26 Transactions. 



says, :;: " The statement of Dr. Don that country rocks can 

 be assayed by panning down a quantity and assaying the 

 residue has been tested, as well as the statement that pyrites 

 must be present in order to find gold ; and my experiments 

 show that both statements are incorrect — or, at least, not in 

 accord with my experience." 



At Te Aroha, near the northern boundary of the central 

 volcanic region, there are in the andesites hot springs ; 

 twenty -five miles distant, soda-water springs; and at the 

 Thames, ten miles further north, gas springs which discharge 

 enormous volumes of carbon-dioxide. 



In the mines in the north end of the Thames Goldfield 

 the CO., issues with great force from cracks and fissures in 

 the rocks. The mine-shafts are situated near the foreshore, 

 and descend to depths varying from 500 ft. to 900 ft. below 

 sea-level. In close muggy weather in summer, with a low 

 barometer, the gas rises in the mines, and, flooding the 

 workings, drives the miners before it. Sometimes the gas 

 rises up to the top of the shafts and overflows at the surface. 

 Notwithstanding the special precautions employed to effect 

 ventilation and to warn the men of danger, several fatal acci- 

 dents have taken place in the past thirty years. 



In the Big Pump shaft the C0 2 escapes with such force as 

 to cause violent boiling all over the surface of the water in the 

 well. The depth of the shaft is 640 ft., but the workings are 

 flooded up to the 500ft. level, in consequence of which the 

 gas escapes against a head of 150 ft., equal to hydraulic pres- 

 sure of 65 lb. to the square inch. The commotion at the 

 surface of the water at the 500 ft. level is caused by the escape 

 of the gas which is not dissolved by the water. The pump 

 has been raising water from this shaft for over a quarter of 

 a century at the rate of 750 gallons per minute. The water 

 is so highly charged with gas as to often cause trouble in 

 working the pumps. 



At Waihi, Kuaotunu, and Great Barrier Island there are 

 huge veins of quartz, mostly chalcedonic, many of which 

 are still capped with wide mushroom-shaped "quartz blows." 



The evidence favours the conclusion that the propylitisa- 

 tion of the andesites and formation of the lodes were the 

 result of hydro-thermal action. 



Posepnyt mentions the remarkable occurrence of ti*ee- 

 stems changed to galena in the Vesuvian Mine, Freihung, in 

 Bavaria. In these the fibre and annular rings can be easily 

 recognised, being extremely plain on polished surfaces. In the 

 tuff-beds associated with the gold-bearing andesites masses 



* T.oc. cit., p. 808. 



t Prof. Franz Posepny, "The Genes-is of Ore-deposits," 1901, p. 129. 



