Falls of the Ohio Archaeological Society
Ask anyone how an archaeologist collects information, and the answer most often offered is…digging! And sure enough, excavation is a primary means of obtaining data, but it is not the only way that we learn about lifeways in the past. Another means is through experimentation. Experimental archaeology can be useful in identifying and evaluating technological options early peoples might have faced. As an example, fire-cracked rock (FCR) is a common use-modified rock found at archaeological sites and is assumed to have been used in cooking. The rocks may be piled in a shallow basin or on the ground surface in a “hearth” or heated and dropped into a liquid to bring the temperature to a level suitable for cooking soups and stews.
The types of rock used in the hot rock cooking process vary across areas, but along the rivers and streams, water-borne rounded hardstone cobbles appear to have been preferred over, for instance, bedrock limestone. When used in a hearth, these stones may cool slowly as the fire dies back and will not necessarily break. When exposed to direct heat and then rapidly cooled in water, however, these cobbles fracture with distinctive cracking that gives the artifact type its name. Depending on the materials used and the manner of cracking, archaeologists may learn something about how the early peoples prepared their food.
Recently, the Falls of the Ohio Archaeological Society (FOAS) experimented with hot rock cooking. The group established controls and recorded results. A five-gallon bucket was filled with various volumes of water. The water temperature and the amount of water were recorded with each experiment. Cobbles were heated in a small grill, and their temperature recorded using an infrared thermometer. A specified number of heated rocks were dropped in and water temperatures were recorded at timed intervals. The rocks were removed and any observed cracking was documented. Safety was a primary concern, as we did not know how explosive the rapid cooling of the rocks might be.
The early findings from Stage 1 of our FCR experiment produced the following information:
- It takes a very small number of fist-sized rocks (four to five) to heat a gallon of water to a temperature sufficient to cook meat.
- Removing a rock and adding another heated one was a simple method to maintain the temperature of the liquid over a period of time.
- Cobbles comprised of different materials cracked differently. Some rocks contained veins of quartz crystals or other inclusions that caused the stone to break quickly. These rocks would not have been of further use in cooking as they were smaller and did not retain heat as long.
- Some rocks did not crack even after multiple, repeated episodes of heating.
- Heated rocks left to air cool did not often crack.
- Water poured over heated rocks spread on the ground or in a small hearth generated steam that may have been used for opening mussels or steaming vegetables. These rocks also did not generally experience cracking, but further experiments will be conducted on this aspect of rock use.
This first set of experiments led FOAS to surmise that native peoples may have intentionally selected cobbles with properties that were suitable for reuse. This would have been especially important for sites such as those in the wetlands interior of Jefferson County which had no immediate access to river cobbles. At these sites, cobbles were transported to the interior from the river, some kilometers distant. Considering the weight of rocks and the distance often required to obtain them, it would have been advantageous to select the smallest number of rocks as required for a family’s use, and those that could have been used over and over again. The large amount of FCR noted at sites such as KYANG in central Jefferson County was found throughout the midden and not within prepared basins. These rocks, most of which were cracked, were not concentrated but rather scattered throughout. This may indicate that the native people had exhausted the usefulness of these items and casually disposed of them in the trash midden.