360 1IR. A. M. FINLAYSON ON THE NEPHRITE [Aug. I909, 



residual mass which composes the summit of the Dun Mountain. 

 Subsequent alterations, due to dynamic agencies, have resulted in 

 the development of uralite, saussurite, and antigorite. 



(3) Hokitika Area. 



The magnesian rocks of this district consist of disconnected 

 outcrops of serpentine and talc-rocks representing sills and dykes 

 of peridotites intruded into the mica-schists on the western side 

 of the Alpine watershed. They have been traced from the 

 Teremakau River in the north to the upper waters of the Hokitika 

 River in the south, occurring, for the most part, in very rugged and 

 inaccessible country. They have been mapped and described by 

 Dr. Bell & Mr. Fraser [8, p. 67]. 



Speaking generally, it may be said that the intrusives show two 

 well-defined types — (a) massive serpentine-rocks and (6) serpentine- 

 talc-carbonate rocks, the two types occurring in distinct and sepa- 

 rate outcrops. The latter type, but not the former, is the matrix of 

 the nephrite. The serpentines occasionally show a mesh-structure, 

 and a fresh dunite has been described from the Hokitika gorge 

 [10, p. 193]. Antigorite-serpentine, with typical thorn-structure, 

 occurs to a notable extent, as first pointed out by Prof. Bonney [21] ; 

 and the same authority has described specimens from the upper 

 Hokitika watershed, which show very strikingly the development 

 of antigorite from augite. Specimens from Captain Jack's Spur, 

 given to me by Mr. P. G. Morgan, also show augite granules pierced 

 irregularly by needles and flakes of antigorite. 



The contact-effects of the intrusive rocks, with the striking 

 development of lime-magnesia silicates and the occurrence of plati- 

 niferous quartz-veins in the vicinity genetically related to these 

 rocks, have been fully described by Dr. Bell & Mr. Eraser [8, p. 70]. 

 Here, as at the Dun Mountain, there is evidence of considerable 

 hydrothermal action accompanying the intrusions. 



(4) North-Western Otago. 



The peridotites of this district occupy a large area. They were 

 described by Ulrich [13] from specimens supplied by explorers. 

 He distinguished two types of olivine-enstatite rock, one occurring 

 in the Red Hill Range, the other in the Olivine Range. These 

 peridotites are the matrix of the peculiar nickel-iron alloy awaruite 

 (FeNi 2 ), which occurs commonly in the sands of the Awarua and 

 neighbouring rivers. 



(5) Cow-Saddle Area. 



This interesting group of rocks has been described by Prof . Marshall 

 [15]. The rock-types in succession from east to west are dunite, 

 lherzolite, pyroxenite, gabbro, and diorite, thus showing a pro- 

 gressive change in basicity. The rocks are, on the whole, much too 



