USING GPR DATA TO APPROXIMATELY DATE UNMARKED GRAVES WITHIN AN ESTABLISHED CEMETARY: AN EXAMPLE FROM A 19TH CENTURY VETERANS CEMETARY IN NEW ENGLAND

At the request of the local historic commission, a GPR study was conducted on a 19th century veterans cemetery in Essex County, Massachusetts. The cemetery served as the burial ground for American Revolution through the Spanish-American War U.S. veterans and some family members and contains 65+ marked headstones and lesser numbers of footstones. The site geology consists of fine to medium grained silty sand. In this laterally and vertically homogeneous material reflector strength is assumed to be primarily a function of sediment compaction as well as uniformly increasing moisture with depth. A GPR survey, using a 400MHz antenna, was conducted on lines spaced 30cm apart and presumed normal to burial direction. It located unmarked graves. Certain graves were distinguished by a general lack of reflectors while others contained reflectors of increasing strength. When the data were analyzed it was found that the unmarked graves could be grouped based upon the strength of the reflectors, as could the marked graves. The reflector groupings on known, dated by headstones, graves were compared to unmarked graves. A rough correspondence in reflector strength allowed the unmarked graves to be dated. The rough dates on the unmarked graves, when compared to dates on surrounding in-situ headstones, were not incompatible. As a result, three age groups of unmarked graves were established: early (up to 1820), middle (up to 1885), and latest 19th, early 20th century. The technique shows promise in geoarchaeological applications.