A modern view of the Chancellorsville battlefield. This geophysical survey was done at the sites of two houses that were destroyed during and shortly after the Civil War battle. The Bullock House was at the north side of the park, while the Fairview House was near the center. The staked areas of the geophysical grids are indicated with dotted rectangles in the figure. This is a redrawing of the 7.5 minute USGS Chancellorsville quadrangle, most recently revised in 1978. Small open squares locate eight buildings that are no longer standing. 

Contexts in source publication

Context 1

... circular fortifications to the west of the chimney are also still visible at the site. I did not map these earthworks during my survey, although one line was roughly along N100; these earthworks might further refine the location of the Fairview house. The well for the house remains from the Civil War period; it is covered by wooden boards and is located in Figures 30 and 31. Figure 30 is a map of features that are visible in the area of the geophysical survey. Two houses are plotted in the USGS map of Figure 1, and their locations are approximated in Figure 30; neither house is still standing. Figure 31 shows the area of this geophysical survey. The geophysical grid that was set up was parallel to the paved road that goes south from highway 3. The southwest corner of the paved road was defined as point E140 N100 in the geophysical grid. The four wooden stakes that were left at the four corners of the geophysical grid are indicated with squares in Figure 31; like the Bullock grid, these stakes extend only a inch above the surface. Blue paint stripes were put on horizontal branches of conifers along line N0 at both the east and west sides of the grid; a blue stripe was also put on the paved road along line N350. At the Fairview site, grid north is a magnetic direction of about ...

Context 2

... circular fortifications to the west of the chimney are also still visible at the site. I did not map these earthworks during my survey, although one line was roughly along N100; these earthworks might further refine the location of the Fairview house. The well for the house remains from the Civil War period; it is covered by wooden boards and is located in Figures 30 and 31. Figure 30 is a map of features that are visible in the area of the geophysical survey. Two houses are plotted in the USGS map of Figure 1, and their locations are approximated in Figure 30; neither house is still standing. Figure 31 shows the area of this geophysical survey. The geophysical grid that was set up was parallel to the paved road that goes south from highway 3. The southwest corner of the paved road was defined as point E140 N100 in the geophysical grid. The four wooden stakes that were left at the four corners of the geophysical grid are indicated with squares in Figure 31; like the Bullock grid, these stakes extend only a inch above the surface. Blue paint stripes were put on horizontal branches of conifers along line N0 at both the east and west sides of the grid; a blue stripe was also put on the paved road along line N350. At the Fairview site, grid north is a magnetic direction of about ...

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... circular fortifications to the west of the chimney are also still visible at the site. I did not map these earthworks during my survey, although one line was roughly along N100; these earthworks might further refine the location of the Fairview house. The well for the house remains from the Civil War period; it is covered by wooden boards and is located in Figures 30 and 31. Figure 30 is a map of features that are visible in the area of the geophysical survey. Two houses are plotted in the USGS map of Figure 1, and their locations are approximated in Figure 30; neither house is still standing. Figure 31 shows the area of this geophysical survey. The geophysical grid that was set up was parallel to the paved road that goes south from highway 3. The southwest corner of the paved road was defined as point E140 N100 in the geophysical grid. The four wooden stakes that were left at the four corners of the geophysical grid are indicated with squares in Figure 31; like the Bullock grid, these stakes extend only a inch above the surface. Blue paint stripes were put on horizontal branches of conifers along line N0 at both the east and west sides of the grid; a blue stripe was also put on the paved road along line N350. At the Fairview site, grid north is a magnetic direction of about ...

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... circular fortifications to the west of the chimney are also still visible at the site. I did not map these earthworks during my survey, although one line was roughly along N100; these earthworks might further refine the location of the Fairview house. The well for the house remains from the Civil War period; it is covered by wooden boards and is located in Figures 30 and 31. Figure 30 is a map of features that are visible in the area of the geophysical survey. Two houses are plotted in the USGS map of Figure 1, and their locations are approximated in Figure 30; neither house is still standing. Figure 31 shows the area of this geophysical survey. The geophysical grid that was set up was parallel to the paved road that goes south from highway 3. The southwest corner of the paved road was defined as point E140 N100 in the geophysical grid. The four wooden stakes that were left at the four corners of the geophysical grid are indicated with squares in Figure 31; like the Bullock grid, these stakes extend only a inch above the surface. Blue paint stripes were put on horizontal branches of conifers along line N0 at both the east and west sides of the grid; a blue stripe was also put on the paved road along line N350. At the Fairview site, grid north is a magnetic direction of about ...

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... land surface dips down toward grid north; the total relief is perhaps 10 ft. Broken lines in Figure 31 approximate the locations of changes in slope; grid dimensions were not corrected for this slope. Several gopher holes are visible at the southeast corner of the grid; one of these has freshly-excavated soil. There are ruts in the soil that go along grid north-south lines; these are about a foot deep and may have been caused by mowing ...

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... bedrock is not visible in this area, five stones were seen during the course of this survey. These are plotted in Figure 31. Four of the stones are rather flat on top and are rust-stained; they are like sandstone and they are firmly set in the soil. The locations were (in decreasing order of size): E32 N69.5, E30 N68, E29.5 N89, and E108.5 N187. In addition, a fifth small stone appears to be massive quartz; it is at E108 N209.5 and it is loose in the soil. Several years ago, a fragment of a brick was found by a park employee during an excavation; this find was in the vicinity of W20 ...

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... radar was a model SIR System-7, manufactured by Geophysical Survey Systems. A test was made of two different antennas on the first profile at the Bullock site; the results are shown in Figure 18. The profile from the lower frequency antenna (180 MHz, model 3105) is shown at the top of the page; the same span was redone with the higher frequency antenna (315 MHz, model 3102), and this is illustrated at the bottom of Figure 18. The high frequency antenna defines features at a depth of 1 -3 ft much more clearly, and this was the antenna that was applied to all of the following profiles. Figure 18 shows that the traversing speed of the high frequency antenna is slower than the low frequency antenna; this allows the smaller features that can be detected by the high frequency antenna to be clearly resolved. The traverse speed with the high frequency antenna was 12 s per 5 ft; this was controlled with a metronome. The radar was set to make 12.8 depth scans per second; these depth scans are the vertical lines on the profiles. The profile printer made four separate radar profiles, so that there were 7.7 scans per foot of distance along each profile; that is, the scan lines on the profiles shown here are separated by about 1.5 inches on the ground. In fact, the scan lines are so close together that they cannot be ...

