CVI. IRRIGATION. GEOLOGICALLY iCONSIDE RED. 
. (3) The Western foothills of the Dividing Range and 
Western Plains.--A considerable portion of the western 
flanks of the Dividing Range from near Texas on the Queens- 
land border to the neighbourhood of Dubbo are composed 
of the Triassic rocks. These consist of sandstones, shales 
and thin seams of coal, (a continuation of the Ipswich coal 
measures of Queensland). Some of the sandstones are of 
an extremely porous character, and these constitute the 
intake beds of the artesian water area. They attain alti- 
tudes of at least 1,200 feet, and have a gentle dip towards 
the west and north-west. Of the rainfall on the western 
slopes of the Dividing Range a portion is lost by evaporation, 
a further portion is absorbed where it falls upon the porous 
rocks, and the balance enters the tributaries of the Darling. 
As most of these tributaries cross the intake beds a con- 
siderable portion of the water which they carry soaks into 
the intake beds beneath their channels, so it is easy to 
account for the fact first pointed out by Mr. H.C. Russell, 
that the annual discharge of the river Darling at Bourke 
only amounted to 1°46% of the total rainfall within its 
drainage area. 
Western Plains.—If a line be drawn from Nevertire 
through Moree to Mungundi, it approximately represents 
the eastern boundary of the plain country which may be 
termed the artesian water area. From Nevertire it is 
‘bounded by the Bogan River towards Bourke, thence in a 
general W.S.W. direction by a line from Bourke towards 
White Cliffs, and thence by an irregular line in a general 
westerly direction to the South Australian border. From 
the boundaries just described the artesian water area 
extends northwards and westwards into Queensland and 
South Australia. | zh 
The rainfall over this area varies from about 9 inches on 
the extreme west to about 22 inches‘on the east. The fall 
