THE FRESH- WATER LOCHS OF SCOTLAND. 77 



approximately the outline of the loch, approaching very close to the 

 west end, where between the mouths of the Ogle and Kendrum burns 

 a sounding of 57 feet was taken about 300 feet from the shore, giving a 

 slope of 1 in 5'3. At the opposite end of the loch the 50-feet contour is 

 met with about one-third of a mile from the bridge across the river at 

 St. Fillans. The 100-feet basin approaches to within less than a quarter 

 of a mile from the west end, and less than half a mile from the east end, 

 and is over 5| miles in length; it covers an area of nearly 2J square 

 miles. The 200-feet basin is 4J miles in length, stretching from three- 

 quarters of a mile from the west end to 1 miles from the east end, and 

 covers an area of 1J square miles. The 250-feet basin is nearly 2 miles 

 in length, and a quarter of a mile in maximum width, extending from 

 1 J miles from the west end to 3 miles from the east end. The maximum 

 depth of 287 feet was observed near the centre of the loch, between the 

 mouths of the Allt Bhacaidh on the north and the Allt Dhunain on the 

 south, about 2| miles from the west end, and 3| miles from the east 

 end. The area of the lake-floor covered by less than 100 feet of water 

 is about 926 acres, or 38 J per cent, of the total area of the loch ; the 

 area between the 100- and 200-feet contour-lines is about 755 acres, or 

 3H per cent. ; and the area covered by more than 200 feet of water is 

 about 700 acres, or 30 per cent. The flat-bottomed character of the 

 loch is indicated by the last-mentioned percentage, which is nearly 

 equal to the preceding one, though the interval of depth is only 87 feet 

 as compared with the previous interval of 100 feet. The comparatively 

 uniform average slope from the shore down to a depth of 100 feet is 

 shown by the fact that the areas on each side of the 50-feet line are 

 nearly equal, viz. 477 acres (or nearly 20 per cent, of the entire area of 

 the loch) between the shore and the 50-feet contour, and 449 acres (or 

 nearly 19 per cent.) between the 50- and 100-feet contours. 



Loch Earn was surveyed on May 14 to 19, 1902, and the level of the 

 surface of the water \vas determined by levelling from Ordnance Survey 

 bench-mark as 317-2 feet above sea-level. This is identical with the 

 level determined by the surveyors of the Ordnance Survey on August 

 25, 1899. 



Temperature Observations. On May 14, at 3.45 p.m., the tem- 

 perature of the surface water near Lochearnhead was 46'l ; at 6 p.m. 

 the surface temperature was 44, and at 7 p.m. near the shore 47'2. 

 On May 15, at 11.30 a.m., the surface temperature near shore about 

 a mile east of Lochearnhead was 44. On May 16, at 10.30 a.m., the 

 surface temperature at the St. Fillans end of the loch was 44-l, and 

 at 1-30 p.m. it was 44. On May 17, at 5 p.m., the surface temperature 

 off Dalkenneth over the deepest part of the loch was 43'8. The range 

 observed in the temperature of the surface water during those four 

 days was thus 3-4, from 43 0< 8 to 47-2, the range in the air temperature 

 during the same period being 7-5, from 40 0> 5 to 48. 



