“At the Minesota mine, near the Ontonagon river, I had an opportunity of examining, in June, the most extraordinary mass yet met with. Two shafts had been sunk on the line of the vein 150 feet apart. At the depth of about 30 feet they struck massive copper, which lay in a huge sheet with the same underlay as that of the vein—about 55° towards the north. Leaving this sheet as a hanging wall, a level was run under it connecting the two shafts. For this whole distance of 150 feet the mass appears to be continuous, and how much further it goes on the line of the vein either way there is no evidence, nor beside to what depth it penetrates in the solid vein. I examined it with care, striking it repeatedly with my hammer in order to detect, if possible, by the sound, any break or interruption there might be in the mass—for a thin scale of stone encrusted it sometimes and concealed the face of the metal. Examinations had been made by drilling through this scale, where it attained the thickness of an inch or so; but in no place had any sign of a break been found. It forms the whole hanging wall of the level, showing a width of at least eight feet above the floor in which its lower edge was lost. It had been cut through in only one place, where a partial break afforded a convenient opportunity. Measuring the thickness here as well as the irregular shape of the gap admitted, it was found somewhat to exceed five feet. Assuming the thickness to _average_ only one foot, there would be in this mass 1200 cubic feet, or about 250 tons—still it is not safe to assume even one foot, for the masses vary extremely in thickness. “The mode adopted to remove these masses is to cut channels through them with cold chisels, after they are shattered by large sand blasts put in behind them. Grooves are cut with the chisels across their smallest places, one man holding, and another striking, as in drilling. A chip of copper three-quarters of an inch wide, and up to six inches in length, is taken out, and the process is repeated until the groove passes through the mass. The expense of this work is from eight to twelve dollars per superficial foot of the face exposed. Fragments of veinstone enclosed in the copper prevent the use of saws. A powerful machine, occupying little room, is much needed, which would perform more economically this work.