ON TUB ROCKS OF THE HAURAKI GOLD-FIELDS. 265 



<Tranting, for the sake of avgument, that he has been able to 

 distinguish two series and to identify them accurately ; still it 

 seems to me that the older series, being composed of viscous laA'a 

 flows, would have consolidated at steep angles and that the later 

 products of eruption would have flowed down these steep slopes 

 and would now he found at all elevations. Viscous lava is known 

 to have consolidated at angles up to 80°, while as the places indi- 

 cated by Mr. Cox in his map are a uiile and a half apart, a slope 

 of 10° would be suflicient to account for the difierence in level. 

 Some also of the supposed newer dolerites are certainly nearly 

 vertical dykes. Also Mr. Cox allows that this younger series at 

 the Thames occupies the spurs anil higher ground only, so that the 

 valleys of the present creeks and rivers must have been entirely 

 cut since these later lava flows took place. 



SOURCE OF THE GOLD. 



To discuss with anything like completeness the question of the 

 sources of the gold requires a knowledge of chemistry far beyond 

 what I possess, but I think that a geologist may be of assistance 

 to the chemist by pointing out to him the lines on which chemical 

 investigation might probably lead to successful results ; and this 

 is all I hope to do here. 



Origin of the Gold-veins. — There can, I think, be no reasonable 

 doubt that the gold came out of the volcanic rocks and was not 

 brought into them from below. Five difierent lines of reasoning 

 tend equally to this result. 



The first is that, after thirty-six years of prospecting, we find the 

 gold-veins to be confined to the volcanic series, or to the slates in 

 immediate contact with the volcanic series and not found in the 

 older formation. At Tapu Creek the auriferous veins pene- 

 trated a short distance down into the slates, but the lodes 

 in the slates always consisted of soft, stiff", blue clay (mul- 

 lock), charged with small nodules of quartz,* and were evi- 

 dently infiltration lodes, from above. Mr. Cox informs us that they 

 soon pinched out in the slates and that the mines were abandonedf 

 There is, I believe, no mine at present working in the slates 

 although some were tried at Tiki near Coromandel. This is a 

 district that I have not examined personally. As the volcanic 

 series is a superficial one, overlying the slates, it follows that the 

 gold must have originated in that superficial series ; for if not, 

 the lodes would have penetrated the older as well as the newer 

 rocks and would have been found equally in both. 



The second argument is founded on the nature of the gold- 

 veins. These are often small, irregulai', branching veins, some- 

 times only a quarter of an inch in thickness, traversing the rock 



* Reports Geological Explorations, 186S-9, p. 24. 

 t Reports Geological Explorations, 1882, p. 40. 



