Natural Drainage

My entry for Ingeborg's Abstract Thursday, AT456, on the theme of 'natural abstract'.

My blip shows the natural drainage patern left on the sand after the tide has gone out and water drains from higher regions of the beach.

The local rocks contain seams of coal so that explains the black grains.  Coal, being lighter (less dense) than sand, it sits on the top and is easily washed forward by even a very weak flow/seepage of water.

The white grains are also light.  They are tiny pieces of broken shells.