Above: They might not look like much, but rocks similar to these fire-cracked pieces of quartzite played an important role in the survival of Montana's first people.
Fire-Cracked Rock . . .
These rocks are the cracked or broken pieces of stones that were used to boil water or roast meat. Fist-sized rocks were heated in fires and then transferred into hide-lined pits or other containers to boil water, or place into dry pits to roast meat. Eventually this repeated heating and rapid cooling cracked the stones, causing them to break into recognizable pieces.
Fire-cracked rocks are especially abundant near bison kill sites . . . places where bison were driven into natural or man-made enclosures, into bogs or snow-banks, or over cliffs, and then finished off with various weapons. Experts estimate there are 8-10 tons of fire-cracked rock at the Head-Smashed-In Buffalo Jump in southern Alberta, and over 3 tons at the First Peoples Buffalo Jump near Great Falls (formerly called Ulm Pishkun).
Processing the kill . . .
This white fat (not marrow) obtained from the boiling of bone fragments was very valuable to the Indians as evidenced by the incredible amount of time and effort they put into removing it from the bones. Perhaps it contained important nutrients that Indians didn't get from the lean meat of bison and other animals. This fat trapped in the bone matrix of the bison was extremely important, and rocks played an important role in helping collect it.
Illustration by Shayne Tolman: Courtesy of Imagining Head Smashed In by Jack Brink
Harvesting the grease . . .
Click here to watch a 3-minute YouTube video called "The Boiling Stones Demonstration".
Quartzite cobbles . . .
Although there are few places east of the Rockies where quartzite was formed, ice age glaciers transported many different types of rocks into Montana from Canada, including plenty of quartzite. Archaeologists who study processing sites find that several different types of rocks were used, but note that Indians preferred rocks that were hard and uniform, including some metamorphic rocks, some fine-grained igneous rocks, and even some well-cemented sedimentary rocks in some cases.
Any student of science knows that materials expand when heated and contract when cooled. So, no matter what kind of rock was used, it eventually fractured from stresses caused by repeated heating and rapid cooling. Eventually the pieces were too small to be conveniently used and the fire-cracked rocks were left behind.
How do they know? . . .
1. The rocks are out of place. The cliffs of the First Peoples Buffalo Jump are made of sandstone and there are no metamorphic or igneous rocks exposed in the immediate area. Thus, the presence of ridiculous amounts quartzite fragments (and few other types of rock) doesn't make sense in terms of natural processes such as weathering, erosion, deposition.
2. They are the wrong shape. A variety of metamorphic and igneous were carried into Montana by glaciers. However, rocks transported great distances by glaciers and/or water will be rounded, not angular like the fire-cracked rocks.
3. The breakage surfaces are not natural. Geologists (and archaeologists) know that when certain types of rocks and minerals break due to natural processes, they break a certain way. The breakage surfaces of rocks found near kill sites are clearly not natural.
Terms: archaeology, cobble, bone matrix, artifact
Sources . . .
Brink, Jack. Imagining Head Smashed In. Edmonton: Athabasca University Press, 2008.
Rennie, Patrick J. (Archeologist, Montana DNRC) Personal Interview. 6 August 2008.
Rennie, Patrick J. "The Interpretive Value of Fire-Cracked Rock." Archaeology In Montana 42.1 (2001): 65-90.
Wilmoth, Stan. (Archaeologist, Montana Office of Historical Preservation) Personal Interview. 6 August 2008.
|Click here to take a virtual tour of Wahkpa Chu'gn|
|Back to the list of Montana Earth Science Pictures|
|More about boiling stones|
Earth Science Teacher at Helena High School