North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: Fort Jemseg Geophysical Survey.
Reference: Jeandron, J. (2003) Geophysical Survey for Fort Jemseg. MS on file. Archaeological Prospectors, PO Box 20042, Fredericton, New Brunswick, E3B 6Y8.
Over 25 years of research has gone into the search for Fort Jemseg - a 17th C trading fort on the shores of the Saint John River. The fort, to this date have been elusive, however, while using the magnetometer in the scanning mode, some elevated readings were recorded. Field work was conducted on May 18, 2003. Field work began at 11:30 hrs with placement of grids followed by the geophysical survey.
Three 20m grids were set up and the area received a detailed survey using the magnetometer in the recording mode. These readings turned out to be a 19th C remains of a home. Follow-up 1m x 1m test units were excavated (within the foundation and the midden) that revealed the structure had been burned and the 'foundation' area contained a representative sample of 19th century house wares, brick, ceramic, glass, burned wood etc. The second test unit was excavated in the western edge of the southern 20m grid and revealed what was likely the associated midden.
The magnetometer survey was conducted using a Bartington 601Grad fluxgate gradiometer magnetometer with a vertical sensor separation of 1m (depth of scan is up to 3m). The lowest sensor was 30cm above the ground. The instrument was zeroed at a location away from any noticeable disturbance at the beginning of the day and before each grid was surveyed. Three 20x20m grids were surveyed, each at 1m traverses with readings every 12.5cm. The data logger was set with a sensitivity of .1nT (nanoTesla). Grids were surveyed beginning in the southwest corner, heading north, and walked in a parallel formation.
The data was dumped using software
provided by the instrument manufacturer that corrects for drift automatically.
Data was processed using Golden Software's Surfer 7 and presented using Surfer's
image map format with interpretation through Adobe Photoshop 7.