Irregular, rudely circular pipe-like bodies of manganese oxides have been mined at the intersection of northeast-trending mineralized fissures and steep faults in Upper Paleozoic limestones. These bodies of ore were mined principally for the silver content, but some were sufficiently large to be mined for manganese alone. The silver values were confined to the core which consisted generally of a soft and porous mass of iron and manganese oxides with variable quantities of lead and zinc oxides. Surrounding this elongated core was a hard, compact envelope of black manganese oxides; chiefly psilomelane and polianite.The part played by sulphate solutions in the formation of the manganese oxides seems to have been ignored generally. Where deposits of manganese oxides like those at Tombstone, Arizona, are known to have been derived from the sulphide, alabandite, in association with sulphides of iron, copper, lead, and zinc, it is believed by the writer that the manganese sulphide was oxidized, the manganese taken into solution as the sulphate and transported or moved in some manner to the limestone walls to be later deposited as compact masses of psilomelane, polianite, and minor manganese oxides.