Hyaloclastite and pillow lavas were dredged a short distance northwest of St. Paul's Rocks. These rocks are more alkaline than basalts erupted from spreading ridges. In addition to olivine and plagioclase phenocrysts, these contain complex sector-zoned pyroxrene phenocrysts. Fe2O3/FeO of around. 20 was calculated for the glass from FeO-MgO partitioning between olivine and liquid. Clay minerals, mainly potssium smectite, are abundant in both rock types. These are divided into three groups on the basis of their composition, optical properties and mode of occurrence. All these groups show an excess of octahedral layers, and Al is abundant in both octahedral and tetrahedral layers. K, Na, and Ca, in order of abundance, are the domiant interlayer cations. These smectites occur with small amounts of analcite and even less abundant phillipsite. The abundance and composition of these clays suggest that they are important traps of K and Mg from sea water.