GROUND PENETRATING RADAR
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Introduction | Site Description and History | Research Goals | References Cited
On November 18, 2000, three Boston University students conducted remote sensing at the Nathan and
Polly Johnson House at 21 Seventh Street, New Bedford, Massachusetts (Figure 1). This was a final
project for a
semester-long class at Boston University ("AR505: Remote Sensing and Archaeology," instructed by
Professor Patrick Ryan Williams). The site provided a real-world setting for students to learn some
of the mechanics, strengths, and limitations of three methods of geophysical prospecting. The New
Bedford Historical Society, owner of the property, is very supportive of this research. The Society
is currently undertaking its own major research and renovation project at the home, a recently
designated National Historic Landmark. Part of this revitalization will include archaeological
excavation of the property. Digging is scheduled to take place in the summer of 2001. State law
dictates that areas of an officially recognized historical site threatened by renovation work
(installation of below ground utilities, ramp construction, landscaping, etc.) must first be tested
archaeologically to make certain no valuable information will be destroyed (950 CMR 70). Excavation
at the Johnson site will go beyond pure mitigation, however, since the Historical Society has an
active interest in learning more about the Johnson family through archaeological evidence. Remote
sensing at the site is the first step of this larger archaeological project.
1. Location of the Nathan and Polly Johnson (NPJ) House marked on the "New Bedford North"
topographic map. North is up, scale = 1:25,000, and the contour interval is 10 feet (USGS
Geophysical prospecting provides a sort of "window" into the soil but alone is not enough to
understand the archaeological record, since it only identifies potential anomalies in the ground.
Remote sensing does not provide evidence that is certain or detailed enough to permit interpretation
without subsequent determination of "ground truth." The physical nature and archaeological context
of anomalies must be determined in order to understand depositional and post-depositional processes
that are representative of human activity. Knowing that radar testing shows a pit in the ground is
not useful unless you also employ archaeological method and theory to answer questions such as: When
was the pit first dug? Why? What was it used for? How long was it used? Did it have any secondary
uses? When did people stop using it? How and when was it filled in? With what? How is the pit
related temporally and spatially to other features on the site? How does all this reflect the lives
and choices of the people who lived on the site? Remote sensing will help researchers to develop a
more sophisticated excavation strategy for the summer of 2001, in order to better answer questions
such as these.
Site Description and History
Figure 2. Front
(east) elevation of the Nathan and Polly Johnson house (original image
The Johnson House site has achieved National Landmark status because of the important role its
original owners played in local and national history and because its phased architecture represents
typical styles from sequential periods. The land was first historically occupied in the 1820s, when
Nathan Johnson had a two-story Georgian or Federal style house (built ca. 1800) moved onto the
property by 1826 (da Silva 1999: 1-2; Grover 1999: 6; Pfeiffer 1999: 1). Documents suggest that
Nathan and his wife Mary, also known as Polly, were at this time free African-American servants of a
prominent local Quaker family (Grover 1999). After their former employer helped them to obtain their
own land and house in the mid-1820s, the couple owned several businesses. New Bedford was in a
"Golden Age" financially during this period, thanks in large part to its success as the largest
whaling port in the world (Clayton and Whitley 1979: 21-22). The Johnson property is therefore
closely associated with small business growth in urban centers of the mid-19th century, as well as
with the thriving free black community in New Bedford (and New England in general) during this
period. Grover's research (1999) shows that some of the Johnsons' businesses were run from their
home at 21 Seventh Street (school for African-American children, bakery), as well as on the
properties at 17-19 (apartment building) and 23 (confectionary shop) Seventh Street. Nathan at
various times also owned other businesses in the area (restaurant, bath house, rental property).
Quakers and former Quakers were a socially and financially dominant group in the city during the 18th
and 19th centuries. Their beliefs regarding the equality of all men in the eyes of God are
implicated in the social consciousness which then characterized New Bedford's population (Clayton and
Whitley 1979; Ricketson 1858). The city was overwhelmingly pro-abolition during the antebellum era.
Historical sources indicate that there were no slaves held in the city after 1785 (Clayton and
Whitley 1979: 31), and that it was known to be a safe-haven for runaway slaves from the southern
states. Much of the historical significance of the 21 Seventh Street property results from its
associations with the anti-slavery movement. Nathan was a noted social activist. He was a member of
several African-American abolitionist organizations and was associated with local Quaker abolitionist
leaders (Grover 1999). The 21 Seventh Street property is known to have served as a stop on the
Underground Railroad, serving as a refuge for Frederick Douglass and others. Grover explains, "it
was not only the first home of the famed fugitive Frederick Douglass after his 1838 escape from
slavery, but it is the only one of Douglass's three New Bedford residences that survives. In
addition, the house is documented to have housed at least one other fugitive slave" (1999: 12).
