THE FRESH-WATER LOCHS OP SCOTLAND, 
137 
wben the elevation was 810 o feet above the sea, nearly identical with the 
elevation determined by the Ordnance Survey on May 18, 189(3, viz. 810*4 
feet. 
Temperature Observations . — The following temperatures were taken in 
the deepest part of the loch : — 
Surface ... 
5 feet . . . 
10 „ ... 
25 „ ... 
56 „ ... 
46°-0 Fahr. 
44°*3 „ 
44°-0 „ 
44°*0 „ 
43°*0 „ 
The range from surface to bottom was 3°, a fall of 1°*7 being observed 
between the surface and a depth of 5 feet, while the readings at 10 and 25 
feet were identical. 
St. Mary^s Loch (see Plate XLIX.). — St. Mary’s Loch is situated about 
10 miles south of Peebles, 12 miles south-west of Selkirk, and 13 miles 
north-east of Moffat, and is somewhat crescentic in outline, the narrower 
upper portion trending nearly north and south, while the wider lower 
portion trends in a north-easterly direction. It is 3 miles in length, the 
maximum breadth exceeding half a mile, the mean breadth being one-third 
of a mile. The superficial area is about 635 acres, or 1 square mile, while 
the drainage area, including the area draining into the Loch of the Lowes, 
extends to about 42 square miles. The maximum depth of 153 feet was 
observed in the wider part of the loch, about Ij miles from the northern 
end. The volume of water is estimated at 2018 millions of cubic feet, and 
the mean depth at 73 feet, or nearly half the maximum. There are two 
deep basins exceeding 100 feet in depth, separated at the entrance of the 
Megget water by a ridge, on which a maximum depth of 88 feet was found : 
the larger and deeper one towards the lower end is nearly IJ miles in 
length, while the smaller one towards the southern end has a maximum 
depth of 112 feet, and is over half a mile in length. The areas between 
the contour-lines, and the percentages to the total area, are as follows : — 
Feet. 
Acres. 
Per cent. 
0 to 50 
229 
35*9 
50 „ 100 
207 
32-6 
100 „ 150 
.. ... 193 
30-4 
Over 150 
6 
1-1 
635 
100-0 
The loch was surveyed on May 5 and 6, 1905, when the elevation was 
found to be 809*5 feet above the sea, or more than a foot higher than the 
elevation determined by the Ordnance Survey officers on May 18, 1896, viz. 
808*2 feet. 
Temperature Observations . — The following temperatures taken in the 
deepest part of the loch at 6*30 p.m. on May 5, 1905, showed that the 
range from surface to bottom was only 1°*8 Fahr. ; — 
