The Importance of Plow Zone Archaeology
From Julia A. King, A Review and Assessment of Archaeological Investigations at 44RD183, Warsaw, Virginia, prepared for the Council of Virginia Archaeologists, June 2004
Plow zone archaeology, or the excavation and analysis of plow zone deposits, has emerged as an important tool in the interpretation of historic period Chesapeake sites. During the 17th, 18th, and 19th centuries, domestic refuse was often tossed into the yards surrounding dwellings and other outbuildings. At most Chesapeake sites, especially those which are located in rural areas, these yard middens have since been plowed, often for decades. Plowing destroys evidence of vertical stratigraphy (or soil layers), physically damages artifacts, and truncates feature deposits. While the damage to these archaeological resources cannot be minimized, the spatial distributions of artifacts and soil chemicals remain relatively intact. Information about room and building use and yard organization and layout, for example, are easily recovered from plow-disturbed soils.
The excavation of plow-disturbed midden contexts was, in the 1970s and 1980s, somewhat controversial in the Chesapeake. One of Virginia's best known archaeologists, Ivor Noël Hume, publicly questioned the value of plow zone deposits while working at Martin's Hundred near Williamsburg. During those years, plow zone deposits at Martin's Hundred and other 17th- and 18th-century sites were routinely removed by machine to expose architectural and other subsurface features. The excavation of feature deposits was preferred over plow zone because subsurface features are often sealed (that is, undisturbed by later activities) and the artifacts in them are often far better preserved. Plow zone excavation is also labor intensive, and can add costs to a project. Fewer laws and regulations were in place in those early years to insure the appropriate treatment of archaeological resources threatened by development, and one of Virginia's leading archaeologists was openly skeptical about the value of plow zone data. It was in this context that the decision to mechanically remove the plow zone was often made.1
In the last 25 years, however, a number of studies have emerged demonstrating that, while vertical stratigraphy is indeed destroyed by plowing, the horizontal or spatial distribution of materials is affected only minimally. Artifacts recovered from plow zone contexts are usually found close to where they were both used and discarded, with important implications for examining the spatial layout of archaeological sites. Distributions of plow zone artifacts and soil chemicals have been used to identify room and building functions, activity areas, architectural features such as chimneys, doors, and windows, and changes in yard organization and use through time.2
For example, at the van Sweringen site in St. Mary's City, Maryland, a late 17th-century building initially (and mistakenly) believed to have served as a bake and brew house was re-identified as a coffee house following the analysis of plow zone distributions of associated artifacts. At the Clifts plantation site in Westmoreland County, Virginia, Fraser Neiman was able to use plow zone data to identify spaces controlled by members of the planter's family and spaces controlled by members of the slave labor force. At the Ashcomb's Quarter site, an early 18th-century slave cabin located at the mouth of the Patuxent River in Maryland, unusual Indian stone tools recovered from the plow zone provided evidence that the cabin's residents were likely collecting these materials.3
While most archaeologists would agree that plow-disturbed deposits have significant analytical value, much work remains to be done to determine the best methods for recovering plow zone information. Archaeologists have experimented with a variety of sampling strategies, with the important variables being size of the test unit and distance between units. Typically at historic sites in the region, plow zone deposits have been sampled in units ranging from one-foot square (i.e., shovel test pit) to ten feet square. Today, most excavations use units ranging from 3 feet square (one meter) to no larger than 5-by-5-feet, with soils screened through 1/4-inch hardware cloth. In addition to size, the spacing of units is critical for the recovery of reliable data, especially if the site will be destroyed. Units spaced systematically across a site are preferred because they recover information about all types of archaeological distributions at a site, including low density ones. These units should be spaced no further than fifteen feet apart.4
With a growing understanding of the interpretive value of plow-disturbed deposits, the excavation of the plow zone has become a standard technique at historic period sites in the Chesapeake. Even in cases where development or other pressures exist, plow zone data are being systematically recovered. This does not necessarily mean that 100 percent of the plow zone is being excavated in 5-by-5-feet units. Sampling strategies allow excavators to recover reliable and representative samples of the plow zone through the combination of hand excavation of test units and machine excavation. While this sampling strategy may not be preferred at a protected site, it has worked well at sites for which plow zone deposits otherwise might not be collected. The Ashcomb's Quarter site, cited above and located aboard a naval base, is an excellent example.5
Endnotes
1 Ivor Noël Hume, Martin's Hundred (Alfred A. Knopf, New York, 1982), 9-11. Noël Hume does acknowledge, however, that artifacts in the plow zone are "in approximately their original positions." Not everyone in Virginia subscribed to Noël Hume’s philosophy. When, in the mid-1960s, Howard MacCord excavated the Camden site, a mid- to late 17th-century Indian settlement in Caroline County, he recovered plow zone data in 5-by-5-foot units. These data continue to be of great analytical and interpretive value; see Howard MacCord, Camden: A Postcontact Indian Site in Caroline County, Quarterly Bulletin of the Archeological Society of Virginia, vol. 24, no. 1 (1969), 1-55.
