"Two short seismic refraction profiles have been shot across the former valley of the river Teifi, above and below Cardigan, with the object of determining the depth to the rock floor. This was found to lie 75 feet below O.D. at Castle Malgwyn, near Llechryd, and 107 feet below O.D. at the present estuary. These figures are consistent with the glacial history of the valley indicated by the geological evidence."