636 DE. J. A. THOMSON ON THE [DeC. 1913, 



and a boring core from the neighbouring old Kaipai Mine, G.M.L. 

 3625 E, has also proved to be a serpentine essentially similar to that 

 from Hannan's Lake, except that it contains more original chromite 

 and secondar}- magnetite. Though no outcrop of this serpentine can 

 be found, the rocks in this neighbourhood (the eastern part of the 

 ' North End ') are largely derivatives of peridotites, and may be 

 classed as talc-magnesite rocks and schists, magnesite-rocks, and 

 fuchsite-magnesite rocks. In most of them all trace of the original 

 structure has been destroyed, bnt the mineralogical composition 

 leaves no doubt as to their original ultrabasic and highly magnesian 

 character. The talcose rocks consist mostly of a schistose matrix 

 of talc with subordinate biotite, chlorite, and quartz, in which 

 matrix large euhedral rhombohedra of magnesite are enclosed. In 

 hand-specimens these rocks are unusually dark for talc-schists, 

 and can be distinguished from the greenstone schists only by 

 their soapy feel. The magnesite-rocks differ mineralogically from 

 the carbonated serpentines of Hannan's Lake in the constant 

 presence of talc and quartz, and structurally by the disappearance 

 of recognizable pseudomorphs of olivine and pyroxene. The 

 fuchsite-magnesite rocks are bright-green variants of the magnesite- 

 rocks on the sides of small quartz or carbonate veins containing 

 tourmaline, and consist of structureless aggregates of magnesite, 

 quartz, fuehsite, and rutile. 



Similar derivatives of peridotites attain a great development in 

 the country east of Kalgoorlie, and particularly in the Bulong, 

 Waterfall, and Kanowna goldfields. A belt of serpentine very 

 similar to that of Hannan's Lake crosses the Bulong Road 6| miles 

 east of Kalgoorlie, and shows clearly the pcecilitic structure of the 

 tremolite-bastite element, as also the invasion of the serpentine by 

 delicate needles of tremolite. A distinct feature is the growth of 

 secondary magnetite within the bastite, in long arborescent crystals. 

 In the dump of the Oversight Mine, Bulong, is a beautifully lustre- 

 mottled rock, obviously derived from a serpentine. In natural light, 

 thin sections of this rock resemble an ordinary serpentine, because 

 of the retention of strings of iron-ores along the edges and cracks 

 of the original olivine. A small amount of serpentine is occa- 

 sionally retained in the centres of these original grains, but the 

 exteriors are generally altered to talc. In parts of the rocks big 

 crystals of carbonate replace the areas originally occupied by several 

 olivine-grains, except for small patches of serpentine or talc in their 

 centres which display in hand-specimens the dull patches of the 

 lustre -mottling. Talc-carbonate rocks showing greater similarity 

 to those of Kalgoorlie are found in the Golden Bidge Mine, "Water- 

 fall. At Kanowna is a hill of tremolite-serpentine north-west of 

 the town, while fuchsite-magnesite rocks are very abundant near 

 the gold-veins. 



Outside the Kalgoorlie fields, serpentines have not been very 

 frequently noticed in Western Australia ; but this does not 

 necessarily mean that they are uncommon. Little exploratory work 

 has been carried out beyond the immediate neighbourhood of known 

 gold-occurrences, and serpentine is not a rock in which auriferous 



