Two shades of yellow

I managed to time my walk badly, so only had about half-an-hour at Old Sulehay before the rain arrived. This lichen was definitely the most vibrant species I saw and I was intrigued by its two shades of yellow. It turn out that this is a characteristic feature of the species Caloplaca dichroa. This was only recognised in Britian in 2006, although it's actually quite common on limestone boulders and headstones, especially on the Oolite.