47 



Post-Ordovician. [Devonian ( ?).] 



In descending order, the next known rock formation is 

 the post-Ordovician conglomerate and sandstones with pebble- 

 beds that flank the Ordovicians on the south, as seen on the 

 northern edge of the Missionaries Plain, in Rudall Creek, 

 Finke Gorge, Ellery Creek Gorge, and in the ranges east of 

 the latter. Tate and Watt found these beds to be not less 

 than 7,000 ft. thick at Ellery Creek Gorge. Temple Bar 

 Well, situated 12 miles south of Alice Springs, was sunk 

 wholly in conglomerate identical in character with the above. 

 Five miles south of Temple Bar Well, low hills of conglomerate 

 occur along the road to Ooraminna. These hills extend for 

 miles in a westerly direction. The writer regards these as 

 belonging to the same formation. Sandhills and sandplains 

 then cover the surface until at 20 miles from Alice Springs 

 the red-and-white sandstone hills of the Ooraminna Range are 

 crossed. These sandstones in places are lithologically similar 

 to the Jurassic (?), but are seen to have been faulted and 

 disturbed to a considerable extent, and moreover, as pre- 

 viously mentioned, three miles north of Ooraminna Waterhole 

 stands a hill of Jurassic ( ?) sandstone, reposing on this 

 Ooraminna sandstone unconformably, and surrounding it as 

 well. The strata of the latter is much disturbed, whereas in 

 the former it is horizontally disposed and undisturbed. The 

 unconformity is unmistakeable, and lithologically the two 

 series are very distinct. At 32 miles south of Alice Springs 

 is Indembo Well. This well was sunk 200 ft. deep wholly 

 in conglomerate, identical in appearance with that at Temple 

 Bar. Indembo Well outcrop of conglomerate is seen to ex- 

 tend both east and west of the well; its thickness is unknown. 

 The writer is of opinion that this conglomerate belongs to the 

 same series of beds as seen at Temple Bar, Ellery Creek Gorge, 

 and elsewhere, and it will thus be seen that it occurs both 

 north and south of Ooraminna Range, but the intervening 

 sandhills preclude the possibility of ascertaining its strati- 

 graphical relationship to the Ooraminna sandstones with cer- 

 tainty. The difficulty is increased by the extensive faulting 

 that has taken place in the Ooraminna sandstones on both 

 sides of the range. However, the writer's opinion is that the 

 conglomerate beds overlie the Ooraminna sandstone, and that, 

 formerly, the conglomerate was continuous from well to well, 

 its absence in places being due to erosion. 



The post-Ordovician conglomerate beds and the Oora- 

 minna sandstone beds are both of some antiquity. Each par- 

 ticipated in the disturbances that threw all the older 

 sedimentary rock systems into anticlinal and synclinal folds. 

 Tate and Watt observed that the post-Ordovician conglomerate 



