216 
BATHYMETRICAL SURVEY OF 
east from Loch Grunavat. An isolated hill, Suainaval, 1403 feet in height, 
stands at the lower end of the loch on the east side. It is one of the 
longest lochs in Lewis, measnring 2| miles in a straight line from north to 
south. The greatest breadth towards the north end is a little more than 
half a mile. 
Loch Snainaval is a simple basin, with the slope of the bottom steepest 
from the shore to the depth of 100 feet. The 100-feet contour closely 
follows the shore-line except at the ends, and the area enclosed by it is 2^ 
miles in length. From the 100-feet contour to the centre the slope is more 
gradual, and only two small areas exceed 200 feet in depth. The larger of 
these areas, in the broadest part of the loch, is one-third of a mile long by 
one-fifth of a mile broad, and is flat-bottomed, with a greatest depth of 
212 feet. The lesser 200-feet area is a little south of the centre, is very 
narrow, and includes the maximum depth of 219 feet. A study of the 
contours shows that the loch has the (J "Shaped cross-section characteristic 
of lochs formed in valleys which have been occupied by glaciers.'^' The 
mean depth, 108J feet, is very great, more than three times that of any 
other loch in Lewis. 
The superficial area is nearly a square mile, or about one-fourth that 
of Loch Langavat. The volume of water, 2843 millions of cubic feet, 
shows that Loch Suainaval is the greatest lake in Lewis, being 450 
millions of cubic feet more than that of Loch Langavat, six times that of 
Loch Grunavat, and eighteen times that of Loch Trealaval or Loch 
Fadagoa, The drainage area amounts to nearly 10 square miles. The 
outflow northward to Loch Stacsavat is by the short river Eyscleit, with 
a fall of about IJ^ feet. The surface was 3 7 '4 feet above sea-level on 
July 24, 1903, which is about a foot lower than the level found by the 
Ordnance Survey on October 2, 1895. 
A series of temperatures taken on July 24, 1903, showed, consistently 
with the great depth of the loch, a greater range than was observed in any 
other loch in Lewis. The range from surface to bottom was 11°*2 Fahr., 
and the distribution as shown in the following table : — 
Surface . 
25 feet . 
50 „ . 
75 „ . 
100 „ . 
200 „ . 
57°-0 Fahr. 
55°-2 „ 
53°-0 „ 
50°-4 „ 
47°*7 „ 
45°*8 „ 
Loch Maonasgail (see Plate LXXXVIII.) is a small loch among the 
high hills which lie between the south end of Loch Suainaval and the west 
coast. It occupies a narrow valley between Tahaval, 1688 feet, on the 
east, and Mealasval, 1885 feet, on the west, which rise in steep crags 
covered with large and small stones on either side. The loch is of oblong 
* See Collet and Johnston, ‘‘ On the Formation of Certain Lakes in the Highands,” 
Proc. Boy, Boc. Edin., vol. 26, p. 108 (1906). 
