Here is my idea on this, I would look cracks in bed rock ,behind boulders beach side, wave coming in fast carrying sand, slows behind bolder's dropping heavy, similar to sluice.
or places were fast current will slow, in rivers where fast water after white water, on inside bend the water is slower heavys settle (outside bend water is cutting at bank), heavy materil will work its way to bottom of lighter materials, get to bedrock .
heavier material is harder to move than lighter material's in current of water. just like panning for gold, and will always work their way to the bottom.
as 4Metals suggest wave action should accumulate heavier material in sand into veins, fast waves constantly washing everything in, and slower return wave pulling back lighter material back towards ocean,
most sand came from rock in some mountain, maybe far up a river, and then far up some creek, and far up some small stream then up on the side of that mountain, may be the source rock that was washed and rolled down towards the ocean in snow melts, rains and flood through the years to get to the ocean jaggad rocks rolling into round boulders some fractuering and constant rolling to smaller siize on there way down rivers rocks turning into pebbles and sand and silts , this sand may also travel around some in the ocean, so the sand at the beach with a river a half mile up the coast may have come from that river, or even many many more miles for some river way far off.
as 4metal says look for sighns, black sand is a good indicator of heavy's, or conglomerate in old ancient river beds (may not have been water in some of these rivers since the dinasor drank from it.
some thing I noticed while typing this if you captilize 4metals name you get $metals :lol:
