Cambrian, Ordovician and Silurian beds have been recognized, the Upper Cambrian consisting of a limestone which is very rich in metalliferous ores (especially galena and calamine).
Cables have frequently been picked up showing after many years of submergence no appreciable deterioration in this respect, while in other cases ends have been picked up which in the course of twelve years had been corroded to needle points, the result probably of metalliferous deposits in the locality.
Barytes is of common occurrence in metalliferous veins, especially those which yield ores of lead and silver; some of the largest and most perfect crystals of colourless barytes were obtained from the lead mines near Dufton in Westmorland.
The hornsilvers all occur under similar conditions and are often associated together; they are found in metalliferous veins with native silver and ores of silver, and are usually confined to the upper oxidized parts of the lodes.
The outcrop of a metalliferous vein frequently manifests itself as a line of rocks stained with oxide of iron, often honeycombed and porous, the " gossan " or " eisen-hut," the iron oxide of which results from the decomposition of the pyrites, usually present as a constituent of such veins.