188 ALEX. L. DU TOIT. 



of vertical plane through the Basin would then be propor- 

 tional jointly to the thickness of the water-bearing beds 

 and the hydraulic gradient at that point. Over the eastern 

 part of New South Wales, using the latest published maps 

 of the isopotentials, there were plotted firstly the hydraulic 

 gradients represented by the reciprocals of the distances 

 between adjoining contours, and secondly the resistance 

 to flow which was reckoned as being inversely proportional 

 to the thickness'of the water-bearing beds. Lines of equal 

 value, that will be referred to as A and B respectively, 

 were drawn for each of these sets of quantities. 



The following relationships emerged: — (a) along the rim 

 of the Basin high values of A accompanied high values of 

 B, (b) low values of A generally coincided with low values 

 of B, (c) but elsewhere there was a marked discordance, 

 and this was especially noticeable just north of Warren, at 

 Kiameron, at Wingadee No. 4, and over a belt extending 

 N., W. and S.W. of Carinda. 



(3) Interference of Bores, — The actually observed cases 

 of direct interference of bores are few in number. Oldham 

 (II, p. 30) records a conspicuous case at Premantle in 

 West Australia, where the wells were about a quarter of a 

 mile apart: in this instance there was an actual flow from 

 one into the other. Jenkins (I, §1030) cites an instance in 

 the Ooonamble district, where the distance was about three 

 miles. Here, however, the effect observed must have been 

 solely that brought about by the hydro-dynamic impulse 

 propagated through the water-filled beds, an action that 

 with distance would be delayed and finally damped out, 

 especially in the presence of small amounts of gas. There 

 could have been no immediate bodily transference of water 

 from the one hole to the other, as the rate of movement 

 underground, as shown earlier, would have been quite low 

 even under the increased gradients developed through 

 closing or opening one of the bores. 



