DISCUSSION ON THE "lEON BLOW ' AT LINDA GOLDFIELD. 27 



" specular iron ; " (b) fibrous, red baematite ; (c) earthy, 

 ochre, but all consisting essentially of peroxide of iron. 



In the Cumberland deposits are found hard or "blast" ore, 

 and soft, or " puddler's " ore, from its use in the puddling 

 furnace : the hard, fibrous, and more common form often passing 

 into the crystallised condition. 



In Elba, bsematite occurs ^^crystallised between talcose (or 

 perhaps hydro-mica) schists and crystalline limestone, and the 

 crystals are frequently associated with iron pyrites. It is also 

 found with other minerals as an abundant component of 

 mineral veins, also in beds interstratified with sedimentary or 

 schistose rocks. 



On the other hand " specular iron " in some cases is a result 

 of igneous action, is abundant around some volcanoes ; and as 

 pointed out by Mr. Thureau, scales of specular iron were 

 found with 15 other minerals in " ash " from Cotopaxi. 



To return to the formation, and quoting Mr. Thureau, we 

 have "An immense bed or vein of solid pyrites filling the 

 greater width of the fissure on its hanging wall, or about 225 ft. 

 out of a total width of 2S0 ft. between walls of that chasm." 

 Also "A soft purply pulverulent mass of oxide of iron about 

 56 ft. wide " on thefoot-ivall. 



Now, as we have already seen, the pyrites decomposes sooner 

 or later according to circumstances, and Mr. Thureau himself 

 found " elongated and spherical nodules, which on examination 

 were found to contain within hard crusts of sesquioxide of iron 

 (hydrated), nuclei of pure iron pyrites . . . the nodules 

 being in very close contiguity to the massive pyrites vein 

 or bed;" these showing that, as might be expected, 

 decomposition is still taking place. 



To the analysis made by me in connection with Mr. 

 Johnston's original paper, I appended a note that " there seems 

 little room for doubt that the ' Iron Blow ' is the result of 

 oxidation of pyrites similar to that now associated so largely 

 with it ; the hydrated oxide first formed subsequently losing its 

 combined water," and I was not a little influenced in forming 

 tbis opinion by finding 17 per cent, of sulphate of barium 

 intimately mixed with the pyrites, and 20 per cent, of that 

 substance, in similar condition, intermixed with the peroxide of 

 iron. This sulphate of barium Mr. Thureau claims to have 

 " first discovered as the necessary adjunct to the gold." While, 

 however, Mr. Thureau ignores or misquotes the evidence from 

 the presence of this common constituent, and also deprecates 

 forming opinions from the examination of specimens only, he 

 yet advances as a most, if not the most, cogent argument in 

 favour of "volcanic agency," the "almost non- auriferous " 

 character of the scraps of pyrites assayed, as contrasted 



