Waves on sandy beach separating differently-sized rocks?
There are two ways in which waves can sort particles on a beach, and both depend on surface area to weight ratio. The larger, toe-sized particles you describe have less surface area to volume (weight) ratio than the sand-sized particles, so were first to drop out of the water flow. The lighter particles had more surface area per unit of weight for the waves to act on, so were slower to drop out and were carried further up the beach. Why the lowest level sand grains were precipitated in deeper water, before the toe-sized particles, is less easy to understand, but one possible reason is that they contained some heavy mineral such as tin, which altered the surface area to weight ratio and caused them to drop out first. This principle is well seen in gold panning machines, where the heavy gold particles drop out of the flowing water first,while the lighter particles are carried further on, even when they are larger than the flecks of gold.