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... radar was a model SIR System-7, manufactured by Geophysical Survey Systems. A test was made of two different antennas on the first profile at the Bullock site; the results are shown in Figure 18. The profile from the lower frequency antenna (180 MHz, model 3105) is shown at the top of the page; the same span was redone with the higher frequency antenna (315 MHz, model 3102), and this is illustrated at the bottom of Figure 18. The high frequency antenna defines features at a depth of 1 -3 ft much more clearly, and this was the antenna that was applied to all of the following profiles. Figure 18 shows that the traversing speed of the high frequency antenna is slower than the low frequency antenna; this allows the smaller features that can be detected by the high frequency antenna to be clearly resolved. The traverse speed with the high frequency antenna was 12 s per 5 ft; this was controlled with a metronome. The radar was set to make 12.8 depth scans per second; these depth scans are the vertical lines on the profiles. The profile printer made four separate radar profiles, so that there were 7.7 scans per foot of distance along each profile; that is, the scan lines on the profiles shown here are separated by about 1.5 inches on the ground. In fact, the scan lines are so close together that they cannot be ...

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... radar was a model SIR System-7, manufactured by Geophysical Survey Systems. A test was made of two different antennas on the first profile at the Bullock site; the results are shown in Figure 18. The profile from the lower frequency antenna (180 MHz, model 3105) is shown at the top of the page; the same span was redone with the higher frequency antenna (315 MHz, model 3102), and this is illustrated at the bottom of Figure 18. The high frequency antenna defines features at a depth of 1 -3 ft much more clearly, and this was the antenna that was applied to all of the following profiles. Figure 18 shows that the traversing speed of the high frequency antenna is slower than the low frequency antenna; this allows the smaller features that can be detected by the high frequency antenna to be clearly resolved. The traverse speed with the high frequency antenna was 12 s per 5 ft; this was controlled with a metronome. The radar was set to make 12.8 depth scans per second; these depth scans are the vertical lines on the profiles. The profile printer made four separate radar profiles, so that there were 7.7 scans per foot of distance along each profile; that is, the scan lines on the profiles shown here are separated by about 1.5 inches on the ground. In fact, the scan lines are so close together that they cannot be ...

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... results of these surveys, the earlier geophysical surveys, and the excavations are plotted in Figure 1. The earlier radar survey found an irregular surface at a depth of about 1 ft; this is outlined with an oval containing zig-zag lines near the middle of Figure 1. The main archaeological excavation of Clarence Geier, marked with a hachured rectangle, located the stone base of a chimney and hearth. Probing with a steel T-bar allowed the dimensions of that hearth to be determined, and it is marked with a rectangle, about 7 ft ...

Context 11

... results of these surveys, the earlier geophysical surveys, and the excavations are plotted in Figure 1. The earlier radar survey found an irregular surface at a depth of about 1 ft; this is outlined with an oval containing zig-zag lines near the middle of Figure 1. The main archaeological excavation of Clarence Geier, marked with a hachured rectangle, located the stone base of a chimney and hearth. Probing with a steel T-bar allowed the dimensions of that hearth to be determined, and it is marked with a rectangle, about 7 ft ...

Context 12

... geophysical detection of these objects is seen in the conductivity map of Figure 4 by the small-area high conductivity patterns at E38 N67 and E39 N70. Profiles across these anomalies are plotted in Figure 11. It is impossible that these anomalies are errors in the measurements. It is not possible to say much about the size of these objects; while it is impossible that they could be as small as about 3 inches in size, they are unlikely to be larger than 2 ft in size. Their depth could be more than 2 ft, but is probably less than 3 ft. While there is a possibility that the features could be caused by another very conductive material such as ash or mineralized stone, these materials are unlikely to cause as strong an anomaly as was detected here. There is no indication that these objects were detected by the metal detector survey that was done during the archaeological excavation; however, metallic objects at a depth of 2 ft or more can be missed by many metal ...

Context 13

... current conductivity survey found that it is likely that there are two metallic objects below the hearth; these objects may be at a depth of 2 ft underground. Their locations are indicated in Figure 1 by two triangles within the hearth rectangle; one of the objects is within the feature found by the ...

Context 14

... drift in Figures 17 and 18 was averaged and the result is plotted in Figure 19. This suggests that the recorded readings were too low near line E80 (measured at about 10:36 am) and were too high near line E30 (measured at about 12:27 pm). On 12 July 1991, I tested for thermal effects on my EM38 and found that a temperature rise of about 3° Celsius would cause the apparent conductivity reading to increase by 1 mS/m. This agrees with Figure 19. The instrument may have cooled down when it was taken out of my car, causing the drop in the measurements near E80. As the survey progressed, the lines of traverse were no longer shaded by the nearby trees; the instrument warmed in the sunshine and the readings increased to more than their correct values. As I approached the western side of the grid, the instrument was probably again shaded by the nearby trees, and the sun was lower, and so the instrument cooled ...

Context 15

... drift in Figures 17 and 18 was averaged and the result is plotted in Figure 19. This suggests that the recorded readings were too low near line E80 (measured at about 10:36 am) and were too high near line E30 (measured at about 12:27 pm). On 12 July 1991, I tested for thermal effects on my EM38 and found that a temperature rise of about 3° Celsius would cause the apparent conductivity reading to increase by 1 mS/m. This agrees with Figure 19. The instrument may have cooled down when it was taken out of my car, causing the drop in the measurements near E80. As the survey progressed, the lines of traverse were no longer shaded by the nearby trees; the instrument warmed in the sunshine and the readings increased to more than their correct values. As I approached the western side of the grid, the instrument was probably again shaded by the nearby trees, and the sun was lower, and so the instrument cooled ...

Context 16

... drift in Figures 17 and 18 was averaged and the result is plotted in Figure 19. This suggests that the recorded readings were too low near line E80 (measured at about 10:36 am) and were too high near line E30 (measured at about 12:27 pm). On 12 July 1991, I tested for thermal effects on my EM38 and found that a temperature rise of about 3° Celsius would cause the apparent conductivity reading to increase by 1 mS/m. This agrees with Figure 19. The instrument may have cooled down when it was taken out of my car, causing the drop in the measurements near E80. As the survey progressed, the lines of traverse were no longer shaded by the nearby trees; the instrument warmed in the sunshine and the readings increased to more than their correct values. As I approached the western side of the grid, the instrument was probably again shaded by the nearby trees, and the sun was lower, and so the instrument cooled ...

