PROBLEM OF THE GREAT AUSTRALIAN ARTESIAN BASIN. 193 



agreeing in position with the underground ridge between 

 Oharleville and Bourke; coincidence in plan is found even 

 in the case of the tributaries between Roma and Warren. 

 Howchin again has pointed out the modifications of the 

 interior drainage brought about in the south-west by the 

 ridging up of the Mount Lofty Ranges and by the trough- 

 faulting in the Spencer's Gulf— Lake Eyre region. 



In addition to this gentle warping the much more extens- 

 ive upheaval just east of the Great Dividing Range came 

 about, whereby the Jurassic beds were brought up some 

 thousands of feet above their level at the centre of the 

 Basin and. laid bare along its eastern margin. If Jack's 

 views in regard to the stratigraphical relationships of the 

 Desert Sandstone to the north and to the south of Hughen- 

 den are correct, certain portions of the intake beds must 

 have remained sealed beneath an unconformable cover of 

 Upper Cretaceous strata as well of Tertiary basalts until a 

 comparatively late period. 



Even without any addition of rain to the outcrops, this 

 tilting would have produced a gravitative movement of the 

 contained or connate water towards the west, and it is 

 suggestive to find that the Oloncurry-Richmond and the 

 Bourke-Oharleville "rolls," when extended, strike the back- 

 bone of Queensland, where the latter attains its maximum 

 height, and where the Jurassic beds rise to over 2,000 feet 

 above sea-level. It is precisely there, also, that the high 

 potential regions are located, and, when comparisons are 

 made with the Hydraulic Diagram (IV), the surface con- 

 tours of the Thomson Valley will be seen to conform with 

 the courses of the isopotentials to an unexpected degree. 



This suggests that very late earth movements rather 

 than mere rainfall, may have determined the main distribu- 

 tion of potential over the eastern side of the Basin. 



M-July 4, 1917. 



