252 



on in some measure the anticlinals and synclinals of the older 

 rocks. As the horizon cannot be determined until fossils are 

 found we must wait their discovery. 



The characteristics of the Ooraminna Sandstone are bold head- 

 lands, precipitous sides for 800 feet, cleavage indistinct. It is 

 usually found in localities protected within the synclinal folds of 

 the Silurian quartzites. This extensive formation at one time 

 covered up the James, Gardiners, Geo. Gills, Lewis, and other 

 Ranges, and much of the MacDonnells, not to speak of localities 

 farther afield. The Finke runs over many miles of it, and in the 

 precipitous walls which rise 800 feet on either side the river-bed 

 I saw, when not distant from MacDonnell Ranges, pebbles freely 

 embedded in the sandstone. Flanking the South MacDonnell in 

 the form of foot-hills, but unconformable to the Silurian rocks, 

 are long ridges of pudding-stone extending some 70 miles east 

 and west, and in strike parallel with the Silurian rocks. I noticed 

 at the Gilbert Spring, situated west of the Lutheran Mission 

 Station, pudding-stone similar to that just referred to, and think 

 it highly probable that when the Devonian (?) sandstone was 

 being deposited the MacDonnell Ranges were higher from their 

 base than they are to-day, though probably islands in the sea ; 

 the waves dashing against the rocks broke off fragments and dis 

 tributed them over that part of the basin nearest the MacDon- 

 nell Ranges, and thus were formed the pudding-stone hills. I 

 consider it probable the red sandstone and the pudding-stone, 

 which are conformable, are one and the same formation. The 

 part that is left can only be called a remnant of what once 

 existed. In many places near the MacDonnells so much mica is 

 in this rock as a constituent that it glistens in the sunlight. 

 Prior to the deposition of this formation the MacDonnells had 

 been denuded in places of all Silurian formations, for I saw a 

 hill of ^:)?'e- Silurian schists capped by mudstone. The capping of 

 mudstone was dark-red in color, and on climbing to the top of the 

 hill I found the strata were twisted and compressed into almost 

 every conceivable shape. 



This brings us to the second series of foldings that Central 

 Australia has undergone. I do not think in this instance there 

 was any great upheaval ; nor, for the matter of that, do I think 

 there was in the Silurian upheaval ; in both instances lateral 

 pressure from the north disturbed the strata, and in this 

 Devonian (?) disturbance the Silurian and pre-Silurian strata 

 were horizontally compressed into sharper folds, the extent of 

 which is indicated by tlie gentle anticlinals and synclinals of this 

 formation. Between the Silurian and the Devonian, if we may 

 judge by the appearance of the rocks, there was a wide break, 

 and I saw no intervening strata ; on the contrary, the mudstone 



