/6 GEOLOGY OF MT. FLINDERS AND FASSIFERN DISTRICTS, Q., 



sandstone, the main stream in hard schists. There is an immense 

 amount of valuable work to be done in working out the history 

 of the drainage of South-eastern Queensland. 



So much for the physiography of the districts around Mt. 

 Flinders. The main facts to be gleaned may be summarised as 

 follows : — 



1. Mt. Flinders is an isolated trachytic volcano. 



2. It rises out of inclined and highl}'- faulted Trias-Jura forma- 

 tion, which it has broken through. The intense folding observed 

 in this belt of country is due to the crushing of the faulted 

 portions. 



3. Trachyte becomes more abundant as the south-western 

 border of the Ipswich Formation is reached near the New South 

 Wales border, viz., in the Little Liverpool Hange. 



4. The trachytes here probably till a gigantic fissure. Evidence 

 pointing this way was found in the presence, in the trachyte, of 

 masses of sandstone altered to quartzite, and often these blocks of 

 included quartzite show slickensided structure on the surface. 



Detailed Account of Mount Flinders. 



The main peak of Flinders consists, as show in figs. 4-5, of a plug 

 of felspar-porphyry, which is surrounded and capped by trachytic 

 breccias. These occur on the mountain all round the summit at 

 a height of 1,800 feet, and the breccia-zone is marked all round 



Fig. 4— Sketch-section of Mt. Fig. 5— Sketch-section of Mt. 



Flinders as before erosion. Flinders after erosion. 



by a circlet of large caves. In one of these caves, on the south 

 side of the mountain, fibrous alum tills the joint-cracks, and occurs 

 as an excrescence on the rock. This is, probably, because the 

 rock (breccia) is rich in sulphur, which by some process is being 

 oxidised, and is reacting with the products of decomposition of 

 the felspar. Right on top occurs the normal alkaline trachyte. 



