Friday's Puzzle!

Last day of the half-term hols so my last chance to catch up with school friends - I probably won't see them again now until the Easter holidays!

Popped to my favourite riverside pub for a quick hot chocolate (we both wanted to get back to watch the GB team in action in the men's curling final!). Sitting in the sun in the pub's conservatory was lovely; the sun also highlighted these strange patterns which cover the stone wall. This wall was originally the pub's outside wall (built in 1719) but since the building of the conservatory and decking, the wall is now an interior wall.

So what are these strange patterns? Fossils? An unusual form of plant life? Or alien life?! Any ideas?