Archaeo-Physics, LLC - geophysical survey and subsurface mapping

Case Study

Ellis Cemetery

Historic Euro-American Cemetery, Fort Bragg, North Carolina

The Ellis Cemetery is a 19th Century Euro-American cemetery located on what later became Fort Bragg, North Carolina. It was one of several cemeteries surveyed by Archaeo-Physics to evaluate geophysical methods by the Fort Bragg Cultural Resources Program.

Ground penetrating radar (GPR) detects changes in the electromagnetic properties of subsurface materials as reflections of a transmitted signal. Many types of features and artifacts may be detected, although sufficient contrast is difficult to predict in field conditions. GPR survey may be performed in on of two ways. Traditionally, data are collected as individual transects and displayed as profile views. While this can provide valuable depth information, horizontal patterning is difficult to interpret. A relatively new technique known as time slicing may be used to construct planview maps isolating specific depths.

Of the various geophysical methods used in archaeology, GPR is generally the most successful because of its ability to detect deeply buried but spatially small targets. The chief disadvantage of the GPR is that its success is very dependent on specific site conditions, and is very difficult to predict. In general, sandy, homogeneous soils are ideal, while clays, silts, and rocky or heterogeneous soils greatly reduce the chances of success. Burial practices and preservation also affect the detectability of graves.

Ground pnetrating radar GPR time-slice showing Civil War and 19th century graves

Survey Results:

  • Number of known grave markers mapped: 18 headstones and 18 footstones.
  • Known grave markers with observable signal response: 16
  • Percentage of known markers with observable signal response: 89
  • Possible graves outside current cemetery boundary: Yes
  • Estimated number of graves outside current boundary: Impossible to determine; anomalies associated with suspected graves are patterned but indistinct; may represent 10 or more graves.

The signal response from known graves at this cemetery was unusually distinct. Several anomalies (outlined in yellow) outside of the current cemetery boundary are thought be associated with unmarked burials. The exact number of unmarked burials is difficult to determine. Anomalies outside the cemetery boundary are somewhat indistinct, but appear to be aligned with rows of marked burials. A linear alignment of anomalies to the east of the current cemetery boundary may contain as many as 9 additional unmarked graves, and more discrete anomalies appear immediately outside the northern and southern boundaries.
The time slice plot shows a lack of strong response at the marked grave of Jesse Ellis (approximately N13/E9), and a particularly strong response from the adjacent grave of his daughter Catherine (approximately N11.5/E9).

GPR profile ohwing historic graves

Examination of profile images shows two strong reflectors at different depths at the marked location of Catherine Ellis' Grave. This suggests that two burials may be nearly superposed, although it might also be caused by separate reflectors within a single burial (e.g., the top and bottom of a coffin).

See also: Location of Human Burials

Reference:

Jones Geoffrey, David L. Maki, and Michael Hargrave
2003 GPR Investigations Of Four Historic Cemeteries On Fort Bragg, NC. Archaeo-Physics Report of Investigation #48.

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