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THE "IRON BLOW" AT THE LINDA GOLDFIELD. 

 By R. M. Johnston, F.L.S. 



At tlie last meeting of this Society a paper, contributed by- 

 Mr. Gr. Tliureau, F.G.S., was read, which calls for some 

 ■observations from me. Before commenting upon the matters 

 which have caused differences of opinion, however, let me 

 ■express my sincere regret that any unfortunate remark of 

 mine should have led him to suppose that I do not appreciate 

 Ihe scientific ability of the author of the paper in question. 

 Having said this much, it will, I hope, be granted that the 

 existence of differences of opinion upon geological matters 

 which are obscure may nevertheless exist, and, in fact, 

 continually happen — between the greatest names in science — 

 without questioning the talents or training of those who may 

 espouse irreconcilable opinions. 



The differences of opinion as between myself and Mr. 

 Thureau, fortunately, are not of a serious nature, and, 

 according to Mr. Thureau's recent explanation, I perceive they 

 are more due to the confused way in which descriptive terms 

 are employed than to any real differences of opinion. The 

 questioa between us has been altogether misconceived by Mr. 

 Thureau, and even in his last paper he often leaves me in 

 doubt whether he is referring (1) to the original agencies by 

 which the original metalliferous deposit was formed, or (2) to 

 the causes which produced subsequent modifications. If Mr. 

 Thureau had discussed the Iron Blow question without 

 confusing these two fundamental considerations it would have 

 placed the issues between us in a very small compass. I shall 

 endeavour to keep free from this confusion by discussing the 

 two questions separately : — 



I. (a) Under what circumstances and by what agency was 

 the fissure formed originally ? 

 (b) From whence and by what agencies were its present 



altered and unaltered contents derived ? 

 (/) By what mode were the original matters deposited 

 or obtained ? 



First, then, we have to enquire — 



Under what circumstances and by what agettcy was 

 the fissure originally formed ? 



The schists and conglomerates in which the great fissure 

 occurs are evidently of Silurian age, and the forces which 

 operated in dislocating them must, therefore, have been 

 -exerted not earlier than this period. From the abundant 



