THE FRESH- WATER LOCHS OF SCOTLAND. 229 



These figures indicate that the average slope is gentle in the 

 shallower water, and much steeper in depths exceeding 50 feet, but 

 it will be observed from the map that the contour-lines approach 

 very close to the shores in certain places, indicating a steep slope in 

 these positions. 



Temperature Observations. The surface temperature at 11.45 a.m. 

 on July 29, 1902, was 56'l, and at 4 p.m. on July 30, when the 

 following series was taken, it was more than half a degree lower : 



Surface ... ... ... ... ... ... ... 55 '4 Fahr. 



10 feet 55'4 



20 55'4 



30 ~ 55'4 



50 53'6 



7-1 49-8 



85 , 48'4 



120 ... 47'2 



This series shows a constant temperature from the surface down to 

 30 feet, then a slight fall of l-8 between 30 and 50 feet, followed by a 

 rapid fall of 5-2 between 50 and 85 feet, thence to the bottom a slight 

 fall of 1 0< 2, the total range of temperature from surface to bottom 

 being 8-2. 



Loch Mhic' Ille Riabhaich (see Plate L.). Loch Mhic' Ille Riabhaich 

 is a small, irregular, shallow loch lying to the south-east of Loch a' 

 Bhaid-Luachraich (into which it flows by the Allt na Criche), surrounded 

 by low, rounded hills ; 011 one of the islands is a fortress, but nothing 

 seems to be known of its history. It was surveyed on July 31, 1902, 

 but its elevation above the sea could not be determined; from the 

 contour-lines on the Ordnance Survey maps it is apparently rather 

 less than 600 feet above the sea. It is half a mile in length from 

 north to south, and rather less in maximum breadth from south-east to 

 north-west. It covers an area of about 36 acres, and drains an area of 

 nearly three-quarters of a square mile. Two soundings of 12 feet were 

 taken near the north end at the outflow, and a sounding of 10 feet off 

 the eastern shore of the larger island ; with these exceptions, the lake- 

 floor is covered by less than 10 feet of water. The volume is estimated 

 at 8 million cubic feet, and the mean depth at 5J feet. 



The temperature of the surface water at 12.30 p.m. on July 31, 

 1902, was 57-0 Fahr. 



Loch nan Dailthean (or na Daline), lying to the south-west of Loch 

 Mhic' Ille Riabhaich, and flowing into Loch Thuirnaig (an inlet of 

 Loch Ewe), was visited by the Lake Survey, but not sounded. It is 

 said to be so shallow that cows may walk over the whole of it, except 

 a small hole near Thuirnaig House, in which the depth is 4 feet. 



