54 
Contact of this oxidised solution with excess of alkaline ground 
water would, from the experiments described above (p. 53), result 
in the precipitation of ferric hydrates, leaving all alkali and sul- 
phuric oxide in solution. This is the result usually observed in 
weathered lodes. 
Many of the lodes of the Kundip district, including the one 
under discussion, are impregnations of amphibolites or other rocks 
carrying sodium-bearing silicates. Were some portion of the oxi- 
dised iron solution for some abnormal reason to remain out of the 
reach of the main underground circulation, the free acid would 
gradually attack such silicates, a neutral or faintly acid solution 
remaining, which contained ferric sulphate and sodium sulphate. 
Hydrolysis of this solution would then give rise to the formation of 
the basic salt Xatrojarosite, since this compound is insoluble in such 
a solution, thus: 
3Fe 2 (S0 4 ) 3 + Na 2 S0. + 12H 2 0 == 6H 2 0.Na 2 0.3Fe 2 0 3 .4S0 3 + 
6H 2 S0 4 . Natrojarosite. 
Perth, 12tli April, 1915. 
