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. They have received little study, perhaps because edged tools and weapons have more intrinsic interest to collectors, but closer study of them might reveal something of domestic practices and toolmaking 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.
This article is primarily concerned with specimens from North America, but similar objects are associated with Celtic Europe and even Australia and Palestine. Some scholars insist the items are "false" artifacts, that is, their form results from natural processes rather than human activity. However, no one has yet described processes that might both produce such effects and also explain the distribution of the effects and the objects. Certainly air-bubbles in stone, broken open and eroded, could produce some of these phenomena. The objects are familiar in Illinois, Ohio, Indiana, Arkansas, Kentucky, Tennessee, Alabama and Mississippi, and occur elsewhere as well.
The pattern, size and number of concavities is not predictable, nor is material -- impressions are found in soft sandstone and hard granite. Cupstones may exhibit a mixture of large and small indentations, perhaps indicating multiple uses over a considerable span of time. Indentations range from barely visible 1/16" to 6". Examination under magnification suggests the impressions were at least in some cases formed by rotary grinding. Typical impressions are of the simple pit type, though some cavities have been excavated to produce an opened-sphere type of pocket, by means and for reasons unknown. Very large specimens weighing several tons and with dozens of impressions several inches across are thought to be cult objects; they have been found throughout the Mississippi Valley.
The most likely interpretation seems that these artifacts represent a single technique of shaping or adapting stone for multiple purposes, some unguessed (for instance, the function of the smallest pits) and that the objects could be used by single or multiple individuals over long periods of time, and for various purposes. Indeed, the apparent randomness of their distribution may indicate that they were left lying as modified natural resources, whether with benevolent intent or because they did not represent a sufficient investment of time and labor to justify transporting them ("opportunistic" tools). More simply, perhaps the users intended to return to the same area during the next year's mast-gathering period.
The now traditional term "nutting stone" may be justified, as may "straightening stone" or "shaft-anchor" (for straightening arrow-shafts) within a larger class we might call "poculoliths," (