Documentary evidence shows that Nathan suffered a financial reversal during the 1840s. According to
Grover (1999: 9), he and many other young men of New Bedford went to California in 1849 to improve
their fortunes. Polly was given power of attorney over his properties before he left and managed
them until her death. It was during this period, ca. 1857, that the first house on the property was
moved back on the lot. Polly had a two and one-half story Greek-Italianate addition built against
its east elevation (da Silva 1999: 1), resulting in a more striking street facade. This structure
fronts Seventh Street today (Figure 2). Polly was an extremely active manager of the Johnson
properties and may be seen as a successful representative of women entrepreneurs and the black
business community. A provision in her will allowed Nathan a yearly stipend "provided he comes home
to New Bedford within two years from the date of my decease" (Johnson 1871). She died on November
19, 1871, and Nathan did in fact return. Documents indicate he was back in New Bedford by February
of 1873, although in his reduced circumstances he was not the social activist he had been during the
1820s-1840s (Grover 1999). Nathan lived at the Johnson house site until his death in 1880 (Grover
1999: 17). The 21 Seventh Street property remained in the Johnson family until 1891. The
and lot have been continuously occupied since then.
The use of conductivity, magnetometry, ground penetrating radar, resistivity, and other methods of
electromagnetic and geochemical prospecting on historical sites is not new; it is a favored
preliminary step toward archaeological investigation (Orser and Fagan 1995: 132-139; Shapiro and
Miller 1990: 95; Yentsch and Kratzer 1994: 173). Electromagnetic remote sensing is most often used on
larger scale projects than the Johnson site, however, and is particularly appropriate for
archaeological landscape studies and the location of sub-surface structural remains. This testing
process permits less destructive excavations by targeting areas of high potential, defining feature
boundaries, and delineating soil interfaces. At sites like Monticello in Charlottesville, Virginia
(Kelso 1990: 17), the Morven estate in Princeton, New Jersey (Metheny et al. 1996: 13), the
Spencer-Peirce-Little farm in Newburyport, Massachusetts (Mary C. Beaudry, personal communication
2000; cf. Beaudry 1995), and the Saratoga National Park in Saratoga, New York (Starbuck 1999: 28),
these techniques were used to evaluate archaeological potential over extensive yards, gardens, farm
fields, and battlefields (albeit with mixed results).
Farm and estate type sites cover a significantly greater area than do urban back lots and, since they
are not enmeshed in a closely-woven urban fabric of utility pipes, telephone lines, and electrical
cables, may provide a (relatively) clearer field for electromagnetic signals. This does not mean
that useful results cannot be obtained on smaller sites in city settings, and a broad-scale research
goal of the Johnson study is to evaluate this possibility. The use of three different kinds of remote
sensing (which respond differently to in-ground materials and types of interference) on the Johnson
back lot provides three comparative, but not identical, datasets. As discussed in the "Ground
Penetrating Radar: Interpretation" section, these suggest certain techniques may work better in
small, tightly bounded, interference-prone urban contexts.
At the site-specific level, goals of the three researchers and the Historical
Society are the same: Figure 3. View from
south side yard: intersection of the ca. 1820s house mid section (left), and
the 1857 front section.
The Johnson site has a complex history of architectural and spatial modifications. The first house
on the property was brought there from another location in the 1820s and was moved farther back on
the lot when a large front addition was built in 1857 (Grover 1999) (Figure 3). In order to
reconstruct and understand these activities better, the location and orientation of the original
house should be determined. Foundation remnants and builders' trenches may provide information
sufficient to address this issue. Direct evidence of these types is more likely to be located in the
front and side yards than the area of testing, since it is surmised the original house was moved from
the front to the middle of the property ca. 1857. Also, the 1970s addition of a narrow ell and
basement on the rear of the original (now middle) house section would have significantly disturbed at
least some foundational evidence of 19th century construction in that area. The front and side yards
will be tested archaeologically, but are too small for the use of remote sensing equipment. If any
large-scale earth moving related to the digging or filling of foundations was done in the back yard,
however, it will likely be detectable using geophysical prospection.
1. Location of the original house foundation
2. Location of outbuildings and other lot features
Historical documents are unclear
regarding the existence of additional structures on the 21 Seventh Street lot. In her will, Polly
Johnson left her daughter "the house and premises occupied by me as a residence at No 21 Seventh
Street together with all the buildings on the same lot of land, including the store [at] No 23
Seventh Street and also my household furniture" (cited in Grover 1999: 11). Although the 17-19 and
21-23 Seventh Street lots were surveyed and (repeatedly) mortgaged as separate properties (Figure 4),
Polly may have included them all in "the same lot of land"; "all the buildings" may refer to the
three-part house at 21 and the shop at 23 Seventh Street, and/or to the apartment building at 17-19
Seventh. Alternatively, the will can be read to refer to additional outbuildings on the property.
