Vol. 65.] NEPHRTTE AND MAGNESIAN ROCKS OF NEW ZEALAND. 351 



19. The Nephrite and Magnesian Bocks of the South Island of 

 New Zealand. By Alexander Moncriefp Finlayson, M.Sc, 

 A.O.S.M. (Communicated by Prof. W. W. Watts, Sc.D., 

 F.K.S., V.P.G.S. Eead April 28th, 1909.) 



[Plates XV & XVI— Microscope-Sections.] 



I. Introduction. 



Ever since Hochstetter's work on the olivine-rock of the Dun 

 Mountain, and on the New Zealand nephrite or ' greenstone,' the 

 rocks of the ' magnesian belt ' of the South Island of New Zealand 

 have had an absorbing interest for students of that district. The 

 term ' magnesian belt ' is here used to denote those peridotites and 

 serpentines that have hitherto been frequently referred to by the 

 names ' serpentine-belt ' and ' mineral-belt.' Until recent years, 

 however, the occurrence and nature of the various exposures which 

 comprise this most interesting and significant petrographic province 

 have remained rather obscure, owing to the rugged nature of the 

 country and the inaccessibility of the chief localities. 



In this paper is given a general account of the peridotite- and 

 serpentine-rocks of the South Island and a discussion of the nature 

 and origin of New Zealand nephrite. Those analyses which are 

 not attributed to others are my own work, and were made in the 

 geological laboratory of the Imperial College of Science & Tech- 

 nology, South Kensington. 



II. The Peridotites and Serpentines. 



General Occurrence and Relations. 



Occurrence. — The position of the known outcrops is indicated 

 on the map accompanying this paper (fig. 1, p. 352). The magnesian 

 belt, as generally understood, first appears as a group of serpentines 

 and peridotites extending from D'Urville Island in a south-westerly 

 direction for some miles past the town of Nelson. Serpentines have 

 also been observed in the Buller basin ; and still farther south, in 

 the western foothills of the Southern Alps, occur the disconnected 

 sills and dykes of serpentine and talc-rocks in the Teremakau and 

 Hokitika basins : these intrusive rocks are the matrix of the 

 nephrite. Large massifs of peridotites compose the Olivine and 

 Red-Hill ranges in North- Western Otago, while a group occurs at 

 Anita Bay (Milford Sound) and another at the Cow Saddle, north- 

 west of Lake Wakatipu. Isolated outcrops of serpentine-rocks, 

 occupying a detached position with reference to this main belt, 



