The Ar+-sputter-induced "cone evolution" on Mo-seeded Cu is known to entail the growth of hillocklike crystallites on the cone surface, Such crystallites have now been identified as Cu, by means of high-resolution energy dispersive x-ray analysis, The Cu crystallites grew selectively on the Mo lattice of seed layers, and sometimes at the seed-layer apex which suffered from head-on ion impact during sputtering. The crystallite growth was thus not a direct consequence of ion impact, leading to a hypothesis that a viscous overlayer of Cv on the growing Mo lattice condensed into dewdroplike crystallites upon switching off the ion beam.