These structures may have left in-ground traces which are remotely detectable. Specialized features
may be associated with the Johnsons' business activities at the 21 and 23 Seventh Street sites
(bakery, confectionary, school). It should be noted that Nathan and Polly were not the only
occupants of the dwelling: Polly's children by a previous marriage, her children with Nathan, and at
times her grandchildren and school-boarders were also members of the Johnson household. Their
potential contributions to the archaeological record should not be ignored.
Figure 4. The Johnson
lots on 17-19 (L#50) and 21-23 (L#49) Seventh Street. This map was surveyed
by R.C.P. Coggeshall on June 2, 1881, and is reference #49919 in Bristol
County Deeds at New Bedford City Hall, New Bedford, Massachusetts. The
"north" arrow has been added.
The Johnsons' purposeful use and manipulation of their domestic space (outdoor and indoor) are likely
to be more informative about their lives and society than household artifacts alone. Urban back lots
were areas where a wide range of daily activities took place, many of which leave archaeological
signatures (cf. Mrozowski et al. 1996). Aside from general detritus, these features could include
wells, privies, cisterns, cesspools, cooking pits, outdoor hearths, trash pits, sheet middens,
gardens, animal pens, fences, storage areas, and specialized task areas; combined, they form a complex
and ever-changing palimpsest of domestic life during the 19th and 20th centuries. Archaeological
remote sensing and excavation at the Johnson site will allow us to re-situate yard deposits in space
and time and, thus, to understand their larger cultural significance.
Beaudry, Mary C.
Scratching the Surface: Seven Seasons at the Spencer-Peirce-Little
Farm, Newbury, Massachusetts. Northeast Historical Archaeology
Clayton, Barbara and Kalthleen Whitley
1979 Guide to New Bedford. The Globe Pequot Press, Chester.
Da Silva, Janine
1999 Nathan and Mary (Polly) Johnson House 21 Seventh Street New Bedford,
Massachusetts: Conservation Assessment. Ms. on file, New Bedford Historical
Society, New Bedford, Massachusetts.
1999 Johnson Properties NHL Nomination: Nathan and Polly
Johnson Properties 17-19 and 21 Seventh Street, New Bedford, MA. Ms. on file,
Massachusetts Historical Commission, Boston, Massachusetts.
Johnson, Mary (Polly)
1871 Mary Johnson Will, no file number, 1871. Ms. on file, Bristol County Register of Probate, New
Kelso, William M.
1990 Landscape Archaeology at Thomas Jefferson's
Monticello. In Earth Patterns: Essays in Landscape Archaeology, edited
by William M. Kelso and Rachel Most, pp. 7-22. University Press of Virginia,
Metheny, Karen Bescherer, Judson Kratzer, Anne E. Yentsch, and Conrad
Method in Landscape Archaeology: Research Strategies in a Historic New
Jersey Garden. In Landscape Archaeology: Reading and Interpreting the
American Historical Landscape, edited by Rebecca Yamin and Karen
Metheny, pp. 6-31. University of Tennessee Press, Knoxville.
Mrozowski, Stephen A., Grace H. Ziesing, and Mary C. Beaudry
Living on the Boot: Historical Archaeology at the Boott Mills
Boardinghouses, Lowell, Massachusetts. University of Massachusetts Press,
Orser, Charles E. and Brian M. Fagan
1995 Historical Archaeology. HarperCollins, New York.
1999 Nathan & Mary (Polly) Johnson House 21 Seventh Street - New Bedford, Massachusetts Preservation
Recommendations. Brian Pfeifer Preservation Advisory Services. Ms. on file New Bedford Historical
Society, New Bedford, Massachusetts.
1858 The History of New Bedford, Bristol County, Massachusetts: Including a History of the Old
Township of Dartmouth and the Present Townships of Westport, Dartmouth, and Fairhaven, from their
Settlement to the Present Time. Daniel Ricketson, New Bedford.
Shapiro, Gary and James J. Miller
1990 The Seventeenth-Century Landscape
of San Luis de Talimali: Three Scales of Analysis. In Earth Patterns:
Essays in Landscape Archaeology, edited by William M. Kelso and Rachel
Most, pp. 89-102. University Press of Virginia, Charlottesville.
Starbuck, David R.
The Great Warpath: British Military Sites from Albany to Crown
Point. University Press of New England, Hanover.
Yentsch, Anne E. and Judson Kratzer
Techniques for Recovering Buried 18th-Century Pleasure Gardens. In The
Archaeology of Garden and Field , edited by Naomi Miller and Kathryn
Gleason, pp. 169-188. University of Pennsylvania Press, Philadelphia.
[images and text ©2001 cjhodge unless otherwise noted]