Reports and Proceedings — Geological Society of London. 285 



British Isles become progressively scarcer from west to east, and the 

 distinctive types are absent to the east of Cambridge. They appear 

 to have been brought by an ice-stream coming from a northerly 

 direction, which probably to a certain extent replaced the Scandinavian 

 ice towards the east. 



2. " The Nephrite and Magnesian Rocks of the South Island of 

 New Zealand." By A. M. Finlayson, M.Sc. (Communicated by 

 .Professor W. W. Watts, Sc.D., F.R.S., V.P.G.S.) 



The magnesian rocks described in this paper are a disconnected 

 series of intrusive peridotites, forming a more or less defined belt 

 along the western portion of the South Island, parallel to the trend 

 of the Island and to the structural and geographic axes of the main 

 Alpine range. The course taken by these rocks apparently follows 

 one of the main Pacific trend lines, the nature of which will be more 

 fully understood with the further elucidation of the structural geology 

 of the region. The rocks are intrusive into sedimentary strata of ages 

 varying from Ordovician to Jura-Trias, and, as far as can yet be 

 determined, all the exposures appear to be of approximately con- 

 temporaneous origin. 



One of the most interesting groups is at the Dun Mountain, Nelson, 

 where the original dunite of Hochstetter occurs, associated with 

 magmatic segregations of chromite, bands of pyroxenite, serpentine 

 rock, and a variety of rock types of contact-metamorphic origin 

 bordering on the Triassic Limestone which is intruded by these rocks. 

 The rocks of the contact zone include grossularite diallage rock, 

 serpentine amphibole rock, and epidote rock. 



In Westland, near Hokitika, the rocks occur as a series of sills 

 which are of two varieties — massive or foliated serpentine rock, and 

 serpentine-talc-carbonate rock. The former are often seen to be of 

 the variety antigorite, with typical thorn structure, and some specimens 

 show the process of serpentinization of augite lately described by 

 Professor 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 Maori. Chemical and microscopic 

 examination leads to the conclusion that the bowenite has here 

 been formed by deep-seated metamoi-phism 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 intrusions. The 

 widespread serpentinization seen in many cases seems to have been 

 largely effected or at least initiated by hydrothermal action. 



