256 
BATHYMETRICAL SURVEY OF 
after heavy rains. The two lochs trend east and west, and the outflow 
from Loch na Creige Duibhe passes into Loch Mama, and thence by 
the Gleann Mama into Loch nan Uamh. 
Loch Mama (see Plate LVI.). — Loch Mama is over one-third of a 
mile in length, one-eighth of a mile in maximum breadth, and one- 
twelfth of a mile in mean breadth. Its waters cover an area of about 
17 acres, and it drains directly an area of two-thirds of a square mile, 
but since it receives the outflow from Loch na Creige Duibhe its total 
drainage area is over 2 square miles, an area seventy times greater than 
that of the loch. Nearly 40 soundings were taken, the maximum depth 
observed being 44 feet. The volume of water contained in the loch is 
estimated at 11 million cubic feet, and the mean depth at 14;^ feet. The 
loch was surveyed on July 11, 1902, and the elevation of the lake- 
surface above the sea was determined from spot-levels as being 359 
feet. It forms a simple basin, the deepest part being found towards 
the east end. The areas between the contour-lines, and the percentages 
to the total area, are as follows : — 
0 bo 10 feet 8'0 acres 
10 „ 25 „ 6-4 „ 
Over 25 ,, 2’6 ,, 
17 0 ,, 100-0 
Loch na Creige Duibhe (see Plate LVI.). — Loch na Creige Duibhe is 
four-fifths of a mile in length, one-eighth of a mile in maximum breadth, 
and one-fourteenth of a mile in mean breadth. Its waters cover an 
area of about 36 J acres, and it drains an area twenty-four times greater, 
or about IJ square miles. Over 70 soundings were taken, the maximum 
depth recorded being 93 feet. The volume of water is estimated at 
52 million cubic feet, and the mean depth at 32 J feet. The loch 
was surveyed on the same day as Loch Mama (July 11, 1902); the 
elevation of the lake-surface above the sea, from spot-level and by 
comparison with Loch Mama, was found to be 359-7 feet. An inspection 
of the map shows Loch na Creige Duibhe to be (like Loch Mama) a long 
narrow basin of very simple conformation. It is much deeper than Loch 
Mama, and the deeper water approaches nearer to the west than to the 
east end, that is to say, nearer to the alluvial cone separating the two 
lochs. A similar state of matters has been noted in the case of Lochs 
Voil and Doine in the Forth basin, formerly a continuous loch, now 
divided into two portions by the deposition of material brought down 
by the river, where deep water approaches close to the dividing 
promontory of land on both sides. 
The areas between the consecutive contour-lines drawn in at equal 
46 '9 per cent. 
37-5 
15-6 
* See p. 9. 
