LICHEN

I took a walk alongside a very ancient wall that had been part of a farm for many years before the land was purchased by the local golf club.
There is lichen along all of the wall, but less is growing on the newer, repaired parts of the wall - as you might expect.
There is some variation in the type of stone too, and some types of lichen seems to favour particular stones. (Extra 1)
The road is about 400 yards between the sea and the green-keeper's house.  More lichen grows where the air quality is better, and I noticed that Old Man's Beard grows on the wall closer to the sea and up to the half-way point, then it stops.  Apparently that lichen is more sensitive to pollution. The green-keeper's house has coal fires.
But the Old Man's Beard doesn't seem to like salt water and isn't typically seen on the sea walls.  Except at this point (extra 3) at a fairly new sea wall.  Maybe it came with the stone?