I have had the good furtune to mention to a fellow student my interest in a type of rock and just as luck would have it he had an previous colleague who is a geologist. I have emailed him this evening and have already had a reply about the rust/grey rock.
Clay formed in the Devonian period as part of the “old red sandstone” when Britain was on the edge of giant desert. Formed in a shallow “playa” (an area of flat, dried-up land, especially a desert basin from which water evaporates quickly) lake formed when a flash flood washed down onto the desert plain.
I do enjoy a good back-story!