Context 17

... conductivity surveys were done on 14 February 2002. At the start of field work, there was some frost on the grass, but it is unlikely that there was any significant freezing of the soil. The sky was completely clear during the day; temperatures started cold, but changed to warm at midday. between the repeated measurements in Figure 17 and 18 therefore reveal a drift that caused the readings to change by over 1 mS/m. With the low conductivity of the earth, this drift needs a ...

Context 18

... radar survey at the Bullock site clearly located a drain field; Figures 6 and 7 show it as a four-pronged feature. The bottoms of the trenches of this drain field were detected most distinctly; perhaps there is a sharp material contrast there. The trenches were found to be about 2 ft wide and 1.5 -2 ft deep. Pipes may have been traced in some parts of the trenches. The north-south distribution line for the drain field was located and perhaps the entrance line was also found. The trenches of the drain field follow curved lines; each of these appears to be a line of constant elevation. The trench bottoms were deeper on the north side; this might be a result of their excavation to a horizontal surface. No significant archaeological features were detected within the area of the drain field; while the trenches for that system could have destroyed earlier features, no features were visible between the trenches. Several other underground pipes or wires were traced also. None these utility lines nor the drain field have iron pipes, for none were detected by the magnetic survey. The utility lines must therefore be copper wires or plastic pipes; ceramic pipes are also possible. The lines in Figures 6 and 7 show the paths of these utilities. Three go parallel to the woods on the south and evidently went to a house that was at the southwest end of the clearing; see Figure 4. During my survey, I noted a multi-conductor telephone cable sticking out of the soil. While I did not locate this, it was probably near E230 N20, where the three utility lines appear to end. Short lines at the right side of Figure 7 show possible continuations of these utilities. The utility line that goes toward the southeast corner of the map is probably directed toward a house that formerly stood there; this is shown in Figure 4. Most of the features that were detected by these surveys were in the southeast quadrant of the area; there were few features that were detected in the northwest. No features were detected within the possible shallow mound near E50 N80. Little was found near a scatter of brick at the surface (E215 S5). Figure 12 shows that there may be two concentrations of iron or other magnetic material near that brick. Brick is visible in a depression at E225 N30 ( Figure 5); the magnetic survey may have detected a minor feature near the depression. The radar survey detected a feature near E165 N95 at a depth of 6 ft; while this is most likely a natural feature, it could also be a well or privy. The magnetic survey suggested that there may be a large magnetic mass south of the area of survey; its estimated location is marked with a broken line rectangle in Figure 12 at E185 S40. A single line of magnetic measurements was made to the west from the main survey rectangle; the findings are in Figure 27 and do not reveal anything ...

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... radar survey at the Bullock site clearly located a drain field; Figures 6 and 7 show it as a four-pronged feature. The bottoms of the trenches of this drain field were detected most distinctly; perhaps there is a sharp material contrast there. The trenches were found to be about 2 ft wide and 1.5 -2 ft deep. Pipes may have been traced in some parts of the trenches. The north-south distribution line for the drain field was located and perhaps the entrance line was also found. The trenches of the drain field follow curved lines; each of these appears to be a line of constant elevation. The trench bottoms were deeper on the north side; this might be a result of their excavation to a horizontal surface. No significant archaeological features were detected within the area of the drain field; while the trenches for that system could have destroyed earlier features, no features were visible between the trenches. Several other underground pipes or wires were traced also. None these utility lines nor the drain field have iron pipes, for none were detected by the magnetic survey. The utility lines must therefore be copper wires or plastic pipes; ceramic pipes are also possible. The lines in Figures 6 and 7 show the paths of these utilities. Three go parallel to the woods on the south and evidently went to a house that was at the southwest end of the clearing; see Figure 4. During my survey, I noted a multi-conductor telephone cable sticking out of the soil. While I did not locate this, it was probably near E230 N20, where the three utility lines appear to end. Short lines at the right side of Figure 7 show possible continuations of these utilities. The utility line that goes toward the southeast corner of the map is probably directed toward a house that formerly stood there; this is shown in Figure 4. Most of the features that were detected by these surveys were in the southeast quadrant of the area; there were few features that were detected in the northwest. No features were detected within the possible shallow mound near E50 N80. Little was found near a scatter of brick at the surface (E215 S5). Figure 12 shows that there may be two concentrations of iron or other magnetic material near that brick. Brick is visible in a depression at E225 N30 ( Figure 5); the magnetic survey may have detected a minor feature near the depression. The radar survey detected a feature near E165 N95 at a depth of 6 ft; while this is most likely a natural feature, it could also be a well or privy. The magnetic survey suggested that there may be a large magnetic mass south of the area of survey; its estimated location is marked with a broken line rectangle in Figure 12 at E185 S40. A single line of magnetic measurements was made to the west from the main survey rectangle; the findings are in Figure 27 and do not reveal anything ...

Context 20

... smooth curve approximates the drift plotted in Figure 19, and this allowed an easy correction of the EM38 conductivity map. The corrected map of Figure 4 shows a contour line along the north side of the west edge that outlines a band of low readings. This band is also seen by the lows at the west edge of Figure 3. It is possible that uncorrected thermal drift remains in the data; the maximum amplitude of the remaining error must be less than 0.4 mS/m. The EM31 is much less affected by thermal drift, and no tests were made for the effect. While the instrument had enough time to reach the ambient temperature before the start of the survey, the north-south trending contour lines on the west side of Figure 6 suggest that there may have been a thermal drift of that instrument also. About seven of the original measurements from the EM31 were found to have an error, revealed by isolated points where the reading was unusually high or low. It is possible that these errors were caused by noise interference (an intermittent connection or wire can also cause this). These errors were found only on lines E15 and E45; the wrong readings have been replaced by the average of the four adjacent readings in Figure ...

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... magnetic field of these dipoles and also the four rectangular prisms that were modeled separately was calculated, and the result is mapped in Figure 14. Rectangles locate the prismatic boxes, and asterisks locate the dipoles. This calculated field was subtracted from the measurements, and Figure 15 shows what remained. Strong anomalies near E170 N30 indicate that there are clusters of magnetic material there that have not been modeled by the simple rectangular box. Many of the other anomalies that remain are too complicated to model easily; these are likely to have a natural, geological origin and their locations are approximated. Circular symbols and solid line rectangles in the interpretation map of Figure 12 show the anomalies that have been ...

