388 W. R. BROWNE AND A. B. WALKOM. 



of the rocks of this area. The rhyolite here does not 

 appear to have suffered so severely from earth movements 

 as that of Drake's Hill, and in appearance differs from it in 

 many respects. Typically the Mount Bright rock is whitish 

 to dark red in colour, sometimes, but not invariably, 

 strongly banded and containing small idiomorphic quartz 

 and felspar crystals sparsely distributed. Secondary 

 chalcedony is found, opaque yellowish to red in colour. 



On the edges of the area a coarse agglomerate is 

 developed, containing boulders of banded rhyolite up to- 

 about a foot in diameter. This may have been produced 

 towards the close of the rhyolite eruptions or may repre- 

 sent the result of the first explosive outbursts of trachytic 

 lava. Overlying the rhyolite, and filling in eroded hollows 

 in it, are flows of trachyte of considerable extent, gener- 

 ally yellowish-brown in colour and containing small laths 

 of felspar in an aphanitic base. The relations of this 

 trachyte to the rhyolite are very definite. 



Only three very small occurrences of basic rocks have 

 been observed among the Carboniferous eruptives, in the 

 shape of what appear to be small necks of basalt and dolerite. 

 The mineralogical and structural points of similarity con- 

 necting these occurrences suggest that they should be 

 correlated, but as the occurrences are isolated from other 

 basic rocks their precise geological age is difficult to 

 determine ; all that can be said is that they are post- 

 trachyte. 



Resting directly upon the acid lavas and underneath 

 the Permo-Oarboniferous conglomerate is a Carboniferous 

 sedimentary series, consisting of conglomerates, fine grained 

 friable chocolate shales and tuffaceous sandstones : some 

 or all of the members of this series can be traced at many 

 points around the area, and up into the Matthews' Gap 

 area. They are well seen on the road about half a mile 



