sentences:  More recently two locations in mid Wales have been selected to globally define stages of the Silurian period.Cefn-cerig Road near Cefn-cerig Farm, Llandovery, is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the Aeronian and Telychian stages of the Silurian period on the geologic time scale.Similarly Trefawr Track, a forestry road north of Cwm-coed-aeron Farm, Llandovery, is the location of the GSSP marking the boundary between the Rhuddanian and Aeronian stages.