consisted of copper-and iron-pyrites, the surface portion being highly coloured with carbonates and oxides of copper. It is enclosed between green foliated slates on the foot-wall side and cherty slate on the hanging-wall. It strikes about north-east, and at the surface dips at about 70°, while lower “down it becomes almost vertical. This lode was opened up by a shaft sunk on the foot-wall side, and was worked by a system of levels and stopes.

Owing to a question of ownership this shaft occupies a unique position, having been started on the beach below high-water mark. In consequence, the collar of the shaft had to be raised out of reach of the tide by means of a double box of planks made watertight by well-puddled clay. The shaft was worked successfully for a number of years, but about forty years ago operations were suspended. At this time the reef was about 15 ft. thick, and averaged 16 per cent. of copper. On this shaft being abandoned the sea very soon found ingress into the mine, and for years past the waves have washed over the mouth of the shaft for several hours every day.

During the present year it was decided to again open up this mine. The collar of the shaft was again built up, and the workings were drained by means of Cameron pumps. It was then found that large masses of native copper were adhering to the sets of timber in the shaft and to the floor-boards in the levels. These masses were generally found as excrescences growing from a nucleus, and varied in diameter from ½ in. to nearly 1 ft. When disclosed in the mine it had the peculiar red colour of pure copper, but on exposing it to the air it quickly became tarnished. I examined this copper both microscopically and chemically. Looking at it casually it appears as small imperfect crystals arranged radially from a centre, with numerous beautiful crystals branching from the main stems. Examined under the microscope it is seen to be composed of crystals of the isometric system, in which octahedral faces predominate, though I noticed some good examples of pentagonal dodecahedra. In one peculiar instance I found that one branch was composed of twinned octahedra, giving the edge of the branch a very regularly serrated appearance.

On examining chemically I found that the crystals were pure copper, but were coated on the outside with compounds of manganese and iron.

I looked for the cause of the tarnishing of these crystals in the presence of these impurities, and found that when the crystals were well washed in water freed from air they were not nearly so liable to become discoloured, but when allowed to dry just as they came from the mine a coating of oxide was

formed which destroyed the lustre of the specimen. The reason of this probably is that the iron and manganese salts, which I found present in small quantities in the mine-water, formed a thin coating of these salts on the crystals. On bringing the copper to the surface this thin film, exposing a large surface to the air, would quickly oxidize to oxide of iron and manganese. These substances would then give up their oxygen to the copper, which would form a layer of black oxide of copper. This iron and manganese therefore appear to act as carriers of oxygen to the copper.

The explanation that one would naturally jump to with regard to these deposits is—(1) That the iron-and copperpyrites have oxidized producing sulphuric acid and soluble iron-and copper-sulphates; (2) that iron has been present in the mine-timbers in the form of bolts and nails, and that this iron has replaced the copper in the soluble copper-sulphate, thus forming deposits of metallic copper. But, with regard to the presence of metallic iron, I ascertained that no bolts were used to suspend the frame-sets in the shaft, and the amount of iron present as nails would not by any means account for the large deposit of copper.

From the fact of the sea being in almost constant communication with the mine for so many years, it appeared that the sodium-chloride of the sea-water would affect the solution of the copper from the pyrites, as it was highly probable that during the oxidation of the copper-pyrites the sodium-chloride would cause a concurrent action, resulting in the formation of copper-chloride and copper-sulphate. To verify this I weighed out two equal portions of copper-pyrites and partly oxidized them under exactly similar conditions, and while still hot, and therefore still oxidizing, I plunged one into pure water and the other into a solution of common salt. In each case a blue solution of copper was obtained, but the brine-solution was found to contain 5 per cent. more copper than the other.

I was unable to obtain an accurate sample of the mine-water for quantitative analysis, but a sample I had showed the presence of sulphates and chlorides of sodium, copper, iron, and manganese, and from the above experiment it seems likely that the copper is present as chloride and sulphate of copper.

As previously stated, the metallic iron is not in sufficient quantity to account for the amount of copper produced; but I think the following explanation accounts for the quantity and also for the crystalline form: As the mine-water was connected with the sea the solution of copper could not become very strong, as the salts of copper and the sea-water would diffuse into each other, thus weakening the copper-solution