THE FRESH- WATER LOCHS OF SCOTLAND. 175 



Feet. Acres. Per cent. 



Oto 50 ... 420 ... 38-8 



50 100 303 ... 27-9 



100 150 272 ... 25-1 



150 200 85 ... 7-9 



Over 200 3 ... 0-3 



1083 100-0 



Temperature observations in the deepest part of Loch Frisa on 

 August 17, 1904, gave the following results : 



Surface 59-l Fahr. 



20 feet 59-0 



50 58-7 



75 58-7 



100 56-6 



175 55-2 



These readings show that the range of temperature from surface to 

 bottom amounted to only 4, a fall of 2 being recorded between the depths 

 of 75 and 100 feet, while the upper layers of water were practically uniform 

 in temperature. 



Loch Ba (see Plate LXVI.) is situated little more than 2 miles to the 

 south of Salen, and is surrounded by high hills except at the northern end 

 where the river Ba flows out. The water in the loch was very clear, not 

 peaty, and no phanerogamic flora was observed around the shores. The 

 loch trends in a north-west and south-east direction, and is 3 miles in 

 length, the maximum breadth near the northern end exceeding three 

 quarters of a mile. The superficial area is nearly l square miles, and the 

 drainage area is relatively large nearly 20 square miles. The maximum 

 depth of 144 feet was observed in the wide northern portion of the loch, a 

 little more than a mile from the lower end. The volume of water is 

 estimated at 1602 million cubic feet, and the mean depth at 47J feet. 

 The loch was surveyed on August 15 and 16, 1904, but the elevation could 

 not be determined by levelling from bench-mark ; in March, 1867, the 

 Ordnance Survey officers found the elevation to be 40'6 feet above the sea. 



The soundings show that the floor of Loch Ba is somewhat irregu- 

 lar, due principally to the fact that a shallow ridge crosses the loch 

 at its narrowest part, a little more than a mile from the southern end. 

 Here the breadth is only a quarter of a mile, and the deepest sounding 

 recorded on the ridge was 00 feet. The 25-feet and 50-feet areas are thus 

 continuous, and extend nearly the whole length of the loch, but the 75-feet 

 area is cut^ into two portions, the smaller portion to the south-east of the 

 ridge having a maximum depth of 95 feet, while the larger portion to the 

 north-west of the ridge includes the deepest water in the loch, the 100-feet 

 basin being nearly a mile in length. The longitudinal section A-B on the 

 map shows the shallow ridge referred to, while the cross-section C-D, taken 

 at the position of maximum depth, shows a regular bottom, but one or two 



