These upper lavas are almost entirely restricted within the caldera but have spilled out over the caldera rim on the outer slopes at two points. The most conspicuous overspill is close to a line of small craterlets South-West of nakuru and there may be some genetic connection. The massive trachyte exposed in the Amolak Sigh Quarry is believed to belong to the upper lava series, though unlike most of these late lavas it is holocrystallive. The overspill probably represents one of the very earliest of these second series eruptions. The later lava seems to continue down the caldera wall into the caldera, and this may well be a ring feeder structure similar to the famous backward flow Crater Lake,USA, a ring feeder actually cut through by the caldera fault. Similar structures are seen in Mount Suswa caldera.