Archaeological Prospection of the Hatfield Site, a Monongahela Tradition Village in Washington County, Pennsylvania

Transcription

1 Archaeological Prospection of the Hatfield Site, a Monongahela Tradition Village in Washington County, Pennsylvania Jason Espino, Seth Van Dam, Ashley Brown, and Marion Smeltzer Report completed for fulfillment of Specialized Methods in Archaeology: Archaeological Geophysics (Anth 584) course requirements. i

2 ACKNOWLEDGEMENTS This project could not have been completed without the generosity of the Anthropology Department at Indiana University of Pennsylvania (IUP). The department provided the geophysical and spatial equipment necessary for the survey as well as transportation to and from Indiana, Pennsylvania. Equally generous were the Mansfield family for allowing access to the property on which the Hatfield site is located. They are thanked for their hospitality, patience, and all-around interest in the project. Dr. Beverly Chiarulli of IUP is thanked for her guidance, suggestions, comments, and technical support throughout every step of the process, from data collection to report preparation. We are especially grateful for her availability at a moment s notice to trouble-shoot problems that invariably arose during the project. Amanda Snyder and Andrea Boon are thanked for rearranging their busy schedules to lend a hand in data collection. Likewise, Allegheny Chapter of the Society for Pennsylvania Archaeology members Nina Larsen, Bob Leidig, Don McGuirk, Ben Scharff, and Don Tanner volunteered their time and aided in data collection. Any errors found herein are the sole responsibility of the authors. i

3 TABLE OF CONTENTS Acknowledgments Table of Contents List of Figures List of Tables Abstract i ii iv iv v Introduction 1 Archaeological Prospection Theory 1 Magnetometry 2 Ground-Penetrating Radar 2 Archaeological Prospection of Prehistoric North America 3 Circular Villages of the Monongahela Tradition 6 A Brief Background of The Hatfield Site 10 Research Objectives 13 Methods 13 Survey Parameters 13 Magnetometry Survey 16 Magnetic Susceptibility 16 Magnetic Gradient 16 Ground-Penetrating Radar Survey 17 Data Integration 19 Results 19 Magnetometry Survey 20 Magnetic Susceptibility 20 Magnetic Gradient 21 ii

4 Ground-Penetrating Radar Survey 24 Interpretations 26 Conclusions 30 References Cited 31 iii

5 LIST OF FIGURES Figure 1. General Location of the Hatfield Site 7 Figure 2. Typical Monongahela Tradition Village 9 Figure 3. Typical Monongahela Tradition Dwelling 9 Figure 4. Topographic Setting of the Hatfield Site 11 Figure 5. Stratigraphic Profile of the Hatfield Site 12 Figure 6. View of Grid 2, facing East 15 Figure 7. View of Grid 3, facing North 15 Figure 8. Seth Van Dam conducting Magnetic Gradiometry Survey in Grid 2 18 Figure 9. Amanda Snyder and Nina Larsen Performing GPR Survey in Grid 2 18 Figure 10. Results of the Magnetic Susceptibility Survey 21 Figure 11. Results of the Magnetic Gradient Survey in Grid 2 23 Figure 12. Results of the Magnetic Gradient Survey in Grid 3 23 Figure 13. Results of GPR Survey in Grid 2 25 Figure 14. Results of the Magnetic Gradient and GPR Surveys in Grid 2 27 Figure 15. Results of the Archaeological Prospection of the Hatfield Site 29 LIST OF FIGURES Table 1. Spatial Information for Grid 2 and Grid 3 14 Table 2. Magnetic Susceptibility Anomaly Attributes 21 Table 3. Magnetic Gradient Anomaly Attributes 24 Table 4. GPR Anomaly Attributes 26 iv

6 ABSTRACT An archaeological prospection survey was undertaken at the Hatfield site in November of The survey utilized magnetometry and ground-penetrating radar techniques to identify subsurface anomalies that may represent cultural features. In total, 28 anomalies were identified through magnetic susceptibility, magnetic gradient, and ground-penetrating radar methods. Several of the anomalies resulted from modern activities at the site, including agricultural plowing and excavations by the Allegheny Chapter. However, at least 10 of the anomalies possibly represent prehistoric cultural remain of the Middle Monongahela component of the Hatfield site. These anomalies comprise two pit features, six dwellings, and a house ring zone. The size and arrangement of dwellings as well as the spatial layout of the house ring is consistent with typical Monongahela Tradition villages. If the anomalies indeed represent a section of a village, the Middle Monongahela village at the Hatfield site would encompass an estimated area of 1.7 to 2.27 acres. In addition, a composite anomaly south of the Middle Monongahela component may represent a second village at the site that covers an area of 0.25 acres. v

