Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. 635 



or pressure-inetamorphism, but Prof. E. Weinschenk has remarked 

 that it is absent in contact-rocks containing calcite. 1 The presence 

 of considerable amounts of chlorite and rutile shows that these rocks 

 are not altered sediments, and suggests that they are formed from 

 the greenstones ; but their field-relationships are not sufficiently 

 clear to give the clue to their probable mode of origin. 



{d) The ' Calc-Schists.' 



The name of ' calc-schists ' was applied to these rocks by Dr. 

 Maclaren before their true nature was ascertained, and has been 

 adopted by Mr. Gibson. These rocks are more often massive than 

 schistose, especially when freshly mined, and hence the name is 

 not quite applicable ; but it will be retained for convenience, since 

 a distinctive name is necessary for the miner. The greatest 

 development of the ' calc-schists ' is on the eastern side of the 

 quartz-dolerite bos3 of ' The Mile ' ; but they persist for some 

 distance northwards, gradually merging into the fine-grained 

 greenstones. In hand-specimens they are whitish-green aphanitic 

 rocks, intersected by dark venules like those of chalcedony in 

 serpentine; and, owing to close jointing, they possess a very 

 short fracture. They are so dense that a high power of the 

 microscope is required to distinguish the individual grains of the 

 carbonate of which the rock is mainly composed, and to reveal 

 the presence of quartz between them. In places, they contain 

 small lath-shaped sericitic areas recalling those of the felspars in 

 the fine-grained amphibolites. Chlorite is absent, or but sparingly 

 present in large flakes. Occasionally, large octahedra of magnetite 

 are scattered through the rock. In the more schistose varieties 

 the muscovite exhibits some approach to parallelism, and large 

 rhombohedra of carbonate are frequently developed. 



[e) The Peridotites and their Derivatives. 



In the hills forming the western shores of Hannan's Lake and 

 the eastern slopes of Mount Hunt, 6 miles south of Boulder, 

 a considerable area is occupied by a dense serpentine and a 

 coarse carbonated serpentine. The former rock consists mainly of 

 serpentine pseudomorphs after olivine-graius, embraced by a turbid 

 mineral resembling bastite, and in addition a variable amount of 

 tremolite, both as fine needles within the serpentine and as 

 coarser prisms lying in the bastite. The original rock was probably, 

 therefore, an augite or enstatite-peridotite. In the carbonated 

 forms, the tremolite and bastite are little affected, but the ser- 

 pentinous areas are almost completely replaced by a carbonate 

 approximating to magnesite in composition. 



Within the Kalgoorlie area proper, serpentiue has been observed 

 in only two places : Mr. Simpson 2 has recorded a rock 'of a serpen- 

 tinous nature ' from the former Black Cat lease, G.M.L. 3862 E ; 



1 ' Grundziige der Gesteinskunde' vol. i (1906) p. 139. 



- ' Ann. Rep. Geol. Surv. W. Austral, for 1900 (1901) p. 9. 



