Welsh Journals

at Dowlais, and determined their specific gravity as 5-278.* Millerite has since been found in clay-ironstone at several places along the south-eastern margin of the coalfield. At the Brynna-gwynon Colliery, about a mile east of Pencoed Station, Dr. H. K. Jordan found the mineral in ironstone a little above the Bodor-fach seamt; at Llanbradach Colliery it occurs above the Four Feet Seam, and at Bedwellty, near Tredegar, a little above the Elled seam, J while it has also been recorded from the Three-quarters or Elled Mine Balls at Ebbw Vale,§ Nantyglo, and Blaenafon.� It is interesting to note that in the instances cited the clay ironstone containing millerite occurs at horizons which, although not strictly comparable, are nevertheless very closely related, and it is highly probable that the mineral might be found at this horizon all round the eastern margin of the coalfield. The mineral has also been found in the Soap Vein ironstone at Blaina, Mon. and in the Spotted Vein ironstone at Dowlais. Millerite is usually regarded as a very rare mineral, but it is really of more frequent occurrence than the specimens in museums and other collections would indicate. Owing to the extreme delicacy of the crystals, and the toughness of the clay ironstone, the shock caused by the blows necessary to break the nodule, more often than not dislodges the crystals, which are then scattered and lost this is especially the case with the greenish-yellow crystals, which are as fine as unspun silk. Even when specimens have been successfully collected, great care is necessary for their successful preservation. Millerite possesses certain magnetic properties, and if pieces of ironstone bearing tufts of crystals are kept in glazed boxes, unless the specimens are placed at some little distance from the glass, the crystals are attracted to it when it is rubbed, as in cleaning, and the crystal group is spoilt. Miller (1842), p. 378. t Jordan (1876), p. 270. 4 Fine specimens from this locality, presented by the Tredegar Iron and Coal Co., Ltd., are now in the National Museum of Wales. § Jordan (1876), p. 270. T Iron Ore Memoir (1861), p. 207. op. cit, p. 195. op. cit., p. 209.