7 INTRODUCTION The following report describes an archaeological prospection survey undertaken at the Hatfield site (36WH678) for fulfillment of course requirements in Specialized Methods in Archaeology: Archaeological Geophysics (Anth 584). Specifically, it attempts to address the nature of the subsurface archaeological record at the site through the use of geophysical methods, including magnetometry and ground-penetrating radar (GPR). The field component of the survey was undertaken during five non-sequential days in November of 2011 while data processing, graphic design, and report production were completed in November and December of The Hatfield site was selected due to the senior author s participation in ongoing excavations there as part of public outreach efforts by the Allegheny Chapter of the Society for Pennsylvania Archaeology. Given that, as Bercel and Espino (2010) point out, one of the primary purposes of excavations at the Hatfield site was to garner public interest in the archaeology of southwestern Pennsylvania through hands-on experience, the chapter decided to excavate the site by hand. The chapter felt that there were a number of benefits to the slowerpaced excavations. First, it allows for the supervision and education of inexperienced fieldworkers. Second, volunteers can be involved in most aspects of the fieldwork. Third, since sites such as Hatfield are among the most complex sites to excavate, there is ample time to properly document the findings without being overwhelmed. Finally, a smaller portion of the site is impacted, thus preserving large areas for future research. Conversely, one of the drawbacks of the chapter s excavation procedures is that there is limited opportunity to excavate large areas and expose settlement pattern information, including the presence of a palisade, the layout of domestic structures, and the organization of activity areas. As a result, archaeological prospection, also referred to as archaeological geophysics, was proposed as a method to better define the subsurface record at the site and help identify settlement patterns that would only be recognizable through extensive and expensive excavations. Archaeological Prospection Theory The following section provides a general discussion of geophysical theory as it relates to magnetometry and GPR. 1

8 Magnetometry. Magnetic methods are based upon localized disruptions in the earth s magnetic field (Hargrave 1999:12). Magnetic surveys measure the variation of the magnetic fields of the earth and the effects of near-surface features that may be overlain upon it. In archaeological applications, the surveys map the contrasting values of buried anthropogenic activities generally characterized through magnetic susceptibility of geological features and ferrous materials. Once the average magnetic susceptibility for an area is established, the magnetic gradient acts as a filter to reduce the effects of background geological magnetic fields and daily effects caused by the interaction between the magnetic fields of the Earth and its atmosphere, allowing anthropogenic activity areas to be viewed as anomalies (Campana 2009). Magnetic gradiometry is a passive detection method that measures the sum of remnant and all forms of induced magnetism at a location, whether forms are natural or anthropogenic (Kvamme and Ahler 2007: ). The range of the spatial frequencies in the collected data depends on the depth of subsurface features, the susceptibility contrast between features and their surroundings, and the height of the measuring instrument above the surface (Scollar 1990:490). Ground-penetrating Radar (GPR). The foundations of GPR lie in electromagnetic (EM) theory that is based upon the relationship of a material s response to EM fields. GPR survey method involves the transmission of high-frequency electromagnetic radar pulses into the ground and measures the time that elapses between each transmission, reflection off a buried discontinuity, and the reception back to the radar antenna at the surface (Conyers and Goodman 1997:23). The frequency of the radar wave transmitted controls the depth to which radar energy can penetrate and the amount of definition that can be expected in the subsurface (Conyers and Goodman 1997). Once the reflected signal is detected by the receiving antenna at the ground surface within close proximity to the transmitter, this reflected signal can then be compared to the original signal. The magnitude or amplitude, phase (negative or positive), and frequency of the received signal offers additional information as to the nature of the materials below the surface (Heimmer 1992:37). The software of the GPR unit has equations of macroscopic (or average behavior) descriptions of how different electron, atoms, and molecules respond en masse to the application of the EM field. These fluctuations from the macroscopic properties stand out from the average macroscopic state (Jol 2009). 2

9 Archaeological Prospection of Prehistoric North America, a Brief Overview The use of geophysical testing at archaeological sites in the United States was first pioneered in 1946 by Richard J. C. Atkinson with the use of electrical resistivity (Scollar et al. 1990). Over the past 70 years, archaeologists have increasingly employed classical geophysical methods to successfully enhance many cultural resource investigations (Heimmer 1992, Weymouth, 1986). Not until recently however, has the use of geophysical testing become a more standard survey technique. When employed, they provide non-destructive methods to access information contained within significant sites. There are many different types of geophysical methods for testing archaeological sites. These include ground penetrating radar (GPR), magnetometry, electrical resistivity, magnetic susceptibility, and profiling to name a few. Improved geophysical instruments and application methods, as well as new innovations in data processing, have allowed for the study and measurement of earth-related physical contrasts with extreme precision (Heimmer 1992). As a benefit of these advancements, minute or small subsurface contrasts attributable to both historic and prehistoric site remains have a greater chance of being detected using high resolution geophysical techniques without being destroyed (Heimmer 1992). The following is a review of several cases in which archaeologists successfully used geophysical testing methods to identify aspects of an archaeological site that otherwise may have required full excavations. In each one of these cases, similar equipment was used as in the archaeological prospection of the Hatfield site. By studying the results of these cases, and how the data was processed, better interpretations of the Hatfield data can be offered. Near-surface geophysical surveys were conducted at three locations at the Poverty Point site (16WC5), Louisiana in 2001 (Britt et.al. 2002). Over the past 100 years, a number of archaeological excavations have been carried out at Poverty Point, but none provided a clear understanding of the nature, distribution, and density of archaeological features such as pits, hearths, postholes, and other structural remains (Britt et.al. 2002). Due to this lack of information, the geophysical survey was designed to emphasize high data density in three target areas instead of covering large tracts of land at the site. The intention of the survey was to collect data in a manner that would permit the detection of relatively small, very low contrast subsurface features (Britt et. al. 2002). Mound E, West Sector and the Southwest Sector (rings 1-5) were selected as the target areas. 3