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... magnetic field of these dipoles and also the four rectangular prisms that were modeled separately was calculated, and the result is mapped in Figure 14. Rectangles locate the prismatic boxes, and asterisks locate the dipoles. This calculated field was subtracted from the measurements, and Figure 15 shows what remained. Strong anomalies near E170 N30 indicate that there are clusters of magnetic material there that have not been modeled by the simple rectangular box. Many of the other anomalies that remain are too complicated to model easily; these are likely to have a natural, geological origin and their locations are approximated. Circular symbols and solid line rectangles in the interpretation map of Figure 12 show the anomalies that have been ...

Context 23

... magnetic field of these dipoles and also the four rectangular prisms that were modeled separately was calculated, and the result is mapped in Figure 14. Rectangles locate the prismatic boxes, and asterisks locate the dipoles. This calculated field was subtracted from the measurements, and Figure 15 shows what remained. Strong anomalies near E170 N30 indicate that there are clusters of magnetic material there that have not been modeled by the simple rectangular box. Many of the other anomalies that remain are too complicated to model easily; these are likely to have a natural, geological origin and their locations are approximated. Circular symbols and solid line rectangles in the interpretation map of Figure 12 show the anomalies that have been ...

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... are only two significant small-area anomalies in the EM38 conductivity map (Figure 4) that are highs; these are located in the middle of the broad high conductivity area, and near E38 N70. While strong, small-area lows are almost always caused by metallic objects that are shallower than 1.5 ft underground, small-area highs are usually caused by deeper metallic objects. During a large survey at the Petersburg battlefield, my measurements showed that it was possible to estimate the depth of the objects causing these highs with a simple procedure: The width of the anomaly at half its peak amplitude is a good approximation of the depth of the object below the EM38. The profiles of these two conductivity highs are plotted in Figure 11; the anomaly width at N67 is 3.3 ft while the width of the anomaly at N70 is 2.7 ft. Since the height of the EM38 was a little less than 1 ft, the depth of these objects may be about 2 ...

Context 25

... smoothed conductivity map of Figure 2 allows the small-area anomalies in the original EM38 measurements to be isolated. This was done by simply subtracting the map in Figure 2 from Figure 4. In Figure 5, only the low readings are plotted; the range of the contour lines is -10 to -2 mS/m. The central points of these anomalies are plotted in Figure 1 with X ...

Context 26

... radar revealed a moderately flat (but lumpy) feature at the south end of the area of survey; it is located in Figures 32 and 40 at E40 N70. It is illustrated by the two radar profiles in Figure 41. This feature is about 10 ft long east-west and 7 ft wide north-south. As Figure 40 indicates, it is close to, but not coincident with, several stones. These stones appear to be similar to sandstone; they have a slightly rounded and flat upper surface. While there is a faint radar echo near one stone, the distinct radar echo is quite separate from these stones. In some soils, a layer of large stones could cause the radar echo that was detected near E40 N70; in the rather sandy soil of this site, it is unlikely that stones will be detected. Instead, the radar echo appears to be caused by another type of pavement that has an upper surface that is not quite ...

Context 27

... magnetic analysis of the Bullock site was done almost entirely with the measurements that were made with the lower sensor. As a test, seven significant magnetic anomalies on the map from the upper sensor were also modeled; this map is illustrated as Figure 16. The dipolar parameters determined by the program MdMagC were very close for the two elevations. The agreement was particularly good if the anomaly was completely included in the magnetic map and if the anomaly was separated from nearby ...

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... the survey of the Bullock site on May 2 and 3, a total of 8833 spatial measurements were made to create the magnetic map in Figure 13. The survey of the Fairview site was done on May 4 and 5, and the 7050 measurements that were measured there are plotted in Figure 37. These plots show the measurements at the lower sensor; the data from the upper sensor is plotted in Figures 16 and ...

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... the survey of the Bullock site on May 2 and 3, a total of 8833 spatial measurements were made to create the magnetic map in Figure 13. The survey of the Fairview site was done on May 4 and 5, and the 7050 measurements that were measured there are plotted in Figure 37. These plots show the measurements at the lower sensor; the data from the upper sensor is plotted in Figures 16 and ...

Context 30

... depths listed in Figure 12 have been determined from the interpretation programs. Some of the elevations listed in Figure 23 are positive, which says that the dipoles were above the ground. This is impossible, and it just means that there was an error in the analysis or the measurements; all of these depths are listed as zero in Figure 12. The estimates of mass in Figure 12 assume that the relative magnetic moment of steel is 0.3 Am 2 ...

Context 31

... depths listed in Figure 12 have been determined from the interpretation programs. Some of the elevations listed in Figure 23 are positive, which says that the dipoles were above the ground. This is impossible, and it just means that there was an error in the analysis or the measurements; all of these depths are listed as zero in Figure 12. The estimates of mass in Figure 12 assume that the relative magnetic moment of steel is 0.3 Am 2 ...

Context 32

... depths listed in Figure 12 have been determined from the interpretation programs. Some of the elevations listed in Figure 23 are positive, which says that the dipoles were above the ground. This is impossible, and it just means that there was an error in the analysis or the measurements; all of these depths are listed as zero in Figure 12. The estimates of mass in Figure 12 assume that the relative magnetic moment of steel is 0.3 Am 2 ...

Context 33

... magnetic traverses went in opposite directions on alternate lines; that is, they were bidirectional. At the Bullock site, all North lines that are multiples of 5 were made with traverses going toward the west. At the Fairview site, all East lines that are multiples of 5 had traverses toward the north. The first magnetic measurements at Fairview were made into the woods west of line E0; each of these lines was made with measurements going toward the west. During my measurement traverses on each line, I walked past the measurement point on the rope and stopped when the backs of my heels were 1 ft past the correct point. This put the sensors over the measurement point. This was tested by making measurements on some lines with traverses in both directions. Figures 61 and 62 show that the locational error was small. Slight undulations on the magnetic maps in areas with a high lateral gradient also reveal these small errors. Undulations on the contours in low gradient areas reveal heading errors caused by iron moving with the sensors; this error was also ...

Context 34

... of the Figures 31 -36 in the geophysical report has a scale bar that is erroneous. It is marked as a 50 ft length, but is actually 40 ft long. The correct scale is shown in Figure ...

