22 THE "lEON BLOW AT THE LINDA GOLDFIELD. 



evidence at our command of crumpled, distorted, folded, and 

 metamorphosed strata, common in I'ocks of this age, there is 

 little doubt of the fact that the dynamic forces at work were 

 far more potent than at present, although not different from 

 forces still in operation, whose throes, like those of Krakatoa 

 and Tarawera, are still mighty enough to produce vast local 

 disturbances. There is little doubt in my opinion, therefore, 

 that the fissure at the Linda was originally caused by the 

 same dynamic forces which caused the dilating, folding, and 

 metamorphosis of the crystalline rocks, and that these mighty 

 effects were primarily caused by the gravitation of the outer 

 crust towards the shrinking and cooling central mass of the 

 earth. Mallet's lucid exposition of this theory, many years 

 ago, has convinced the large body of geologists of the 

 reasonableness of this ; and I may be pardoned if I cannot 

 discover any flaw in its sufficiency to account for all the 

 dynamical phenomena observable at the Iron Blow. 



The next consideration is — Was the opening of the fissure 

 accompanied by the expulsion of heated materials from the 

 interior of the earth by volcanic agency ? This brings us to 

 the second part — 



From whence and by what agencies were the present 

 altered and unaltered materials derived! 



"With respect to this question, I am still in accord with Mr. 

 Thtireau, for I am of opinion that the expulsion of heated 

 materials from the interior of the earth by volcanic agency 

 has occurred, and to this expulsion may be attributed the 

 immediate cause of the opening of the Iron Blow fissure. My 

 original suggestion, that the materials now forming the 

 contents of the fissure does not " necessitate their having 

 been formed originally in the way of ' volcanic mud,'" is 

 incorrectly interpreted by Mr. Thureau as a denial of volcanic 

 action. 



This interpretation, moreover, is hardly warranted; for 

 Mr. Thureau is well enough aware that elements such as 

 barium, sulphur, iron and gold, now contained in the fissure 

 are, and may have been, expelled from the interior of the 

 earth as volcanic products by way of sublimation or heated 

 solutions, or by both together or alternately. Mr. Thureau 

 elsewhere admits this, for he states the discharges of the 

 volcanic vents alluded to by him " leave a thin deposit or 

 lamina in the ' cups ' at the surface which, after hardening, 

 was found on analysis to be chiefly charged with silica 

 (quartz), and to also contain a sensible percentage of gold 

 and silver." Now this deposit, it is clear by his own showing, 

 was not composed of "volcanic mud" seen in ebulition as 

 " a greyish semi-liquid mass . . . within the mouth of 

 the ' f umaroles,' " but was essentially a distinct chemical 



