Pwllywrach Nature Reserve near Talgarth is owned and managed by the Brecknock Wildlife Trust. Local fossil-hunter Rod Williams sent us a series of photos of the reserve's falls which he took on Boxing Day 2005. He's also written about some of the area's geological features.
"This may look like another limestone but is in fact a conglomerate, it is fairly lime rich, containing nodules of calcrete and gravel. These rocks are typical of channel lag deposits of large rivers interbedded with mudstones. Again some 400 million years of age. Sometimes they contain the fragments of ancient fishes. I have searched them microscopically for rare minerals but not seen anything of value." - Rod Williams
