HuTTOK. — On the Tlmmes Gold Fields. 283 



trachyte and trachytic agglomerate, which, in Sykes Creek, contains gold. At 

 this place the coal is underlaid by a grey fire-clay, which rests unconformably 

 on slates, while at the Hinan the coal rests upon trachytic agglomerate, which 

 again rests unconformably on slates. The coals from the two places are 

 similar to one another (for analysis see Geological Reports, 1870-71, p. 175). 

 These facts thei'efore prove that the trachyte formation lies in a nearly- 

 horizontal position, or in the position in which it was originally formed ; and, 

 as the underlying slate rocks are always highly inclined, it necessarily follows 

 that the trachytic formation lies unconformably on their upturned edges, and 

 this can be distinctly seen at the point north of Tararu, at Tapu Creek, on the 

 coast between the Mata and the Waikawhau, and at the Waiau, Coromandel. 

 I have now, I think, proved — 



1. That no line of separation can be drawn showing the existence of two 

 volcanic formations separated from each other by a long period of time. 



2. That the rock in which the auriferous veins are found does not run in 

 neai'ly vertical bands, but is lying in its original (nearly horizontal) position. 



3. That all the phenomena are consistent with the idea that the formation 

 is one, the older portions forming the centre, and the younger the outskirts. 



With regard to the age of the older part of the formation, we have no 

 palgeontological evidence, but there appears to be no reason for separating it 

 from the trachytes of the Great Barrier to the north, nor those of the Aroha 

 to the south, which are undoubtedly tertiary, as they are connected with still 

 existing craters. We have also no evidence of the occurrence of any volcanic 

 rocks in this part of New Zealand befoi'e the deposition of the Waitemata 

 sei'ies, which I consider to belong to the oligocene period. The rocks them- 

 selves, both the trachytes and the dykes, closely resemble those of the gold- 

 bearing rocks of Hungary, which have been lately pi'oved by the Austrian 

 survey to belong to the miocene period, as was indeed long ago pointed out by 

 Professor v. Pettko (Q. J.G.S., 1848, ap. 61) ; and although I cannot attach so 

 much importance to the nature of volcanic rocks in determining their age as 

 is done by most German geologists, still in this case the two kinds of evidence 

 point the same way. I therefore think that the gold-bearing trachytes of the 

 Thames belong to the oligocene period, a period when volcanic action was 

 active not only near Auckland, but also in the South Island and in the 

 Chatham Islands. 



