THE FRESH-WATER LOCHS OF SCOTLAND. 
175 
Feet. 
Acres. 
Per cent. 
0 to 50 
420 
38-8 
60 „ 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 folio win 
g 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 LX VI.) 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 1| square miles, and the 
drainage area is relatively large-— nearly 20 square miles. The maximum 
depth of 144 feet was observed in the wdde 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 47| 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 ofiicers 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 j^art, 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 60 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 deej)est 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 
