_Iron and Copper Pyrites_.--Both of these common but frequently beautiful minerals occur in the tunnel and adjacent rocks in great abundance. The crystals are generally about one-fourth of an inch in diameter, and groups of these may be frequently obtained on the dump in the shafts, especially No. 1 and 2, and where the rock is being cleared away for the eastern entrance to the tunnel. They resemble each other very much; the iron pyrites, however, is in cubical forms and having the great hardness of from 6 to 7, while the copper pyrites, less abundant and in forms having triangles for bases, but having sometimes other forms and a hardness of but 3 to 4. Both are similar in aspect to a piece of brass, and cannot be mistaken for any other mineral. The form of the copper pyrites is shown in Fig. 8; the iron is, as before noted, in cubes, more or less modified. _Stilbite_.--Small quantities of this beautiful mineral have been found in Shaft No. 2, in a small bed of but a few square feet in area, but quite thick and appearing much like natrolite. This bed was about one hundred feet east from Shaft No. 2, and in the center of the heading when it was at that point. It has been encountered since in small quantities, and it would do well to look out for it in the fresh tunneled portion after the date appended to this paper. It generally occurs in the form shown in Fig. 9, grouped very similarly to natrolite, and being right upon the rock or a thin bed of itself. The crystals are generally half an inch long, but often less. The modifications of the above form, which are frequent in this species, strike one forcibly of the resemblance they bear to a broad stone spear head on a diminutive scale, with a blunted edge; their hardness is about 4, specific gravity 2.2, the color generally a pearly white or grayish. After a long boiling with nitric acid it gelatinizes, but it foams up and fuses to a transparent glass before the blowpipe. A little stilbite may often be found on the dumps. _Laumonite_ occurs in very small quantities on calcite or apopholite, and can hardly be expected to be found on the trip; but as it might be found, I will detail some of its characteristics. Hardness 4, specific gravity 2.3; it generally occurs in small crystals, but more frequently in a crumbly, chalky mass, which it becomes upon exposure to the air. The crystals are generally transparent and frequently tinged yellow in color. It gelatinizes by boiling with acid, and after intumescing before the blowpipe, fuses to a frothy mass. To keep this mineral when in crystals from crumbling upon exposure it may be dipped in a thin mastic varnish or in a gum-arabic solution.