The purpose of this article is to suggest the hypothesis that one of the possible uses of cupmark production on weathered granite boulders in the Upper Midwest may have been as a readily available method of procuring Kaolin in a clean, powdered ingestable form from the Native American environment.
Cupmark, cupules, or pits are found around the world and were made by many cultures at many times during the past.
Cupmarks are not hard to make. Chimpanzees will even inadvertently make something that looks like a cupmark over time when they leave a stone "anvil" at the base of a tree that produces nuts and repeatedly break open nuts using a stone tool at the same place.
A pink granite boulder such as the Fort Ransom Writing Rock at Fort Ransom, North Dakota and other granite boulders such as the boulder at Blood Run, Iowa are covered with cupmarks.
Cupmarks are usually about 2 inches wide and 5/8 inch deep. My experiments with making a cupmark using a weathered granite field stone indicates that it took about 15 minutes to make a cupmark by striking the same spot with a hard object such as another stone or in my case using a ball peen hammer. This produces a fine white powder (resembling talcum powder) which would make an excellent drying agent for wound care such as results from stinging nettles in the region.
There is some suggestion in the ethnographic literature of the Far West that the powder from cupules was ingested by women to enhance fertility.
If we explore this idea, it may be that Native Americans were making Kaolin which is a fine white clay with the chemical composition of (OH)8 Al4 Si4 O10. This is the active ingredient in Kaopectate available in drugstores to treat diarrhea and amoebic dysentary. Clay is also frequently craved by pregnant women as a part of their diet according to Laura McIlrath who recently delivered her first baby.
If Kaolin was mixed with water, I assume it would resemble Kaopectate. There is some slight suggestion that the ingestion of the powder referred to in ethnographic sources may have been gynecological in nature. Kaolin is used by our culture to make fine white porcelain.
Regents Professor George (Rip) Rapp, Jr. pointed out the geological and chemical composition of Kaolin to me in his course on Geoarchaeology at the University of Minnesota without knowing anything about cupmarks or the Native American ethnographic sources on the use of the resulting powder. After discussing this possible source of Kaolin he pointed out that the Feldspar powder that would accompany the Kaolin produced by pounding a well weathered boulder should pass through the human intestinal system.
By creating cupmarks on a well weathered boulder by repeatedly pounding the same spot a fine white powder would result which would have been a source of the clean absorbant clay that human beings seem to instinctively crave during pregnancy and to cure amoebic dysentary. It may be that other primates also use clay for the same purposes. This would be consistent with the hypothesis of E. Breck Parkman that many of these cupmarks may be some of the oldest "rock art" in North America. As David Whitley has also pointed out, however, cupmarks were made during historic times and ethnographic interviews exist suggesting the recent making of cupmarks.
This hypothesis regarding a connection between Kaolin and cupmarks obviously will not apply to all cupmarks, for example those on non granite surfaces or those on vertical surfaces that were symbolic in nature, but it may be a possible explanation for the often observed pits on well weathered glacial erratics in the Upper Midwest and Canada.
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