THE FRESH-WATER LOCHS OP SCOTLAND. 
125 
feet to the west. To the south and east of the inch depths of 22, 25, 
and 26 feet were found, separated from the deep water to the west by 
depths of 13 to 16 feet. The 10-feet basin is a continuous area, nearly 
three-quarters of a mile in length, following approximately the outline 
of the central portion of the loch, the two ends of the loch being com- 
paratively shallow, and weeds are abundant off the northern shore at 
the east end. The area of the lake-floor covered by less than 10 feet 
of water is about 56 acres, or 54 per cent, of the total area of the loch ; 
that covered by water between 10 and 25 feet in depth is about 39 
acres, or 38 per cent. ; and that covered by more than 25 feet of water 
is about 8 acres, or 8 per cent, of the entire area of the loch. The Loch 
of Forfar was surveyed on June 26, 1903, and its elevation above the 
sea was determined, by levelling from bench-mark, as being 166’3 feet; 
when levelled by the officers of the Ordnance Survey in 1861, the 
elevation was found to be 170*5 feet above sea-level. 
Temperature Observations. — Temperatures taken in the deepest part 
of the loch gave the following results : — 
Surface ... ... ... ... ... ... ... 58°‘9 Fahr. 
10 feet 58° .3 ,, 
15 „ 57°-7 ,, 
20 ,, 56° -0 ,, 
27 ,, 56° -0 „ 
This series shows a range of temperature from surface to bottom of only 
2°’9, the greatest fall being one of l°-7 between 15 and 20 feet. 
The particulars regarding the different lochs within the Tay basin 
are collected together in the table on next page for convenience of 
reference and comparison. Where the elevation above the sea has 
not been determined by levelling from bench-mark, the approximate 
elevation has, where possible, been indicated within brackets. 
From this table it will be seen that in the 59 lochs under con- 
sideration 6850 soundings were taken, and that the aggregate area of 
the water surface is about 40 square miles, so that the average number 
of soundings per square mile of surface is 172. The aggregate volume 
of water contained in the lochs is estimated at 151,353 millions of 
cubic feet. The area drained by these lochs is 1100 square miles, or 
27 J times the area of the lochs. 
