Country diary: dinosaur poo on the banks of the Severn

Aust Cliff, South Gloucestershire: We are after fossils from the upper strata, inaccessible until chunks are torn off by winter's teeth

Aust Cliff is half a hill, sliced open like a birthday cake by the River Severn's slow knife, exposing two ornamental layers of pink and blue-green mudstone. Right here, about 200m years ago, a red desert was overwhelmed by a balmy ocean. Today, a cold northern sea mingles with a slowly churning river of mud, crossed at this point by the old Severn Bridge, once the longest single-span bridge in the world. The scale of this place, in time, space and ambition, is magnificent.