270 Transactions. 



640 ft. is in well-marked layers with a dip of 21° to 22° to the southward. 

 At some depth not exactly ascertained by the writer this shaft enters the 

 older rocks of the auriferous series. 



Pieces of much-altered wood still retaining about 10 per cent, of carbon 

 were common in the material excavated from the shaft at 620 ft. to 630 ft. , 

 or thereabouts. These, evidently derived from shrubs or small trees, 

 averaged less than 1 in. in diameter, and were in no case more than a few 

 inches long. Sections made of the enclosing tuff show its fragmentary 

 character very well, especially by reflected light. The constituents appear 

 to be mainly highly decomposed broken feldspar crystals, with a few grains 

 of quartz and other minerals. The secondary products present are calcite, 

 chlorite, pyrite, and nearly opaque kaolinitic matter (probably mainly 

 sericite). 



The well-stratified tuff at 630 ft. appears to have suffered l)ut little 

 alteration comparable to that involved in the propylitic facies of the under- 

 lying auriferous series. There is therefore some reason for thinking that 

 propylization of the latter rocks preceded the deposition of the tuffs ; but 

 before any definite conclusion, if such is possible, can be drawn from the 

 line of reasoning here indicated a more detailed study of the tuff than 

 that made by the writer will be advisable. 



(3.) Andesites and Tuffs of the " Second Period.'''' 

 (a.) Andesites. 



Near Waihi the rocks of the " Second Period " are almost wholly ande- 

 sitic lavas, which in the main closely resemble one another. They are 

 greyish, bluish, or even nearly black rocks, with numerous phenocrysts of 

 feldspar and pyroxene. Macroscopically they differ from the earlier quartz- 

 andesites or dacites chiefly in being, as a rule, very much less altered. Under 

 the microscope the younger andesites show practically no orthoclase, and, 

 though primary quartz grains are usually present, these occur to a notice- 

 ably less extent than in the older volcanic rocks. 



The chief type represented is a hypersthene-augite-andesite with a 

 pilotaxitic or semi-pilotaxitic base. The feldspars are usually fresh and 

 well-twinned basic andesine or acid labradorite. The twinning is generally 

 of the ordinary albite type, but other forms are occasionally seen, and good 

 zonary banding is quite common. In very rare instances a crystal of what 

 appears to be orthoclase may be seen in a section. 



Quartz, usually present, is in rounded grains of moderate size, and has 

 the same characters as in the auriferous rocks. The occurrence of a very 

 large bleb of white quartz in a sample of andesite collected near the Mataura 

 track by Mr. F. T. Seelye, of the Waihi School of Mines, deserves note. 

 Sections of this, microscopically examined, were found, except in small 

 areas, to be optically homogeneous. 



Augite occurs in the usual way, and is in many cases very finely twinned. 



A rhombic pyroxene is usually present in abundance. In some slides 

 it predominates over augite, while in others the reverse is the case, but, on 

 the whole, the rhombic and monoclinic pyroxenes are about equal in amount. 

 Generally the rhombic pyroxene is hypersthene, which, while showing 

 well-marked pleochroism, is not of a very ferriferous type, and probably 

 approaches bronzite. In many cases more or less enstatite is present, in 

 some to the total exclusion of hypersthene. The rhombic pyroxenes are 

 decidedly more subject to alteration than the augite. In sections of 



