A variety of low temperature alteration products occurs in the 573-m-thick section of basaltic rock from Site 395. Carbonate veins, smectities (predominantly saponite), zeolites, goethite, opal, and gypsum, listed in order of decreasing abundance, are present. Values of Δ18O (SMOW) of calcite veins range from +31.8 to +34.80/00, and Δ13C (PDB) ranges from +2.3 to +4.40/00. Apparently the calcite veins were formed at 0--15 ¿C in equilibrium with deep ocean water. Some veins may have formed during glacial periods, when Δ18O of the deep water was higher than it is presently. The deepest calcite veins were formed in the temperature range 8--15 ¿C. Saponite veins associated with an intrusive dolerite sill (Δ18O = +9.8 to +24.3%0, SMOW) are estimated to have formed in the temperature range 30--160 ¿C. Very extensive circulation (i.e., large water/rock ratios) predominated during alteration of the basalts as evidenced by seawater carbon and sulfur istope ratios in calcite and gypsum and carbon, sulfur and magnesium mass balance considerations.