CXII. IRRIGATION GEOLOGICALLY CONSIDERED, 
The only exceptions to the. general rule.as to the level con- 
figuration of the artesian area within New South Wales, 
are (1) the intake beds, which, as already stated, attain 
altitudes of at least 1,200 feet along its eastern margin, 
and form hilly to mountainous country along the western 
flanks of the main Dividing Range; and (2) the inliers of 
Paleozoic sediments and igneous rocks such as Mount 
Brown (Silurian slate), Mount Foster (Felspar-porphyry), 
Tibooburra (granite). These inliers formed islands in the 
Triassic Lakes and Cretaceous Seas during the deposition 
of their respective sediments; and (3) Outliers of Desert 
Sandstone (Upper Oretaceous). These cappings of Desert 
Sandstones are mostly met within the N.W. corner of New 
South Wales. Over a considerable area they form low 
isolated hills, rising to not more than 20 or 30 feet above 
the general level of the surrounding country, but in places 
they attain to larger dimensions, up to 500 feet, as for 
example in the case of Mount Oxley near Bourke, Mount 
Poole near Milparinka and the Gray Ranges north of Tiboo- 
burra. For the most part these Desert Sandstone outliers 
rest on the Triassic or Cretaceous rocks of the artesian 
water area, but occasionally asat Mounts Oxley and Poole 
they repose upon Paleozoic rocks. 
In Queensland a very large portion, (estimated at about 
377,000 square miles, or more than half the area of Queens- 
land) of the artesian area is composed of undulating downs, 
the surface rock being of Lower Cretaceous Age (the Rolling 
Downs Formation) which has not as yet been observed to 
outcrop in New South Wales unless the thin series of marls 
and sandy shales outcropping in the north bank of the 
Darling near Bourke Bridge be referable to that formation. 
What are considered by the Queensland geologists to be 
the intake beds, and termed by them the Blythesdale 
Braystone (the basal beds of the Lower Cretaceous System), 
