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Discussion: Pre-Glacial archeological evidence at Grimshaw, the Peace River area, Alberta.
Chlachula and Leslie (1998), attempt to extend the chronology of the occupation of North America by over 11 000 years into the middle Wisconsinan by the analysis of flaked stone recovered from glacial till. I have reservations concerning the actual human origin of the artifacts and their significance to the early population of the Americas. These reservations center on the geologic context of the flaked stone and the assumption that they could only represent a humanly created assemblage. I believe there is sufficient cause to treat this assemblage as suspect, and therefore not incontrovertible evidence of early occupation.
The assemblage in question is composed of simply modified lithic material found scattered throughout the basal part of glacial till at a gravel pit near Grimshaw, Alberta (Chlachula and Leslie: 1998:873). The lithics are composed of quartzite and there is evidence of glacial transport as indicated by the presence of striae and abrasion. This is a small collection of 17 modified lithics (Chlachula and Leslie: 1998:876). The lithics were classified as simple, crudely modified choppers, scrapers and retouched flakes. The authors believe that the "regularity of flaking", "standardized tool forms ", "recurrent and technologically coherent patterns of flaking" and the "presence of similar patterns of modification on tools" associated with "undoubted human occupation" (Chlachula and Leslie: 1999:876), prove that this is a humanly created assemblage. The significance of this is that it would constitute direct evidence of Pre-Clovis occupation in North America.
The difficulty of differentiating between natural and cultural modification of lithics is well documented (Warren: 1920), (Brian and Shnurrenburger: 1985), (Mason: 1965), (Barnes: 1939), (Roebucks and Van-kolfschoten: 1995). Often this problem can be resolved by the context of the lithic assemblage in its geological setting. Another way of proving cultural origin is the presence of abundant accessory evidence such as hearths, modified bone, human remains and the presence of undoubtedly humanly created lithics in direct association with them. If nothing else is available, artifacts themselves can be used as evidence of cultural processes. These three criteria can be used to test if the lithics represent a culturally created assemblage or not. In this discussion, the author will examine the Grimshaw assemblage based on the three criteria.
The geological context of the tools is the greatest argument against a human origin for the assemblage. Glaciers are powerful modificatory agents (Brian and Shnurrenburger: 1985), and they can duplicate human flaking to a startling degree. Mason (1965) looked at the Permian tills of the Karoo series in South Africa and described several specimens as hand axes or choppers (Mason: 1965:8). As S. H. Warren noted in 1920;"The likeness between the flaking produced by nature and that produced by human agencies is sufficient to shift any burden of proof upon those who maintain the human origin of the stones: this must not be done by the careful selection of picked specimens but by careful survey of the whole group." (Warren 1920). Since glaciers can modify, clasts to look like culturally created tools, the presence of a few apparent specimens among many fractured clasts should be expected. Considering the geological context the Grimshaw lithics, these is a strong possibility that they are nothing more than glacially modified clasts that have been selected out of a sample of tens of thousands of possible candidates.
In addition, the concept that only humanly created artifacts will display non-random flaking patterns is erroneous. Natural fracture will for the most part be uncontrolled due to the randomness of the process at work but it would be unwise to assume that it cannot duplicate human efforts, especially at a simple level of technology. Thus imposing an arbitrary distinction between artifact and geofact based on the criteria of whether it looks like a tool or not, is injudicious. Figures one, two, and three all show modified flakes and a cobble that come from convincing natural contexts but show modification such as edge retouch and repeated flake removal in a specific area that could be interpreted as cultural.
The context of the artifacts at Grimshaw does not support a human derivation of the assemblage. Simple, crudely modified, core and flake tools occur in many assemblages throughout the plains (Leblanc et al: 1981) but usually with abundant accessory evidence to attest to their human origin. This evidence includes the presence of hearths features, faunal remains, lithics of undoubted human origin, and human remains. The Grimshaw assemblage does not have any accessory evidence except from a site with an equally controversial geological context (Chlachula and Le Blanc: 1996). The only reason to suspect that this is a human assemblage is the modified clasts themselves, which as has been shown above may well be the product of natural fracture.
The artifacts themselves do not offer any highly convincing proof of human derivation. They are all simple, crudely modified clasts that fall into recognized tool classifications (Chlachula: 1998:876). Some display retouch along previously flaked edges whereas others are abraded and striated which is evidence of glacial transport. They do not fall outside the range of natural fracture and could well have been produced by a glacier. It must be said that some tools are beyond natural duplication because of their complex, multistage manufacture. A glacier cannot create a Clovis point due to the three different types of reduction flaking required (hard-hammer, billet and pressure) but it could easily create a chopper, massive scraper or retouched flake, by shearing/pressure flaking, and hard hammer percussion. These would be present if the appropriate rock type, a cryptocrystalline silicate that fractures with conchoidal fracture, in this case quartzite, was abundant, as it is at the Grimshaw site (Chlachula: 1998:872)
In conclusion, the geological context, the cultural context and the artifacts themselves do not support the hypothesis that the lithics described in the paper in Chlachula and Leslie (1998) represent a humanly created assemblage. The obvious natural source for the modifications and the lack of cultural material associated with the assemblage argue against their origin by human manufacture. I support the idea that the occupation of the New World could pre-date the Clovis culture by many thousands of years but do not believe that this assemblage offers definite proof. To be entirely convincing the proof would have to come from a geologic context were cultural processes were the only logical or possible way to explain the fractures present.
References:
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