Context 35

... radar echoes were found to fall into three main categories: Rather flat (horizontal or dipping interface), moderately complex (irregular or undulating interfaces), and small-area (compact object). Figure 50 shows the symbols that marked the different types of echoes. In Figure 7, there are a pair of triangles along line E140; at these points, it is likely that the same objects were detected by the radar profiles going toward the east and toward the north. The estimated depths from the perpendicular profiles differed by 0.7 ft, and this is an indication of likely error in the other estimates of depth. The scatter of the velocity estimates in Figure 52 also suggests the errors in depth; the standard deviation of these estimates was 18 per cent of the average depth. Figure 51 shows that many more echoes were detected at the Bullock site relative to Fairview. The frequency of echoes at the Bullock site is mostly due to the density of modern features there. At the Bullock site, the distance from the start of one echo to the start of the next was an average of 13.4 ft; at the Fairview site, this distance was 40.3 ...

Context 36

... high voltage power lines to the east of the Bullock site appear to have caused electrical or magnetic interference to the magnetometer to a distance of about 100 ft from the wires. This effect was tested by making repeated measurements while I stood stationary at three points. Figure 57 shows the greater noise near the power line; the reading that is plotted as an anomaly of zero actually goes to -42.7 nT. The errors are not single measurements; instead, there are several readings in a row that are abnormally low. There was an interval of about 1.3 s between these measurements. Similar errors were found in the spatial measurements. In Figure 16, these errors have been corrected, but their locations are marked with asterisks; there are 33 of them. Most concentrate in the northeast corner, closest to the power line; see Figure 4. There are also many errors along line N67.5; this was the first line surveyed on May 3, and for some reason there was more interference from the power line at that time in the early morning. The errors were easy to spot in the initial magnetic map, for each one was abnormally low at one point (one point because of the greater time between measurements). Typically, the reading was about 20 nT too low, but this could be as much as 120 nT too low. Almost all (31) of the errors were found in the measurement of the upper sensor; the reason for this is not known, but it implies that the upper sensor is more susceptible to this noise. Two errors were found at the lower sensor, but these were a different type. At points E272.5 N100 and E295 N77.5 the gradient of the magnetic field was so large that the instrument could not get a reading. For these two points, and the 31 others, the correct values were estimated by interpolating from the adjacent four ...

Context 37

... results of this survey are illustrated in several figures. At the Bullock site, Figure 6 has the important findings; Figure 7 has more detail about the results of the radar survey and Figure 12 has an interpretation of the magnetic map. The results from the Fairview site are described in Figures 32 and ...

Context 38

... similar conductive ring was found around the Bullock house cellar, but that site is complicated by the nearby drain field. It appears that similar conductive rings have been found around the two slave quarters at Malvern Hill within the Richmond National Battlefield; therefore, this effect should be studied further. The interpretation of the radar survey. This is derived from the echo maps in Figures 8, 9, and 10. The three prominent utility lines may extend to the east, where segments of buried lines were detected. Four locations are marked with small squares; it is possible that the magnetic survey located iron objects at those points also. Two small triangles indicate where echoes were detected by perpendicular radar profiles. (Figure 13) after the calculations (Figure 14) have been subtracted. This shows the magnetic objects that have not been interpreted. It also shows that some objects were more complex than the simple models of them. Figure 13 is enlarged by a factor of two here; this reveals the complex anomalies in that quadrant of the grid. Most of these anomalies may have a natural, geological origin. Most were found between a depth of 1 and 2 ft, but the maximum depth was 5.6 ft. While echoes were more frequent at the Bullock site, deeper echoes were more likely at Fairview. These curves include only those 94% of echoes which had a depth estimate. Part of the changes are due to instrument errors, and part due to electrical interference. However, part of the effect is also due to a lateral gradient at the location; this was about 16 nT/m. The variability was not much larger while pacing in place, and there is no evidence of microphonic spikes. ...

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... similar conductive ring was found around the Bullock house cellar, but that site is complicated by the nearby drain field. It appears that similar conductive rings have been found around the two slave quarters at Malvern Hill within the Richmond National Battlefield; therefore, this effect should be studied further. The interpretation of the radar survey. This is derived from the echo maps in Figures 8, 9, and 10. The three prominent utility lines may extend to the east, where segments of buried lines were detected. Four locations are marked with small squares; it is possible that the magnetic survey located iron objects at those points also. Two small triangles indicate where echoes were detected by perpendicular radar profiles. (Figure 13) after the calculations (Figure 14) have been subtracted. This shows the magnetic objects that have not been interpreted. It also shows that some objects were more complex than the simple models of them. Figure 13 is enlarged by a factor of two here; this reveals the complex anomalies in that quadrant of the grid. Most of these anomalies may have a natural, geological origin. Most were found between a depth of 1 and 2 ft, but the maximum depth was 5.6 ft. While echoes were more frequent at the Bullock site, deeper echoes were more likely at Fairview. These curves include only those 94% of echoes which had a depth estimate. Part of the changes are due to instrument errors, and part due to electrical interference. However, part of the effect is also due to a lateral gradient at the location; this was about 16 nT/m. The variability was not much larger while pacing in place, and there is no evidence of microphonic spikes. ...

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... similar conductive ring was found around the Bullock house cellar, but that site is complicated by the nearby drain field. It appears that similar conductive rings have been found around the two slave quarters at Malvern Hill within the Richmond National Battlefield; therefore, this effect should be studied further. The interpretation of the radar survey. This is derived from the echo maps in Figures 8, 9, and 10. The three prominent utility lines may extend to the east, where segments of buried lines were detected. Four locations are marked with small squares; it is possible that the magnetic survey located iron objects at those points also. Two small triangles indicate where echoes were detected by perpendicular radar profiles. (Figure 13) after the calculations (Figure 14) have been subtracted. This shows the magnetic objects that have not been interpreted. It also shows that some objects were more complex than the simple models of them. Figure 13 is enlarged by a factor of two here; this reveals the complex anomalies in that quadrant of the grid. Most of these anomalies may have a natural, geological origin. Most were found between a depth of 1 and 2 ft, but the maximum depth was 5.6 ft. While echoes were more frequent at the Bullock site, deeper echoes were more likely at Fairview. These curves include only those 94% of echoes which had a depth estimate. Part of the changes are due to instrument errors, and part due to electrical interference. However, part of the effect is also due to a lateral gradient at the location; this was about 16 nT/m. The variability was not much larger while pacing in place, and there is no evidence of microphonic spikes. ...

