THE FRESH-WATER LOCHS OF SCOTLAND. 
375 
which extends 5 miles west from the loch, among peaks rising to 
nearly 2500 feet. Two branch glens extend several miles to the 
north, and one of these brings the overflow of a small loch, Lochan 
na Beinne Baine, which was not surveyed. As a consequence of the 
extensive drainage area, the loch is subject to great alterations of level. 
The river has laid down long spits of sand, and threatens to silt up 
the loch altogether. A very short stream conveys the overflow to the 
sea; there is a boss of rock on the north side where it leaves the loch. 
In volume Loch nan Gabhar is the last in the basin, containing only 
5 millions of cubic feet, or one million less than the volume of an Dubh 
Lochan. 
The temperature of the water on May 12, 1903, was 51°-5 Fahr. at 
the surface and at the depth of 5 feet. 
The particulars regarding the lochs in the Lochy basin are collected 
together in the table on p. 374 for convenience of reference and com- 
parison. From this table it will be seen that in the twelve lochs under 
consideration, which cover an area of about 20 square miles, nearly 
2600 soundings were taken, or an average of 214 soundings per loch, 
and an average of 129 soundings per square mile of surface. The 
aggregate volume of water contained in the lochs is estimated at 85,855 
millions of cubic feet, or more than one-half of a cubic mile, and the 
area draining into them is over 270 square miles, or nearly fourteen 
times the area of the lochs. 
The Red Lochan at Tulloch . — The Bed Lochan, called in Gaelic by 
a name which signifles ‘'brown eye,” is a very small pond lying in an 
extensive morainic terrace at Fersit, near the north end of Loch Treig. 
It is only about 3.0 yards in its longest diameter, and 5 feet deep in 
the centre, is fed only by rains, and has no outflow except by percolation 
through the gravel, yet its surface is maintained almost constantly at 
the same level. The water is always turbid, and varies in colour from 
dull green to brown or red. 
It was first examined by Sir John Murray in May, 1902. The water 
was then brown ; the collection taken with the coarse net very pale 
yellow; that taken with the fine net a decided red. At that time there 
were only two very abundant organisms — the larva of an insect, 
Corethra, known as the “phantom larva,” and a reddish-coloured rotifer, 
Anurcea valga. There were many other rotifera, entomostraca, and 
other organisms common in ponds, but none of these were abundant 
enough to be held responsible for the colour of the water. The 
collection made with the fine net was examined by Dr. T. N. Johnston 
and Mr. James Murray. On adding a little formalin, which killed the 
animals, a blood-red sediment was deposited, which was found to 
consist chiefly of A. valga and myriads of its red eggs. At that time 
this species seemed to be mainly the cause of the red colour. 
