This reef number previously Pen Island Llandovery/Wenlock. More detailed stratigraphy required replacement.

The mud mounds are thin (<2 m), closely spaced, laterally linked, symmetrical domes composed of massive, fenestral, peloidal
to clotted microspar with sparse unoriented, poorly sorted skeletal material,
calcitized bacterial(?) filaments/tubes and abundant fenestrae and stromatactoid
structures.