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... surveys located about 16 metallic objects that are at a shallow depth in the soil. It is likely that two deep metallic objects (perhaps 2 -3 ft underground) were also detected; both of these objects were in an unexcavated area beneath the hearth stone. One of these deep objects is centered within the distinctive radar anomaly that was found by the survey in 2000. These two objects are marked with triangles in Figure ...

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... surveys found that the soil has a high electrical conductivity in an area of roughly 20 by 40 ft. This conductive patch is centered on the buried base of the fireplace at Fairview. The findings of this survey are summarized in Figure ...

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... April-May 2000, I did a geophysical survey at Fairview for Robert Krick and Noel Harrison; my report is dated 11 June 2000. In July 2000, Clarence Geier (James Madison University) directed some excavations at the site; those findings are described in his report dated October 2000. The excavations located the stone base of a fireplace, marked in Figure 1 with a rectangle near E40 N70. With the information from the excavations, I prepared a follow-on report dated 21 March ...

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... map of Figure 3 reveals some areas with low conductivity near the southern end of the survey area. In principle, these patterns could be caused by an accumulation of stone or sand in the soil. Perhaps a scatter of very small metal objects, such as small bits of rusted iron, could also cause this pattern. The readings of the earlier magnetic survey are plotted in Figures 9 and 10; those maps do not reveal any patterns that correlate with any of the conductivity anomalies. It is almost certain that the magnetic anomalies are caused by natural mineralized rock below this site. Circular symbols in Figure 1 show the interpretation of some of the magnetic anomalies; the shallowest object was estimated as 2.7 ft ...

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... map of Figure 3 reveals some areas with low conductivity near the southern end of the survey area. In principle, these patterns could be caused by an accumulation of stone or sand in the soil. Perhaps a scatter of very small metal objects, such as small bits of rusted iron, could also cause this pattern. The readings of the earlier magnetic survey are plotted in Figures 9 and 10; those maps do not reveal any patterns that correlate with any of the conductivity anomalies. It is almost certain that the magnetic anomalies are caused by natural mineralized rock below this site. Circular symbols in Figure 1 show the interpretation of some of the magnetic anomalies; the shallowest object was estimated as 2.7 ft ...

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... radar profile that reveals this feature is at the upper side of Figure 19; it is located at N30 there. Part of this feature is also shown in the lower profile, at N35. The magnetic character of the feature is shown in Figure 13, and its conductive character is revealed in the profiles of Figures 28 and ...

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... radar profile that reveals this feature is at the upper side of Figure 19; it is located at N30 there. Part of this feature is also shown in the lower profile, at N35. The magnetic character of the feature is shown in Figure 13, and its conductive character is revealed in the profiles of Figures 28 and ...

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... some time since the excavations were made, the Park Service has placed four plastic posts in the soil; these form an approximate rectangle and they are located with small squares in Figure 1. The posts are solid brown plastic, 0.5 ft square, and they extend to a height of about 2.5 ft above the surface. Plastic is a good material for marker posts, since it is completely invisible to any type of geophysical ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... is likely (but not certain) that the conductivity survey has detected a pair of metallic objects below the hearth. Since these objects were not found by the metal detector survey that was done by the archaeological crew, it is unlikely that they will be detected by an illegal artifact hunter. figure; the conductive area is marked with a curving solid line. This geophysical survey also found that there may be a pair of metallic objects below the hearth and at a depth of 2 -3 ft; these objects are marked with triangles. The original measurements of shallow conductivity. The high conductivity area can be seen only as a faint and irregular oval contour line. The small-area irregularities in this map are caused by electrical noise, metallic objects, and other small changes in the soil. Metallic objects that are at a shallow depth cause low readings that are extended along north-south ovals for a distance of 3 ft; these typically show a dumbbell pattern. i Figure 5: The small-area conductive lows. These lows are all probably caused by metallic objects that are less than 1.5 ft underground. The objects are located at the middle of each elongated pattern, and they are mapped with X's in Figure 1. While metal is an excellent conductor, metal causes the reading of apparent conductivity to be very low or negative. The most detailed map of deep conductivity. This shows the original measurements with the Geonics EM31, and it reveals that there are a pair of high conductivity peaks near the hearth. Electrical noise and irregularities in the soil cause the many small-area patterns in this map. The conductivity is lower than with the EM38 because low conductivity bedrock is detected by this instrument. Note the cluster of echoes near E40 N70; these were caused by some features at the hearth, and which are at a depth of over 1 ft. Circular symbols locate echoes from small objects (circle-dot means most distinct; circle means clear; dot means faint). Undulating lines indicate irregular strata, a straight line marks a planar interface, and asterisks locate reverberations of the pulse. Figure 39 from the earlier report. The magnetic sensor was at a height of 6.7 ft for these measurements. At this height, only very magnetic features are detected, and all of the patterns in this map are probably caused by the mineralization of bedrock. Figure 10: Another magnetic map. The magnetic sensor was only at a height of 1.7 ft for these measurements, and this allowed small and faint objects to be detected. However, almost all of these patterns are caused by natural, geological effects of magnetic stone. The measurement spacing was 2.5 ft. Contours are drawn in the range of -200 to 200 nT; abrupt clearings indicate higher or lower values. Figure 11, there are also two conductivity peaks near the middle, but the peaks in this figure are not caused by metallic objects. The northern peak, near N70 is located at the hearth; the southern peak, near N55, has another, but unknown, cause. These two peaks are also revealed in Figure 7. Interference to the EM31. While it is smaller than the noise detected by the EM38, the conductivity readings from the EM31 were also lower. This means that there was a not a lot of difference in the noise detected by the EM38 and EM31 as a fraction of the measurement. Note that fewer measurements were made for these tests as compared to Figure 13. The repeatability of the EM31 measurements. The anomalies that are wide or have a high amplitude repeat moderately well. The differences between these measurements are almost entirely due to electrical interference detected by the EM31 instrument. While there may also be a longitudinal offset error between the measurements, this cannot be reliably determined on this line. Figure 17: The thermal drift of the EM38. It is revealed by the offset between these two curves. The solid line shows the measurements on line N0 that were made during the main survey (this required about four hours); the dashed line shows a resurvey of line N0 that was later done in only two minutes. Figure 18: Another test of thermal drift of the EM38. This check was done at the north end of the grid, and it reveals the same differences as those seen in Figure 17. This drift is caused by the heating and cooling of the electrical components in the EM38 as the instrument is warmed by the sun or cooled in the shade. Figure 19: The average thermal drift of the EM38. The differences that are plotted in Figures 17 and 18 are averaged here. The broken line shows a third-degree polynomial that approximates the drift, and its equation is listed in the figure. The north-south columns of measurements were corrected for drift by subtracting a constant from each column equal to the error shown ...

