70 



The country gives every evidence of great and conflicting 

 earth movements. The Wirrealpa Hill, which forms the 

 terminal point of the Mount Lyall Range (which extends in 

 a north-easterly direction), is the exact counterpart of the 

 Parachilna quartzite escarpment. The dip of this hill is 

 also on the curve. The southern side of its termination dips 

 south-west: whilst, on the opposite side, the dip is W. 20° N. 

 The Archaeocyathinae limestone overlies the quartzite at the 

 base of the hill (as it also does in the Parachilna Gorge) : 

 dip in the centre of the curve is W. at 45°. The last ex- 

 posure of the quartzite, in the big creek, on its eastern side, 

 has a dip S.W. at 40°. 



The Archaeocyathinae beds have some features of special 

 interest. In one part the rock is of a light colour and very 

 pure, and although the larger forms of organic remains are 

 somewhat scarce at this horizon, those that are there are 

 well jDreserved, and the rock mass is largely made up of small 

 sponge spicules, which can only be detected in microscope pre- 

 parations and do not admit of further determination. 



XIII. Visit to Mount Chambers Creek. 



Mount Chambers is an important "trig." hill situated 

 about 23 miles to the south-eastward of Wirrealpa. The inter- 

 vening country is mostly low. Mount Chambers Creek comes 

 in from the north-west and penetrates the mount, where it 

 makes a bold and rugged gorge with nearly vertical faces. 

 The mount has a limestone cap, formed into a shallow 

 syncline. The limestone is somewhat impure, resting on 

 purple shales, which show a sudden increase of dip. A fault 

 is probably present, as the rocks, extending over a large out- 

 crop, are in the condition of breccia. In one of the outcrops 

 the shales have a bluish colour: dip W.N.W. at 27°. The 

 limestone underlies thick purple quartzites, which can be 

 seen in the gorge, and also in a small tributary creek that 

 flows into Chambers Creek. In this small tributary there 

 is a remarkable amphitheatre in the rocks, almost hid from 

 view, in which is a spring of good water, and the walls, 

 above the height where a man could reach, are well covered 

 with native drawings, cut into the rock faces: dip W.N.W. 

 at 24°. At a lower stage in Chambers Creek, about 2 miles 

 lower down than Mount Chambers, is an important outcrop 

 of the Archaeocyathinae limestone. 



XIV. Mount Lyall. 

 Travelling from the present Wirrealpa Head Station, 

 by the Tea-tree Well road, at half a mile distant beyond 

 the gate which admits to the Woolly Paddock, a small lime- 



