- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
The Ponterwyd district, east of Aberystwyth, western Wales, is part of a dissected plateau modified by localized glacial deposition and subsequent fluvial erosion. In connection with the recent construction of a dam and reservoir, a survey has revealed four buried channels, filled with boulder clay. These relic river valleys of the Rheidol resulted from a progressive localized diversion due to glacial interference.