18 
BATHYMETEICAL SUEVEY OF 
The volnme of water is estimated at 21 million cubic feet, and the mean 
depth at one-half the maximum depth. The loch was surveyed on 
October 11, 1902, when the elevation of the lake-surface was found to be 
112*8 feet above the sea, which is almost identical with the elevation 
determined by the officers of the Ordnance Survey on December 12, 1870, 
viz. 112*9 feet above sea-level. The surface temperature on the date of the 
survey was 46° *0 Fahr. 
St. John’s Loch (see Plate V.). — St. John’s Loch lies a little over half 
a mile to the north-east of Dunnet Bay, into which its overflow is carried 
by the Burn of Dunnet. It is a small shallow loch ; the western end is 
stony, and here many shells of lamellibranchs and gasteropods were 
found on the shore, having been thrown up by the wind. The loch is 
subcircular in outline, with a maximum diameter from east to west of less 
than a mile, the maximum breadth from north to south exceeding half 
a mile, its waters covering an area of about 195 acres, or nearly one- 
third of a square mile. The maximum depth of 7 feet was observed in the 
south-eastern part of the loch. The volume of water is estimated at 38 
million cubic feet, and the mean depth at 4^ feet. The loch was surveyed 
on October 10, 1902, when the elevation of the lake-surface was found to 
be 71*3 feet above the sea ; when levelled by the officers of the Ordnance 
Survey on February 4, 1871, the elevation was 72*1 feet above sea-level. 
The highest drift-mark observed was a foot above the level of the water on 
the date of the survey, and it was stated that the water might fall to the 
extent of 1| feet. 
St. John’s Loch is a shallow flat-bottomed basin, the deep water 
occupying the eastern half of the loch, the deepest cast in 7 feet having 
been taken about 100 yards from the southern shore and less than 400 
yards from the eastern end. The area of the lake-floor covered by more 
than 5 feet of water is about 114 acres, or 58 per cent, of the total area. 
The temperature of the surface water on the date of the survey was 46°*4 
Fahr. 
