40 C. U. Shejmrd's Reply to F. A, Genth. 



stoiild be developed where tte atmosplieric influences liave been 

 favorable to sucn changes." " 



NoM^ the facts in the case are these. At 90 feet from the top 

 of the ground, the ore-bearing schists begin to lose their tenden- 

 c}^ to decomposition. Galena is here visible in a perfectly fresh 

 condition, between the lamina of the slate and upon the cross- 

 joints of the rock. At a depth of 116 feet, every vestige of 

 alteration has disappeared. Here commences, in the form of a 

 mere thread, the dropper- vein that carries the harrisite. It de- 

 scends, gradually enlarging out to fifteen or twenty inches in 

 thickness, at an angle of between 30 and 40°, when it is suddenly 

 pinched off, and whollj disappears, in the 141 foot level. Fresh 

 galena has accompanied the metalliferous stratum, exterior to 

 the dropper, for the whole course of its descent, and continues 

 onward in increasing quantity, below the point of its termination. 

 But no galena or any other ore of lead, or even a single mould 

 or impression of any lead ore has been detected within the 

 dropper. On the other hand, no harrisite to my knowledge, has 

 been found in the rock, exterior to the dropper- vein. 



Dr. Genth recognizes the force of the argument from the per- 

 fect cleavage visible in every fragment of the harrisite, agamst 

 the view he has undertaken to support: but cites the pseudo- 

 morphs of gypsum after anhydrite which have the perfect cleav- 

 age of the latter, together with some other instances of the like 

 nature. To this, perhaps, it is sufficient to observe, that it is 

 at best evidence only of a negative character ; for our knowledge 

 of pseudomorphism is still very imperfect, and further investiga- 

 tions may modify much our present views. Add to this, the 

 opposite facts of wulfenite after galena, wolfram after scheelite, 

 and gypsum and polyhalite after salt unattended by the easy 

 cleavages which his hypothesis demands. 



Dr. Genth attaches weight also to the consideration, that the 

 harrisite has a similar proportion of silver to the galena of the 

 Canton mine. But the content of silver constantly varies in 

 the galena of the mine. I have found a variation of from 30 to 

 56 oz.,, in 2000 lbs. of the ore; and Mr. Pratt in his valuable 

 communication upon this locality, published in the same number 

 of this Journal, observes that '*the percentage of silver in the 

 galena of any mine varies with the position of the lead ore, and 

 my examination shows, that in this view, it increases with its 

 approach to the north wall. In different determinations, I have 

 found, from 0*1 to O'S p. a, equal to 32 and 96 oz. per ton of 

 the ore," (p. 413)- Besides the presence of silver in an ore of 

 copper, is a fact by no means unfrequcnt 



The locality of copper-glance after galena in Saxony, cited on 

 the authority of Breithaupt may be a correct determination, the 

 attending circumstances being such as to support the conclusion. 



