Hammer dressed stone hatchets in the Lake Eyre Basin. (Research Reports).
Examination of 137 edge ground stone hatchets from the Lake Eyre Basin suggested that as distance from the source increases the artefacts were more intensively reduced by hammer dressing. By reducing the thickness of the hatchet with hammer dressing an acute edge angle can be maintained as resharpening ingresses towards the original thicker centre of the hatchet. I hypothesise that hammer dressing is a curation practice to extend the use-life of hatchets.
The northern regions of the Lake Eyre Basin have significantly lower percentages of hammer dressed stone hatchets compared with the southern regions (Tibbett 2000:35). I hypothesise that as distance from the source increases, acute edge angles are being enhanced by hammer dressing which reduces the thickness of the stone hatchet. Dickson (1981) suggested that there is a correlation between thickness and edge angle. My examination suggests that there is a slight negative correlation coefficient between hammer dressing and thickness and a very strong negative correlation between hammer dressing and edge angles in the Lake Eyre Basin. Shott's (1989) hypothesis that reduction and curation should vary directly appears to be supported by the statistical analysis of hatchets provenanced along the exchange route for hatchets in the Lake Eyre Basin.
Horne and Aiston (1924:34) presumed a connection between the metabasalt hatchets from Cloncurry and those found at Lake Eyre. These authors postulated the idea that Kopperamanna was the Aboriginal bartering post for stone hatchets entering the Lake Eyre region. Previously I suggested that the Leichardt-Selwyn Ranges near Mt Isa in northwest Queensland appeared to be the primary source of stone hatchets entering the Lake Eyre Basin before European contact in the 1860s (Tibbett 2000).
Based upon a metrical and petrological examination I suggested (Tibbett 2000) that the exchange route for stone hatchets in the Lake Eyre Basin was a combination of McBryde's (1997) ethnographically documented route from Mt Isa to Glenormiston and McCarthy's demarcation of the Red Ochre Route from Glenormiston southwards to Lake Eyre. McCarthy (1939a:423; 1939b:101) argued for an almost direct route in explaining the Cape York to South Australia route. Isabel McBryde (1997:10) on the basis of Aboriginal cultural landscapes outlined a different exchange route for stone hatchets entering the Lake Eyre Basin. In the northern regions of the study area this interpretation deviated significantly from the courses outlined previously by her and others (McBryde 1987, 1989; McCarthy 1939b; Roth 1897). This pathway moved southwest from Mt Isa through the pituri (Duboisia hopwoodii) growing region at Glenormiston before reaching Boulia. From Boulia southwards McBryde's (1997) exchange route followed those demarcated in previous publications (McCarthy 1939b, Roth 1897).
The archaeological evidence for hammer dressing (defined by Dickson 1981: 215) was derived from metrical and descriptive analysis of 137 edge ground stone hatchets provenanced to the exchange route between Mt Isa and Lake Eyre. Data recorded were the maximum dimensions of length and thickness and the actual measurement of hammer dressing and edge angle.
Museum records were used to provenance the stone hatchets to 1:250,000 scale topographic maps (1999, AUSLIG). When deciding which stone hatchets belonged to what arbitrary map grid the Gazetteer (1975) was consulted. The data were entered onto a computer database and a separate file was created for each map grid. A comparative analysis between the arbitrary grids was then conducted to interpret morphological changes across space.
I used a protractor to measure edge angles. I did not estimate the original edge of the stone hatchet, but recorded the edge angle present, even when the edge was worn and blunted. This methodology provided the functional (systemic edge) edge angle, rather than an estimation of the resharpening process. (Compare Dickson (1981:104) who suggested that it is possible to estimate the original position of the edge to a millimetre.
Collector bias was assessed by measuring edge angles on hatchets provenanced to Glenormiston. The median edge angle of 89 degrees for six hatchets collected by three known collectors is similar to the median of 88 degrees for hatchets collected by anonymous collectors, suggesting little selectivity in collection. Similarly, my recent study (Tibbett 2002) of 95 hatchets from Boulia also suggested collector bias is negligible.
The edge angles for the stone hatchets (Table 1) increase with distance from Mt Isa until the central latitudinal map grid of Birdsville. Further south Pandie Pandie, Gason, Kopperamanna and Lake Eyre show significantly reduced edge angles compared with the grids to their north.
In the northern regions of the Lake Eyre Basin there are lower percentages of hammer dressed stone hatchets compared with the southern portions (Table 1). In the south of the Lake Eyre Basin hammer dressing appears to effectively reduce the thickness of the stone hatchet and allows resharpening without marked increase to the edge angles. When hammer dressing is found on more than 80% of the sub-population, edge angles decrease. The latitudinal changes in edge angles from north to south in the Lake Eyre Basin (Table 1) support many of the assumptions of Shott (1989).
The peak in edge angles at Bedourie could be due to ingression towards the thicker centre of unpecked stone hatchets. The decrease in edge angles at Lake Eyre is correlated with hammer dressing. In the south of the Lake Eyre Basin hammer dressing appears to effectively reduce the thickness of the stone hatchet and allows resharpening without marked increase to the edge angles.
The Birdsville sample, with a median thickness of with 32mm has an unusually high edge angle of 92 degrees (Table 1) and appears anomalous in comparison with the other nine grids between Mt Isa and Lake Eyre. However, edge angles in the other nine areas are more clearly negatively correlated with thickness.
A correlation coefficient test was applied to the data to examine the probability that the variations did not occur by chance. The results are in Table 2. These results indicate a very strong negative relationship between hammer dressing and edge angles and a slight negative relationship between thickness and edge angles. There is a slight negative relationship between hammer dressing and thickness. Figures 1a, 1b and 1c emphasize the changing variables of thickness, hammer dressing and edge angles as distance from the source increases. It appears that edge angles are influenced by curation in the Lake Eyre Basin.
The use-wear analysis and curation hypothesis of Shott (1989) provides an explanation for the higher percentages of hammer dressing recorded as distance from the source increases (Table 1). Shott (1989:23-27) suggested that reduction and curation should vary directly, as more heavily curated tools should be more extensively reduced. This appears to be supported by the high percentages of hammer dressed hatchets in the sub-populations of shorter and thinner hatchets from the southernmost regions of the study area (Table 1). Shott's (1989) hypothesis is to some extent supported by Hodder and Lane (1982:203) who suggested that curation and the amount of re-use partly depends on availability of replacement and alternate materials.
Shott (1989:22) suggested that the relationship between cost and use-life is substantial. At about 1,000km from the source, the cost of stone hatchets in the southern parts of the Lake Eyre Basin would probably be high. An indirect method of inferring a prolonged use life of stone hatchets might be the degree of hammer dressing in a sub-population.
As distance from the source increases, hatchets decrease in length (Table 1). In addition, decreasing thickness associated with hammer dressing appears to provide a method of obtaining acute edge angles with a minimum of resharpening. The reduced thickness of the hatchet head enables resharpening to extend closer to the haft, while on unpecked hatchets the edge angle would progressively increase as the edge gradually moved towards the thicker centre of the hatchet head. Thus hammer dressing extends the use life of a hatchet by increasing the increased percentage of length used whilst maintaining an acute edge angle. An indirect method of inferring a prolonged use life of stone hatchets might be the degree of hammer dressing in a sub-population.
Dickson's (1981) hypothesis that there is some correlation between thickness of the stone hatchets and edge angle seems to be supported by Table 2. Hammer dressing or pecking appears to be a curation method to reduce the thickness of hatchets.
The northern regions of the Lake Eyre Basin have significantly lower percentages of hammer dressed stone hatchets in comparisons with the southern regions. At Bedourie and Birdsville where the percentages of hammer dressing are the lowest along the exchange route between Mt Isa and Lake Eyre, edge angles are the highest at 92 degrees. Birdsville is a slight anomaly as thickness is less than at Bedourie although this may be due to small sample size. South of these map grids the degree of hammer dressing increases with a marked decease in edge angles.
Shott's (1989) suggestion that reduction and curation should vary directly is supported. From 440km to 990km south of Mt Isa hammer dressing rises from 22% to 100% and the median edge angles decrease from 92 to 84 degrees. Hammer dressing appears to be a curation practice that prolongs the use of the hatchet.
I acknowledge the assistance of my supervisors, Shelley Greer and Peter Veth who commented on successive drafts of this paper. John Edgar, Michael Morrison and Celmara Pocock also provided advice on earlier drafts. I sincerely thank the two anonymous referees for their helpful comments in the final formatting of this report. A preliminary version of this paper appeared in my Honours thesis.
Table 1. Lake Eyre Basin: Analysis of hammer dressing, thickness and edge angles. Locations are 110km apart in a direct line. n HD% Median Median Median thickness edge length (mm) angle (mm) (deg) Mt Isa 19 30 32 86 121 The Source Urandangi 2 50 44 No 125 110km data Glenormiston 37 30 34 88 134 220km Mt Whelan 12 50 32 87 118 330km Bedourie 29 22 36 92 122 440km Birdsville 4 25 32 92 119 550km Pandie Pandie 5 80 34 82 115 660km Gason 5 100 34 85 106 770km Kopperamanna 4 80 31 83 129 880km Lake Eyre 20 100 31 84 104 990km Table 2. Correlation coefficient between hammer dressing, thickness and edge angles. Variables Result Hammer Dressing and Thickness neg. 0.19 Hammer Dressing and Edge Angle neg. 0.80 Thickness and Edge Angle neg. 0.38
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School of Anthropology, Archaeology and Sociology, James Cook University, Townsville Queensland 4811
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|Publication:||Archaeology in Oceania|
|Date:||Apr 1, 2003|
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