CHABACTERISTICS AND DISTRIBUTION OF LAKES 565 
country. It is enclosed by a rim of old rocks, which, so far as we 
know, is complete to the west and south, and has only a narrow, 
shallow lip to the north, and perhaps another to the east, so that 
there is no escape for a subterranean river. Wells have been bored, 
and furnished an abundant supply of water. The high temperature 
gradient, and the occurrence of free gases in the wells, indicate that 
the water rises from great deptlis. Again, the decrease in the yield 
of many of the wells shows that they are the modern artificial outlets 
from a vast reservoir, or underground terminal lake, the waters of 
which must have been collected during the course of centuries. 
The water from the artesian wells is mainly used for watering 
stock. The irrigation of ordinary crops in an arid country consumes 
a larffe amount of water, and the areas which could be irrio-ated from 
the wells are small in comparison with that which must lie idle. 
Henderson ^ estimated that under the most favourable conditions, and 
even if the water were lost neither bv soakage nor by evaporation, 
only the three-hundredth part of the western districts could be 
irrigated. Again, the artesian waters are not always suitable for 
irrigation, being highly saline, and especially apt to be charged with 
carbonate of soda. Luxuriant crops are produced for the first few 
years, but the evaporation of the water leaves a deposit of carbonate 
of soda, which is very injurious to the growth of the plants. 
Lake George, the largest lake in New South Wales, is 25 miles 
long, 8 miles broad, and lies at an elevation of 2100 feet above sea- 
level. It occupies an area of subsidence in the Blue Mountains, about 
135 miles to the south-west of Sydney, bounded by a fault plane of 
about 400 feet drop. It is not always a lake, for at intervals it 
shrinks for years and finally becomes dry, when it is portioned into 
grazing leases, fences running nearly across the bed, and it yields very 
good pasturage for sheep. The basin of Lake George contained 
water in the years 1816-1830, 1852 (when it attained its maximum 
depth of rather more than 10 feet), 1864, and 1874-1900; it was 
practically dry again by 1905. It occupies the southern portion of 
a depression in the Cullarin Range called the Lake George Depression, 
490 square miles in extent, and the only example in New South 
Wales of a purely inland drainage area. It is watered by several 
small streams, but has no visible outlet. Taylor corroborates the 
theory that the lake never had an outlet ; no evidence of a flood more 
than 30 feet deep can be traced as having occurred for many centuries, 
while nearly 200 feet are necessary to provide an outlet north, west, 
or south. Probably since its inception the lake has been receiving 
silt, which has gradually filled up its bed. A local flood has no 
^ See Seventeenth Ann. Rep. Hydraulic Engineering., p. 16, Brisbane, 1901. 
2 Proc. Linn. Soc. N.S.JV., vol. xxxii. p. 335, 1907. 