10 Methods employed during the survey included magnetic field gradiometry, electrical resistivity, electro-magnetic in-phase/conductivity, and GPR. The following systems and parameters were used: Geoscan Research FM-36 gradiometer with two fluxgate sensors; Geoscan Research RM-15 resistence meter equipped with an MPX15 multiplexor and a PA5 Probe array; Geonics Ltd. EM-38 terrain conductivity meter; and a Sensor & Software, Inc. Noggins GPR system with 250 and 1000 MHz antennas. All resistivity and gradiometer survey data was processed using Geoplot 3.0 software and exported into Surfer 7.0 to produce image maps. The GPR data was processed using GPR Slice, but was considered unusable due to a high clay soil content that obscured the detection of anomalies. Furthermore, datasets recovered from Mound E were considered unreliable due to the proximity of modern field road, the incidence of recent metal artifacts, and the presence of an overhead electrical power transmission line (Britt et. al. 2002). Geophysical surveys at both the West and Southwest Sectors (rings 1-5) of the site did however produce interesting and usable results. In the West Sector, geophysical surveys indicated magnetic variability in the composition of the sediments, such as would be seen in compositional differences between sands and clays. The results lent support to Jon Gibson s position that Crowley s clay, which is exposed along Bayou Macon, was consistently mined and used for construction by the people at Poverty Point (Britt et. al 2002). In addition, numerous anomalies were detected in the West and the Southwest Sectors, respectively, and are suggestive of midden deposits. Several targets were identified for exploration, though no work has been conducted to investigate these anomalies. In 2003, geophysical surveys were conducted at four prehistoric and historic fortified earthlodge settlements located in the Middle Missouri River Basin of North and South Dakota (Kvamme 2003). The surveys were conducted to provide interpretive details that could bolster information provided to tourists for the then upcoming bicentennial of the Lewis and Clark expedition. The surveys included large scale magnetic gradiometry and electrical resistivity along with the use of soil conductivity measurements and GPR. The following systems and parameters were used: Geoscan Research FM-36 fluxgate gradiometer with 4-8 samples per meter in m traverses; Geoscan Research RM-15 resistence meter in four parallel twin configuration with 0.5 m probe separation; Geonics Ltd. EM-38 electromagnetic conductivity 4

11 quadrature phase data in vertical dipole mode with 1 x 0.5 m sampling; and GSSI SIR-2000 with a 400 MHz antenna with 0.5 m traverse interval (Kvamme 2003). The magnetic surveys proved to be the most consistent in providing subsurface details of the village sites. At every site surveyed, the magnetic surveys revealed the presence of fortifications, houses, hearths, and other features, such as storage and trash pits. Electrical resistivity and GPR proved unsuccessful in defining subsurface anomalies. At one of the villages, the Whistling Elk site, electrical resistivity, soil conductivity, and magnetometry were successful in identifying an outer fortification ditch with five evenly-spaced bastions and 67 anomalies that represent houses (Kvamme 2003). The magnetometry survey further defined 34 of these houses as being burned, including what is known as the Big House. Ground-truthing revealed that the Big House had indeed been burned. These results suggest that the Whistling Elk prehistoric village had been sacked by another prehistoric group. At the historic village of Mitu tahaktos, the magnetic survey revealed household differences in the distribution of iron artifacts, suggesting potential social and economic differentiation at the site (Kvamme 2003). In November of 2008, geophysical investigations were conducted at the Late Prehistoric, Monongahela Tradition Dividing Ridge site (36WM477) located in Westmoreland County, Pennsylvania (Johnson 2008). Two methods were used for this investigation, magnetometry and electrical resistance (Johnson 2008). For the purpose of this review, only the magnetometry survey will be discussed since an electrical conductivity survey was not preformed at the Hatfield site. The objective of the investigation at Dividing Ridge was to use geophysical methods to map prehistoric features present at the site (Johnson 2008). The magnetometer survey was conducted using a Geometrics G-858 Cesium magnetometer. Readings were taken at a rate of 10 per second resulting in approximately 10 measurements for every meter (Johnson 2008). All magnetic data was collected along profile lines with a constant one-meter line separation. All data maps were then produced using Surfer software. The effect of recent human modification to the landscape can be seen in the data by the presence of linear anomalies representing plow furrows. Even though the landscape had been previously disturbed, numerous curvilinear magnetic features were observable in the maps. The longest observable magnetic feature forms a large semi-circle at the western edge of the surveyed area. Johnson (2008) interpreted this large feature as the palisade wall that once surrounded the Dividing Ridge village site. Apart from this large palisade feature, numerous circular anomalies 5

