566 THE FRESH-WATER LOCHS OF SCOTLAND 
effect on the lake, the dry silt acting as a sponge. The conditions 
are extremely favourable for great evaporation. The wind may drive 
a layer of water several miles from the actual lowest spot, and before 
it can flow back the sun's heat has reclaimed it for the atmosphere. 
Lake Bathurst, lying about 12 miles east of Lake George, has an 
area of 5 square miles when full, but like the latter it sometimes dries 
up entirely. Taylor^ is of the opinion that in earlier geological 
periods the Mulwaree Creek, which drains a fairly large basin and 
flows past Lake Bathurst about half a mile to the west, received two 
tributaries, one from the north-east and the other from the south-east, 
both of which crossed the bed of the present lake. In periods of 
drought these lateral streams probably ceased flowing, with the result 
that their entrance to the main stream became blocked by material 
washed down by the Mulwaree, and a lake was formed. In 1844 the 
lake was dry ; in 1873 it overflowed into the Mulwaree ; in 1890 it 
was within a few feet of overflowing; in February 1907 only a 
quarter of its bed was covered, and the maximum d6pth was not more 
than 1 foot. Taylor found the ground at the east end of the lake 
littered with the bodies of tortoises which had been driven from the 
lake by the increasing salinity, and as there is no permanent water on 
the eastern shore, they perished. He suggests that in some such way 
many of the huge deposits of fossil vertebrates found in various parts 
of the world took their origin. 
Southern The inland drainage area of Southern Africa has been estimated 
Africa 
by Murray to exceed 110,000 square miles (see fig. 68). 
Kalahari The Kalahari extends north from the Orange River as far as Lake 
Desert 
Ngami, and is situated in the two divisions of South Bechuanaland, 
now incorporated with Cape Colony, and North Bechuanaland, a 
British protectorate. It is regarded by many as a very old accumula- 
tion of wind-blown sand ; Livingstone,^ on the other hand, spoke of 
the decrease of precipitation over the Kalahari in historic times, and 
considered that the Central and Northern Kalahari was formerly a 
lake. He went still further, stating that the manner in which the 
Zambesi River breaks through the hilly land at the Victoria Falls led 
him to think that the river probably cut down the barrier of the 
former lake, and thus drained it. Passarge ^ recounts the following 
evidence given by Livingstone as to the drying up of the Kalahari 
region : — The River Kolobeng, once rich in fish, dried up in Living- 
stone's time, and has had no water since. Lopepa, in Western 
Bamangwatoland, was at the time of his first visit a large pool of 
1 Op. cit, p. 344. 
2 See Missionary Travels a?id Researches in South Africa, p. 527, London, 1857. 
^ See Die Kalahari, pp. 98-103, Berlin, 1904. 
