What is "cupstone"

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.