628 DE. J. A. THOMSON' ON THE [Dec. 1913, 



In this map, the jasper-reefs were coloured as quartzites, being 

 evidently therefore considered as sediments, and an extraordinary 

 number of ' felsite '-dykes were shown accompanying the jaspers. 

 The peridotite-intrusion in the ' North End ' was not recognized, 

 and the distinctions made among the amphibolites did not corre- 

 spond to any very clear natural divisions in the rocks themselves. 

 Consequently, the publication of the map had little or no influence 

 in directing mining operations, more particularly as no explanatory 

 memoir accompanied it. 



The rocks collected during the preparation of the map were 

 examined and described in the same year by Mr. E. S. Simpson 1 in 

 a short but concise paper, illustrated by numerous chemical analyses. 

 The rocks were classified as follows : — 



I. Amphibolites and their derivatives (massive greenstones, chlorite- 

 scbists, massive and foliated siderite-rocks). 



{Felspar-porphyry. 

 Porpbyrite. 

 Peridotite. 



III. Older sediments. 



IV. Newer sediments. Chemical: — Salt, travertine, siliceous sinter, and 



laterite. 

 Mechanical :— Sand, clay, and ironstone-gravel. 



That writer's treatment marked a great advance in Kalgoorlie 

 petrology, not only because of its comprehensive character, but 

 also on account of the importance conceded by it to the amphi- 

 bolites. Dr. Vogelsang, 2 who had previously made a study of the 

 rocks of other Western Australian goldfields, had suggested the 

 derivation of the amphibolites occurring in them from diabases, 

 and Mr. Simpson applied this explanation to those of Kalgoorlie, 

 pointing out that they were too poor in silica to be termed diorites. 

 He further recognized the close connexion between the amphibolites 

 and the greenstones, rejecting Mr. Card's explanation of the latter 

 as altered granites, a view which the analyses abundantly disproved. 

 His failure to distinguish between the older and the younger 

 amphibolites and greenstones may probably be put down to lack of 

 opportunity of studying the field-relations in sufficient detail. The 

 differences of interpretation on some points between Mr. Simpson 

 and myself are fully discussed below. 



Until quite recently, subsequent authors (Krusch, Lindgren, 

 Maitland, etc.) have, in general, followed Mr. Simpson ; but Mr. T. 

 A. Kickard, 3 writing about the same time, quoted a determination 

 of the dominant rock by Prof. J. "VV. Judd as a ' highly-altered 

 quartz-andesite,' a view that might easily be taken after study of 



1 'Notes from the Departmental Laboratory: Rocks of Kalgoorlie' Bull. 

 Geol. Surv. W. Austral. No. 6 (1902) pt. 2, pp. 62-79. 



2 In K. Schrueisser, 'Die Goldfelder Australasiens ' Berlin, 1897, p. 45 

 (English transl. : The Goldfields of Australasia, London, 1898, pp. 63-83). 



3 ' The Veins of Boulder & Kalgoorlie ' Trans. Am. Inst. M. E. vol. xxxiii 

 (1903) pp. 574-75. 



