132 E. F. PITTMAN. 



to show that most of the Darling rainfall is lost in that 

 way rather than by percolation underground. He states 1 

 that evaporation would get rid of more rain than ever falls 

 in Central Australia. No one would think of questioning 

 the truth of this statement, but it has little or no bearing 

 upon the subject under discussion. The water does not 

 enter the porous beds in Central Australia, but on the flanks 

 of the Dividing Range, at high altitudes, where the rainfall 

 is much greater, and the evaporation much less than it is 

 in the central plains. 



Internal Heat of the Earth.— The objections to the 

 hydrostatic pressure theory having been discussed and 

 answered, Professor Gregory's suggestions as to the cause 

 of the ascent of the water in the flowing wells may now be 

 briefly considered. They are that it is due to the internal 

 heat of the earth, and to the effects of rock pressure. With 

 regard to the first it may be stated that if the earth's 

 internal heat were sufficient to cause the water to rise 

 above the surface in bores, it would, before the bores were 

 put down, have forced it back along the porous beds, with 

 the result that it would have overflowed at the surface; 

 in other words, the porous beds would never have become 

 saturated with water. Another objection is that the water 

 is not hot enough to be accounted for in this way, the hottest 

 water flowing from an artesian bore being 10° below boiling 

 point. 



Rock Pressure.— The second suggestion is that the water 

 is forced to the surface by the pressure of an overlying 

 sheet of impermeable rock. On this subject Gregory writes 2 : 



"Attention was first called to the importance of rock pressure 

 in reference to flowing wells by R. Hay. . . . See e.g. F. B. 

 Gipps, Journ. R. Geogr. Soc. Austral. (New South Wales Branch), 

 Vol. vi., 1896, p. 4." 



1 Dead Heart of Australia, p. 325. 2 Ibid., p. 289. 



