The presence of carbonate minerals in association with moderately altered basalts is not unexpected. In his description of basalts drilled beneath the limestone on Eniwetok Atoll, Macdonald (1963) describes carbonate veins which appear to be very similar to those found on Suiko Seamount. In the case of Eniwetok, it was concluded that alteration of the basalt and formation of the veins must have occurred when the top of the basalt was only slightly submerged below sea level. Stable isotopic evidence indicates that alteration of the Suiko basalts began very early, perhaps, while the basalts remained subaerially exposed. The alteration continued with submergence and produced carbonate minerals whose stable isotopic ratios represent at least two stages in the subsidence history of the seamount: early, shallow-water and later, deeper-water environments. The data clearly demonstrate, along with the other evidence gathered by Leg 55 investigators, that Suiko Seamount underwent subaerial and shallow-water periods in its genesis.