174 BATHYMETRICAL SURVEY OF 



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 Keal, an arm of the sea 

 which nearly cuts the island into two portions, the connecting isthmus 

 between Loch na Keal 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 4J 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 width is greatest. The 

 volume of water is estimated at 3603 million cubic feet, and the mean 

 depth at 76 J 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 1 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 : 