12 measuring 8 to 12 m in diameter were identified. They are interpreted as possible houses based on their size and distribution (Johnson 2008). Other anomalies were identified in the data, and they may represent hearth, pit, or midden features. Although no ground-truthing of the anomalies at the Dividing Ridge site have been conducted, the survey shows promise in providing data related to settlement patterns at a Monongahela Tradition village. The last example discusses a successful attempt in identifying subsurface archaeological remains through GPR in an area with an abundance of clay soils, and it is offered because subsoils at the Hatfield site have high clay content. Clay soils often will yield poor GPR results; this is mostly due to clay having a high electrical conductivity. The survey was conducted at the Riverfront Village, a prehistoric Mississippian site along the Savannah River in South Carolina (Weaver 2006). A GSSI SIR-3000 system with a 400 MHz antenna was used to collect data, and it was processed to produce profiles in 3 ns slices. Processing revealed linear and circular features within the ns slice, which converted to depths of cm below the ground surface. This level laid below flood deposits that contained clayey soils. Anomalies that were identified were interpreted as a palisade of the Mississippian village (Weaver 2006). Subsequent archaeological excavations exposed a linear palisade 10 cm beneath the clay horizon. The reflection profiles created in this area were so ambiguous that no usable interpretations could be made from them. Even though this reflection data appeared ambiguous, the amplitude maps that were constructed from all the combined reflection profiles provided useful data and maps. Circular Villages of the Monongahela Tradition The Hatfield site is a large, multi-component archaeological site located approximately 30 km (18.9 mi) south of Pittsburgh in North Strabane Township, Washington County, Pennsylvania. One of the principal components represents a Late Prehistoric, Monongahela Tradition village that was occupied during the Middle Monongahela period. The Monongahela Tradition is an archaeological term used to define the people that inhabited the lower portion of the Upper Ohio River Valley during the Late Prehistoric period, or between circa A.D and A.D This region encompasses much of southwestern Pennsylvania and contiguous portions of Maryland, Ohio, and West Virginia. Following Johnson s (2001) chronology, the Early Monongahela period dates to between A.D. 1050/1100 to A.D. 1250, the Middle 6

13 Figure 1. General Location of the Hatfield Site 7

14 Monongahela period dates between A.D to A.D. 1580, and the Late Monongahela period dates between A.D.1580 and A.D Villages are the most archaeologically visible Monongahela Tradition settlement. Of over 400 Monongahela sites or components in which function has been determined, 74 percent of these are identified as villages (Johnson 2001:68-69), and most are situated in upland settings (Hasenstab and Johnson 2001; Johnson et al. 1989:1-9). Typical Monongahela villages consisted of an outer fence or palisade with a concentric ring of houses surrounding an open area in the center of the village that is commonly referred to as a plaza (Figure 2) (Johnson et al. 1989). At some villages, especially during the Middle and Late Monongahela periods, there are more than one palisade and more than one ring of houses. Palisades were usually constructed out of large wooden posts, and often, a trench was excavated adjacent to the palisade. Soil from the trench was added to the base of the palisade to provide structural support for the posts, especially at villages that sat on shallow soils where bedrock precluded their deep placement. Within the house ring, or domestic zone, a variety of features are typically found. They include domestic structures, unattached storage facilities, fire pits, smudge pits, refuse pits, and burials, to name a few. Plazas are usually devoid of domestic activity, perhaps because they were treated as communal and/or ritual space. Some villages show evidence that a large hearth and/or central post once stood at the center of the village (Means 2007). Monongahela houses were usually circular or oval (Johnson et al. 1989:12-13), ranging between three and ten meters in diameter. The interior of a typical house consisted of a central hearth, support posts, and little else (Figure 3). Occasionally, burials are found underneath house floors, but these are almost exclusively of young children or infants. It is estimated that Monongahela houses may have been occupied by seven or eight individuals (Means 2006). During the Middle Monongahela period, some of these domestic structures began to have pear or horseshoe-shaped storage facilities attached to them (Hart 1995:46). With access through the interior of the house, these appendages were used to store surplus agricultural goods among other things. Over time, the number of houses with appendages increased (Hart et al. 2005:352), as did the number of appendages that appear on households. Later in time, specialized structures that may have complex social implications appear at Monongahela villages, and mostly within plazas or near the center of the village (Anderson 2002). One such structure is referred to as a petal house because of its distinctive lay-out. 8

15 Figure 2. Typical Monongahela Tradition Village (Courtesy of the PHMC) Figure 3. Typical Monongahela Tradition Dwelling (George 1997) 9

16 Occurring within at least three Late Monongahela period villages, petal houses exhibit multiple appendages, from as few as 11 to as many as 24 (Anderson 2002: ). Interpretations of these structures have ranged from communal storage, to sweat baths or council houses, to communal ritual space (Anderson 2002:125; Hart 1995:50; Herbstritt 1984, 2003:31). The other type of specialized structure is recognized because of its mortuary function. Known as charnel houses, these structures were used primarily for the burial of adults (Anderson 2002: ). They are identified at four terminal Middle Monongahela and Late Monongahela villages, with two of these possibly representing early progenitors of the type (Johnson 2001:73). These structures suggest that certain individuals were treated, at least in death, differently than other members of the village (Anderson 2002:127). A Brief Background of the Hatfield Site The Hatfield site is situated on a long peninsular hill spur oriented north to south at an elevation of 360 m above sea level (Figure 4). This hill spur is flanked by springs on both the eastern and western sides as it gently slopes down to a small unnamed tributary of Little Chartiers Creek at its southern tip. Little Chartiers Creek joins the larger Chartiers Creek about seven km northeast of the site. Chartiers Creek is a north-flowing, major tributary of the Ohio River that is more or less paralleled by the Monongahela River to the east and a portion of Raccoon Creek to the west. Cross-cutting Allegheny and Washington Counties, the stream drains approximately an area of 446 square-kilometers (277 square-miles). The headwaters of the creek originate just south of the City of Washington in south-central Washington County. The creek empties about 50 km (31 miles) from its origin into the Ohio River near the Borough of McKees Rocks, just upriver from Pittsburgh. The site is situated within the Pittsburgh Low Plateau Section of the Appalachian Plateaus Physiographic Province, which is characterized by narrow summits, narrow stream bottoms, and steep linear valley slopes. This highly dissected terrain results from the erosion of flat lying bedrock that belongs to the Pennsylvanian aged Washington Formation, and is composed of cyclic sequences of sandstone, shale, limestone, and coal (Wagner et al. 1975). The base of the Washington Formation is defined by the Washington coal. Overlying the coal are three limestone beds (lower, middle, and upper) that are readily identifiable on many hilltops across Washington County. The weathering of these various beds provides the parent material from which the soils on the Hatfield site have formed. Soils 10

