These structures are a sub division of groove casts, oscillation ripples. Found in a shoreline or shallow marine environment, they are the result of two directional currents. The cross section is not immediately obvious, but my close inspection of the specimen as a whole is conclusive. The specimen was collected from Tan y Foel quarry, 5 Km. S.W. of Llanllugan, near Newtown, and is from the Penstrowed grits formation in the Silurian