202 ALEX. L. DU TOIT. 



been diluted the least, aud it is suggested therefore, that 

 some of the supplies struck above the main flow, represent 

 wholly or in part, "residual waters" enclosed in the strata 

 at the time of their deposition or introduced at an early 

 stage of the Tertiary. 



According to the rate of flow calculated, assuming the 

 same fall of the hydraulic surface as at present, water 

 would take about 20,000 years to cross the widest part of 

 the Basin, and knowing the great affinities that fine sedi- 

 ments and clays have for soluble salts, it is only to be 

 expected that the beds would require the passing of much 

 water to accomplish the forward transference of saline 

 matter, so that the time involved for this action may there- 

 fore have been very considerable. 



While the total yield of the Mound Springs cannot be 

 estimated, even roughly, all observers are agreed that their 

 output, judging from their numbers, must be enormous — 

 take the case alone of the Boiling Springs near Coward 

 Springs in South Australia, estimated at a million gallons 

 per day— while there are many small springs on the eastern 

 side of the Basin as well (I, pp. 50-1). 



Their action as safety-valves implies that they were able 

 to discharge water sufficiently rapidly to prevent the excess- 

 ive rise of the hydraulic surface in that quarter. It is 

 reasonable to conclude therefore, that this volume might 

 have been approximately equal to the quantity absorbed 

 by the intake and transmitted westwards, due allowance 

 being made for the amount lost by leakage below the Gulf 

 of Carpentaria, and perhaps some to the south and south- 

 west also. 



On the other hand the observation of extinct mound 

 springs, such as on the western plains of New South Wales 

 by Pittman, in South Australia at Dalhousie Head by H. 

 Y. L. Brown, and near Langlo Downs (S.W. of Tambo) by 



