The deeper holes drilled at the Guadalupe site bottomed in basalt. Most of the basalt has a subophitic texture. It consists of subradiating laths of plagioclase and augite, with rare phenocrysts of olivine, fine-grained magnetite, ilmenite, calcite, serpentine, chlorite, palagonite, hematite, and zeolites. Amygdules occur locally. The chemical analysis and a norm of the Mohole basalt are listed. Average analyses and norms of somewhat similar basalts from oceanic and plateau areas are included for comparison. It is apparent that compared with the Hawaiian and plateau basalts, the Mohole basalt is relatively high in CaO and in the ratio Fe 2 O 3 /FeO. It contains less TiO 2 , total Fe, and K 2 O. The high ratio of Fe 2 O 3 /FeO and the abundant total water may reflect the emplacement of the basalt in watery muds at or near the interface with ocean water.