Over the decades, grave markers in old cemeteries have been lost. Geophysical exploration can sometimes locate the unmarked burials. The two techniques which may be best for this search are a ground‐penetrating radar survey and a soil conductivity survey. A ground‐penetrating radar survey, with its capability for estimating the depth and shape of buried objects, is particularly suitable. With an electromagnetic induction survey, the disturbed soil in the grave shaft can sometimes be detected as a change in electrical conductivity. Both of these surveys also can locate large metal objects. These surveys have limitations. At some sites, the radar cannot profile deeply enough; at others, the soil strata are so complex that graves cannot be distinguished. A conductivity survey can be degraded by metallic trash and other small objects in the topsoil; it can give the best results where the earth is distinctly stratified. Results from nine surveys are illustrated here. The sites are all in the U.S.A. and the graves are not older than the 17th century. Magnetic and resistivity surveys may be suitable for some sites, but they have not been very successful for the sites discussed here. The success of these surveys has ranged widely, from excellent to poor. While little archaeological excavation has followed these surveys, geophysical tests at marked graves show the capability of the instruments.
An interdisciplinary team studied Guajará , a prehistoric artificial mound in the Brazilian Amazon. The geophysical surveys and excavations were interactive; this interaction furnished more information than either geophysics or excavation alone could have provided. While seven different geophysical methods were applied, the magnetic survey reported here was particularly valuable. A detailed interpretation of this survey quantified the magnetic material in the mound, and this furnished an initial estimate of the number of cooking hearths in the mound. Ten test excavations were concentrated at magnetic anomalies. These excavations located cooking hearths and burial urns. A reevaluation of the magnetic survey was then done in order to refine the estimate of the number of hearths in the mound; this yielded an estimate of 2200 hearths. This allowed the population of the site to be approximated at 78-156 people. The geophysical survey and excavations also identified possible locations for subsequent broad-area excavations. ᭧
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