192 ALEX. L. DU TOIT. 



IX. The early Tertiary History of the Basin. 

 It seems to have been tacitly assumed that the Basin 

 has suffered but slight changes during the late Tertiary 

 and Quaternary Epochs, though Gregory has indeed pointed 

 out that the crest of the Great Dividing Range must have 

 been experiencing a gradual westerly shift and diminution 

 in altitude owing to the headward erosion performed by 

 the easterly flowing rivers. Since this implies a reduction 

 of intake area, he reaches the conclusion that the present 

 absorption from rainfall is probably insufficient to feed the 

 Basin, though such an action might have been adequate in 

 the past. 



Australian geologists appear to favour the view that 

 there was a complete withdrawal of the sea from over the 

 limits of the Basin after the deposition of the Desert Sand- 

 stone. Because of the widespread development of marine 

 tertiaries in the Murray River, Adelaide and Eucla basins, 

 and from other considerations, there is just a possibility 

 that similar beds extended into the heart of the continent, 

 but were subsequently removed by denudation; in this con- 

 nection the evidence from Western Australia is very sug- 

 gestive. Certainly, as stated further back, such a history 

 would help to explain the abnormally high temperature 

 within the Basin. 



Modification by warping of the primitive drainage is to 

 some extent evinced by the relationship of the present 

 river systems to the sub-surface contours of the Basin. The 

 ridging up of the floor at the narrowest part of the hollow 

 — between A and B — coincides with the water-parting 

 between the Flinders and the interior drainage, making 

 allowance for some capture effected by the former river. 



The deep trough south-west of Longreach is coincident 

 with the courses of the Thomson and the Barcoo rivers, the 

 watershed between these rivers and the Darling system 



