Geoffrey Whittum, a Suffield resident, has found dolmens (megalithic tombs, similar in structure to Old Stonehenge artifacts) and large, unusual rock structures throughout the forests of New England and the Middle Atlantic states.   He will present a PowerPoint presentation demonstrating that these megalithic structures may represent the work of ancient civilizations on Tuesday, February 27 at 7:00 p.m.  The program, sponsored by the library, will be held at the Suffield Senior Center.  Please register to attend by calling the library at 860-668-3896 or registering on-line at suffield-library.org.