BY FREDERICK DAN VERS POWER, F.G.S. 43 



interstitial spaces and replaced the materials of the adjoining 

 country rocks to a greater or less extent by the materials 

 they held in solution, but are not the filling of any consider- 

 able open cavities." Mr. Richard Pearce in 1869 noted 

 that the gangue material of the veins of Cornwall was the 

 more or less completely altered country rock, and not foreign 

 material brought from a distance. 



Now, rocks may be so strained that faults result, 

 but it is seldom that these faults leave open cavities that 

 warrant the term fissure ; for what would otherwise be a 

 fissure is occupied by broken rock at the time of their forma- 

 tion. They are, therefore, not " true fissure lodes," such as 

 may be seen in process of formation at the Steamboat 

 Springs in Western Nevada, but fault lodes pure and simple, 

 which show a brecciated structure, flucan, partings, slicken- 

 sides, etc., all indicative of motion, and that usually gradual 

 and under great pressure. 



My idea of the genesis of the " Iron Blow " was that the 

 hematite was segregated first in a layer of schist favourable 

 for it ; that after the peaks of Mts. Lyell and Owen were 

 elevated they sank slightly, when the saddle connecting 

 them was strained ; the hematite being hard and strong was 

 enabled to resist this force better than the weaker rock to 

 its west, which, being loosened, located the site for the pyrites 

 deposit. There is nothing peculiar in both the hematite and 

 pyrites containing baryta, since they both, in my opinion, 

 obtained their mineral from the same source, but there is no 

 trace of any intimate connection between these two deposits, 

 as there is a sharp line at their junction, and where we do 

 find the pyrites decomposed it is converted into a gossan 

 or hydrated oxide of iron, not hematite. Although the 

 hematite deposit was not easily ruptured when pressed 

 end on, yet the lateral thrust from the direction of the coast 

 caused strike faults in it, as indicated by the soft rubbed-up 

 portions where one part has slid over another. 



Before condemning this opinion in an offhand manner, one 

 should carefully weigh the pros and cons, utilising such 

 knowledge as is possessed to enable a fair judgment to be 

 arrived at. It is not very scientific to rest content with 

 hypotheses because they happen to be generally accepted ; we 

 should be active in searching out the truth, and by upsetting 

 one theory we advance one step nearer our goal, so that by 

 opening the above questions fresh points should be gained, 

 either by ridding ourselves of unnecessary theories or by 

 adding fresh facts to our stock of knowledge. 



