41 



Notes on the stratigraphy of Central Australia. 



By Charles Chewings, Ph.D., F.G.S. 

 (Communicated by Walter Howchin.) 



[Read April 2, 1914.] 



Typical examples of the principal rock formations observed 

 in the Central Australian region to the present time are as 

 follows, viz.: — (1) Tertiary to Recent: gypsum beds of Lake 

 Eyre, Burt Plain shale, tops of hills around Lake Eyre ( ?) ; 

 (2) Lower Cretaceous : Lake Eyre blue shales; (3) Jurassic ( ?) : 

 Finke River sandstones ; (4) Post Ordovician : Ellery Creek 

 •conglomerate; (5) Ordovician: South MacDonnell Ranges (in 

 part); (6) Cambrian: South MacDonnell Ranges (in part) 

 and MacDonnell Ranges (in part) ; (7) Pre-Cambrian : 

 •crystalline schists, granite, etc., of the central plateau. 



Tertiary. 



The township of Oodnadatta stands upon gypseous sand- 

 stone beds which were deposited after the Cretaceous shale 

 beds had been eroded well down towards their present level of 

 erosion. Its total thickness may have been 100 to 200 ft. 

 Before erosion started on these gypsum beds only the higher 

 levels of the valleys remained unfilled. The remnants show 

 that the formation was laid down upon the uneven bottom and 

 sides of the valley of the Neales River, in a continuous sheet, 

 that stretched horizontally for many miles. The Neales River 

 has since cut its way right through the gypsum beds and down 

 into the former floor of the valley, perhaps another 50 ft. It 

 would be interesting to know whether the quartzite capping 

 to the Cretaceous beds was in existence or not when the 

 gypsum beds were laid down. If so, fragments of the 

 porcelainized sandstone should be found at the base of, and 

 also in, the gypsum beds where they impinge on the Cretaceous 

 shale, unless they were dissolved. 



On the Burt Plain, a few miles south of Burt Well on 

 the central plateau, are low-lying beds of shale and ferru- 

 ginous sandstone, calcareous grit, indurated clay, etc. These 

 beds occupy the bottoms of the valleys and represent the 

 older wash as the watercourses gradually filled to the present 

 level of the sand plains. Similar deposits occur in nearly 

 all the valleys over the plateau, in which many successful wells 

 have been sunk. These deposits may be of Tertiary age. 