17 Figure 4. Topographic Setting of the Hatfield Site underlying the site are mapped as Guernsey silt loam on 3 to 8% slopes (NRCS 2007a), and are excellent for growing staple crops such as corn and wheat (NRCS 2007b). A geomorphologic study of the site revealed that a pronounced plow zone with a depth ranging between 23 and 26 cm ( in) was clearly shown by the unusually dark humic soils of the Ap horizon (Figure 5) (Fritz and Valko 2007). It is possible that midden deposits resulting from prehistoric occupation of the site have enhanced the darkness of the Ap horizon. Based on the auger probes, the artifact density within the plow zone was relatively high, with two artifacts recovered per 1.2 liters of soil. The bottom of the Ap horizon is sharply contrasted against the lighter and more yellow Bt horizons. Formation of these Bt horizons is the result of in situ weathering of bedrock over thousands of years. It was determined that artifacts were 11

18 unlikely to be found within the Bt horizons except where human features, bioturbation, or any other types of disturbances have intruded into the Bt horizons. Figure 5. Stratigraphic Profile of the Hatfield Site In total, seven features, over 150 postmolds, and more than 20,000 artifacts have been documented by the Allegheny Chapter s excavations (Bercel and Espino 2010). The field work has exposed a 40 m 2 ( ft 2 ) area of contiguous units arranged more or less linearly along the eastern section of the village. Features include two refuse pits, two fire pits, two post-enclosed storage pits, and a burial, all of which are found within the domestic zone, or house ring, of typical Monongahela villages. However, the limited areal extent of the excavations has 12

19 precluded any positive identification of domestic structures and other large-scale village features. A fragment of hickory nut (Caryan sp.) from Feature 2, a refuse pit, produced an Accelerator Mass Spectrometry (AMS) radiocarbon date of 545±15 radiocarbon years before the present (rcybp) (ISGS-A1409; Bercel and Espino 2010). This date has a one sigma calibration of A.D and a two-sigma calibration of A.D Research Objectives Due to the limited extent of the Allegheny Chapter s excavation, little can be said of the settlement patterns at the Hatfield site. Therefore, the primary objective of the archaeological prospection survey is to identify subsurface anthropogenic features that may help develop interpretations about the spatial structure of the village. Similarly, the project is intended to identify areas of archaeological interest as the Allegheny Chapter continues research at the site. Prior to the survey, a number of research questions were developed to help guide data collection: (1) Can overall boundaries at the Monongahela component be defined using geophysical methods?; (2) Does the village contain a defensive stockade and associated trench?; and (3) Can the domestic zone of the village be identified, and if so, can activity areas and domestic structures be identified and measured? Delineating the spatial extent of the village within the surveyed area is integral to understanding settlement patterns. With better-defined boundaries, the size of the village may be extrapolated onto the neighboring property, and with an extrapolated size, estimates of the number of houses and overall population size can be developed. Similarly, identifying the stockade will help to more accurately define the aerial extent of the village. Finally, identifying and interpreting anomalies within the domestic zone may reveal patterns associated with the organization of the village, i.e. whether there are one or two rings of houses, clustering of houses, and areas of specialized activities. METHODS The following section describes the data collection and processing methods and systems used during the archaeological prospection of the Hatfield site. Survey Parameters Archaeological prospection of the Hatfield site commenced with the establishment of a large grid (Grid 1) across the eastern section of the hill spur on which the site is situated. The purpose of this grid was to provide an area to systematically collect magnetic susceptibility data over most of the site. A shapefile of points spaced five meters apart was created using 13

20 AUTOCAD 2004 and ESRI s ArcGIS v. 10.0, the shapefile was then uploaded into a Trimble TSC2 data collector through the use of Trimble s GPS Path Finder Office 3.0 for field use. Grid 1 measured 35 x 265 m ( x ft) for an area of 9,275 m 2 (2.29 acres). Subsequently, two areas were selected for magnetic gradient and GPR sweeps based on their proximity to the Allegheny Chapter s excavations where cultural features had been identified. The survey areas were established through spatial control points belonging to the chapter s existing localized excavation grid. The excavation grid originally had been created and aligned to magnetic north using a Berger transit (Fritz and Valko 2007). For the purpose of the geophysical survey and future work at the site, the excavation grid was updated with a Nikon DTM-520 (with 3 angle accuracy, +/- [3mm+2ppm]) and a Trimble TSC2 Data Collector (256 MB), thereby establishing sub-millimeter accuracy for regions within the site. Once the excavation grid was updated, the two geophysical survey grids (Grid 2 and Grid 3) were established, and the corners of each grid were located using a Trimble R8 GNSS Global Positioning Systems (GPS) unit (horizontal accuracy 3mm+0.4ppm RMS, vertical accuracy 3.5mm + 0.4ppm RMS). This process established real world coordinates for the project area using the Universal Transverse Mercator (UTM) projection and a World Geodetic System (WGS) 1984 datum. Grid 2 measured 20 x 30 m (65.62 x ft) (Figure 6) while Grid 3 measured 10 x 40 m (32.82 x ft) (Figure 7). Table 1 contains spatial information for both these grids. Table 1. Spatial Information for Grid 2 and Grid 3 Point #'s Desc Local Northing/Easting UTM Zone 19N Coordinates Grid 2 Northing Easting Elevation 1004 NW 1010N,1000E SW 990N,1000E SE 990N,1030E NE 1010N,1030E Grid NW 990N,1002E NE 990N,1012E SE 950N,1012E SW 950N,1002E

