546 THE FRESH-WATER LOCHS OF SCOTLAND 
temperature varies greatly : thus, on 2nd May it was 73J° Fahr. 
(23° C.) at 8.45 a.m., 79° Fahr. (26° C.) at 2.30 p.m., and 69° Fahr. 
(20° -5 C.) at 9 p.m., the fall being caused by a fresh north-westerly 
breeze. The temperature was 68° to 69° Fahr. (20° to 20°-5 C.) at a 
depth of 30 feet, and fell to 62° or 63° Fahr. (16°'7 or 17°-2 C.) at 50 
feet. Between 65 and 130 feet the water had a uniform temperature 
of 59° Fahr. (15° C). This is a much higher temperature than is 
observed in the Swiss lakes at the same depth, and is partly due to 
the lower latitude and lower altitude (682 feet below sea-level), and 
partly to the hot springs which pour their waters into the lake, 
besides others which probably rise from the bottom. 
Dead Sea lies 1292 feet below sea-level. It is 46 miles long, 
and varies in breadth from 5 to 9 miles, the area being about 360 
square miles. The greater part of what is known regarding the 
depths and shore-line of the Dead Sea was ascertained by the United 
States expedition sent out in 1847 under Lieutenant Lynch,^ who 
found a maximum depth of 1278 feet in the northern portion. 
The affluents of the Dead Sea carry to it every twenty-four hours 
from six to ten million tons of water, which must all be lost by 
evaporation, so that the water of the sea contains much dissolved 
matter (24 to 26 per cent., as compared with the 3 to 4 per cent, of 
ordinary sea- water), and its specific gravity is 1T3, while that of the 
Atlantic in lat. 25° N., long. 52° W., is 1*02. Mr W. Ackroyd^ 
believes that the two causes usually assigned for the saltness of the 
water — viz. the accumulation of chlorides derived from the rocks of 
the Holy Land by solvent denudation, and the cutting off of an arm of 
the Red Sea by the rising of Palestine in past ages — are inadequate, 
and that a third cause, probably more important than either, is the 
atmospheric transportation of salt from the Mediterranean. The salt 
is brought from the sea by winds, finds its way into the rivers and 
thence into the Dead Sea, where the saline solution continually becomes 
Salter by evaporation. 
The surface of the Dead Sea is liable to frequent fluctuations in 
level, due to a succession of exceptionally dry or rainy seasons, to the 
greater or lesser activity of subaqueous springs, to landslips, to changes 
in the drainage, to the gradual silting up of the basin, and possibly 
to slight earth-movements which escape detection. The annual rise 
and fall is estimated at from 6 to 10 feet, but there seem to be also 
prolonged periods of high and low level. Lines of driftwood and 
marks on the rocks show the limits of rise which might occur under 
existing conditions, and a fall of 15 feet is quite possible during ex- 
ceptional periods of dryness. 
^ See Amer. Journ. Sci, vol. Ivii. p. 324, 1849. 
" See Quarterly Statement, Palesti?ie Exploration Fund, January 1904, p. 64. 
