PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN RASIN. 153 



In regard to the figures computed from the bore records, 

 some are certainly not quite exact, since the depth to the 

 principal water-bearing stratum is not always exactly 

 known, or there may be a mixing of the main flow with 

 cooler water from a higher horizon. All figures from very 

 shallow bores, and also any particularly discordant numbers, 

 have been excluded, but at the same time it is only fair to 

 point out that the curves obtained (see Diagram II) from 

 the evaluations cannot be " smoothed down " unduly, since 

 it is precisely towards the detection of such thermal irregu- 

 larities that the analysis is being directed. 



In addition to the mean temperature gradient calculated 

 in this way, there is also the very interesting problem of 

 the change of temperature increment ivitli depth, but here 

 the lack of the necessary data prevents more than a state- 

 ment of the position as regards a few cases. Thus some- 

 times, where two or more flows have been struck, the 

 respective gradients (measured downwards from the surface 

 zone of constant annual temperature) are the same, for 

 example, Darr River Downs No. 3 in Queensland; but there 

 are cases in which the upper flow possesses a steeper 

 gradient than the lower, as in Ounnamulla and Northampton 

 Downs in Queensland, and in Beanbah No. 1, Bundy, Quam- 

 bone Nos. 1 and 2, and Wiogadee Nos. 2 and 4 in New South 

 Wales. 



In these the apparent rate of increase of earth temper- 

 ature between the upper and lower flows ranges between 

 1° F. in 64 and 1° F. in 127 feet. Making the extreme 

 assumption that the issuing water includes the whole of 

 the upper supply (which, be it noted, actually possesses a 

 lower static pressure) the theoretical temperature of the 

 bottom supply can be calculated, but this computed inter- 

 artesian gradient, though now steeper, is still far less rapid 

 than the figures obtained for the upper flow in the instances 

 quoted. 



