8 



ON HAUYNE-TRACHYTE AND ALLIED ROCKS. 



The minerals which we have detected in these rocks 



may be enumerated as follows : — 



Aplite. 



Orthoclase 



(Sanidine) 

 Aiigite 

 Biotitf! 



Trachyte. 



m^isentinl — Orthoclase 



(Sanidine) 

 Oligoclase 

 Aiisrite 



Hornblende 



Accessory — Haiiyne Haiiyne 



Aegirine Apatite 



Melanite-Garnet Sphene 



Biotite Zircon 



Secondary- 



Syenite. 



Orthoclase 



Microperthite 



Albite 



ElaeoHte 



Augitft 



Hornblende 



Melanite-Garnet 



Biotite 



Apatite 



Alkali Syenite (Augite Syenite). 



Sp.gr. 2-6. 



Found in sitii on beach south of Regatta Ground. Port Cygnet, 

 massive exposure, but lying at the water-leveL 



No 



MacroHcop ic characters. 



Medium grain ; brownish grey, syenitic looking : has 

 an elaeolitic appearance, with greasy feel. With porphy- 

 ritic tendency by reason of a few large glistening felspars 

 (nearly y long) scattered sparingly. No rhomb-shaped 

 sections of felspars seen. Numerous small brilliant dark 

 garnets appear as specks, which can be well recognised 

 with the pocket-lens ; many of these seem enclosed in the 

 felspars. The rock resists decay well, as shown by the 

 thinness of the weathered crust, decomposition not extend- 

 ing far into the interior of the stone. 



Microscopic characters. 



Structure, normal hypidiomorphic-granular (granitic), 

 with an occasional leaning to the trachytic type by an 



