THE FRESH- WATER LOCHS OF SCOTLAND. 301 



The floor of Gorm Loch M6r is most irregular, islands and banks 

 and deep soundings being found here and there in close proximity, 

 while in other places deep water approaches close to the shore. The 

 contour-lines are of the most sinuous description, with isolated deep 

 and shallow patches. The deepest part of the loch runs along the 

 western shore, off which the slope is uniformly rather steep, and occurs 

 towards the north-western end, as will be seen in the longitudinal 

 section A-B on the map. The areas between the contour-lines, and 

 the percentages to the total area of the loch, are as follows : 



to 25 feet 126 acres 68 per cent. 



25,, 50 35 19 



50,, 75 16 8 



Over 75 , 8 , 5 



185 100 



Temperature Observations. A surface reading at 10 a.m. on October 

 22, 1902, when commencing the survey, gave 44 Fahr., but at 2 p.m. 

 in the deepest part of the loch a series of temperatures gave identical 

 readings, viz. 46'2, at the surface and at 10, 25, 50, and 75 feet. 



LochAilsh (see Plate LXIX.). Loch Ailsh lies about 10 miles to the 

 west of Loch Shin, with the heights of Ben More Assynt and Coniveall 

 rising to the north. It is a moderate-sized but rather shallow loch, 

 containing trout and an occasional salmon or grilse. It is irregular in 

 outline, slightly under a mile in length from north to south, with a 

 maximum width in the northern portion exceeding half a mile. Its 

 waters cover an area of about 245 acres, and it drains an area 44 

 times greater an area of nearly 17 square miles. The maximum depth 

 of 24 feet was observed in the north-eastern part of the loch, less than 

 a quarter of a mile from the alluvial cone laid down at the mouth 

 of the river Oykell on the northern shore. The volume of water is 

 estimated at 88 million cubic feet, and the mean depth at 8J feet. The 

 loch was surveyed on September 6, 1902, when the elevation of the 

 lake-surface above the sea was found to be 498'5 feet, almost identical 

 with that observed by the Ordnance Survey officers on August 29, 1871, 

 viz. 498-4 feet. The highest drift-mark observed was 4 feet above the 

 level of the water on the date of the survey. The southern and western 

 portions of Loch Ailsh are covered by less than 10 feet of water, the 

 deeper part lying along the eastern shore and towards the north-eastern 

 angle of the loch. The area of the lake-floor covered by less than 10 

 feet of water is about 173 acres, or 71 per cent, of the entire area, while 

 that covered by more than 20 feet of water is only about 12 acres, or 

 5 per cent. The temperature of the surface water at 2 p.m. on the 

 date of the survey was 55 0> 3 Fahr., and a reading at a depth of 20 feet 

 gave 54. 



