This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
In general, the greater number of the specimens which are to be found in the tunnel occur in veins generally perpendicular, and with other minerals of little or no value, as calcite, chlorite, and imperfect crystals of the same mineral. A few occur in nodules inclosed in the solid body of rock, and in which condition they are seldom of value. The greater abundance are in the veins of the dark-green soft chlorite, and some few in horizontal beds. The minerals are found in the first condition by examining all the veins running from floor to ceiling of the tunnel. The ores of calcite first mentioned are very conspicuous, they being white in the dense black rock. They may be chipped from, as there are about thirty or forty of them exposed in each shaft, and the character of the minerals examined to see if anything but calcite is in it. This is ascertained by a drop of acid, as explained before, and by the descriptions given further on. The veins of chlorite are not so conspicuous, being of a dark-green color; but by probing along the walls with a stick or hammer, they may be recognized by their softness, or by its dull glistening appearance. They are comparatively few, but from an inch to three feet wide; and minerals are found by digging it out with a stick or a three-foot drill, to be had at the headings. Where the most minerals occur in the chlorite is when plenty of veins of calcite are in its vicinity, and its edges near the trap are dry and crumbly. It is here where the minerals are found in this crumbly chlorite, and generally in geodes--that is, the faces of the minerals all point inward, formerly a spherical mass--rough and uncouth on the outside, and from half an inch to nearly a foot in diameter. These are valuable finds, and well worth digging for. The beds of minerals generally are of but one species, and will be mentioned under the head of the minerals occurring in them. Besides, in the tunnel there are generally more or less perfect minerals upon the main dump over the edge of the bluff toward the river. Here many specimens that have escaped the eyes of the miners may be found among the loose rock, being constantly strewn out by the incline of the bed; in fact, this is the only place in which quite a number of the incident minerals may be found; but I will not linger longer on this, as I shall refer to it under the minerals individually.
The minerals occurring at the tunnel are as follows, with their descriptions and locations in the order of their greatest abundance: