The Identification and Prehistoric Selection Criteria of Fire-Cracked Rock: An Example from Dust Cave, Alabama
Homsey, Lara K., Southeastern Archaeology
This paper reports on two experimental studies designed to assess how Tuscumbia limestone from northwestern Alabama responds to heating. Experimentally derived fire-cracked rock was examined petrographically in order to develop physical correlates for thermal alteration. The experimental samples were then compared to archaeological samples taken from the Late Paleoindian through Middle Archaic site of Dust Cave, Alabama, to determine whether or not the limestone found there deserves a designation as fire-cracked rock. Results suggest that Dust Cave's occupants made use of locally available Tuscumbia limestone as part of their cooking and processing technologies rather than transporting more distant Tennessee River cobbles to the site. Results further suggest that the cave's occupants preferentially selected massively bedded varieties of Tuscumbia limestone over more thinly bedded varieties due to its higher tolerance for thermal stress and overall greater resistance to degradation during use.
Fire-cracked rock (FCR) servedA an important and flexible purpose in prehistoric technologies. The archaeological and ethnographic literature is replete with examples of rock use as heating elements in roasting ovens, heat "radiators" for drying and processing food, sources of steam in sweat lodges, and boiling implements in cooking (Dering 1999; House and Smith 1975; Rapp et al. 1999; Sassaman 1993; Thorns 1989; Wandsnider 1997). Unfortunately, FCR has historically been an understudied-and arguably undervalued-artifact class compared to flaked and ground stone tools (Wilson and DeLyria 1999). And because of its shear abundance and cumbersome nature, FCR is often cursed for its space consumption rather than embraced for its interpretive potential.
As a result, the archaeological literature offers comparatively few robust discussions of the variability in FCR and only a few address the nuanced perspective that FCR research can impart to archaeologists' understanding of human behavior (Birk 1994; Hester 1991; Wilson and DeLyria 1999). Yet where such studies have been undertaken, particularly in southcentral Texas and the Pacific Northwest, they add greatly to our knowledge of prehistoric cooking and food-processing technologies (e.g., Birk 1994; Dering 1999; Hunziker 2006; Jackson 1998; Kritzer 1995; McDowell-Loudan 1983; Wendt 1988; Wilson and DeLyria 1999). For example, by studying the forms and rate of decomposition of FCR, Wilson and DeLyria (1999:87) concluded that significant quantities of labor and expertise were required to manage the raw materials necessary for large · scale camas roasting. Their experiments also allowed for the identification of stages of FCR use, from new rock, to recycled rock, to abandoned stones fractured beyond use. Other researchers such as Birk (1994) and Wendt (1988) have shown that preceramic populations had clear preferences for the rocks they chose as heating elements; understanding the selection criteria of FCR not only demonstrates that prehistoric cooks had a thorough knowledge of the performance characteristics of the rocks they used but also that stone cooking technologies may have required more foresight than initially meets the eye. As Wilson and DeLyria (1999:81) note, the "selection and management of rocks . . . were not trivial concerns for prehistoric households."
FCR is typically identified by one or more thermal alteration features, including irregular fracture surfaces, potlidding, and reddening (House and Smith 1995; Wilson and DeLyria 1999). These attributes have been well documented for igneous and metamorphic cobbles (e.g., quartzite), which frequently exhibit all three (House and Smith 1995; Rapp 1999). As such, they have become "iconic" characteristics of FCR. However, as this paper will show, sedimentary rocks such as sandstone and limestone do not necessarily display these same physical attributes (Bearden and Gallagher 1980; Rapp et al. 1999). Experimentation may perhaps be the most useful method for identifying and investigating FCR, for it has been shown that heated rocks may vary widely in appearance from region to region, depending on the raw material used (Wilson and DeLyria 1999).
This paper reports on two such experiments conducted to explore how Tuscumbia limestone responds to heating. At the archaeological site of Dust Cave, a Late Paleoindian through Middle Archaic cave site in northwest Alabama, fist-sized rocks of Tuscumbia limestone are ubiquitous. Many occur scattered throughout the cave deposits and probably originate as roof fall, but others are clearly associated with cultural activity. Indeed, limestone rocks occur in at least half of the excavated features and sometimes are smeared with charcoal or ash. Yet because they display no obvious signs of thermal alteration, they cannot be assumed to represent heating elements in primary deposition. Other interpretations that could explain their presence in features are that they were accidentally burned but not intentionally used as heating elements, or that they were simply used as "fill" by the cave's inhabitants.
To assess if the limestone at Dust Cave is indeed thermally altered, FCR was experimentally created and petrographically examined in order to develop physical correlates for thermal alteration. The experimental samples were then compared to archaeological samples from Dust Cave. This experiment was not designed to identify specific physical conditions under which thermal alteration takes place (e.g., length of time, temperature grathent, wet vs. dry heat, etc); to do so would require multiple laboratory experiments designed to hold constant as many variables as possible. Rather, this study prioritized identifying morphological changes resulting from thermal alteration of a sitespecific material. In so doing, it has successfully developed morphological correlates for thermally altered Tuscumbia limestone and allowed for the positive identification of FCR at Dust Cave. It is hoped that this paper will encourage additional experimentation to investigate how other lithic materials respond to heat, and under what conditions those changes take place. Indeed, such experimentation is vital to improving archaeologists' understanding of prehistoric technologies.
Dust Cave lies within a limestone bluff of the middle Tennessee River Valley, in northwest Alabama (Figure 1). Numerous limestone caverns, including Dust Cave, developed within the bluff, though only a few contain archaeological deposits (Collins et al. 1994). Initially sponsored by the Office of Archaeological Research (OAR) at the University of Alabama at Tuscaloosa, and later by the Archaeological Research Laboratory (ARL) at the University of Tennessee- Knoxville, excavations have been carried out at Dust Cave since 1989 under the direction of Dr. Boyce Driskell (Driskell 1996; Walker et al 2001). Over 100 m2 of cave floor have been exposed within the entrance chamber (Figure 2) (Driskell 1996). These excavations have revealed over 5 m of stratified deposits replete with exceptionally well-preserved animal and botanical remains, as well as microstratigraphy, features, and intact occupation surfaces (Sherwood et al. 2004). The earliest occupation dates to the Late Paleoindian period, from 10,650 to 9200 cal. B.C. One Early Archaic occupation follows: the Early Side Notched (10,000 to 9000 cal. B.C.). Three Middle Archaic components overlie the Early Archaic: the Kirk Corner Notched (8200 to 5800 cal. B.C.), the Eva/Morrow Mountain (6400 to 4000 cal. B.C.), and the Benton (4500 to 3600 cal. B.C.) (Sherwood et al. 2004).
Over 400 features are documented from all five components. Morphologically, they range from shallow ash and charcoal deposits overlying fired clay surfaces, to deep pit "ovens" dug into the substrate, to large superimposed hearths (Homsey 2004). Many of these features contain blocky, fractured limestone rocks, sometimes occurring as circular rings (typical of hearths) and at other times mixed in with the feature fill (typical of deeper pits). In one case, the rocks were shown to refit together (Homsey and Capo 2006). While the rocks are generally broken, giving one the impression that they are fire-cracked, they do not exhibit other characteristics traditionally attributed to FCR, making if difficult to determine if they are thermally altered. Since identifying feature function is an important goal at Dust Cave (Homsey 2004; Homsey and Capo 2006), it was therefore necessary to determine whether people intentionally used these rocks as part of their cooking technology, or if the rocks simply served as fill when the features were abandoned.
Dust Cave lies within the southern Interior Low Plateau physiographic province in the Highland Rim section of northwestern Alabama (Raymond et al. 1988). Here, horizontal Mississippian age rocks create an undulating karst plateau on either side of the Tennessee River and its floodplain. The general stratigraphy of the region consists of the Upper Mississippian Fort Payne, Tuscumbia, Pride Mountain, and Hartselle Formations (Thomas 1972) (see Figure 2). The Fort Payne Formation, which forms the base of the local sequence at Dust Cave, is composed of finely crystalline to microcrystalline siliceous limestone containing irregular nodules of dark blue-gray chert (Raymond et al. 1988). The blue-gray variety of this chert comprises over 90 percent of the Dust Cave stone tool assemblage (Johnson and Meeks 1994). Overlying the Fort Payne Formation is the Tuscumbia limestone, a generally thick-bedded fossiliferous crystalline limestone (Raymond et al. 1988). Locally thinly bedded zones occur, including the portion that Dust Cave is formed within. Regionally, the Tuscumbia limestone is overlain by the Pride Formation and the Hartselle sandstone, though neither is present at the Dust Cave locale.
Limestone from the Tuscumbia Formation comes in three varieties: (1) thinly bedded biosparite, (2) massively bedded biomicrite, and (3) weathered upland gravels (Table 1). All three varieties outcrop within 100 m of Dust Cave, though the weathered gravels must be procured from the plateau above the cave. The biosparite (sensu Folk 1962) is thinly bedded, occasionally with microbeds less than 1 cm thick (Figure 3a). It is a well-sorted, grayish brown limestone with approximately 40-60 percent allochems (i.e., fossil grains, predominately crinoids and bryozoans) (Figure 3b). Porosity is low, only about 5 percent, while spar cement holds the allochems together in a framework supported structure. The biomicrite (sensu Folk 1962) is massively bedded and blocky, often breaking at near 90-degree angles (Figure 4a). It is a moderate to poorly sorted gray limestone with approximately 30-40 percent fossil grains (crinoids, bryozoans, and brachiopods) (Figure 4b). Like the biosparite, porosity is low, approximately 5 percent, but unlike the biosparite, lime mud accounts for nearly 40 percent of the matrix, with only about 20-30 percent spar cement.
In contrast, the weathered upland gravels occur as gravel to cobble-sized pieces scattered across the karst landscape above the cave (Figure 5a). The gravels are composed of highly weathered, siliceous (20-30%) limestone and are characterized by a white color, high iron-rich residual clay content, and high porosity (greater than 30%) (Figure 5b). Fossils are abundant (40-60%) and consist of crinoids, bryozoans, solitary corals, and brachiopods. Localized lenses of this siliceous limestone form an upper lens within the portion of the Tuscumbia Formation where Dust Cave is formed. The gravels are weathering in situ from this layer; chert-rich nodules can be found inside the cave, though their poor quality precludes their use in stone tool production.
To investigate the effects of heat on Tuscumbia limestone, two fires were constructed, one an open campfire, the other a closed earth oven. The open campfire, measuring approximately 75 cm in diameter, was constructed outside in a field directly above the cave, and was used as the field school's evening campfire. This Smokey the Bear-style fire was created for two reasons. First, it replicated the numerous rock rings found at Dust Cave, which are suspected to be hearths altered postdepostionally by millennia of flooding (Homsey 2004). Second, it created a fire in which the rocks were not directly in the flames but slightly removed from the heat, assuming that the heat would be less here than in the earth oven created (see below). The fire's perimeter was defined with Tuscum- bia limestone, using approximately one-third from each of the three varieties described above. The fire was burned for several hours each evening for four days using a combination of pine (Pinus spp.) and oak (Quercus spp.) woods.
A simulated closed-basin earth oven, measuring approximately 1 m in diameter, was also constructed on the plateau above the cave, in a process similar to that described by Hunziker (2006) (Figure 6). A pit was excavated to approximately 50 cm deep; inside the pit a bonfire was built out of pine (Pinus) and oak (Quercus) woods. As the fire burned down, Tuscumbia limestone was added, again using approximately one-third of each variety. The fire was left to burn down to coals, at which time the entire oven was covered with several layers of backdirt. The oven was then left to stand until it was cool to the touch, approximately 48 hours.
Self-supporting pyrometric witness cones (i.e., potter's cones) were used to qualitatively estimate maximum temperature.1 Several cones were placed into each fire. Potter's cones are designed to melt and bend once a particular temperature (standardized in degrees Fahrenheit) is met. Three cone "grades" were used: #1 = 2800° F (1538° C), #3 = 2000° F (1093° C), and #021 = 1000° F (538° C). While the cones are not exact temperature measurements, they served as a reasonable estimate of maximum temperature. Cones were recovered from each fire by dry screening the combusted materials through 1 /4-in wire mesh.
Rocks were examined both before and after heating. Table 1 provides descriptions for each limestone variety prior to heating, while Table 2 provides descriptions for each variety subsequent to heating. Rocks were marked in permanent ink before firing; when possible, these same specimens were retrieved for analysis after firing. In many cases, however, the original rock was too degraded or broken to be found. In these cases, a substitute was randomly selected from the feature fill. Two samples of each limestone variety from each fire were studied, as well as two unheated samples from each variety, for a total of 12 samples. They were first examined macroscopically by cutting a section with a rock saw and polishing a chip for analysis under a binocular stereoscope at 2× to 4 × magnification. Chips were subsequently thin sectioned and examined petrographically under plane (PPL) and cross-polarized light (XPL) between 4× and 40× magnification. In order to standardize petrographic descriptions, all samples were classified according to the Folk (1959) classification scheme for carbonate rocks.
Table 2 summarizes the experimental results. The campfire did not get hot enough to melt even the lowest temperature cone (#021, 1000° F or 538° C). With the exception of the cherty upland gravels (which became friable, chalky, and broke along fossil inclusions), the limestone around the campfire underwent little visible alteration in the campfire. In contrast, the earth oven did melt the #021 (1000° F) cone, although it did not get hot enough to melt the #3 (2000° F) cone. Rocks from the earth oven also showed few obvious signs of alteration, although several fractured and changed color to various shades of blue, white, and bluish gray.
The following section reports on the changes in the three different varieties. Since the earth oven rocks showed the most significant alteration, the comments below are restricted to the earth oven experiment; the less altered rocks of the campfire are discussed later when comparing the experimental and archaeological samples.
With heat, the thinly bedded biosparite samples turned from gray to bluish gray on the outside; inside they turned from grayish brown to pinkish brown with occasional reddish brown veins running through it (Figure 3c). This reddening is likely due to the oxidation of iron-rich residual silts and clays in the lime mud. The fact that the thinly bedded samples reddened more than the massively bedded samples may indicate greater iron content than the massively bedded layers. Texture changes were also readily apparent: the rocks became very friable and small, sand-sized fragments spalled off (often as crinoid stem segments). In thin section, recrystalization from fine to medium spar cement was clearly evident. Fracturing occurred both at a large scale, along bedding surfaces, as well as microscopically. Angular micro-fractures generally occurred along the edges of fossils grains and along calcific cleavage surfaces (Figures 3c and 7b). Hairline fracturing and oxidation around allochems gave them a very pronounced appearance in thin section. A thin (<2 mm) oxidation layer was also noted on the outside edges (see Figure 7a). In general, thinly bedded samples showed the greatest difference between the unaltered and thermally altered samples.
The massively bedded samples also turned from light gray to bluish gray on the outside; inside less color change was noted, though some samples took on a slightly browner hue, again likely due to the oxidation of iron-rich residual silts and clays in the lime mud. The samples that cracked tended to break in angular blocks, at near 90-degree angles (see Figures 4a, 8b, 9b). Pieces could be refit together in several instances. No texture change was noticeable in hand sample, though some recrystalization of micrite to fine spar (a texture resembling poorly metamorphosed marble) was observed in thin section (see Figure 4c). Some micro-fractures were also visible in thin section, though not as pronounced as in the thinly bedded variety. Some oxidation of residual clays was noticeable under magnification; this oxidation appeared brown, and tended to enhance the outlines of fossils, especially crinoids and bryozoans (Figure 4c). Overall, the biomicrite variety showed the least change after heating.
Weathered Upland Gravels
The weathered upland gravels taken from above the cave lost nearly all of their original yellow and red coloring and turned white on both the inside and outside. Like the thinly bedded samples, pink "veins" due to oxidation of iron inclusions appeared. Occasionally, blackening occurred due to temporary reducing conditions associated with the fire. Most notably, these samples became very chalky as the heat forced the dissociation of carbon dioxide from the carbonate ions, yielding calcium oxalate (i.e., CaO, or "quick lime"). Upon heating in the earth oven, many of the less siliceous gravels began to glow bright orange and exploded violently within minutes of heating. Samples broke with very sharp and angular fractures. Another obvious macroscopic change included breakage along fossil inclusions, particularly around large brachiopod casts (see Figure 5a). Surprisingly, in contrast to the obvious macroscopic changes, in thin section it was difficult to distinguish clear thermal alteration features. Some reddening due to oxidization of residual clays was noted (Figure 5b), but not significantly more than was observed in unaltered samples. However, based on the chalky texture and extremely sharp edges of these gravels, it quickly became clear that this siliceous limestone would not have made a practical heating element, especially not in cooking.
Summary of Experimental Samples
The conventional attributes used to identify FCR include fracturing, potlidding, and intense reddening (House and Smith 1975). However, these experiments indicate that Tuscumbia limestone responds to heat differently than igneous and metamorphic materials. Significant changes are most readily observed microscopically and include micro-fracturing along fossil inclusions and calcific cleavage surfaces, recrystallized micrite, pronounced calcite and fossil grains, and the subtle oxidation of residual silts and clays.
The upland gravels and biosparite degraded noticeably after heating: The gravels exploded violently to create sharp angular edges while the biosparite became more friable-almost crumbly-with sand-sized fragments of allochems rubbing off at a light touch. In contrast, the massively bedded biomicrite samples exhibited few, in any, thermal alteration features. A subtle texture change, enhanced fossil grains, and hairline micro-fractures were most easily discerned in thin section. Moreover, while some large-scale fracturing occurred, it did so in blockier pieces than the other two varieties.
Finally, these attributes were not visible until temperatures reach greater than 1000° F (538° C).2 Many of the thermal attributes seen in rocks from the earth oven (>1000° F) were not seen in rocks from the open campfire (<1000° F), suggesting that low-temperature fires may not produce visible signs of thermal alteration. With the exception of the upland gravels, thermal alteration in the samples from around the campfire could only be recognized petrographically.
Comparison to Archaeological Samples
Samples of possible fire-cracked rock from four features (two Middle Archaic ash pits and two Late Paleoindian hearths) at Dust Cave were compared to the experimental samples in order to assess whether they had been altered by heat. In the field, both of the Archaic ash pits (Features 440 and 412, Figures 8a and 9a, respectively) contained several large blocky fragments of massively bedded biomicrite. In one case, Feature 440, several of the fragments refit together, suggesting that they were indeed fire-cracked (Figure 8b). In thin section, these rocks showed evidence for thermal alteration, most commonly in the form of micro-fractures and pronounced fossils (Figures 8c and 9c). These two features (440 and 412) have been identified elsewhere as pit hearths, most likely used to process hickory nuts for their oil (Homsey 2004; Walker et al. 2007). Oil production likely involved boiling the shelled nuts in water, a process which causes the nutmeats to sink while the nut oil floats to the top where it can be skimmed off (Hudson 1976; Sassaman 1993). Stones heated in a fire elsewhere (probably a small, open fire nearby) would have served as heating elements to boil the water. Future experimentation will focus on how rocks respond differently to dry versus wet heat. Information such as this will be crucial to determining whether nuts were processed via boiling or via a dry method such as parching.
Feature 117, a Late Paleoindian hearth, appeared in the field as a large concentration of ash with a highly burned periphery (Figure 10a). It is interpreted as a large hearth used for grilling or parching directly on the surface (Homsey 2004; Walker et al 2007). Crosscutting the southeast corner of this hearth is a shallow charcoal lens-Feature 429-which contained several stones of massively bedded biomicrite (Figure 10a). Elsewhere, Homsey (2004) identified the charcoal lens as an "accessory" fire in which boiling stones were kept ready near the fire, a feature type commonly used by modern cave-dwelling groups (Gorecki 1991). Thin sections taken of the rocks in the charcoal lens (Feature 429) appear to be thermally altered, with angular edges, breakage along calcific cleavage surfaces, and very pronounced allochems (Figure 10b). Thin sections taken of the fill in the main hearth (Feature 117) contain rocks that also look thermally altered based on the pronounced allochems and a thin (1 mm) oxidization layer on the outside edge (Figure 10c).
The fourth feature, Feature 423 (Figure 11a), appeared as a roughly circular feature approximately 1 m in diameter. It contained a dark brown (7.5YR3/4) fill lightly flecked with charcoal and its circumference was defined by a ring of both thinly bedded biosparite and massively bedded biomicrite (Figure lib). Previous study of rock rings at Dust Cave have demonstrated them to be surface hearths which have been altered postdepositionally by extensive fluvial activity (Homsey 2004; Homsey and Capo 2006; Walker et al. 2007).3 Surface hearths should not be confused with earth ovens in which rocks are used as a heating element. Instead, the Dust Cave surface hearths appear to have functioned as fires over which spits were constructed and the food roasted over the fire rather than within the fire (Homsey 2004; Walker et al. 2007). In this case the rocks most likely functioned to define the periphery of the feature and contain the fire. Petrographic examination of the rocks from the ring showed no indication of thermal alteration (Figure 11c). Based on the results of the campfire experiment, this suggests that temperatures may have been too low, the rocks too far away from the heat source, or the heat too quickly dissipated to thermally alter the rocks.
Interestingly, with the exception of the surface hearth discussed above, the limestone found in features where rock functioned as a heating element is of the massively bedded variety (Features 412, 440, and 117). This study has shown that massively bedded rock is less affected by thermal alteration than the other two varieties. It appears that it was this very quality that made it desirable as a heating element. Unlike the thinly bedded biosparite, it does not spall into gritty sandsized fragments, which would have been an undesirable byproduct in processed foods such as nut oil. However, such spalling would pose no problem in a hearth in which food was roasted over the fire rather than in it. Thus, in a surface hearth, both massive and thinly bedded varieties could be utilized without worrying about food contamination. The only variety that would have been impractical in a surface hearth would be cherty upland gravels, which explode and can hurl sharp shards in all directions; these easily could become embedded in food roasting overhead. It therefore comes as little surprise that they are not found in any type of feature, despite their ready availability around Dust Cave.
These findings mirror others which suggest that prehistoric populations had a preference for certain stone types. For example, at the Archaic period Rice Creek site in Minnesota, Wendt (1988) experimentally demonstrated that coarser-grained igneous rocks, such as granite, have a higher tolerance for thermal stress and are less prone to shatter when heated and rapidly cooled compared to finer-grained igneous rocks, such as basalt. According to Wendt, basalt traps steam, making it more susceptible to shattering even during initial use. Wendt therefore concluded that the residents of several Archaic period sites in Minnesota preferentially selected coarser- grained rocks as heating and/or cooking stones (see also Birk 1994). Similarly, massively bedded Tuscumbia limestone has a high tolerance for thermal stress and is less prone to degrade compared to thinly bedded Tuscumbia limestone. Like the Archaic residents at Rice Creek, the residents of Dust Cave also appear to have intentionally selected preferred stones for their cooking and processing activities.
At some archaeological sites FCR is easily recognized in the field by morphological characteristics such as reddening, potlidding, and fracturing. At other sites, however, FCR may show few, if any, identifying features. Dust Cave is one such site where FCR is difficult to identify in the field, and much of what we now know to be culturally created was initially interpreted as natural roof fall, feature fill, or accidentally burned rock. Fired rock at Dust Cave ranges from a bluish gray to grayish brown color-not much different than native stone. Moreover, heated Tuscumbia limestone rarely potlids and cracks may mimic natural fractures. Only petrographic analysis can illuminate the more reliable characteristics of FCR compared to unburned stone, including angular micro-fracturing along fossil and mineral surfaces, recrystalization of microcrystalline calcite, and subtle oxidation of silts and clays. Thin-section microscopy is thus a significant means by which to identify thermal alteration.
