PRELIMINARY RESULTS OF AN INTEGRATED GEOPHYSICAL SURVEY OF THE FIELD-BICKFORD GARRISON HOUSE SITE, DURHAM POINT, DURHAM, NEW HAMPSHIRE

The extent of the 17th century Field-Bickford Garrison House, Durham Point, Durham, NH was subjected to geophysical surveys employing ground penetrating radar, multiple frequency electromagnetic induction, seismic refraction, and geomagnetic gradiometer. The Garrison House was originally built and owned by Darby Field prior to 1638 as a homestead, tavern and ferry landing. The buildings were destroyed early in the 19th century and no surface trace remains. Initial archaeological work has identified the probable house cellar. Site overburden is from 0 to 2+ meters thick and consists of variably silty, fine to medium sands with some clay lenses. Bedrock topography is extremely irregular as confirmed by seismic refraction and direct observation along the shoreline. Coarse geophysical grids with spacing from .5 to 1 meter were established. The GPR used a mid-range 400 mHz antenna and the EM data were collected with 13, 11, 8 and 6 kHz frequencies. The results from both instruments were calibrated to the initial 2007 archaeological site test pits. The irregular bedrock topography coupled with mafic intrusions has rendered the geomagnetic, one meter grid, data set problematic. The GPR and EM data establish the extent and orientation of the irregular stone foundation footings as well as cellar hole of the garrison. In addition, data analysis shows the location of areas of probable interest surrounding the main cellar hole.