852 GEOLOGY OF GLASS HOUSE MTS. AND DISTRICT, 



On the other hand, the trcichytes are older than the other 

 volcanic rocks of the district. There is evidence that basalt flows 

 from Mt. Mellum have once extended to Coochin and covered 

 trachytic rocks in that vicinity. The remarkable quartz-augite- 

 hornblende andesite, vvhich forms the surface rock at Grigor's 

 place (Bankfoot House) contains abundant trachytic inclusions. 

 Some of these inclusions, those obtained by me close to Bankfoot 

 House, are analogous to the Beerwah trachyte; others, obtained 

 at Mt. Bokay, close to Mt. Conowrin, consist of Conowrin 

 trachyte. 



The rock of the more rounded and less elevated members of the 

 Glass House Mountain group is in general more basic than that 

 of the steeper and higher mountains. The rock of Mt. Cooee, a 

 hill lying a few hundred yards north of Mt. Tibrogargan, seems 

 of very varying basicity, merging in places into a rock indistin- 

 guishable in hand specimens from the Bankfoot House andesite. 



(2). The order of eruption seems to have been — 



1. Tutfs like those of Trachyte Range. 



2. Compact trachytes like those of Conowrin, Tibrogargan, 

 Beerwah and Ewin. 



3. More basic trachytes of Mt. Ngun-Ngun, Mt. Cooee, Mt. 

 Beerburrum, Mewett's Mountain, and Medway's Mountain; 

 trachytes containing much blue hornblende and jegerine. 



4. Quartz andesites — the Bankfoot House formation. 



5. Basalts, erupted at Mt. Mellum in the Blackall Ranges, and 

 at Buderim Mountain. 



(3). Occurrence of Dykes. — D\^kes are abundant. On the main 

 Gympie road, between Mt. Tunbubudla and Bankfoot House, 

 one meets with a number of long narrow dykes running across 

 the country in straight lines. They form a very noticeable 

 feature, inasmuch as they can be seen at some distance and resemble 

 artificial stone )>arricades when viewed from afar. The dykes 

 met with on the main Gympie Road between Mt. Tunbubudla and 

 Conowrin Creek all seem to radiate from the two Tunbubudla 

 mountains (locally known as Tlie Twins). 