2 An important early study was produced by the National Park Service; see Valerie Talmage, Olga Chesler, and Staff of Interagency Archeological Services, The Importance of Small, Surface, and Disturbed Sites as Sources of Significant Archeological Data (United States Department of Interior, National Park Service, Washington, D.C., 1977). The literature on the analysis of plow zone deposits from Chesapeake sites is large and growing; see Robert W. Keeler, The Homelot on the Seventeenth Century Chesapeake Tidewater Frontier (unpublished Ph.D. dissertation, Department of Anthropology, University of Oregon, 1978); Fraser D. Neiman, Field Archaeology of the Clifts Plantation Site, Westmoreland County, Virginia (Robert E. Lee Memorial Foundation, 1980); Julia A. King and Henry M. Miller, The View from the Midden: An Analysis of Midden Distribution and Composition at the van Sweringen Site, St. Mary's City, Maryland, Historical Archaeology, vol. 21, no. 2 (1987), 37-59; Dennis J. Pogue, Spatial Analysis of the King's Reach Homelot, Historical Archaeology, vol. 22, no. 2 (1988), 40-56.
3 King and Miller, The View from the Midden; 37-59; Neiman, Field Archaeology of the Clifts Plantation; Wade P. Catts et al., Phase III Data Recovery Investigations at 18CV362, Ashcomb's Quarter (Historic Component) and Awapantop (Prehistoric Component), Solomons Naval Recreational Center, Solomons, Calvert County, Maryland (Prepared for the Calvert Soil Conservation District, Prince Frederick, Maryland by John Milner Associates, West Chester, Pennsylvania, 1997).
4 Jay F. Custer, A Simulation of Plow Zone Excavation Sampling Designs: How Much is Enough?, North American Archaeologist, vol. 13, no. 3 (1992), 263-280; Timothy B. Riordan, The Interpretation of 17th Century Sites through Plow Zone Surface Collections: Examples from St. Mary's City, Maryland, Historical Archaeology, vol. 22, no. 2 (1988), 2-16. The St. John's and the van Sweringen sites in St. Mary's City were excavated in units of multiple sizes; see Julia A. King, A Comparative Midden Analysis of a Household and Inn in St. Mary's City, Maryland, Historical Archaeology, vol. 22, no. 2 (1988), 17-39 and King and Miller, The View from the Midden, 37-59; units measuring 2.5-by-2.5-feet were used at the 17th-century Compton site in Solomons, Maryland, see Louis Berger Associates, Inc., The Compton Site, Circa 1651-1684, Calvert County Maryland, 18CV279 (Report to CRJ Associates, Inc., Camp Springs, Maryland, 1989); shovel tests measuring one foot in diameter and systematically spaced at ten feet revealed important distributions at the 19th-century Susquehanna site at Patuxent River, Maryland; see Julia A. King, Rural Landscape in the Mid-Nineteenth Century Chesapeake, Historical Archaeology of the Chesapeake, edited by B. Little and P. Shackel (Smithsonian Institution Press, 1994), 283-299; many projects undertaken by the Colonial Williamsburg Foundation use units measuring one meter square (approximately 3.2-by-3.2-feet), see Leslie McFaden, David Muraca, and Jennifer Jones, Interim Report: The Archaeology of Rich Neck Plantation (The Colonial Williamsburg Foundation, 1999).
5 Plow zone recovery is now standard on many cultural resource management projects in Maryland and Virginia. See Catts et al., Phase III Data Recovery Investigations at 18CV362; Louis Berger Associates, Inc., The Compton Site; McFaden et al, Interim Report; Raymond Tubby and Gordon P. Watts, Jr., Phase II Archaeological Investigation of the NAVAIR Site–18ST642, Patuxent River Naval Air Station, Patuxent [River], Maryland (Prepared for Turner, Collie and Braden, Inc., 1995); Gordon P. Watts, Jr. and Raymond Tubby, Phase III Archaeological Investigations of the NAVAIR Site, 18ST642, Patuxent River Naval Air Station, Patuxent River, Maryland (Prepared for Turner, Collie and Braden, Inc.,1998); Joseph B. Jones, Martha W. McCartney, Dennis B. Blanton, and Donna C. Boyd, An 18th-Century Tenant Site in the Lower Tidewater: Phase III Data Recovery at Site 44SK309, Associated with the Route 164 Project, City of Suffolk, Virginia (Center for Archaeological Research, The College of William and Mary, 1991).