Perhaps more important is that this study illustrates that experimentation is vitally important in the development of frameworks for the analysis of FCR in archaeological contexts. At Dust Cave, comparison of experimental samples to archaeological samples not only allowed for the positive identification of FCR but also provided some insight into the selection criterion of prehistoric cooks. Although a variety of raw materials was available, such as river cobbles from the Tennessee River and weathered gravels from the upland plateau, the Late Paleoindian and Archaic occupants of Dust Cave appear to have made use of the limestone rocks they found near the cave. Moreover, based on the prevalence of massively bedded varieties in feature context, it appears that they preferentially selected this blocky, more resistant biomicrite for food processing and cooking due to its minimal alteration and degradation at high temperatures.
Thus the experiments described herein have added significantly to our understanding of the morphological variability of FCR at Dust Cave. However, recognition of the morphological changes in specific lithic materials is just the first step. It is recommended that future research additionally focus on understanding the variables underlying those morphological changes. At Dust Cave, one such experiment should focus on differentiating FCR produced by wet methods of heating, such as stone boiling, versus dry methods of heating, such as parching or pit roasting. Such knowledge will doubtless improve our understanding of, and appreciation for, prehistoric cooking technologies.
Acknowledgments. The research and archaeological field schools at Dust Cave were supported in part by grants from the National Science Foundation (Grant No. SBR-9619841), National Geographic Society (Grant No. 5023-93 and No. 5260-94), the Alabama Historical Commission Preservation Trust Fund, Tennessee Valley Authority, IBM Corporation, and the Alabama Humanities Foundation. Many thanks go to Boyce Driskell, Principal Investigator of the Dust Cave Archaeological Project, for all of his support and encouragement, and to Eddie de la Rosa, who threw himself into this experiment with much gusto. Thanks also to the Dust Cave field staff, including Sharon Freeman, Kandace Hollenbach, Scott Meeks, Meta Pike, Asa Randall, Nick Richardson, Sarah Sherwood, and Renee Walker, for their insight, suggestions, and enthusiasm; and to Joe and Nancy Copeland, who provided a home away from home to weary field school staffers. Thanks are also extended to Renee Walker, LuAnn Wandsnider, and Steve Black for providing valuable feedback which significantly improved this manuscript.
1 The experiment described was designed and carried out at the beginning of the 10-week field season. Due to our location in a backwater swamp, and the limited time frame available to us, it was decided that potters witness cones would be a reasonable substitute for a pyrometer.
2 Following a series of thermal experiments in which they heated limestone and dolomite in a Thermolyne Type 1500 furnace, Bearden and Gallagher (1980) found that samples heated to temperatures below 400° C produced only "slight changes in color and no changes in the texture" to the naked eye (p. 446). Samples heated to temperatures between 400° C and 1000° C "changed markedly," but these changes are unfortunately not identified or described. The raw data provided by Bearden and Gallagher are neither quantified nor analyzed in their two-page report and therefore do not provide comparable data to the present study.
3 Micromorphological analyses indicate that Feature 423 has been extensively postdepositionally altered by sheetwash, which removed much of the lighter ash and charcoal from the feature fill; adjacent ash and charcoal lenses are shown in Figure Ha. Petrography samples were collected from the large rocks comprising the circular ring. Smaller rocks scattered in the center of the feature were unavailable for study due to partial excavation of the feature fill prior to sampling.
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Publication information: Article title: The Identification and Prehistoric Selection Criteria of Fire-Cracked Rock: An Example from Dust Cave, Alabama. Contributors: Homsey, Lara K. - Author. Journal title: Southeastern Archaeology. Volume: 28. Issue: 1 Publication date: Summer 2009. Page number: 101+. © Southeastern Archaeological Conference Summer 2008. Provided by ProQuest LLC. All Rights Reserved.
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