It must be some sort of combination of wind and bacteria that makes the surf break onto the sand and leave clumps of foam behind.  Some of it looks clean and light and sudsy and then some of it looks like this.  The varying texture and thickness and density of color make for mini-landscape drawings on the beach, all soft with craters and edges and thick and thin places.  The two stones also add the possibility of a face, yes?  A walrus mustache, a rather sad one?