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... tall grass during this survey caused little difficulty, although positional locations may be slightly less accurate (by perhaps a foot). There was no trace of the former excavations, and the stones that were visible before could not be seen in the tall grass; the locations of those three stones are indicated in Figure 1 with filled ...

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... that the brick at the Bullock site has properties similar to the brick at Malvern Hill (Richmond National Battlefield), the magnetic properties of the brick can be set at 2.4 Am^2/kg for the remanent moment and 0.25 Am^2/kg for the induced moment. Assuming that the mass of a whole brick is 3 kg and 25 randomly-oriented bricks are in a compact mass, the total magnetic moment of the mass would be 54.75 Am^2 (= 25 * mi + sqr(25) * mr). If the central depth of this mass was 1.5 ft, and the parameters of the magnetic measurement were those of the field survey, the peak magnetic anomaly can be calculated and it would be about 5.3 nT. Since the contour level of the magnetic map ( Figure 13) is 10 nT, the small anomaly from brick would almost always be ...

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... EM31 conductivity map of Figure 7 does reveal a pair of highs. One of these is centered on the hearth; however, the other is 15 ft to the south and this southern anomaly is marked in Figure 1 with a dot-dot-dash line. While this EM31 pattern is not symmetrical with either the hearth or the depression (making it interesting), it is also somewhat less reliable than the conductivity patterns from the shallower-exploring ...

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... of the frequency of cars and trucks on highway 610 at the Bullock site, it was not possible to stop the magnetic survey when a heavy vehicle was passing; at the closest point, the highway is 100 ft distant from the survey area. At this minimum distance, a typical car could cause a magnetic low of -2 nT; it is possible that some of the erroneous readings near the power line could also be due to large trucks that were passing. At the northern side of the Bullock grid, Bullock road is about 60 ft distant and passing cars could cause an anomaly of -8 nT. The effects of vehicles on this road is readily seen in the magnetic maps of Figures 13 and 16 by horizontal stripes where the reading is low. One is on line N142.5 near E250. Two are on line N147.5; there is a small anomaly at E140, and a large one at E50. This latter anomaly may be caused by a large vehicle or a bus that was stopped at the signs on the north side of the road; Figure 4 shows that these signs are at E25. Because of the trees on the north side of the grid, I did not notice this vehicle. The other linear anomalies were probably caused by vehicles that were either moving, or were stopped at highway 610. The two sensors of the Gem magnetometer make their measurements simultaneously, and the gradient map of Figure 17 completely eliminates the magnetic anomaly of these passing vehicles; however, there are no spatial anomalies of interest in the area where the gradient measurements improve the ...

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... of the frequency of cars and trucks on highway 610 at the Bullock site, it was not possible to stop the magnetic survey when a heavy vehicle was passing; at the closest point, the highway is 100 ft distant from the survey area. At this minimum distance, a typical car could cause a magnetic low of -2 nT; it is possible that some of the erroneous readings near the power line could also be due to large trucks that were passing. At the northern side of the Bullock grid, Bullock road is about 60 ft distant and passing cars could cause an anomaly of -8 nT. The effects of vehicles on this road is readily seen in the magnetic maps of Figures 13 and 16 by horizontal stripes where the reading is low. One is on line N142.5 near E250. Two are on line N147.5; there is a small anomaly at E140, and a large one at E50. This latter anomaly may be caused by a large vehicle or a bus that was stopped at the signs on the north side of the road; Figure 4 shows that these signs are at E25. Because of the trees on the north side of the grid, I did not notice this vehicle. The other linear anomalies were probably caused by vehicles that were either moving, or were stopped at highway 610. The two sensors of the Gem magnetometer make their measurements simultaneously, and the gradient map of Figure 17 completely eliminates the magnetic anomaly of these passing vehicles; however, there are no spatial anomalies of interest in the area where the gradient measurements improve the ...

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... quality of the magnetic survey was tested by repeating four lines, two at each site. Figures 61 through 64 show that the measurements duplicated closely. The measurements in Figure 61 were made 2.5 ft north of the guide ...

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... quality of the magnetic survey was tested by repeating four lines, two at each site. Figures 61 through 64 show that the measurements duplicated closely. The measurements in Figure 61 were made 2.5 ft north of the guide ...

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... archaeological excavations began just after a heavy rain, and there was a pool of water at the site then; a dot-dash line approximates the outline of the shallow depression that was revealed. The archaeological crew measured a topographic map of the area, and it shows that the depression is about 0.2 ft deep. The archaeological report also noted the valuable information that a soldier (Rice Bull) at the Civil War battle mentioned that the cabin was in a depression. The same report also suggests the possibility that the depression that is visible at the site may have been caused by the excavations of power machinery that removed the stone of the hearth and chimney. Figure 1 shows that the EM38 conductivity survey found that the soil has a high electrical conductivity in an area centered on the hearth, and which approximates the visible depression; this high conductivity area is bounded with a solid line. The map of the measurements in Figure 3 gives a more objective indication of the pattern of the high conductivity area; the pattern is simplified in Figure 2 to show how unusual and strong the anomaly is. Figures 2 through 4 were measured with the EM38 conductivity instrument, which detects objects that are generally less than 5 ft underground. The same area was explored with a deep-measuring instrument, the EM31, and its readings are plotted in Figures 6 and 7. Both conductivity instruments reveal the same general pattern: Unusual high conductivity in an area that is about 20 by 40 ft in size. This high conductivity may be caused by a concentration of one or more different types of soil in that area. This could be a concentration of natural silt, clay, or organic matter; it could also be a concentration of a completely cultural material such as organic refuse or ash. It is impossible to distinguish these materials with the conductivity ...

