150 ALEX. L. DU TOIT. 



ably exists at greater depths ; this series is indeed well 

 developed in the Leigh's Creek Artesian Basin 1 due south of 

 Hergott. 



To the west of Oodnadatta 2 the covering of blue shales 

 gradually grows less, but the porous water beds are over- 

 lapped by the Upper Cretaceous series, or are concealed by 

 superficial deposits in that direction ; they seem to crop 

 out to the north-west in the Northern Territory, however. 



It is moreover precisely in those parts of the basin where 

 such is the case, not only along the outer edge, but around 

 inliers of older rocks as well, and at a few other points 

 where the cover is thin, that the waters have burst out at 

 the surface; such springs have unanimously been regarded 

 in the light of safety-valves for the relief of hydraulic 

 pressure. There is a chain of cold springs on the east, 

 between Aramac and Richmond, but those across the 

 shallow tract between Croydon and Cloncurry, and thence 

 halfway round the periphery, past Hergott and at intervals 

 to Bourke, are generally warm, having the same chemical 

 composition as the waters of the Great Basin. 



The annual outflow from the Mound Springs must be of 

 no small magnitude, even without taking any account of 

 the water that is escaping laterally into porous drifts, such 

 as are met with in the upper levels of many of the bores, 

 and that, though usually dry, somtimes provide small flows. 

 The part played by the Mound Springs in the hydraulics of 

 the basin will be considered later. 



Considering the thousands of bores that have been sunk, 

 the geological information recorded from them is remark- 

 ably meagre, and this is all .the more regrettable, in view 

 of the immense value of the data that could have been 

 acquired systematically during the past quarter of a 

 century. 



1 Brit, Assoc. Handbook, S.A., pp. 174 and 223-6, 1914. 

 2 Geol. Surv. 8. Australia, Bull. No. 5, 1915. 



