BY W. N. BENSON. 449 



It may be suggested tliat the suite is related to the granophyres 

 and audesites of the West Moreton District, described by Messrs. 

 Wearne and Woolnoughf. The latter has found a very interesting 

 igneous complex to occur associated with the andesitic mass of 

 Mount Warning, adjacent to Nullum Mountain. + A rich field of 

 discovery awaits the petrological investigator in this district. 



ii. Inclusions in a dyke at Gerringong. 



The dyke under consideration occurs on the beach at Gerringong, 

 and is recorded as No. 16 in Mr. Harper's list*. It splits up into 

 overlapping lenticular branches. In places, the rock is full of 

 steam-cavities, which are arranged in bands parallel to the boun- 

 daries of the intrusion. Here and there are inclusions in the vol- 

 canic rock, at one spot so abundant as to make up nearly half the 

 bulk of the rock. About thirty slices of these have been studied, 

 with the results here presented. The dyke-rock itself is a basalt, 

 consisting of idiomorphic prisms of purple augite and laths of 

 labradorite, Avith a fine even grain-size. As accessory constituents 

 are present magnetite, small brown pleochroic crystals of horn- 

 blende, and very minute needles of apatite. No glass is to be seen. 

 Chlorite and epidote are present in varying amount. 



The rocks of the inclusions are derived from a gneissic complex, 

 that must lie at great depth below the present surface (Upper 

 Marine Permo-Carboniferous rocks). They consist of alkali- 

 felspar gneisses and quartz-schists, with a few gabbroid rocks. 

 Interesting features are brought about by the partial melting and 

 absorption of the inclusion in the basalt-magma, some of which 

 recall the observations of Lacroix on the granite-xenoliths in the 

 basaltes of the Auvergne. 



The best preserved gabbro was obtained by Mr. Aurousseau, 

 who kindly permitted me to study it. It is a coarse-grained rock 

 consisting chiefly of labradorite. The augite is in large ophitic 

 grains, and slightly chloritised. Magneti'te is also present. Another 



t '* Notes on the Geology of West Moreton, Queensland." Proc. Roy. 

 Soc. N. 8. Wales, 1911, pp. 137-159. 



iJlVeibal communication. ^ 



* Rec. Geol. Surv. N. S. Wales, 1905, Vol. viii., Pt.2, p. 105; also PIat«dtix, > ." i 



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