Yol. 62.] GEOLOGY OF DTTNEDIN (NEW ZEALAND). 409 



A. B. 



Per cent. Per cent. 



SiO, 42-36 39-29 



TiO; 4-86 



A1 0, 17-66 16-57 



Fe;0 3 10-72 9-18 



FeO 6-51 319 



CaO 1010 12-90 



MgO 10-46 1040 



Totals 97-81 96'39 



A = Hornblende from andesite, Dunedin (N.Z.). Ti0. 2 not determined. 

 B= Hornblende from andesite, Wolkenburg (Siebengebirge). Rosenbusch, 

 'Elemente der G-esteinslehre ' 2nd ed. (1901) p. 303, No. 4. 



The alkalies were not estimated in either case. The comparison 

 shows that the amphibole is of an ordinary type, and must be 

 included among the pargasites ; see Dana, ' System of Mineralogy ' 

 6th ed. (1892) p. 396. 



The principal occurrence is at the Paper-Mills and Golf-Links, and 

 on the summit of Eoslyn. The rock occurs below the trachytoid 

 phonolites at the See House, and above the Papanui dolerite that is 

 exposed there. The andesite forms a lava-flow about 100 feet thick. 



Mineralogically, it lies between a hornblende-basalt and a 

 trachytoid phonolite. 



15. Nepheline-basanites. — The most prominent phenocrysts 

 in these are of nepheline, but olivine can generally be distinguished 

 as well. Slices show that the nepheline is rounded, and fringed with 

 a border of minute felspar-prisms. The olivine is rounded in the 

 larger grains, but the smaller are sometimes idiomorphic. The rock 

 is completely crystalline, the finer portions being composed of an 

 intimate mixture of felspar, augite, and olivine. Many of the 

 augites have a core of aegirine, with a mantle of brown augite. 

 The felspar is labradorite. At first sight, one is inclined to regard 

 the nephelines as xenocrysts ; but their very regular occurrence 

 throughout the rock, as well as the presence of some aegirine, compels 

 the opinion that they form an essential constituent. An analysis 

 showed that the rock does not differ very widely from other 

 basanites : — 



A. B. 



Per cent. Per cent. 



Si0 o 49-39 48-41 



A1,0 3 14-86 16-24 



F e ;d 3 7-35 4-89 



FeO 5-42 6-41 



CaO 7-08 9-38 



MgO 562 7-25 



Na„0 4-71 323 



K 2 2-54 2-33 



P 2 5 0-20 — 



H 2 2-52 211 



Totals 99-69 100-25 



A = Basanite, Otago (N.Z.). Anal. P. Marshall. 



B = Basanite, Hesse. U.S. G-eol. Surv. Prof. Paper No. 14, 1903, pp. 322-23. 



