624 DE. J. A. THOMSON ON THE [DeC. I913, 



south-south-easterly trend of the field; and similar dykes are known, 

 both in the fine-grained greenstones and in the eastern mass of 

 peridotite. South of ' The Mile ' the tongue of rock between the 

 two southern dykes of quartz-dolerite is occupied, so far as the 

 dumps show, by albite-porphyry and graphitic schists in numerous 

 alternations. 



Slaty rocks, which present superficially the appearance of sedimen- 

 tary origin, occupy parts of the valleys both east and west of the 

 main ridge, and are well exposed in quarry-pits. They are really 

 more siliceous than true slates, and never show traces of clastic origin 

 or contain any indications of fossils. Similar slaty rocks are found 

 on each side of the many jasper-reefs which intersect the igneous 

 rocks of the field, and are undoubtedly of igneous origin : -wherefore, 

 until some criteria are found for distinguishing the two sets of 

 rocks, it is unsafe to assert that any sedimentary rocks occur in the 

 valleys. An undoubtedly sedimentary series, composed of thick beds 

 of sheared conglomerates, interstratified with reddish and chocolate- 

 coloured grits and sandstones, occupies a high ridge at Kurrawang, 

 about half way between Kalgoorlie and Coolgardie. In strike and 

 dip it conforms to the foliated igneous rocks of Kalgoorlie, but 1 he 

 lack of continuous exposures in the intermediate ground makes it 

 impossible to say what is the geological relationship of the two 

 series. The pebbles in the conglomerates consist chiefly of liver- 

 coloured quartzites, haematite-jaspers, and albite-porphyries, the 

 last-named being very similar to those of Kalgoorlie, whence the 

 inference may be drawn that the Kurrawang Series is the later. 



The gold of Kalgoorlie is contained mostly in ' lode-formations,' 

 which are shear-zones impregnated with sulphides and tellurides. 

 They may occur in any class of rock, but those in the quartz- 

 dolerites are the most regular and the richest, the other two most 

 favourable rocks being the fine-grained greenstones (calc-schists) 

 and the schistose derivatives of the peridotite. In the ' North 

 End ' the lodes in the quartz-dolerite are of low grade, but they 

 are often crossed by small quartz-reefs carrying rich ore, though 

 without tellurides. 



II. Histoeical Review. 



The earliest geological notices of Kalgoorlie are found in general 

 accounts of the parent Coolgardie field, and contain few observa- 

 tions of value. At a later date many contradictory determinations 

 of the country-rock of the lodes, based solely on the inspection 

 of hand-specimens, were made by visiting mining engineers, but 

 their enumeration here would serve no useful purpose. The 

 earlier microscopical identifications were made by petrologists 

 who had not the advantage of collecting their own specimens ; and, 

 considering the excessive alteration displayed by the rocks near the 

 lodes, it is not surprising that views widely at variance were put 

 forward. The subjoined correlation (on pp. 626-27) of the various 

 classifications proposed will render the following account of them 

 more easily intelligible. 



