Abstract Two andradite garnets are described from the mid-Atlantic ridge near 43° N., 27° W., depth 2200 to 2500 m. One is nearly pure ahdradife (topazolite). The other is titanian andradite (melanite)with 9.3 percent TiO 2 . Btfth are in a diopside-chlorite matrix associated with serpentinized peridotite. This appears to be the second known occurrence of melanite in serpentinized peridotite,the other being in San .Benito County, California.

Abstract Hyaloclastite and pillow lavas were dredged a short distance northwest of St. Paul’s Rocks. These rocks are more alkaline than the basalts erupted from spreading ridges. In addition to olivine and plagioclase phenocrysts, the rocks contain complex sector-zoned pyroxene phe-nocrysts. Fe 2 O 3 /FeO of about 0.20 was cal-culated for the glass from FeO-MgO partitioning between olivine and liquid. Clay minerals, mainly potassian 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 have structural formulas that are intermediate between dioctahedral and trioctahedral smectite. Potassium, sodium, and calcium, in order of abundance, are the dorninant interlayer cations. These smectites occur with small amounts of analcite and even less abundant phillipsite. The abundance and composition of these clays suggest 4 that they are important traps lor potassium and magnesium from sea waiter.