24 THE "iron blow" at the LINDA GOLDFIELD. 



part of the lode, have been derived by subsequent decom- 

 position of the parts more exposed to decomposing agencies, 

 is a most unsatisfactory position for him to assume. It is not 

 true, as stated by him, that the iron pyrites contain "no 

 baryta to speak of." At page 218, " Eoyal Soc. Proc, 1886," 

 the analysis given by Mr. Ward shows iron bisulphide pyrites, 

 83*0 per cent.; barium sulphate (barytes), 17 per cent., i.e., 

 actually 2*85 per cent, less than the decomposed pulverulent 

 mass, which Mr. Ward, no doubt, rightly attributes to oxida- 

 tion of pyrites. 



Mr. Ward nowhere states that the entire mass of pyrites 

 has undergone decomposition. On the contrary, he refers to 

 the exposed surface of one portion of the original lode. The 

 very fact that the undecomposed pyrites analysed by him was 

 stated to be taten from a section described as two chains 

 wide is proof that this is so. Mr. Thureau's most extravagant 

 allusion to the fissure collapsing in consequence of a partial 

 decomposition is therefore too preposterous to dwell upon. Has 

 Mr. Thureau ever known pyrites, long exposed in lodes to air 

 and water, not to have suffered from decomposition ? That both 

 decomposition and recomposition in mineral veins are among 

 the most common of all occurrences cannot reasonably be 

 disputed. Geikie, surely, may be trusted in a simple matter 

 of this kind. At page 597, " Text Book of Geology," he 

 states : — " It has been noticed that the ' country ' through 

 which mineral veins run is often considerably decomposed. 

 In Cornwall this is frequently very observable in the granite. 

 Moreover, in most mineral veins, there occurs layers of clay, 

 earth, or other soft, friable, loamy substances, to which various 

 mining names are given. In the south-west of England the 

 great majority of the remarkable minerals of that district 

 occur in those parts of the lodes where such soft earths 

 abound. The veins evidently serve as channels for the 

 circulation of water both upward and downward, and to this 

 circulation the decay of some bands into mere clay or earth, 

 and the recrystallisation of part of their ingredients into rare 

 or interesting minerals are to be ascribed." So much for 

 decomposition. Mr. Thureau, curiously enough, makes no 

 allusion to the remarkable strings and veins of solid barytes 

 penetrating the decomposed part of the lode. He would 

 find it a difficult task to account for these strings on the 

 assumption that they were formed contemporaneously with 

 the pyrites mass, or even with the decomposed portion of the 

 original lode, 



Mr. Thureau's inexactness is also conspicuous in his 

 references to baryta. In the first part of his paper, referring 

 to iron pyrites (bi-sulphide), he states that it contains " no 

 baryta to speak of," and yet he had Mr. Ward's analyses 



