Cupstone

Cupstone, Poculolith, Pitted Cobble, Nutting stone
A cupstone
General
Category	Archaeological Artifact

Variously known as cupstones, "anvil stones," "pitted cobbles" and "nutting stones," among other names, these roughly discoidal or amorphous groundstone artifacts are among the most common lithic remains of Native American culture, especially in the Midwest, in Early Archaic contexts. The hemispherical indentation itself is an important element of paleoart, known as a "cupule". Cup and ring marks are also common in the Atlantic and alpine regions of Europe, sometimes associated with complex petroglyphs or megalithic monuments.

One encyclopedia of archaeology treats "pitted stone," "cupstones," and "nutting stones" as synonyms and says that they "may have been formed by cracking nutshells, though this activity lacks adequate confirmation through ethnographic examples or published experimentation."

These objects have received little study, perhaps because edged tools and weapons have more intrinsic interest to private collectors, but closer study of them might reveal something of domestic practices and technology. There is no agreement upon their purpose or purposes, which may have included the processing of food, medicine or pigments, storage, arrow-production or fire-drilling. As such, they could represent a primitive form of mortar and pestle. The age of these man-made structures are difficult to ascertain, but generally they are believed to have been produced in the bronze-age and Upper Paleolithic although some, for example in North America and Europe, were generated at a later date.

Visually, they may resemble omarolluks, a naturally occurring feature of sedimentary rock occurring exclusively in the Belcher Islands, an archipelago accounting for 0.25% of Hudson Bay, whence they are thought to have been spread by glaciers.

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Wikipedia