Fabulous Question! Actually it is sandy lots of places but plants grow over it, then dirt, then more plants. Near the shore the dynamics of the water edge either wash away the land or deposit more sand. Sometimes people add more sand by the giant truckloads. Sand is made by several mechanical processes, often by parrotfish who eat coral and excrete sand as waste. Glaciers grind rocks into sand. When sand builds up in layers it eventually becomed sandstone.