The highest beach is very irregular. The first or highest beach exposure to wave action that the other beaches do not reflect. The second beach is more regular, and on the whole somewhat stronger than the highest. There is a third beach, which is generally weak and in places difficult to trace. The third beach connects with well-defined deltas which the higher levels do not have. The most notable are at the Raisin and the Huron rivers. The third beach is below the Imlay outlet. The outlet at that time may be across the "Thumb" in a lower passage a few miles north. The readvance of the ice sheet may have closed this outlet with a moraine closely bordering the Imlay outlet.