21 Figure 6. View of Grid 2, facing east Figure 7. View of Grid 3, facing north. 15

22 Magnetometry Survey As noted earlier, magnetic surveys measure the variation of the magnetic fields of the earth and the effects of near-surface features that may be overlain upon it. In archaeological applications, the surveys map the contrasting values of buried anthropogenic activities generally characterized through magnetic susceptibility of geological features and ferrous materials. Once the average magnetic susceptibility for an area is established, the magnetic gradient acts as a filter to reduce the effects of background geological magnetic fields and daily effects caused by the interaction between the magnetic fields of the Earth and its atmosphere, allowing anthropogenic activity areas to be viewed as anomalies (Campana 2009). Magnetic Susceptibility. The magnetic susceptibility survey was conducted in Grid 1 on November 13 and 15, It employed a MS2F probe with a 15mm diameter tip that penetrates to a depth of mm (Bartington OM0408, Issue 42). The Trimble TSC2 data collector was used to locate 417 pre-designated grid points where measurements were taken. Probe readings were recorded in the field and transferred into a Microsoft Excel file containing spatial information for each point. The Excel file was used to create a grid file in Golden software s Surfer 9, where processing and spatial analyses were conducted. The grid file was converted into a contour map of the dataset. It should be noted that Surfer 9 created a contour map that extrapolated a larger surface area than what was actually collected in the field, possibly because the data points were collected on a grid oriented to magnetic north and therefore tilted from the true north layout used by Surfer. In other words, large areas that were not surveyed were given values based on statistical extrapolations from known points. The farther away the extrapolated surface was from known points, the less accurate it appeared. Magnetic Gradient. A magnetic gradient survey was conducted within Grids 2 and 3 on November 13, 2011 through the use of a FM 256 Fluxgate Gradiometer data processing unit (Figure 8). Specifications for the equipment include sensor separation of 500mm, operation field range of +/- 100nT, analogue ranges of +/- 5, 10, 20, 40, 80, 160, 320, 640 nt, digital ranges of +/ , 2000, & 200 nt, digital display resolution of 10, 1, 0.1 nt and a response time of 20, 40, 120 ms (GeoScan Research 2005). Data from Grid 2 was collected at a sampling interval of 25 cm (9.84 in) along 50 cm (19.69 in) spaced transects traveling along the east-west axis. Data from Grid 3 was collected at a sampling interval of 12.5 cm (4.92) along 50 cm (19.69 in) spaced 16

23 transects traveling along the north-south axis. Both grids were collected in a zigzag fashion (Clay 2006). Data analysis was completed with Geoplot software produced by Geoscan Research. The following steps were followed in the processing of data from Grid 2: (1) clipping of seven areas of extremely low reading, (2) Zero Mean Traverse, (3) De-stagger of the grid, (4) Interpolation of Y & X axis Sin X/X, x2, and (5) Low Pass Filter, X=1,Y=1, Weight: Uniform. Grid 3 was processed as follows: (1) Clipping of four areas of extremely low readings and two areas of extremely high readings, (2) Despike of the entire grid, (3) Zero Mean Traverse, (4) Interpolation of Y & X axis Sin X/X, x2, and (5) Low Pass Filter, X=1,Y=1, Weight: Uniform. Anomalies that are identified will be classified according to magnetic gradient codes developed by Burks (2009). Ground-penetrating Radar Survey (GPR) The foundations of GPR lie in electromagnetic (EM) theory, which is based upon the relationship of a material s response to EM fields. For GPR, the electrical and magnetic properties are of importance. The software of the GPR unit has equations of macroscopic (or average behavior) descriptions of how different electron, atoms, and molecules respond en masse to the application of the EM field. These fluctuations from the macroscopic properties stand out from the average macroscopic state (Jol 2009). This survey was conducted using a GSSI SIR-3000 GPR model with a 400 MHz antenna. It can penetrate into the ground to a depth of 0-4 meters (0-12 feet) (Figure 9). The equipment specifications include Scan Rate Examples of 8 bit 220 scans per second at 256 samples per scan, 16 bit 120 scans per second at 512 samples per scan, a Number of Samples per Scan of 256, 512, 1024, 2048, 4096, or 8192, Time Range of 0-8,000 nanoseconds full scale, userselectable, a Gain of Manual or Automatic, 1-5 gain points (-20 to +80 db), Vertical Filters: Low Pass and High Pass IIR and FIR, and Horizontal filters: Stacking, Background Removal (GSSI 2009). The GPR survey within both grids was conducted via north-to-south zigzag sweeps spaced at 25 cm (9.14 in) intervals along the Y-axis (Conyers 2004). Datasets were collected along parallel transects separated by 25 cm (9.84 in) intervals (Conyers 2004). The collection of the data in Grid 2 occurred over two nonconsecutive days (November 5 and 8, 2011). Transect 17

24 Figure 8. Seth Van Dam conducting Magnetic gradiometry survey in Grid 2 Figure 9. Amanda Snyder and Nina Larsen doing GPR survey of Grid 2 18

