In general, weathering of lead ores at the surface and secondary sulphide enrichment below are not so extensive as in the case of copper and zinc. Galena is fairly stable in the oxide zone, and even in moist climates it is found in the outcrop of many veins. Weathering removes the more soluble materials and concentrates the lead sulphide with the residual clay and other gangue. In some districts cerussite and a little anglesite are also found in the oxide zone. The carrying down of lead in solution and its deposition below the water table as a secondary sulphide is not proved on any extensive scale. In this respect it contrasts with zinc; and when the two minerals occur together, lead is likely to be more abundant in the oxide zone, and zinc in the sulphide zone below. Such a change in composition with depth is also found in some cases as the result of primary vertical variations in the mineralization. ZINC ORES ECONOMIC FEATURES Zinc metal has commonly gone under the name of "spelter." Brass and galvanized iron contain zinc as an essential ingredient. Of the total United States zinc consumption in normal times, about 60 per cent is used in galvanizing iron and steel objects to protect them from rust, 20 per cent is used in the manufacture of brass and other alloys, 11 per cent goes into the form of rolled sheets for roofing, plumbing, etc., 1 per cent is employed in desilverizing lead bullion, and the remaining 8 per cent is used for pigments, electrodes, and other miscellaneous purposes. During the war the use in brass-making was greatly increased. The zinc content of the ores mined today ranges from a little over 1-1/2 per cent in the Joplin district of Missouri, to 25 per cent and higher in some of the deposits of the Coeur d'Alene and other western camps, and over 40 per cent in certain bonanzas in British Columbia and Russia. The ores usually contain both zinc and lead in varying proportions, and sometimes gold, silver, and copper are present. Of the zinc produced in the United States, about 73 per cent is obtained from ores containing zinc as the principal element of value, about 25 per cent from zinc-lead ores, and 2 per cent from copper-zinc and other ores. The average grade of the straight zinc ores is about 2-1/2 per cent.