GEOLOGICAL SOCIETY. 



29 



place above the depth of 100 feet, which could alone 

 have originated in the action of water for a lengthened 

 period on the sulphuret. The pyritical cubes have been 

 converted into brown, red and purple hydrates of iron ; 

 sometimes a cube is found only half decomposed. In 

 the centre of the solid quartz itself, cavities are met 

 with resembling a honey-comb, entirely empty, but 

 which bear the impress of the shape of the pyritical 

 cube, and coating richly the interior of each minute 

 cavity is found a quantity of gold. There is one point 

 clearly shown : it is, that all the gold which is obtained 

 by amalgamates from these pyritical ores of gold is that 

 portion which has been disintegrated, and left isolated 

 in its native state by the decomposition of the sulphuret. 

 The residue of metallic sulphuret, if collected and con- 

 centrated, would yield and does by experiments fre- 

 quently repeated by the writer of this essay, afford a 

 large portion of the precious metal by lire assay. 



Pyritical ores of gold constitute the mass of the loads 

 of Columbia, the Brazils and the United States ; if then 

 a process was employed which would in the first place 

 obtain by amalgamation nearly all the disintegrated 

 gold, and the balance of metallic matter was concen- 

 trated, many rich mines, which at present are consider- 

 ed to consist of very untractable ores, would yield vast 

 profits. 



During an extensive series of practical operations in 

 the gold regions of the United States, many experiments 

 and processes have been attempted and put in operation 

 on a large scale, by the writer. He deems that a 



