North American Database of Archaeological Geophysics
North American Database of Archaeological Geophysics
Abstract/Summary:
Project Name: Silver Bluff Plantation (38AK7)
Reference: Maki, David (2003). Ground Based Geophysical Investigations of Two Archaeological Sites 9CE1 (Kasita Town) and 38AK7 (Silver Bluff) Archaeo-physics report of Investigation Number 66. Prepared for the Center of Advanced Spatial Technologies, University of Arkansas.
Silver Bluff is located on the Savannah River in Aiken County, South Carolina. The bluff is about 15 miles downstream of Augusta, Georgia, and rises approximately nine meters above the river. The plantation, an area of 1,275 hectares, is part of a site owned by the National Audubon Society. The property is managed to demonstrate the compatibility of agriculture with wildlife and environmental concerns. Approximately 324 hectares are under cultivation while most of the area is comprised of woods and swamp. Little is known of the early history of Silver Bluff. William Bartram, the pioneer naturalist, visited the site in 1776 and noted the presence of ‘various monuments, terraces, areas, as well as traces of fortresses of regular formation.
Archaeological investigations were performed in 1979 and 1980. The diagnostic artifacts found at Silver Bluff plantation indicate occupations dating as far back as 8000 BC. Archaic occupations were sparse and the major occupation period appears to have occured during the Woodland periods (between 1000 BC and AD 1000) and the Early Mississippian (AD 1000 to 1500). A low density of artifacts and the sporadic nature of the temporal sequence suggests short term subsistence and maintenance activities. Subsequently during the hisoric time period (1750's) the plantation was used as a trading post and then (1760's) as a plantation. George Galphin purchased the plantation in 1752 and established a trading post in the area. The main historic occputaion occured between 1750 and 1830, after George Galphin's death. In 1975, after years of deterioration, the property was willed to the National Audubon Society. It was placed on the National Register of Historic Places in 1977.
Archaeophysics, LLC was contracted by the University of Arkansas to conduct the geophysical survey for both Kasita Town (9CE1) and Silver Bluff Plantation (38AK7) between the dates of November 17-8 and December 9-11, 2003. The Geoscan Research FM36 fluxgate gradiometer, Geoscan Research RM-15 resistance meter, and the Sensors and Software pulseEkko 1000 with a 450 Mhz antenna were employed. The FM36 was operated in the 0.1 nT sensitivity range and data were collected using a transect spacing of .50m with 8 samples per meter. The resitance meter was operated in twin electrode configuration with a mobile probe spacing of .5 meters with a transect spacing of 1 meter. Both the magnetic and resistance surveys were done in a zig-zag mode. The GPR data were collected using a transect spacing of .50m with 20 traces per meter along each transect. Each GPR trace consists of data points within a 100 nanosecond time window. Data were recorded every .2 nanoseconds with this window, resulting in 500 dtat points per trace. GPR data were collecte in transects running from south to north in a unidirectional manner. Many small trees, brushy undergrowth, and modern iron debris (pinflags) were removed from the site prior to geophysical data collection.
The magnetic data revealed the location of numerous pinflags and rebar datums which unfortunately obsure the archaeological data. With some image processing but other metal artifacts and lineations fairly typical for historic archaeological sites were drawn out. The extremely high electrical resistance of the soil at this site was somewhat problematic. Survey speed was reduced due to high contact resistance problems and we were unable to get valid data in some locations. The high resistance (low conductivity) of the background soil did, on the other hand, create a nearly ideal medium for the GPR. Tree roots appear to be the main source of GPR signal clutter. Both the GPR and resistance instruments were successful in finding possible road and structure foundations.