Xanthoria parietina Lichen.

This picture was taken on a concrete post, located by the side of a park and river, taken on transparency film and stored away for 30 years, not until I Scanned the 35mm image and looked closer did I realise what a very interesting image it is with so many different lichens
filling all the space on a concrete post.  The scaly, orange-yellow lichen in the centre is Xanthoria parietina, which is common on posts and walls.