Hutton.—On the Thames 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 Hinau 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 therefore 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— 
l. 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 
nearly 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 
paleontological 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 before the deposition of the Waitemata 
series, 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 proved 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. 