25 m were collected on the first day and transects m were collected on the second day. The collection of the data from Grid 3 occurred on November 13, GPR Slice v7.0 was used to process the datasets from both grids (GPR Slice 2011). Settings for Grid 2 included the number of samples per scan as 512 with a sample start of 58 and a sample end of 512. Twenty slices were created with sample thickness of 4.4 ns and a sample 0 ns of 58. Since the datasets were gathered on separate days, the combined dataset s slices required a mosaic correction of increased batch gains to make the two dataset represent equal reflective values. Once corrected, the slices were further processed through a 3x3 Low Pass Filter. Settings for Grid 3 included the number of samples per scan as 512 with a sample start of 64 and a sample end of 512. Twenty slices were created with sample thickness of 4.39 ns and a sample 0 ns of 64. The dataset s slices were further processed through a 3x3 Low Pass Filter. Data Integration Once the data from the magnetic susceptibility, magnetic gradient, and GPR were processed and analyzed, the results were integrated into a Geographic Information System (GIS) via ArcGIS v10.0. The datasets were combined by georeferencing select Joint Photographic Experts Group (jpeg) files and layering them with varying transparencies in order to locate anomalies that are represented in all three geophysical datasets. Shapefiles of the Allegheny Chapter s excavations were also combined to provide contrasting views of real-world cultural features and geophysical anomalies that may represent areas of anthropogenic activities (Bercel and Espino 2010). RESULTS Integration of the datasets into a geographic information system allowed for a layered visualization of the data that greatly enhanced the interpretation of the results. Both the magnetometry and GPR survey data strongly suggests that these particular archaeological prospection methods are very effective in defining subsurface anomalies that may represent cultural zones and smaller cultural features. Both methods provide complimentary results that, together, begin to shed light on the settlement patterns and village organization of the Hatfield site. In total, 28 anomalies were identified through archaeological prospection. Anomalies are labeled sequentially according to grid number. Grid 1 contained eight anomalies labeled G1-1 through G1-8, Grid 2 contained 14 anomalies labeled G2-1 through G2-14, and Grid 3 contained six anomalies labeled G3-1 through G3-6. The results of the surveys are described below. 19

26 Magnetometry Survey Magnetic Susceptibility (Figure 10). The magnetic susceptibility portion of survey proved highly efficient in collecting data from a large area in a relatively short time. Measurements were recorded at 417 points spaced at five meter intervals within Grid 1. As mentioned earlier in the Methods section, Surfer 9 created a contour map representing a larger surface area than what was actually collected. In interpreting features, special care was taken to not give too much weight to possible anomalies in the areas if the map that were extrapolated. Initially, the magnetic susceptibility data revealed an arcing pattern (G1-1) trending eastto-west that was dominated by relatively low magnetic values ranging between -10 to 60 nt. The portion of the anomaly that was recorded during the survey measured 80 to 90 m north-south and m e-w. The ellipsoid has an extrapolated area ranging between 6,908 and 9,185 square-meters ( acres). There was an area of higher magnetic value that peaked near 90 nt adjacent to the arc. When this area was examined, it became apparent that measurements were affected by the Allegheny Chapter s staging area, where screens, wheel burrows, shovels, and other metal objects are stored. Since the resulting peak may have obscured true anomalies, seven data points in that portion of Grid 1 were removed from the analysis and a modified contour map was created. The modified contour map retained the arcing pattern of low magnetic values seen in the earlier version. However, new anomalies appeared that indeed were masked by the high magnetic values associated with the staging area. These anomalies (G1-3, 4, 5, 6, and 7) appeared as small circular areas of higher values that ranged between 50 and 70 nt. They measured between 5.7 and 29.4 square-meters ( square-feet). An interesting area of anomalies (G1-7) was identified approximately 90 m ( ft) south-southeast of the Allegheny Chapter s excavations. Similar to the pattern noted above, the anomalies consist of a ring of low to moderate magnetic values (50-80 nt) accentuated by smaller areas of higher values (up to 110 nt). The center of the ring displayed relatively low magnetism ( nt). The area encompassed by these anomalies measures approximately 1,107 square-meters (0.25 acres). Finally, large areas (G1-2) of high magnetic value were measured in the southern portion of Grid 1. Values here peaked at 170 nt. The cause of these anomalies is uncertain, though they are unlikely to represent archaeological remains since this 20

27 Figure 10. Results of the Magnetic Susceptibility Survey portion of the grid is steeply sloped. The definitions and details of anomalies identified during the magnetic susceptibility survey are available in Table 2. Table 2. Magnetic Susceptibility Anomaly Attributes Grid 1 Northing Easting Readings/Areas Comments G1-1 N/A N/A 60nT, -10nT Probable House Ring G mN mE 147nT Unknown magnetic Anomaly G mN mE 55nT, 13.74sq m Probable Domestic Structures G mN mE 55nT, 29.43sq m Probable Domestic Structures G mN mE 56nT, 18.65sq m Probable Domestic Structures G mN mE 46nT, 5.7sq m Probable Domestic Structures G mN mE nt, sq m Possible Second Village Site. Magnetic Gradient (Figures 11 and 12). Map surfaces covered in full, grid-length linear features oriented north-to-south is immediately apparent from the magnetic gradient data. These linear features are present in both grids, and are consistent with agricultural plow scars. The presence and similar orientation of plow scars have been noted during excavations of the 21

