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Microdrills from the Powell Mound.
Modified after Yerkes, R. W. 1991. Specialization in Shell Artifact Production at Cahokia. In New Perspectives on Cahokia, edited by J. B. Stoltman, pp. 49-64. Monographs in World Archaeology, No. 2. Prehistory Press, Madison. Fig. 3.1, p.53
Image courtesy of Prehistory Press.