ON THE ROCKS OF THE HAURAKI GOLD-FIELDS. 249 



adjective chloritic, but as there is no unanimity of opinion, I will 

 use them here. In my collections I tind the following rocks : — 



Riiyolite(?). It occurs in numerous narrow branching veins pene- 

 trating the andesites on the beach between Tararu and Waiohanga. 

 It is a compact pale-grey rock, with a specific gravity of 2.62, but as 

 no chemical analysis has been made, I do not feel quite sure of its 

 true nature. It is generally much decomposed, but I obtained a 

 specimen fit for partial microscopic examination. With crossed 

 nicols it shows a ground-mass considerably devitrified and mottled 

 with light and dark patches, which retain their I'elative tints while. 

 the stage is revolved. Through this ground-mass small angular 

 grains of quartz and crystals of pyrites were abundantly scat- 

 tered. The quartz contains, very rarely, small glass inclusions 

 with a fixed bubble, generally it has only clouds or sheets of 

 minute gas-pores, sometimes it is quite clear. There are also 

 patches of a colourless irregularly fibrous minei'al, which shows 

 between crossed nicols an aggregate with rather brilliant polari- 

 zation colours, and with occasional greenish inclusions. This 

 mineral may be talc, secondary after a bisilicate. Calcite occurs 

 in grains in the ground-mass and occasionally in larger patches, 

 which were probably once felspars. 



Hornblende Dacite. — This rock occurs in the Waiotahi Creek' 

 and on the shore a little north of Tararu Creek, and is the 

 timarzite of my report of 18G8-9. It is a compact greyish-green 

 rock with white felspars and distinct black prisms of hoi'nblende 

 scattered thickly through it. Pyrites may or may not be visible. 

 The specific gravity ranges from 2.62 to 2.76. Two partial 

 analyses of these rocks by Mr. W. Skey in 1869, gave the following 

 results : — 



I. — From dyke in Heart and Hand Claim, Wiseman's Gully, Thames. 

 II. — From the dyke in Ballynure Claim, Waiotahi Creek, Thames. 



The specimens from the Waiotahi Creek have not undergone 

 much change. The ground-mass is still glassy and of a pale- 

 brown colour. 



