What's this?

I presume it is lichen/ fungus. A bit drizzly today with the sun fighting to get through the clouds, but not quite making it. We decided to go on our Saturday walk nevertheless. We stopped on an old stone bridge to watch the torrents of water running under it and I have to give the credit for spying this tree trunk to Jim. I don't think it is dead, but it is lying amidst lots of black muck and as you can see, covered in lots of moss in addition to this very interesting lichen and fungus.