Wall flowers part 2

I could be in danger of starting a series - Flowers Growing in Strange Places - see my Blip from 14 May (Don't know how to add links I'm afraid).

I believe these are erigeron, possibly Mexican Fleabane?!, and there are lots of them growing in our on the walls around the Cathedral here in Norwich.

I have some in my garden at home as o think they are lovely, but mine are in a more conventional place, ie the ground.