380 E. W. Skeats: 



rock is essentially an altered olivine nionchiquite, with larger and 

 smaller foreign pebbles. 



Fragments from Bore at F, occurring round the l)ore hole, deptli 

 unknown (Section No. 1020). 



This rock is essentially similar to the last described. It is 

 j)orphyritic and hyalopilitic, contains phenocrysts of altered olivine, 

 and in the ground-mass purple prismatic titaniferous augite, with 

 extinction angle of 40 deg.-46 deg., abundant minute magnetite 

 or ilmenite crystals, and the remainder consists of brown isotropic 

 material, probably glass. One corroded fragment of quartz is 

 embedded in the rock. The rock is a fragment of an olivine 

 nionchiquite. 



The nionchiquite dyke cutting the deposit at its north-west end 

 has the following microscopic cliaracters, (Section, No. lOll). 

 (Plate xxxii., Fig. 4). For chemical analysis, see below. 



The olivine crystals occur as serpentine pseudomorphs. Abun- 

 dant faintly purple augite needks, probably titaniferous, extinc- 

 tion angle 40 deg. -46 deg., and lath-shaped brown biotite crystals 

 occur, but magnetite is practically absent. Some of the cavitites in 

 the rock are lined with secondary chalcedony, and filled with pale 

 serpentine. The ground-mass is colourless and isotropic, and may 

 be glass or analcite. 



The rock is an Olivine-Monchiquite. 



From Jenkins and Bielski's shaft (S. on map) a large fragment of 

 rock was found in the heap surrounding the shaft. Its nature was 

 not at first recognised, but the chemical analysis quoted below, and 

 the evidence in section under the microscope show that it is a frag- 

 ment of Ordovician sandstone, which became embedded in the 

 volcanic material. 



In Section No. 1014, it consists of angular and sub-angular 

 quartz fragments in a felspathic and micaceous cement. A band of 

 argillaceous material partly iron-stained, and partly changed to 

 chlorite occurs in one part of the section. The lock is an altered 

 felspathit: sandstone. 



The Chemical Characters of the Rocks 



Analyses of the fi-agmental rock from the main shaft were made 

 by Mr. T. H. Plante, B.Sc. and of the nionchiquite dyke, and the 

 fragment of ordovician sandstone from Jenkins and Bielski's shaft 

 by Mr. H. C. Kichards. M.Sc. Mr. E. O. Thiele. M.Sc, redetm- 

 niined for me the alkalies in the fragmental roik from the main 



