BY H. I. JENSEN. 91 



the present sea as far as Mudjimbah Island. It was laid down 

 in a swamp or lake which became submerged and subsequently 

 re-elevated, after which the sea cut rapidly into it. 



Aboriginal kitchen-middens are also abundant along the 

 Coolum beach. 



Distinct from the black, peaty sandstones on the beach are the 

 "black sands" which, after south-easterly gales, contain payable 

 gold. They contain also ilmenite, rutile, spinels, minute rubies, 

 silver, tin, monazite, and white silvery flakes, probably osmiridium. 

 The small rills descending from Mt. Eurungunder contain black 

 sands after rains. It therefore seems to me that they are derived 

 from the porphyrite and dioritic rocks of the district, which 

 probably outcrop under the sea, as well as at Pt.Arkwright and 

 Noosa. The Boonaiah (North Maroochy) River brings down 

 similar sands after rain, probably from the monzonites in the 

 vicinity of M t. Cooroy. The gold and silver may have the same 

 source, or may be concentrated out of the old North Maroochy 

 alluvials 



Recent calcareous conglomerates exist in places. More impor- 

 tant are the recent ironstone conglomerates which abound on the 

 coast. Often we find shell-banks or kitchen middens (at Tewan- 

 tin) turned into ironstone by the precipitation, on organic matter, 

 of carbonate of iron in solution. 



Contact Metamorphis m. — The alteration of the Trias- 

 Jura sandstones and conglomerates of the district to hard 

 quartzite is commonly observed near the igneous intrusions. 

 Notable instances may be seen at Point Arkwright and Noosa 

 Head (Text figs.l3and 14). 



(c) Plutonic Rocks. — The oldest plutonic rocks are probably 

 the muscovite granites of Cooran, and the dykes of augen-ovtho- 

 gneiss in Fife's Range and the Delaney's Creek Mountains. 



The Enoggera granite near Brisbane clearly intrudes the 

 metamorphic Gympie rocks, in which it has effected great harden- 

 ing, and has given rise to small pegmatite dykes and quartz veins. 

 The most important plutonic rock, the Neurum granite, covers a 

 large area on the Woodford peneplain (Plate v.), and occurs again 



