the concentration of sulphur in its different forms varies in the different lithological types of platform rocks. Reduced sulphur is highest in clayey rocks, lower in siltstones and sandstones, and is usually minimal in carbonate rocks. Pyrite predominates as the reduced form of sulphur; organically bound forms account for no more than 10% of the value of the pyrite sulphur ans elemental sulphur is usually less than 5%. The monosulphide form is usually absent or is found only in trace quantities (0.001-0.0003%). The sulphate sulphur concentration varies greatly; it may vary from a few per cent of the total sulphur in humid pelagic formations, to completet predominance in evaporite beds.