49 



Petermami Creek, and elsewhere. The limestones and 

 quartzites in many places have furnished ample fossiliferous 

 evidence to set the age of these beds at rest. The limestones, 

 etc., forming the core of the Ooramimia Range are similar 

 to those in the James Range, but in the latter brittle hard 

 shales and conglomerate-quartzite and slaty bands are also 

 much in evidence. Possibly, Cambrian strata may be repre- 

 sented there as well, but until proven the whole may well be 

 included in Ordovician. The Ordovician rocks are well 

 developed in the South MacDonnell, where they form flanking 

 ranges to the Cambrians and the granitic rocks of the central 

 plateau. They dip off the Cambrians in a southerly direction 

 at high angles, also vertically, and in one spot they are over- 

 folded. The strike of the strata is east-west, and the post- 

 Ordovicians repose upon them without any appreciable uncon- 

 formity. Tate and Watt found 1° only of difference in their 

 angles of dip. They form the core of what is locally known 

 as the South MacDonnell, and also the ranges to the south, 

 where, frequently, they are seen to stand vertically. They 

 also dip north and south of the anticlinals at varying angles, 

 and in places form gently-undulating beds which cover ex- 

 tensive areas. They dip under the Jurassic ( ?) sandstones at 

 Francis Well, on the Hugh, and also near Idracowra, on the 

 Finke. They extend west and south-west of George Gill 

 Range, and run well on towards Lake Amadens. In short, 

 this formation has a wide distribution throughout Central 

 Australia, the extent of which is still undetermined. 



The author has not yet been able to satisfy himself that 

 the red sandstone in which the Francis Well is sunk, and the 

 sandstone composing Mount Charlotte — which is visible from 

 the well — belong to the Jurassic ( ?) formation. The same 

 difficulty presents itself a few miles north of Idracowra, on 

 the Finke. There the red sandstone range to the west of the 

 road also looks older than the Jurassic ( ?). 



The eruptive rocks have not intruded the Ordovicians 

 so far as yet observed. In all probability many of the 

 quartzite and shale cappings of the granitic hills, scattered over 

 the plateau, north and also south-west of the MacDonnells, 

 are Ordovician, and much of the so-called desert sandstone 

 (e.g., at Glen Edith) belongs here as well. 



Cambrian. 



The Cambrian quartzites, quartz-conglomerates, dolomitic 

 limestones, sandstones, micaceous clay slates, shales, etc., so 

 well represented in the MacDonnell Ranges, follow next in 

 sequence, on which the Ordovicians repose unconformably. 

 The Cambrians, in turn, rest upon the granitic rocks of the 



