THE FRESH- WATER LOCHS OF SCOTLAND. 169 



The loch was surveyed on April 17 and 18, 1903, when the elevation 

 was found to be 702 '9 feet above the sea, or a little higher than that 

 observed by the Ordnance Survey officers on April 8, 1871, viz. 702'3 feet 

 above sea-level. Temperatures taken on April 18 showed that the water 

 was practically uniform in temperature throughout, the readings being : 



Surface 39 0> 5 Fahr. 



100 feet 39-4 



190 39-2 



Loch ' Chlachain (see Plate LXIV.) lies immediately to the east of Loch 

 Dim na Seilcheig, the difference in level being about 20 feet. The western 

 shore consists of moraine mounds, which, where cut through by the road, 

 are seen to be composed of yellow gravel, with many immense boulders, 

 some perched; a very large boulder forms a projecting point near the 

 northern end of the loch. To the e*ast the whole hillside is strewn with 

 large boulders, with perched blocks on the higher hills. 



The loch is irregular in outline, trending nearly north and south, 

 and is half a mile in length by one-third of a mile in maximum 

 breadth, covering an area of about 6< > acres. The drainage area exceeds 

 10 square miles, including Lochs Ceo-Glas and Dun na Seilcheig. The 

 loch forms a simple basin with an extensive shallow flat at the southern 

 end, due, apparently, to the deposition of material by the inflowing stream. 

 The deeper water lies towards the central part of the eastern shore, off 

 which two soundings at the maximum depth of 80 feet were recorded. The 

 volume of water is estimated at 78 million cubic feet, and the mean depth 

 at 30 feet, nearly one-half of the lake-floor being covered by less than 25 

 feet of water. The loch was surveyed on April 29, 1903, when the eleva- 

 tion was found to be 683*7 feet above the sea, or a little higher than that 

 observed by the Ordnance Survey officers on April 13, 1871, viz. 683'3 

 feet. 



The temperature of the water from surface to bottom varied little, the 

 reading at the surface being 42' -7 Fahr. ; at 10, 25, and 50 feet, 42-5 ; and 

 at 75 feet, 42'0. 



From the following table it will be seen that in the ten lochs under 

 consideration 655 soundings were taken, and that the aggregate area of the 

 water-surface is 3J square miles, so that the average number of soundings 

 per square mile of surface is 187. The aggregate volume of water con- 

 tained in the lochs is estimated at 5179 millions of cubic feet. The area 

 drained by these lochs is nearly 42J square miles, or about twelve times 

 the area of the lochs. 



