THE FRESH-WATER LOCHS OF SCOTLAND. 



265 



maximum depth of 217 feet, and the largest one extending from north 

 of the Douglas water delta as far as Ardvorlich, about 2 miles from the 

 head of the loch, enclosing all the deeper basins. The 300-feet and 

 400-feet contours are continuous, and enclose areas respectively over 8 

 and nearly 7 miles in length, lying to the north of the Douglas water 

 delta. The 500-feet basin is cut in two portions by a ridge, on which the 

 greatest depth is 483 feet, crossing the loch just south of Tarbet, the 

 smaller southern portion being over a mile in length, and having a 

 maximum depth of 564 feet, while the northern portion exceeds 3 miles 

 in length and encloses the maximum depth of the loch. The 600-feet 

 basin is a mile in length, and lies to the north of Tarbet, the maximum 

 depth of 323 feet having been recorded little more than half a mile to the 

 north-east of Tarbet island. 



The survey of Loch Lomond occupied from May 30 to June 19, 1903. 

 On commencing work the elevation of the surface of the water was 

 determined by levelling from two bench-marks as being 23*9 feet above 

 mean sea-level, and during the progress of the survey the water slowly fell 

 to the extent of more than a foot, but all the soundings were reduced to 

 that datum level ; the elevation determined by the officers of the Ordnance 

 Survey on October 12, 1896, was 26*9 feet above the sea, or 3 feet higher 

 than on May 30, 1903. A drift-mark measured on June 9, 1903, was 

 found to be 7J feet above the water surface, so that the range in level is 

 considerable. 



Temperature Observations. The temperature conditions in Loch Lomond 

 have been studied by Mr. J. Y. Buchanan and others, and for purposes 

 of comparison half a dozen serial observations taken during the survey 

 are given here, arranged geographically from north to south. 



SERIAL TBMPEBATUBES IN LOCH LOMOND. 



