Far more than any other members of the Castle Archaeology team, Ken Kosidlo and John Heintz have spent countless hours sorting the “heavy fraction” of flotation samples from our excavations at the late Prehistoric Clunie site. (The heavy fraction includes all of the stuff that sinks to the bottom during the flotation process – typically bones, sherds, flakes, shell, etc.) The samples derive from features such as trash pits, storage pits, and hearths. To make the process easier, samples are first size-sorted into three grades – >4mm, 2<4mm, and <2mm. Having caught up on all of the >4mm material, they are now engaged in sorting the 2<4mm grade. This stuff is tiny! It takes a practiced eye (and a tolerance for tedium) to separate a pile of miniscule fragments into categories of like materials. Yet this is the only way to ensure that the fullest possible range of material is recovered from an archaeological deposit. Items like beads, retouch flakes (made while sharpening the edge of a stone tool), seeds, and the bones of small animals could easily be missed without employing a fine-grained recovery technique like flotation.
A find earlier this week demonstrates the utility of this approach for recovering rare items that would otherwise have been missed. A close examination of a tiny shell fragment found in a sample from Feature 9 (a trash pit) revealed it to be from a marine gastropod in the Prunum (formerly Marginella) genus. The most likely candidate appears to be Prunum apicinum, the Common Atlantic Marginella. A bit of web-sleuthing reveals that this species ranges from the tidal flats and coastal waters off the Carolinas through the Caribbean, and the Gulf of Mexico to the Yucatán Peninsula (Smithsonian Marine Station at Fort Pierce website). From the Archaic through the early Historic Period, shells of this species were traded across much of eastern North America in the form of beads fashioned by grinding an oblique facet across the apex of the shell.
A complete Marginella shell bead was recovered during the excavation of Feature 28, another trash pit located in a different area of the Clunie site, and a fragment of a second Marginella bead was previously found in a flotation sample from Feature 28. Although the two fragments are small, they each exhibit structural traits not shared by any of the local gastropod species. By comparing the fragments with the complete specimen, you can see the traits used to clinch the ID.