162 Notes on the Geology of the 



magnetite is polar-magnetic, some simply magnetic. The 

 flat pieces are all magnetic; but one specimen was polar- 

 magnetic at right angles to the striations. The massive 

 limonite occurs in large irregularly rounded blocks, imbedded 

 in a ferruginous gravel. It becomes more compact in depth, 

 and has an average thickness of about twenty feet. Borings 

 on Mount Vulcan were stated to have passed through strong 

 lodes of magnetic iron ; but some shafts put down by Mr. 

 Scott, the Company's manager, and myself, proved their utter 

 unreliability, as no magnetite was met with at considerably 

 below the depths stated. The chromium occurs in the limonite 

 in the form of chromite or chromate of iron, as glittering black 

 specks, and seems to be in the largest quantity in the densest 

 ore. The magnetite does not appear to contain chrome. At 

 Barnes' Hill there is a very large extent of ore of a similar 

 character to that already described. A peculiarity of it is 

 that all the surface specimens of limonite were more or less 

 magnetic, though I failed to detect any magnetite, as at 

 Mounts Vulcan and Scott. 



Mr. Gould supposes these ironstone deposits to be the 

 " backs" of strong lodes of magnetic iron ore, and that the 

 drift of magnetite on the flanks of the hills points to the 

 existence of veins of magnetic oxide of some size. This 

 may or may not be the case; but the ironstone is, I think, a 

 secondary product, formed by deposition from ferruginous 

 waters issuing as springs round the shores of the then arm 

 of the sea, when the land was at a much lower level, and the 

 gabbro was undergoing metamorphism into serpentine by 

 the process of double decomposition described by Dr. Sterry 

 Hunt. The chromium has been picked up, together with 

 the sand the ore contains, during the contemporaneous forma- 

 tion of the ore and the denudation of the neighbouring hills. 

 The ores vary from ferruginous grits to solid limonite; 

 cavities between the denser ore bands are filled with ochreous 

 clay and quartz grains, and the ore is concretionary. The 

 boulders of solid ore have probably once belonged to a solid 

 mass, which, in cracks and joints, has undergone partial 

 oxidation and decomposition in situ, the looser gravel and 

 ferruginous ochery clays being the result. Wherever iron- 

 stone occurs off the serpentine it contains no chromium. 



This ore produces a metal much resembling " spiegel- 

 eisen," or manganese iron, and makes good steel, but the 

 percentage of chromium is too high for pig iron. In the 

 present state of metallurgical science, chromium cannot be 



