Vol. 62.] GEOLOGY OF DUNEDIN (NEW ZEALAND). 399 



The classification as camptonite is rather unsatisfactory, as the 

 rock is more acid and contains more alkali than is usual. However, 

 structure and mineralogical composition alike appear to justify this 

 classification. 



7. Teschenite. — The rock described here occurs as a small 

 dyke penetrating the Port-Chalmers Breccia at Mussel Bay. Hand- 

 specimens are black and dense. The thin slices show a mixture of 

 labradorite and augite, displaying (but not very conspicuously) the 

 violet pleochroism usual in these rocks. There are a few serpentine- 

 pseudomorphs after olivine. Analcite is rather frequent in large 

 rounded grains, showing the typical cleavage, and is almost 

 certainly primary. B-ound the analcite are some narrow prisms of 

 hornblende and sanidine-microliths. These form small complexes 

 exactly similar to portions of the camptonites described above. 

 They seem to be xenoliths of camptonites that have been included 

 in a basic magma, rather than original secretions from the magma. 



8. Trachyte. — This rock consists almost wholly of felspar. In 

 hand-specimens it is white, and glassy crystals of sanidine almost 

 rectangular in shape can often be distinguished in it. 



In thin slices no coloured constituent can be seen in specimens 

 from most of the localities. Felspar-microliths exhibiting flow- 

 structure, with a few felspar-phenocrysts, constitute the whole 

 mass of the rock. In most cases the felspar does not show the 

 microscopic structure of anorthoclase ; it is therefore ascribed to 

 sanidine. In some examples (Hooper's Inlet) the rock has small 

 grains of magnetite. In one example (Omihi) much of the felspar is 

 anorthoclase, and there is some aegirine-augite. The rock weathers 

 readily, and is often stained red by infiltrated iron-salts. 



As would be expected from the mineralogical composition of this 

 rock, analysis shows that a very small quantity of iron, calcium, 

 and magnesium is present : — 



A. B. C. 



Per cent. Per cent. Per cent. 



Si0 o 66-04 66-50 66-20 



TiO; ... 0-70 



Al,6 3 18-38 16-25 19-86 



Fe;0 3 1-05 2-04 1-03 



FeO 0-19 



MnO 0-20 



CaO 0-96 0-85 0-80 



MgO 0-69 0-18 0-17 



Na o 7-22 7-52 7'45 



K 5-09 5-53 4-10 



H" 2 1-50 -50 



Totals 100-93 10046 99-61 



A = Trachyte from Portobello, Dunedin (N.Z.). Anal. P. Marshall. 



B = Lestiwarite from Kvelle. ' Die Eruptirgesteine des Kristianiagebietes 



III — Das Ganggefolge des Laurdalits ' Chri9tiania, 1898, p. 235. 



Anal. W. C. Brogger. 

 C = Anorthoclase from Rakhale. Anal. Forstner, quoted by Dana, ' System of 



Mineralogy' 6th eel. (1892) p. 324. 



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