32 Transactions. 



here and there still open, but mostly closed by the deposit 

 of silica on their walls. From some of the springs hot- 

 vapours and gases, chiefly C0. 2 and £LS, still issue. 



Becker found in the mineral water small amounts of 

 mercury-sulphide and sodium-sulphide. About a mile to the 

 west of the main group there are similar fissures yielding 

 steam and C0. 2 . In the sinters of these occur several metallic 

 sulphides. Becker analysed the filling of several fissures and 

 found, besides hydrated ferric oxide, lead, copper, and mercury 

 sulphide, gold and silver, and traces of zinc, manganese, 

 cobalt, and nickel. 



Thermal Action in relation to Vein-formation. 



The occurrence of metallic sulphides in the sinters at 

 Sulphur Bank, Steamboat Springs, and Ohaeawai hot springs ; 

 the mushroom-capped lodes at Waihi and Great Barrier 

 Island ; and the tree-stems replaced by sulphides found in 

 veins at great depths below the present surface, afford con- 

 clusive evidence of the filling of veins by hot ascending 

 waters and gases in areas occupied by later eruptive rocks. 

 It is a notorious circumstance that ore-deposits are most 

 numerous in the neighbourhood of extended zones of eruptive 

 rocks, as in Hungary, Transylvania, Nevada, Colorado, and 

 New Zealand, where the vein-bearing rocks are principally 

 andesite, phonolite, and trachyte. In other rocks veins are 

 fewer and more scattered. 



For veins in these altered later eruptives Lindgren suggests 

 the name " propylite veins," but it is doubtful whether the 

 genetic difference between propylite veins and true fissure- 

 veins is sufficiently marked to justify the distinction. _ More- 

 over, the roots of propylite veins will be difficult to distinguish 

 from fissure-veins connected with a plutonic intrusion. 



Professor Suess, :;: speaking of the importance of the role 

 played by the waning phases of volcanic phenomena in the 

 formation of mineral veins, says, "Hot springs may be taken 

 as the latest phase of a whole series which led up to the 

 present deposits of ore." 



In Nevada the sulphur-bearing rock occurs in beds lying 

 between limestone and magnesian rocks. In Utah the sul- 

 phur occurs associated with gypsum near an old crater. 



At Tikitere, in New Zealaud, there are extensive deposits 

 of sulphur in an old crater. A large proportion of the sulphur 

 is the black amorphous variety. The heat of the fumaroles 

 and hot springs is too great to permit the excavation of the 

 sulphur to a greater depth than 6 ft. or 8 ft. 



* Professor Edward Suess, Lectures, Royal Geographical Journal 

 vol. xx, Nov. 1902, p. 520. 



