Yol. 62.] GEOLOGY OF DTJNEDIN (NEW ZEALAND). 393 



fragments is striking, when considered in reference to the minera- 



logical composition of the phonolites. No chemical analysis of 



these rocks has been made, but a crystal of segirine was analysed 

 with the following result : — 



A. B. 



Per cent. Per cent. 



SiO, 4910 51-60 



ALO, 1-46 1-92 



FeJX 25-14 26-29 



FeO 9-26 420 



CaO 2-95 4-25 



MgO 0-13 1-15 



]N T aX> 8-11 889 



K 2 6 1-79 1-05 



Totals 97-94 9935 



A = Inclusion in breccia, Port Chalmers (N.Z.) ; anal. P. Marshall. 



JB = JEgirine in elasolite-syenite, Barreros, Serra dos P090S de Caldas, Sao 



Paulo (Brazil) ; Rosenbusch, ' Elemente der Gesteinsiehre ' 2nd ed. 



(1901) p. 125, No. 10. 



The result (A) which was obtained from the examination of a 

 very small quantity of material, shows that the mineral is a typical 

 segirine. 



The foyaite has only been discovered in situ at the spot already 

 mentioned, at the eastern base of Harbour Cone, near the shore of 

 Hooper's Inlet. It does not crop out at the surface, but was exposed 

 near the bottom of a shaft sunk to prospect for gold-mining. The 

 rock carries a certain amount of gold, varying from 2 to 14 dwt. per 

 ton. The methods employed for saving the gold were not efficient 

 enough to make the venture a paying one. 



This rock was classed by Ulrich as a 



' trachyte-greenstone, though hardly distinguishable from the quartzose- 

 diorite greenstone of some of the dykes Avhich in Victoria traverse Upper 

 Silurian rocks.' x 



Prof. Park describes the rock as 



' a hornblende-andesite, although it is probably more closely allied to 

 porphyritie diorites.' 2 



The reasons for its classification as a foyaite have been given above. 

 Although this rock has practically no outcrop, its lateral extension 

 is probably considerable, for fragments of it are frequently met with 

 in the Port-Chalmers Breccia. 



Other syenites are found rather frequently as fragments in the 

 breccia. Some of these are described in the preceding notes on the 

 petrography, and it will be seen that in them the amphibole is 

 replaced by segirine, which is in some specimens present iu large 

 crystals. None of these nepheline-syenites with segirine have been 

 discovered in situ. 



1 Hutton & Ulrich, ' Geology of Otago ' 1875, p. 167. 



2 N.Z. Geol. Surv. Reports, 1888-89, p. 35. 



