This path is defined by the high aluminum basalt magmas and the majority of the high TiO 2 basalt magmas which plot near the 5kb olivine-pyroxene cotectic and by the high olivine magmas which plot along or near a single olivine control line. It is further shown that, when these 16 magmas are plotted on the pseudo-ternary phase diagram for the system anorthite-olivine-quartz and the quaternary phase diagrams for the systems which include augite or ilmenite, the magmas all lie along a common, equilibrium melting path. At the present, only first order estimates of the compositions of the magmas of the remaining four units are possible. The currently published data are sufficient to allow reasonably good estimates of the compositions of the parental magmas of 12 of these units to be made. Based on a synthesis of available mare basalt data, it is shown that the samples which were returned to Earth via the various Apollo and Luna missions were derived from at least 16 separate eruptive events.
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