67 



NOTES ON THE GEOLOGY OF THK MT. FLINDERS 

 AND FASSIFERN DISTRICTS, QUEENSLAND. 



Bv IT. I. Jensen, D.Sc, formerly Linnean Macleay Fellow of 

 the Society in Geology. 



(Plates i.-vi.) 



]Mount Flinders is a rugged peak attaining an altitude of 2,240 

 feec, and situated about 11 or 12 miles S.S.E. of the town of 

 Ipswich, Queensland. Surrounding the main peak there are a 

 number of smaller cones and rugged rooks, most of which repre- 

 sent remnants of former parasitic vents or smaller foci of 

 eruption which encircled the large volcano. 



The rocks composing the main peak are felspar-porphyry, 

 trachyte, trachyte-breccia, tuffs, and occasionally a little andesite, 

 dacite, and dacite-breccia. The smaller conos consist likewise of 

 trachyte-breccia and andesite, and some of the most rugged rocks 

 (see fig 8) consist of a plug of trachyte or trachy-rhyolite. The 

 andesite is not by any means abundant, and may be looked upon 

 as merely a more basic phase of the trachyte. It occurs here an'd 

 there interbedded with or overlying trachyte-flows or sheets of 

 breccia. 



It is noteworthy that the conical mountains are usually com- 

 posed of breccia, with more or less of basic trachyte, dacite and 

 andesite; and, further, they are characterised by better soil (usually 

 of a red or brown colour), and a thicker vegetation; patches of 

 vine-scrubs occur on them. 



The Physiograpeiy of the surrounding Region. 



To the north of Mount Flinders lies the Coalfield area of 

 Ipswich and Bundamba, which has been described in a Report by 

 ]\lr. W. E. Camf^ron, B A.* This area forms part of a series of 



* Geology of the West More ton or Ipswich Coalfield. Geol. Surv. of 

 ^^ueeasland, Rep. 1899. 



