Three presentations in Catskill that deal with the ancient stone sites of the Hudson Valley. Glenn Kriesberg will present, "Lithic Alignments in the Northeast, Natural, Native or Nonsense." Polly Midgley will present, "Enigmatic Stone Chambers in Westchester, Putnam and Dutchess Counties." And Matt Bua will present, "When Walls Talk: Casting out the Myth that all Stone Walls were built Post-Colonially." Live WGXC webcast and broadcast at 90.7-FM from 7-9 p.m.