SALMON — MINERALOGICAL NOTES. 



63 



tin-stone or tin-ore), the former mineral is made, in the Profesor's 

 reasoning, a kind of middle term to prove the isomorphism of its in- 

 dividual components (silicic acid and zirconic acid), TN-ith stannic acid. 

 He considers, in fact, that silicic acid may faii'ly be considered to be 

 already found in the form of cassiterite, in zii'con ; and believes it 

 would not be a matter for sm'prise to find stannic acid in the form of 

 quartz. 



Dr. Genth's paper, in the September number of the " American 

 Journal of Science and Arts," on the " Occurrence of Gold" is very 

 suggestive. After the mass of vague verbiage with which we have 

 been inflicted on this topic, it is really refreshing to find a man who, 

 whether right or wrong, is at least possessed of a definite and com- 

 prehensible idea. 



Dr. Genth maintains that the gold found in veins and allu^^al de- 

 posits has been carried there in a state of solution ; and he brings tlie 

 folloT\4ng instances to prove that, in those cases at least, such must 

 have been the case. If these are accurately stated, of which there 

 seems every internal evidence, this certainly cannot be questioned : — 



" a, Specimen from Whitehall, Spotsylvania co., Ya., shows gold 

 associated with tetrad^nnite [telluride of bismuth], limonite [hydrous 

 per-oxide of iron], and quartz. The gold is crystallized in forms be- 

 longing to the rhombohedi'al system, and shomng very distinctly one 

 rhombohedron, scalenohedron and basal plan ;* it is coating tetra- 

 dymite, and is evidently a pseudomorph of it. 



" h, The tetradymite of the Tellurium Mine, Fluvanna co., Ya., 

 and the native bismuth from the peak of the Sorato, in Bohvia, are 

 frequently interlaminated with gold. 



" c, In the upper portion of the ore-bed in the metamorphic slates 

 at Springfield, Carrol co., Md,, which near the surface consists of 

 magnetite [magnetic proto-per-oxide of iron], and at a greater depth 

 of chalcopyrite [copper pyrites] and other ores, films of native gold 

 have sometimes been observed coating the cleavage-planes of the 

 magnetite. On close examination it can be perceived that below the 

 film of gold the magnetite is oxidized into hydrated sesquioxide of 

 iron." 



In attempting to establish an hypothesis of this kind, the greatest 

 * These are the ciystaDine forms of tetradymite. 



