174 
BATHYMETRICAL SURVEY OP 
the two largest lochs in the island (Lochs Frisa and Ba) could be sounded. 
The first-named lies in the northern portion of the island near Tobermory, 
while the other lies near the head of Loch na Real, an arm of the sea 
which nearly cuts the island into two portions, the connecting isthmus 
between Loch na Real and Salen bay being less than 3 miles across. The 
scenery around the lochs is very fine, and the fishing, which is preserved, 
includes salmon, grilse, Salmo ferox, sea-trout, and brown trout. 
Loch Frisa (see Plate LXVII.) is the largest loch in the island, and 
is distant about 3 miles from Tobermory. The margin is nearly all stony 
and free from weeds, except at the south-east end, where the Ledmore 
river flows out through an alluvial flat. The loch is elongate in outline, 
and trends north-east and south-west, being miles in length by over 
half a mile in maximum breadth, the mean breadth exceeding one-third of 
a mile. Its waters cover an area of If square miles, while the drainage 
area is small, about 8 square miles. The maximum depth of 205 feet was 
recorded near the middle of the loch, where the wddth is greatest. The 
volume of water is estimated at 3603 million cubic feet, and the mean 
depth at 764 feet. The loch was surveyed on August 16 and 17, 1904, 
but the elevation could not be determined ; the Ordnance Survey officers 
found the elevation on November 22, 1866, to be 245'4 feet above the sea. 
The soundings show that the floor of Loch Frisa is irregular. It is true 
that the shallower contours are continuous, but they are in places sinuous 
in character, while the 150-feet contour encloses no fewer than three 
isolated areas. The largest and deepest of these 150-feet areas is centrally 
placed, and is separated from the other two — one lying to the north-west, 
the other lying to the south-east — by ridges covered respectively by 138 
feet and 146 feet of water ; the northern area is based on soundings in 
163 and 173 feet, while the southern area is based on a sounding in 165 
feet. The deepest sounding (205 feet) is the only one recorded in over 
200 feet of water. The longitudinal section A-B on the map shows 
these three 150-feet basins separated by shallower water, and the cross- 
section C-D, at the position of maximum depth, shows a conspicuous rise 
of the bottom towards the western shore. The next line of soundings 
farther to the north also shows a conspicuous rise of the bottom in the middle 
of the loch, where a sounding in 95 feet was taken between soundings in 
128 and 170 feet. The soundings off-shore do not show any steep 
gradients exceeding 1 in 1, the steepest shore-slope being observed in the 
central part of the loch, opposite Lettermore, where, off the eastern shore, 
a sounding was taken in 36 feet at a distance of 40 feet from shore, and off 
the western shore soundings in 60 feet and 85 feet were taken at distances 
of 80 and 100 feet respectively from shore. 
The following table shows the approximate areas between the contour- 
lines, and the percentages to the total area of the loch : — 
