After returning from MCRD Parris Is. I visited an old WWI Marine and we talked about the Island , the heat, etc. So at one point I mentioned in the middle of the PT field were sea shells, and wondered how the got so far inland. To my suprise he started telling me about when they "built" PI and they hauled wheel barrows full of shells to be used for pathways around the island. So now we know where the damn things came from that cut our hands as we did leg thrusts and pushups.