28 Hatfield site (Bercel and Espino 2010). Additional agricultural disturbances are seen in Grid 3, where a series of mixed positive and negative readings were recorded along the western edge of the grid. Likewise, a series of mono-polar positive and mono-polar negative anomalies are aligned linearly along the 1010E transect of Grid 3. Four of these are mono-polar positive anomalies while the fifth one is a mono-polar negative anomaly. The sources of both sets of anomalies are likely agricultural furrows noticed during data collection. In addition, two anomalies in Grid 2 were influenced by recent activity at the site. One is a large mono-polar negative anomaly located around the existing excavation trench, and likely caused by a large number of 25.4 cm (10 in) iron spikes demarcating the corners of excavation units. The other represents a multi-polar complex anomaly whose source is a 30.5 cm (12 in) iron spike at the location of one the excavation s spatial control points. Efforts to buffer these areas by a distance of a meter in all directions were insufficient in reducing the magnetic noise caused by the ferrous metal. Despite these modern disturbances, the magnetic gradient survey proved relatively effective in revealing a number of subsurface anomalies within Grid 2. In total, nine magnetic anomalies were identified. None of the anomalies produced readings higher than 40 nt, suggesting an overall lack of historic iron in the survey grid (Burks 2009). Three (G2-3, 6, and 8) of the observable anomalies are classified as mono-polar positive and two (G2-4 and 7) as dipolar simple. Mono-polar positive and dipolar simple anomalies are typically classified as undefined feature types due to difficulties in discerning their true polar nature, i.e. mono-polar positive or only a portion of a dipolar simple anomaly (Burks 2009). Prehistoric features that may produce these types of anomalies include pits as well as some hearths and earth ovens. One large positive anomaly (G2-9) was detected near the southwestern edge of the grid. Initially, this anomaly was observed as three monopoles, or a multi-monopositive anomaly, though by the end of data processing, the anomalies blended into one mass. Though rare to detect, such anomalies represent clusters of positive mono-poles arranged in linear or arcing patterns likely representing postmolds (Burks 2009). Finally, one anomaly (G2-2) was identified as a dipolar complex anomaly due to the presence of three negative peaks surrounding a large positive peak. This type of anomaly is often associated with burned areas or prehistoric structure floors (Burks 2009). The definitions and details of anomalies identified during the magnetic gradient survey are available in Table 3. 22

29 Figure 11. Results of the Magnetic Gradient Survey in Grid 2 Figure 12. Results of the Magnetic Gradient Survey in Grid 3 23

30 Table 3. Magnetic Gradient Anomaly Attributes Anomaly Northing Easting Readings (High,Low) Comments G Dummy Caused by 10" spikes from previous excavation grid G nT, -7.33nT Dipolar Complex - Probable Hearth G nT, 1.89nT Mono-Polar Positive G nT, -9.21nT Dipolar Simple G Dummy Caused by a 1" Rebar set as a local datum point G nT, -0.28nT Mono-Polar Positive G nT, nT Dipolar Simple Probable Pit Feature G nT, -0.69nT Mono-Polar Positive G nT, -0.43nT Multi-Monopolar Positive G nT, nT Caused by agrilcultural furrows G nT, -0.86nT Mono-Polar Positive G nT, -0.65nT Mono-Polar Positive G nT, -1.41nT Mono-Polar Positive G nT, nT Mono-Polar Negative G nT, -2.19nT Mono-Polar Positive Ground-penetrating Radar Survey (Figures 13 and 14) Six anomalies were identified during the GPR survey of Grid 2 and none were recognized completely in Grid 3. This includes an area (G2-10) of high reflection in the northwest section of Grid 2 where test units had been excavated by the Allegheny Chapter. A small anomaly (G2-15) of high reflection values is located at 1000N 1020E. This anomaly was caused by an existing spatial control point for the chapter excavations. Another high reflection anomaly (G2-12) is situated on the western edge of the grid south of the chapter s excavation area. The cause of this anomaly is uncertain. Two anomalies that produced similar moderate reflection values are also present in Grid 2. One (G2-13) is circular in shape located in the south-central portion of the grid with its center point located at 995N 1020E. This anomaly has an area of approximately m 2 ( ft 2 ) and reflective values ranging between 0.25 to 1 ns. The location of this anomaly corresponds to the location of anomaly G1-5 identified during the magnetic susceptibility survey. The second anomaly (G2-11) has a roughly circular shape with an area of m 2 ( ft 2 ). It is located due north of G2-13 near the northern edge of the grid, with its center point located at 1007N 1020E. It appears as if the anomaly extends northwards beyond the survey area. The anomaly has reflective values that range between 0 and 1 ns. While the boundaries of this anomaly were not as well defined, it contains a few more areas of high reflection than G2-13. Interestingly, the 24

31 Figure 13. Results of GPR Survey in Grid 2 Dipolar Complex anomaly identified during the magnetic gradient survey is located near the center of G2-11. Both G2-11 and G2-13 were identified in the same slice, and their parabolas occurred at similar depths of cm ( in) below the antenna. While zero time was not calculated, and therefore the exact depth of the anomalies is uncertain, this range of depth encompasses the plowzone-subsurface interface at this portion of the site (Bercel and Espino 2010). A third anomaly (G2-14) is identified as a partial arc of mainly low reflection values ( ns). It is located along the southern edge of the grid at 990N E and extends slightly into Grid 3. The definitions and details of anomalies identified during the GPR survey are available in Table 4. 25