The solubility of water in a basaltic and in an andesitic melt has been determined in the pressure range from approximately 1,000 to 6,000 bars at 1,100° C. The solubility in basaltic melt is 3.1 weight percent at 1,000 bars and 9.4 weight percent at 6,000 bars; in the andesitic melt it is 4.5 weight percent at 1,000 bars and 10.1 weight percent at 5,300 bars. The temperatures of appearance of the primary, secondary, and tertiary phases in the basalt have been determined at 1,000 bars water pressure and at the fo2's of the magnetite+hematite (MH), magnetite+fayalite+quartz (MFQ) and magnetite+wüstite (MW) buffers. Results are as follows: