PEOCEEDINGS OF SECTION C. 36& 



rocks. Every section that has been examined to the east of them 

 shows that the sedimentary rocks that border them become more 

 and more metamorphic as the granites are approached. They pass 

 from shale through phylhte to slate, mica schist, and gneiss. This 

 seems to constitute an immense but definite contact area. As, how- 

 ever, the age of the sedimentaries is not unquestioned, the fact that 

 the contact changes prove the granites to be of subsequent origin is 

 of little use. 



The largest mass of this granite extends from Kahurangi Point to 

 the Little Wanganai River, and reaches 20 miles inland. 



There are two other plutonic masses rather further to the east. 

 The one is MacKay's Bluff, 10 miles north-east of Nelson. The rock 

 has been called syenite by Hutton and others, but the relatively large 

 quantity of interstitial c[uartz perhaps justifies one in calling it a horn- 

 blende granite. A bar of boulders of this rock forms the bank that 

 separates Nelson Haven from Tasman Bay. 



The other plutonic mass forms the well-known peridotites of the 

 Dun Mountain of Nelson. The characteristic dunite occurs here in 

 large quantity, but many other varieties of rock occur as well. It is a 

 curious fact that the gabbro with isotropic matter {a), the pyroxenite, 

 and serpentine diallagites occur here as well as in the southern area 

 previously described. Chromite occurs in masses of notable size in the 

 dunite, and segregations of copper ores have been found in several 

 places, but no awaruite or platinum have been recorded. 



It is notable that at Milford Sound hartzbergite occurs near the 

 dunite. At the Cow Saddle, in the southern area to the north of Milford 

 Sound, the associated rock is therzolite, and in the Dun Mountain no 

 pyroxene peridotite occurs, though there are apparently serpeutinised 

 representatives of such rocks. Bronzite and hypersthene have been 

 frequently recorded from the Dun Mountain area. During a recent 

 visit the author could find neither of these, though in the pyroxenite 

 bastite occurs rather frequently. Other plutonic rocks occur near the 

 west coast, for boulders collected for me by Mr. J. P. Smith in alluvial 

 drifts at Brunner are mica olivine gabbro. (&) 



In his recent report Dr. Bell refers to serpentines, bowenite, and 

 nephrite as representatives of original dunite. In regard to the two 

 former there can be no doubt, for both occur at Milford Sound, alongside 

 of the dunite. I have long believed in the probability of the derivation 

 of nephrite from dunite. 



The North Island contains no large plutonic masses, but at Cabbage 

 Bay and elsewhere in the Coromandel Peninsula there is a mica quartz 

 diorite (tonalite) forming minor intrusions, (c) 



(a) Recent analyses have shown that the isotropic matter is grossularite. 



(b) Fiu-ther researches by JVlr. J. P. Smith have shown that a complete voge- 

 site-camptonite-theralite series is represented in the boulders, and there is also 

 a highly-interesting rock — a spherulite porphyry with much riebeckite. 



(c) A recent expedition by the author showed that there is a large mass of 

 diorite at Mongonui, and another large mass of olivine norite with Ahipara as a 

 centre. This rock is very fresh, but contains little hypersthene, and olivine is 

 usually abundant and unweathered. 



a2 



