214 BATHYMETRICAL SUKVEY OF 



volume of water 2388 millions of cubic feet. It is the only loch in Lewis 

 the area of which exceeds a square mile. Though four times the area of Loch 

 Suainaval, the next to it in size, the volume is less by 450 millions of cubic 

 feet. The drainage area measures nearly 28 square miles. The feeders 

 are all small local streams, the largest, Glen Langadale, at the upper end 

 of the loch. From near the northern extremity of the loch two wide 

 channels lead into Loch Airidh na h'Airde, whence a chain of lochs, with 

 only very short connecting streams, extends some 4 miles northward to the 

 head of Loch Koag near Callernish. Loch Coirigerod, 1J miles long, 

 which stands at a higher level than Loch Langavat, was not surveyed. 



The surface at the time of the survey (July 13 to 18, 1903) was 

 108-0 feet above sea-level. 



Temperature Observations. The following^ serials were taken during 

 the survey : 



July 16. July 17. 



Surface 56-8 56-l 



20 feet 56-2 56-l 



50 55-4 56-0 



87 55-l 



92 55-0 



Loch Grunavat (see Plate LXXXVI.) is a fairly large loch, lying about 

 2 miles to the west of Little Loch Roag. Though of the narrow form of 

 valley lochs, it does not occupy a well-marked valley. High land 'occurs at 

 the ends of the loch, while the sides are comparatively low. The length 

 is 21 miles, and the greatest breadth, about the middle of the loch> half a 

 mile. The shore-line is irregular, with several promontories and deep 

 inlets. A large island occupies almost the exact centre of the loch, South 

 of the island the loch is almost everywhere shallow ; north of it is a simple 

 and comparatively deep basin. The 25-feet and 50-feet contours extend a 

 short distance south of the island, the deep channel passing between the 

 island and the west shore. Halfway between the island and the north end 

 is a small area over 75 feet in depth, with the maximum of 90 feet. The 

 mean depth is 28 feet, the area about 387 acres, and the volume of water 478 

 millions of cubic feet. The area draining into the loch is 3 square miles ; 

 there are no inflowing streams of any size. The outflow, near the southern 

 end of the loch, through the inlet called Loch na Ciste, which could not be 

 entered, is by the Gisla river, flowing 2 miles eastward into Little Loch 

 Roag. The surface was 365-4 feet above sea-level on July 28, 1903. 



The temperature had a range of 6 Fahr. from surface to bottom, the 

 readings being : 



Surface 61'5 Fahr. 



15 feet 59-2 



25 58-0 



50 56-l 



80 , 55-6 



