668 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iii., 



The very coarse-grained dolerite-pegmatite, that occurs in the 

 dolerite of Bowling Alley Point ( 'Possum Mine), is also not albi- 

 tised; the felspar is andesine and the pyroxene is only slightly 

 uralitised. It is intersected by many small veins of quartz and 

 epidote. 



In the neighbourhood of Horsearm Creek, Attunga, there is a 

 series of dolerites altered by the granite-intrusion, and closely 

 resembling the contact-altered albite-dolerites of Cornwall(35). A 

 typical example [M.B., 177] has a structure approaching the 

 ophitic type. Plagioclase is the dominant mineral, in large grains 

 and smaller laths. The strongly pleochroic, green hornblende is 

 probably derived from ophitic augite. Some crystals of the same 

 mineral are scattered about interstitially. Numerous aggregates 

 occur, composed of small crystals of biotite, together with some 

 magnetite. A little interstitial quartz occurs with magnetite and 

 abundant apatite-needles. 



(4) Lower Carboniferous Lavas. — It has been shown that the 

 Rocky Creek conglomerates are interbedded with flows of rhyolite 

 and other lavas, and contain numerous beds of acid tuff. The 

 pebbles of the conglomerate largely consist of material derived 

 from the interstratified flows, together with much quartz, porphyry ; 

 granite, et cetera. While, as yet, the actual lava-flows have not 

 been studied in detail, and the collections made are entirely from 

 the pebbles of the conglomerate, it will be best to describe the lavas 

 among them in this place, rather than as inclusions in the sedimen- 

 tary series, to show better the sequence of igneous activity in the 

 area studied. 



A dozen rocks were sliced, which have all proved to be rhyolites 

 of very varying character. The ferromagnesian minerals are very 

 subordinate, and are usually biotite, often containing zircon. Mag- 

 netite is present in small quantity only. 



The structures present differ considerably. In some [M.B., 9], 

 the rock is noncrystalline, with phenocrysts of quartz and oligo- 

 clase, full of glassy inclusions set in a matrix of small felspar- 

 grains, in a granophyric ground-mass. In another [M.B., 10], the 

 flow-structure is well pronounced, the flow-lines being marked by 



