Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/63

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53
Dr. Berger on the Isle of Man.

The walls of the vein are formed of silky greywacke with pieces of bitterspath, and a few flesh-red and lamellar crystals of calc spar.

Foxdale Mines.

The specific gravity of a rather impure specimen of lead-ore, I found 6.095.

Amongst the stony substances that fill up the vein, I remarked the following varieties:

A semitransparent and bluish chalcedony passing to white; it is zoned, but the zones are not apparent without the assistance of a magnifying glass; common galena and some iron pyrites are disseminated throughout the mass.

Sometimes the chalcedony verges into white quartz, blended with sparry iron-ore scarcely effervescent with nitric acid, turning almost black before the blowpipe and acting very powerfully on the magnet. It is likewise accompanied by iron-pyrites.

The sparry iron-ore in larger lamellar crystals appears of a dark colour, and contains so much of iron as to act by itself on the magnet. Galena adheres to it.

The greywacke that forms the South side or cheek of the vein, is of a greyish colour with a silky lustre; the common lead-ore adheres to it. In a granular and drusy quartz filling up the vein, I noticed a few garnets.

Brada-head Mines.

The specific gravity of a less impure specimen of lead-ore than that of Foxdale, was 6,622.

The principal vein-stone through which the ore is disseminated, is a yellowish granular quartz that includes iron pyrites.