4 THE IRON BLOW AT THE LINDA GOLDFIELD. 



denser kind and of a darker colour, as, in all probability, the 

 result of these ore-deposits having become saturated with 

 steam or hot-vapours, and by means of segregation and 

 expansion of these high-pressure volcanic emanations, the 

 cavities or cells were firstly formed and subsequently filled, 

 thus explaining the so-called "schistose" appearance, which, 

 from all appearances was principally due to the gradual 

 cooling of a seething mass of volcanic mud or ash which was 

 ejected in combination of several kinds of metallic vapours, 

 such, as for instance, specular iron, which not only forms a 

 conspicuous constituent of that volcanic material, but also 

 occurs quite frequently in the wall-rocks of that immense 

 fissure. In my opinion everything in connection points to a 

 more drastic process of origination than simple and quiescent 

 decomposition only. 



That there is strong evidence of the former ebullition and 

 belching forth of metalliferous and mineral vapours at high 

 temperatures within certain ejective points of discharge with 

 the volcanic muds and ashes, is clearly demonstrated by the 

 occurrence of elongated or spherical nodules in these muds 

 and ashes, which nodules on examination are found to 

 contain, within hard crusts of " Limonite " — sesqui-oxide of 

 iron — nuclei of pure iron pyrites, thus pointing the way how 

 the decomposition of pyrites under precisely similar circum- 

 stances has actually occiirred, and caused the formation of a 

 secondary and hydrated iron ore, and not of purple rock, 

 though in very close contiguity to the massive pyrites vein 

 and beds referred to. Those nodules, it is submitted, present, 

 neither more nor less, former gaseous bubbles surcharged 

 with vaporous sulphuretted solutions of iron, becoming rigid 

 when nearer the cooler atmosphere, and which from compres- 

 sion by the surrounding muds, etc., assumed their present 

 characteristically elongated forms. 



When it is borne in mind that geologists have concluded 

 that " the nature of vapours evolved depends on the tem- 

 perature or degree of activity of the volcanic orifices ; chlorine 

 and fluorine emanation indicating the most energetic j)hase 

 of eruptivity, sulphurous gases, a diminishing condition and 

 carbonic acid (with hydro-carbons) the dying out of that 

 activity, and that sublimed by volcanic heat or chemical re- 

 actions, causing the decomposition of metals and minerals from 

 condensing vapours along crevices and surfaces wherein they 

 reach the outer air and are cooled ; and further that, besides 

 sulphur there are chlorides, and in a lesser degree, iron, 

 copper, and lead ; also free sulphuric acid, sal amonia, 

 specidar iron, oxides of copper, boracic acid, alum, sulphate 

 of lime, baryta and others, are formed whilst at very high 

 temperatures, and in connection with simultaneously en- 



