208 Geological Society. 



be of the variety antigorite, with, typical thorn-structure, and some 

 specimens show the process of* serpen tinization of augite, lately 

 described by Prof. Bonney from this region. The serpentine-talc- 

 carbonate rocks are the matrix of the New Zealand nephrite or 

 greenstone, which also occurs as boulders in the adjacent river- 

 valleys and glacial drifts. 



At Anita Bay (Milford Sound) occur a dunite with marked 

 cataclastic structure, a hartzbergite in which the enstatite is 

 often completely altered to magnesite, and a foliated talcose 

 rock containing stringers and veins of the tough and highly 

 translucent bowenite — the tangiwhai or 'tear-drop' of the 

 Maories. Chemical and microscopic examination leads to the 

 conclusion that the bowenite has here been formed by deep- 

 seated metamorphism of a talc-rock, with the development of 

 serpentine and magnesite, the former being transformed into 

 the tough fine-grained bowenite by dynamic forces of considerable 

 intensity. 



A notable feature of all the rocks of this peridotite-belt is the 

 close association of the most highly serpentinized varieties with 

 evidences of former hydrothermal action accompanying the intru- 

 sions. The widespread serpentinization seen in many cases appears 

 to have been largely effected, or at least initiated, by hydrothermal 

 action. 



The nephrite, or pounamu of the Maories, occurs as nodules 

 and veins in the serpentine-carbonate and talc-carbonate rocks 

 of the Griffin Range (Westland). Its commonest colour is a deep 

 translucent green, but many different shades occur, depending 

 on the percentage of ferrous silicate, on the presence or absence 

 of flaws and cracks, and on included or infiltrated oxides of 

 iron. Some of the dark green nephrites are among the finest 

 specimens of this mineral in existence. A pale whitish-green 

 variety is also occasionally found. It is, however, rather 

 opaque, and never approaches in sheen the famous pale 'jades' of 

 Turkestan. 



Microscopically, the nephrite shows a foliated or confused aggre- 

 gate of very fine fibres, the denseness of the fibrous mass being 

 evidently the cause of its hardness. It appears to have been 

 originally formed by several modes: (1) By contact-action between 

 peridotites and lime-bearing rocks ; (2) by uralitization of pyro- 

 xenes ; (3) by direct transformation of olivine into finely fibrous 

 amphibole ; and (4) by deep-seated metamorphism of serpentine- 

 talc-carbonate rock or its prototype. These modes all suffice 

 to produce the necessary chemical changes ; but the transfor- 

 mation into true nephrite has involved, in addition, intense 

 rock-pressure and movement. Thus has finally resulted the 

 dense foliated or felted aggregate of fibres which characterizes 

 nephrite. 