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... EM38 conductivity survey located about 15 metallic objects that are at a depth of less than 1.5 ft underground. These are marked in Figure 1 with X patterns. The large X's mean the detection was stronger, and may mean that those objects are larger than the objects marked with small x's. An oval dashed line at the bottom of Figure 1 shows where the earlier radar survey suggested that there may be a concentration of metallic objects. The conductivity survey found no metallic objects in that area. This could be due to the fact that those objects were located and removed during the metal detector survey of the archaeological crew; it is also possible that the objects that were detected by the radar were actually not ...

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... EM38 conductivity survey located about 15 metallic objects that are at a depth of less than 1.5 ft underground. These are marked in Figure 1 with X patterns. The large X's mean the detection was stronger, and may mean that those objects are larger than the objects marked with small x's. An oval dashed line at the bottom of Figure 1 shows where the earlier radar survey suggested that there may be a concentration of metallic objects. The conductivity survey found no metallic objects in that area. This could be due to the fact that those objects were located and removed during the metal detector survey of the archaeological crew; it is also possible that the objects that were detected by the radar were actually not ...

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... the magnetic map of Figure 13, there are a pair of linear and parallel magnetic anomalies near E100 N25. The magnetic measurements in this area were rotated so that the lineaments were vertical; Figure 25 shows the result (the rotation has changed the coordinates). The average cross-section in a typical span of the anomaly is plotted with the solid line in Figure 26. These measurements were approximated by a two-dimensional magnetic model in a program called MagPoly; this is based on the algorithm of Won and Bevis (Geophysics 1987, p. 232). At this site, the Earth's magnetic field has a magnitude of 53,000 nT, and an inclination of 67.1° (determined from the IGRF95 parameters). The calculated anomaly of the best model is plotted in Figure 26 with a broken line. For this calculation, it was assumed that the inclination of the total magnetization of the prisms was 37°, quite different from the actual direction of the Earth's field. The best angle for the declination of magnetization was 44° clockwise from the northerly direction of the elongated anomalies; this also differs from the current direction of the Earth's magnetic field. This difference from the direction of the Earth's field reveals that the underground feature has a strong remanent magnetization whose direction is quite different from the Earth's field at this time. The calculated field was closest for the anomaly on the west. Figure 26 shows that the calculation is not as close to the measurements for the anomaly on the east. The shift of all the measurements to more positive values means that the magnetization of the eastern feature has a steeper angle of inclination. This suggests that the two parallel features do not have the same ...

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... EM31 conductivity map of Figure 6 shows a distinct area of high conductivity at the southeast corner; this pattern was much fainter in the EM38 map. An aerial photograph made in 1975 showed that there was a vegetable garden near that corner then; this garden is roughly located in Figure 1. It is possible that the high conductivity is caused by cultivation or fertilization of that garden. During a recent conductivity survey for the NPS at the West Findings of the conductivity surveys Page ...

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... magnetic survey revealed many linear features. Thin rectangles in Figure 12 approximate their locations. An analysis of three of these (the solid line rectangles) indicated that the features are shallow. They could be only 1 -2 ft underground, and they must be less than 4 ft underground. While linear fortification trenches are expected in this area, it is almost certain that these features are natural in the soil. There are two major reasons for the interpretation of a geological origin for these features. The first is that they were undetected by the radar survey; in this soil, it would be reasonable (although not certain) that a refilled ditch would be detected by the radar. The second reason was provided by a technical analysis of the magnetic maps of these features. The features have a strong permanent magnetization, and the direction of the magnetization differs widely from feature to feature; this direction is also far from the direction of the Earth's present magnetic field. In the 19th century, there were mines for both gold and iron in this vicinity. These deposits can be found in hydrothermal veins, which can be ...

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... interpretation of the magnetic survey is given in Figure 12. It is seen that three large magnetic masses are within the dotted line rectangle that approximates the location of the 20th century house. The foundations of this house were not detected by this survey, although a planar feature was discovered within; this is at E270 N60 in Figure 6 or ...

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... major magnetic anomaly at the Bullock site was also evaluated with the Cprism program; this anomaly is located at E165 N30 on the magnetic map of Figure 13. The program found the best approximation of the measurements was provided by a rectangular box whose center was 3.9 ft underground; it is located with the rectangle shown in Figure 12. The magnetic moment of this model was 126 Am 2 ; the angle of magnetization was: I = 34.0°, D = 2.5° ...

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... major magnetic anomaly at the Bullock site was also evaluated with the Cprism program; this anomaly is located at E165 N30 on the magnetic map of Figure 13. The program found the best approximation of the measurements was provided by a rectangular box whose center was 3.9 ft underground; it is located with the rectangle shown in Figure 12. The magnetic moment of this model was 126 Am 2 ; the angle of magnetization was: I = 34.0°, D = 2.5° ...

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... linear magnetic anomalies at the Bullock site were analyzed with a different procedure. Rather than assuming that they were infinitely long (2D models), they were modeled with truncated prisms, with a program called Cprism. These prisms are rectangular boxes, and they can be rotated and scaled by the program until the measurements most closely match the calculations; the location and magnetization of the boxes are also adjusted for a best fit to the measurements. The resultant calculations from this program are plotted in Figure 14 near E100 N25, and the boxes are located in Figure 12. A similar analysis was made of the linear anomaly near E75 S30 in the magnetic map of Figure ...

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... linear magnetic anomalies at the Bullock site were analyzed with a different procedure. Rather than assuming that they were infinitely long (2D models), they were modeled with truncated prisms, with a program called Cprism. These prisms are rectangular boxes, and they can be rotated and scaled by the program until the measurements most closely match the calculations; the location and magnetization of the boxes are also adjusted for a best fit to the measurements. The resultant calculations from this program are plotted in Figure 14 near E100 N25, and the boxes are located in Figure 12. A similar analysis was made of the linear anomaly near E75 S30 in the magnetic map of Figure ...

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... linear magnetic anomalies at the Bullock site were analyzed with a different procedure. Rather than assuming that they were infinitely long (2D models), they were modeled with truncated prisms, with a program called Cprism. These prisms are rectangular boxes, and they can be rotated and scaled by the program until the measurements most closely match the calculations; the location and magnetization of the boxes are also adjusted for a best fit to the measurements. The resultant calculations from this program are plotted in Figure 14 near E100 N25, and the boxes are located in Figure 12. A similar analysis was made of the linear anomaly near E75 S30 in the magnetic map of Figure ...

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... site of the Fairview house is about two-thirds of a mile southwest of the Bullock site; see Figure 1. In 1978, Berry-Paxton drive extended to highway 3; now, it stops ...