 



40 56-5 



45 56-0 



48 52O 



50 52-0 



60 51-0 



This series shows a range of 6'l, the position of the " sprungschicht " 

 being well marked, viz. between 45 and 48 feet, where a fall in tempera- 

 ture amounting to 4 was recorded a fall exceeding 1 per foot of depth. 



