253 



and sandstone abutt right on to the Silurians. Subsequent to 

 the Devonian (?) epoch, it is evident that the MacDonnells were 

 meanwhile degraded to their present level, or nearly so, for out 

 of the valleys in the heart of the MacDonnell rise flat-topped 

 hills, chiefly of coarse sandstone rock frequently porcelainised. 

 Mr. H. Y. L. Brown has expressed the opinion that they may 

 be of 



Mesozoic (?) 



age. The strata dip south, as a rule, but sometimes to the north. 

 In the valley in the MacDonnell on which Glen Helen Station 

 stands a few miles of this formation is exposed, but it is beino* 

 fast eroded. It is probable the horizon will prove to be early 

 Mesozoic. Again, on the sides of the Silurian anticlinals in the 

 James Range remnants of a deposit, containing a large percent- 

 age of manganese and iron, resemble these hills in the Mac- 

 Donnell, as also do several hills in the valley of the Finke, where 

 it debouches from the ranges on to the Great Southern Plain and 

 in other places. A striking resemblance in the dip is noticeable 

 wherever these hills are met with, and they are seen to dip be- 

 neath the clays of the Lake Eyre basin. 



I have now to record the third series of foldings, and it was 

 lesser than either the Silurian or Devonian (?), and may be termed 

 the " Mesozoic " upheaval. 



Cretaceous. 



How much folding has gone on since the Cretaceous clays of 

 the Lake Eyre basin were laid on is a matter for conjecture, but 

 from exposures I saw near the junction of the Finke and Huo-h 

 Rivers, I judge it has undergone slight folding. I saw no trace 

 of this formation within the range-country — it has been pierced 

 where only a few feet thick at the junction of the Palmer and 

 Walker Creeks, and also to the south of that in wells. A lime- 

 stone-rubble closely compacted with flints and gypsum is the 

 characteristic of this rock on its northern edge, where it rests 

 unconformably on the supposed earlier Mesozoic rocks. 



Resting, I take it, unconformably on these rocks, without any 

 very marked change in appearance, and horizontally stratified, 

 next follows the supra-Cretaceous or 



Tertiary 



formations, so noted, so weary to travel over. For a description 

 of which I must refer those interested to a paper read before this 

 Society on April 2nd, 1889, by Mr. J. J. East, F.G.S. His 

 travels led him over the eastern part of the MacDonnells, mine 

 the western. For the most part he travelled outside of the Finke 

 valley. In that paper mention is made of some white gritty hills 



