362 
BATHYMETRICAL SURVEY OF 
the river Pattack, some 9 miles long, into the upper end of Loch Laggan. 
It is a loch of somewhat irregular form, about a mile long by half a mile 
broad, its long axis running nearly north-east and south-west. The 
maximum depth is 58 feet, and the mean depth 14 feet. The volume of 
water is estimated at 106 million cubic feet. The superficial area is 
about 173 acres, or fully a quarter of a square mile, and it drains an 
area of 18 square miles. It receives the greater part of the drainage of 
the east side of the mountain mass, of which Ben Alder (3757 feet) is 
the highest peak. In this drainage area are three smaller lochs, which 
were not surveyed. When surveyed in May, 1904, the height above 
sea-level was estimated (from spot-levels) at 1419 feet. 
The basin is quite simple, the contours roughly following the 
irregular outline of the shore, and the deepest part almost in the centre 
of the loch. The slopes are gentle, except opposite the mouths of the 
two rivers, both of which have laid down alluvial promontories, with 
small islands, from which the incline to the deepest water is rapid. The 
loch is on the whole shallow, for 78 per cent, of the lake-floor is covered 
by less than 20 feet of water, and 60 per cent, by less than 10 feet of 
water. 
Temperature Observations . — A series of temperatures, taken in the 
deepest part of the loch, gave 42°-6 Fahr. at the surface, 41°*4 at 25 
feet, and 40°*8 at 50 feet. 
Loch an na h-Earha (see Plate LXXXV.). — The two lochs which 
bear this name may have formed at no very distant date a single loch, 
as suggested by the common name and by the appearance of the ground. 
Be that as it may, they are now two distinct lochs, differing by nearly 
10 feet in level. In April, 1873, the Ordnance Survey officers found the 
elevation of the west loch to be 1151*7 feet, and that of the east loch 
1142*3 feet, above sea-level. They lie in a valley which runs nearly 
parallel to that occupied by Loch Laggan, to the south side of that loch, 
and distant from it about a mile. Hills of over 3000 feet rise close on 
the east ; on the west they are separated from Loch Laggan by a ridge 
of between 2000 and 2500 feet in height. The shores are for the most 
part wooded. 
The West Loch . — This is the larger, broader, and deeper of the two. 
It lies at an elevation of about 1150 feet, some 330 feet higher than 
Loch Laggan. It is fully 1| miles in length, rather less than one-third 
of a mile in greatest breadth, and a quarter of a mile in mean breadth. 
The greatest depth is 81 feet, the mean depth over 35 J feet. It has a 
superficial area of about 263 acres, or less than half a square mile, and 
drains an area of fully 5 square miles. The volume of water amounts to 
408 millions of cubic feet. The loch is fed chiefly by two small streams, 
coming down from Beinn a’ Chlachair, which unite just before entering 
the loch. A stream, half a mile long, winds through a boggy flat, con- 
