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region is very precarious, success being as it were almost accidental. 

 Thousands of " Gopher holes," as the rude pits are called, exist in 

 the bluffs around Dubuque and Galena, and the lead ore, when found, 

 is raised by the windlass and tub, by hand labor, no horse or steam 

 whyms being erected at any of the " diggings," as these shallow mines 

 are justly called. 



Dr. Jackson then gave some theoretical views as to the origin and 

 deposition of galena in the crevices and caverns of these rocks, and 

 stated that since galena is readily volatilized at a temperature below * 

 that required for its reduction, it could have been easily raised in the 

 form of vapors, which would arise either through crevices or even 

 through the very porous white sandstone and be deposited in vacant 

 spaces in the rocks, and even in the cavities of fossil shells. The 

 occurrence of galena in such fossils had been cited to prove the 

 aqueous origin of that mineral, but he thought the known facts 

 could be more easily and satisfactorily accounted for by the theory of 

 sublimation or of metalliferous vapor emanations from the interior of 

 the globe ; while it would be very difficult to prove galena to have 

 been derived from aqueous solution and deposition from water, since 

 it is wholly insoluble. 



He thought the copper and iron ores might have been formed by 

 sublimation of the chloride of copper and of the sesqui-chloride of 

 iron, and these chlorides having been decomposed by emanations of 

 gaseous sulphide of hydrogen, would form the sulphides of copper 

 and of iron, which would unite in various proportions, producing the 

 -well known sulphides of copper and iron, such as are found in most 

 copper mines. Water alone will convert the sesqui-chloride of iron 

 into peroxide of iron, the hydrogen of the water taking the chlorine 

 and forming chlorhydric acid, while its oxygen unites with the iron, 

 forming either specular or htematite iron ores. 



In illustration of the porosity of the white sandstone rocks. Dr. 

 Jackson observed that a pit was sunk 184 feet deep at Dubuque, to 

 serve as a " shot tower," and that no water stood in the bottom of 

 that pit. He also observed that no water was drawn up at the 

 numerous lead mines which he visited, and that wells were quite im- 

 practicable in these sandstones when above the river level. 



Specimens of the haematite contained bunches of silky green car- 

 bonate of copper, a secondary product of the decomposition of the 

 copper pyrites; su\-phiiret of copper being first converted into the 

 sulphate, and then, by the action of cai'bonate of lime, decomposed 

 into sulphate of lime and carbonate of copper. This ore is found 

 like the lead ore in chasms in the white sandstone, associated with 

 ferruginous clays, and does not form regular deep seated veins, so 

 that no dependence can be placed upon it by miners. Indeed, both 



