74 



Discussion. 

 Professor Tate was not satisfied as to the evidence of contact - 

 metamorphism submitted by the author, or to that of alluvial 

 deposition contended for by Mr. Bethune. He considered that 

 those phenomena were explainable by the diminishing effects of 

 disintegration in depth upon the same rock. The shapes of the 

 pyritous bodies could not, in his opinion, be referred to bivalved 

 moUuscan casts, 



Mr. J. G. O. Tepper, F.L.S., remarking on the acute edges of 

 the supposed fossils, said that the figure could not be due to 

 lateral pressure, otherwise the edges would be perpendicular to 

 the diameter as in ordinary discs, or at least a very blunt round- 

 ing off. The objects could not be compressed nodules, in his 

 opinion, and that they were of organic origin was a view receiving 

 .some support from the great development of graphite associated 

 with them in the containing rock. Graphite in rock-formations 

 had long been claimed to have been derived from organic matter, 

 since no other satisfactory theory to account for the isolation of 

 the carbon had been advanced. 



Mr. W. HowcHiN, F.G.S., considered that in view of the 

 " augen " structure so often produced in metamorphic rocks, the 

 argument that the flattened shape was not due to pressure could 

 scarcely be applied. A fuller knowledge of the actual local con- 

 ditions and constitution of the rocks was required to make 

 generalizations safe. 



Mr. J. J. East, F.G.S., speaking from personal knowledge of 

 the Kalgoorlie field, stated that the occurrences cited were in no 

 way peculiar to the locality dealt with by Mr. Corbin. In the 

 i^ueen Margaret mine at Bulong the same kind of thing was 

 common. Where the graphite occurred plentifully the miners 

 sought to get beyond it as quickly as possible, for, though seldom 

 unassociated with gold, it rarely formed the matrix of good ore. 

 The rocks of Kalgoorlie form a low range of ferro-magnesian 

 silicates of diabasic character, which were broken up by intrusive 

 dykes of diorite and porphyry. The diorite-dykes seem to be the 

 dominant feature, and extend for miles in thin and thick bosses, 

 alternating along the line of direction in such manner that a plan 

 of them would suggest the figure of a huge cable. Each "link" 

 forms a boss, and along the sides of the " link " the richest gold 

 veins occur in the contact-zone. The graphitic belt is well marked 

 in places, and its connection with the gold-deposit is evident. He 

 regarded the graphite as having been derived from the breaking 

 up of liquid carbonic acid contained in inclosures in the rocks, 

 and by its agency the gold was precipitated from the waters holding 

 it in solution. The nature of these waters we could only guess 



