Hurtron.—On the Thames Gold Fields. 275 
visited the Thames gold fields, and, in April, 1870, he made a report 
(Geological Reports, 1871—72, p. 88) in which he somewhat altered his former 
views, although still not agreeing with me. After giving Professor Hoch- 
stetter’s opinion, he says (p. 89) that “the gold is not, however, as he 
- (Professor Hochstetter) supposed, derived only from quartz-veins in clay-slates, 
for, as Captain Hutton very justly points out in his report on this district, the 
area of these exposed at the surface is very limited. Оп the other hand 
Captain Hutton, in the same report, does not distinguish between the 
comparatively modern breccias and agglomerates, which he describes as 
containing blocks of variously-coloured scorias and lavas, and the more ancient 
formation of green tufaceous sandstone and porphyry, in which most of the . 
auriferous lodes occur." And in the section that accompanies this report he 
makes his “greenstone tufa” and “greenstone porphyry,” as he here calls 
them, conformable to the clay-slates and dipping with them at a high angle. 
But speaking of the Tapu district, he says (/с., p. 98) that here the reefs 
occur in *the decomposed slates and bands of greenstone porphyry which 
intersect them with a prevalent north-east strike.” It therefore appears that 
more extended observations led Dr. Hector to abandon the idea that the 
“grey pyritiferous rock,” in which the auriferous veins ocour at Coromandel, 
is a dyke of trachyte, and to suppose now that it is part of a “ green tufaceous 
sandstone and porphyry,” belonging to a formation distinct on the one hand 
from the older slates, and on the other from the newer trachyte tufa ; but he 
still thinks that at Tapu the reefs are in dykes of « greenstone porphyry ” 
intersecting the slates. 
The late Mr. E. H. Davis also visited these gold fields in May, 1870, and 
reported (Geological Reports, 1870-71, p. 56), as far as I can understand him, 
in favour of two volcanic formations, one of ** diorite sandstone,” the other of 
“tufa”; and these are, I presume, meant to be identical with Dr. Hector’s 
“greenstone tufa” and “trachyte tufa” formations respectively. But he 
describes Tinker’s Gully as “a mass of diorite sandstone with dykes of tufa 
passing through it” (!) (p. 60), from which I infer that he supposed these two 
* formations" (1) to be interstratified and elevated on edge; and in other 
places he seems to think that the *tufa" is only the “diorite sandstone” 
decomposed. But however this may be, he was, at any rate, of opinion 
(according to Dr. Hector, lc., p. 98) that “the Tapu district furnishes very 
conclusive evidence of two distinot and two widely Separated volcanic 
formations." 
In April, 1872, I again visited Coromandel, in order to examine some coal 
seams which had been lately discovered, айа which I shall presently deseribe, 
and I then saw sufficient evidence to confirm me in the views that I had 
previously expressed. 
