150 J. A. Thomson — Rocks of Western Australia. 



In some districts there appear also to be sedimentary rocks associated 

 with them. The -whole complex is generally referred to as the 

 ' Auriferous Series '. All these rocks occur in relatively narrow 

 belts, separated by wider belts of granite and gneissic rocks, which 

 when foliated possess the same general direction of foliation. All 

 these belts possess a trend, so far as known, parallel to the foliation. 

 Within the auriferous belts in almost every goldfield there are 

 elongate lenticular bands of ferruginous and non-ferruginous jaspers 

 and graphitic schists which also follow the same lines of trend. 

 In most fields there are relatively unaltered intrusive rocks of various 

 natures, viz. felsites, porphyries, porphyrites, and more basic rocks, 

 which in some cases run parallel to, and in others cross, the direction 

 of foliation. 



A peculiar feature of many of the schistose rocks of the State is 

 that when cut in depth by mining operations they are frequently 

 stated to be quite massive.^ In some cases this statement may be 

 based on a faulty correlation : the shafts may pass through a band of 

 schist into an unsheared phacoid of massive rock of similar constitution 

 to the schists. It is, however, undoubtedly the case that many rocks 

 which are apparently quite massive when mined, develop a latent 

 schistosity after some years' exposure in mine dumps, and since this 

 is so it is also reasonable to admit that this latent schistosity may be 

 developed in the weathered parts near the surface. Dykes of sericite 

 schist not unfrequently pass in depth into massive porphyries. 



H. P. Woodward^ in 1895^ relegated these rocks to the Archaean, 

 and divided them into granites, gneisses, and schists. He described 

 the existence of six great belts crossing the country from sea to sea 

 in a north-south direction. Commencing from the west coast near 

 Perth, these belts are consecutively ' crystalline ', ' crystalline ', 

 granite, western auriferous belt, granite, and eastern auriferous belt. 

 The relationship of these belts to one another is not clearly indicated, 

 but apparently he recognized that the granites are intrusive into the 

 auriferous series, for he mentions that the western auriferous belt is 

 broken and faulted by granite and diorite dykes. Subsequent 

 observations have been very largely confined to the auriferous belts, 

 and do not seem to have greatly modified Woodward's statement. 

 A seventh belt of gneiss-granite has, however, been recognized on the 

 eastern boundary of the Coolgardie-Kalgoorlie belt by Gibson.* A map 

 of the State embodying the recently acquired knowledge is a great 

 desideratum. 



Much of the earlier literature relates to the Coolgardie Goldfield 

 and its immediate surroundings, but is, unfortunately, of a very 

 vague character. Coolgardie is situated on the. contact zone between 

 a granite on the west intrusive into the auriferous series in the east. 



^ Bull, xxii, pp. 15, 16, 1906. In this and subsequent references ' Bull.' 

 stands for Bulletin of the Geological Survey of Western Australia. 



^ Mining Handbook to the Colony of Western Australia, Perth, by Authority, 

 1895, pp. 37, 38. 



' The -writer has not had access to Government publications prior to 1894. 



^ C. G. Gibson, Bull, xxiv, pp. 29, 30, 1906, and Bull, xxxvii, p. 23, 1909. ■ 



