The thermal regime in the neighborhood of a crystal suspension embedded in a hot magma ocean is tied to the crystal-plus-liquid equilibrium temperature. Any such internal suspension will tend to melt because it overlies hot magma. Internal cumulates cannot form by crystal flotation because the crystals melt upon rising along the hot magma. Internal cumulates cannot form by crystal flotation because the crystals melt upon rising along the hot adiabat. Transient formation of a perched crystal layer is considered for the upper mantle stage of a magma ocean, after fractionation has enriched the liquid in olivine components. Olivine crystals accumulate at a neutral point in the density contrast, aided by two-phase (solid+liquid) convection in cold plumes from above. The cold plumes extract heat from the region of the neutral point. Crystals can survive there only if forced deposition exceeds the melting rate; the suspension cumulate is intrinsically ephemeral. Heat transfer occurs by addition of mass at the top and melting at the bottom of the layer. The liquid in the lower cell becomes more olivine-rich and more Fe-rich because of partial melting, increasing the buoyancy and thermal stability of the crystal layer. However, melting and physical disruption will still occur. Forcing must cease when a subsolidus lid to the magma ocean is established. The perched layer is now destroyed by melting, but the neutral point remains a site of heat transfer between lower and upper cells. The former neutral point becomes the original lithosphere/asthenosphere boundary. Subsequent diapirism leads to the internal generation of ultramafic and then mafic magmas. ¿ Americal Geophysical Union 1993