THE FilESH-WATER LOCHS OF SCOTLAND. 
155 
Loch na Cuaich (see Plate LVII.) lies on the east side of Glen Truiin, 
about 5 miles north-east from the head of Loch Ericht. Stac Meall na 
Cuaich rises to a height of 3000 feet immediately to the east of the loch. 
Trending in a north-east and south-west direction, the loch is nearly a 
mile in length, with a maximum breadth of a quarter of a mile near the 
south-west end, whence it narrows gradually towards the opposite end. 
The superficial area is about 116 acres, and the drainage area exceeds 
2h square miles. The maximum depth of 85 feet was observed approxi- 
mately near the centre of the loch, but towards the south-west end. The 
volume of water is estimated at 214 million cubic feet, and the mean depth 
at 42^ feet. The loch was surveyed on May 12, 1904, and the elevation 
from S 2 )ot-levels was estimated to be about 1296 feet above the sea. The 
loch forms a simple basin, the contour-lines coinciding approximately 
with the outline, but approaching closer to the eastern than to the western 
shore, indicating a steep slope on the eastern side ; in fact, in one place a 
sounding in 50 feet was taken about 50 feet from the eastern shore, equal 
to a gradient of 1 in 1. The surface temperature was 41°-8 Fahr. 
Loch an Dum (see Plate LVII.) lies about 7 miles to the east of the 
head of Loch Ericht, and 5 miles south-east from Loch na Cuaich, at an 
elevation of 1600 feet among the mountains, which rise on the west to 
2707 feet, and on the east to 2844 feet, above the sea, the lower slopes 
forming steep screes of small material. The shores are all stony, and the 
outflow to the north is among stones. Loch an Duin drains northward 
into Loch Bhradain, and thence into Loch an t-Seilich. It is a long and 
narrow loch, trending almost north and south, and over a mile in length, 
the maximum breadth being less than one-fifth of a mile. The superficial 
area is about 102 acres, and the drainage area exceeds a square mile. The 
maximum depth of 102 feet was observed in the middle of the loch. The 
volume of water is estimated at 134 million cubic feet, and the mean depth 
at over 30 feet. The basin is simple, the deeper water occupying a central 
position, where the contour-lines approach close to the shores, showing 
that the sides are very steej) ; in one place off the eastern shore a sounding 
in 45 feet was taken about 50 feet from shore. The 25-feet basin is rather 
more, and the 50-feet basin rather less, than half a mile in length, the two 
ends of the loch being comparatively shallow, about two-thirds of the lake- 
floor being covered by less than 25 feet of water. The deep, central j>art 
is flat-bottomed, with the U "shaped section characteristic of ice-eroded 
basins. The loch was surveyed on October 14, 1904, but the elevation 
could not be determined ; from spot-levels it was estimated to be about 
1590 feet above the sea. A gravelly beach was seen at places 2 feet above 
the water. Temperatures taken in the position of the deepest sounding 
showed that the water was practically uniform in temperature throughout, 
the reading at the surface being 44°*2 Fahr. ; while at 50 and 100 feet 
identical readings of 44°' 0 were recorded. 
