KE. F. PITTMAN AND T. W. E. DAVID. CXXXVII,. 
may be provisionally stated to be approximately 18,000 
square miles. As the mean annual rainfall on this area is 
25 inches, it follows that 1,045,000,000 cubic feet of water 
falls upon it annually. If it be assumed that only 20% of 
this rainfall is absorbed by the intake beds (and we con- 
sider that this is a low estimate),a volume of water equal 
to 3,580,273,972 gallons per day would percolate through 
the porous beds under the western plains. This volume is 
more than 274 times the amount which at present flows 
from the 284 bores which have been put down. 
VI. THE STORAGE CAPACITY OF THE PoROUS BEDs.—The 
area of country underlain. by water bearing beds in New 
South Wales is 83,000 square miles. The thickness of the 
water bearing beds, intersected in the bores varies from 
600 feet on the east near the intake to 100—200 feet on 
the western side of the area. There are therefore about 
471 cubic miles of water bearing sandstones in the artesian 
area of New South Wales, and assuming that this sandstone 
will absorh 12% of water, these 471 cubic miles of porous 
stone will hold 564 cubic miles of water.’ As the six 
principal tributaries of the Darling have eroded their 
channels through the intake beds there must be a great 
leakage of their water into the porous beds of the artesian 
area, and this is no doubt the reason why such important 
rivers as the Macquarie never reach the Darling except in 
flood time. Hence the estimate already given of the 
* Experiments with a sample of Blythesdale Braystone, taken by one 
of us (E. F. Pittman) from 8 miles north of Roma, Queensland, made by 
Mr. F. B. Guthrie, F.c.s., F.1.c., at the Agricultural Laboratory of the 
Department of Mines and Agriculture, show that this rock will absorb 
quite 123% of water, while a sample of the Triassic sandstone from near 
Yetman was found to be capable of absorbing 25%. As the bulk of the 
artesian water of New South Wales is stored in Triassic rocks, and the 
estimates quoted above are based on the porosity of the Cretaceous sand- 
stone, which is less than that of the Triassic, the above estimate may be 
taken as a minimum. 
