190 R. LOGAN JACK^ LL.D., F.G.S., ETC., ON 



Actual measurements of pressure in the ilowiug- bores — 

 from wliich, of course, the height to which water would rise 

 in a pipe can be calculated — sliow that the hydraulic surface 

 of fact corresponds so closely with the hydraulic surface, on 

 the theory of a submarine outlet, that I regard the theory as 

 practically justified. 



10. Mr. Hendpvsons ho-Potential Map. — From the data 

 afforded by the existing bores, Mr. Henderson (who 

 watches the progress of the bores Avitli paternal care) 

 has prepared a chart, of which a second issue is given 

 with his "Report for the year ending oOtli June, li)00," 

 showing what he calls Iso-potential lines, or lines along 

 which the pressure would raise water to equal heights above 

 the sea. The value of these iso-potentials cannot be 

 over-estimated; for where the observations are sufficiently 

 numerous to allow them to be drawn with accuracy, they 

 enable an intending borer to judge beforehand, if he knows 

 the level of his groun-:!, Avhether he can hope to strike a 

 flowing supply or whether his expenditure will be thrown 

 away. 



11. Mr. Cameron's Equi-AItitndinal Map. — j\Ir. Walter E. 

 Cameron, of the Geological Survey of Queensland, has 

 constructed an " Equi-altitudinal " map, in which, by treat- 

 ing the various bores as so many soundings, he has given 

 a fair idea of the contour of the upper surface of the 

 water-bearing beds at the base of the Cretaceous forma- 

 tion. From this map it appears that these beds come 

 near the surface, or even reach the surface, on a saddle 

 extending east and west from the Woolgar to the Cloncurry 

 in a manner which is suggestive of a delta thrown across 

 one of the narrowest parts of the sea which in Cretaceous 

 times divided Australia into two islands. By referring all 

 the bores to the sea-level, and making contour lines joining 

 those in which the beds are the same height above or depth 

 below the sea, Mr. Cameron brings out the fact that the 

 water-bearing beds form two basins or scoops, one deepening 

 northward to the Gulf of Carpentaria and the other deepen- 

 ing from Hughenden to the south-west, or towards Lake 

 Evre and the Great Australian Bight. This, to my mind, 

 amounts to a demonstration of the seaward flow of the 

 underground water. 



12. Regarding the Permanence of the Underground Supplies. — 

 The questions of the permanence of the present flow of 

 .subterranean water and how far it may be increased are of 



