Considerable interest is felt by both geologists and mineralogists in regard to the geological position and mode of occurrence of the “ Silver Ore ” in this oft-described locality. On the Geological Survey map, Sheet 31, the mine is shown, by three short gilded lines, about two miles NNE. of Bathgate, and near one of the highest points of the Bathgate hills. Its geological position is in the upper part of the Lower Carboniferous Rocks in connection with a series of basalt lavas and tuffs, which occur interstratified with marine limestones, charged with numerous specimens of Productus giganteus. This fossil is now generally recognised as being confined, all over Western Europe, to the limestones near the base of the Yoredale Rocks, to which horizon, therefore, the Hurlet or Main Limestone of the Bathgate hills, in which the silver mine is situated, must henceforth be referred. One or two small dykes are intruded into the rocks adjoining the veins. These latter appear to be fissure veins, which probably coincide with faults of no great magnitude. The minerals themselves may be noticed under two heads. The first of these comprises those which, not being original constituents of the rock, yet occur in noticeable quantity around the veins. Of these the only ones calling for any special remark are some fine crystals of Calcite, chiefly of the form e ; and besides this, somewhat extensive deposits of Dolomite. This latter occurs as a replacement-product of part of the limestone, and may be referred to