Oil Creek in northwestern Pennsylvania runs over a very shallow oil deposit. Dotting the banks of the creek are hundreds of artificial pits, 4 to 6 feet deep, 20 to 35 feet across, some of them shored up with timber. After a heavy rain, oil seeps into the pits and rises to the top as they fill with water. Someone clearly built the pits to collect oil, but no one knows whether the builders were Seneca Indians or French traders.
Judith Thomas, an archeologist at Mercyhurst College in Erie, tried to resolve the issue by examining historical documents and archeological data from Oil Creek. "In the nineteenth century there was a terrible bias against Native Americans, so people thought, 'Oh no, they couldn't possibly have done it.'" But Thomas found letters written by missionaries in the 1700s who described Seneca using oil as a salve, mosquito repellent, purge, and tonic.
The most crucial evidence, though, came from new dating by Erv Taylor at the University of California at Riverside. Thomas sent Taylor a wooden stake from an oil pit. In 1971 carbon dating had suggested the stake was 300 to 400 years old. But the uncertainty of the date was so great that it wasn't clear whether the wood predated Seneca contact with Europeans.
Taylor minimized the carbon-date uncertainty by creating homogenized samples of wood taken from each of the ten growth rings in the stake. To avoid the problem of petroleum contamination, he extracted amino acids from the wood and dated the acids directly. The stake, he found, dates from between 1415 and 1440, well before the arrival of Europeans and even predating the presence of Seneca in the region. So another tribe must have exploited the resource before the Seneca moved in.
Thomas isn't sure when oil mining first began, or how the Seneca or earlier tribes went about it. A newspaper ad for Seneca Oil from 1792 (claiming to cure ailments ranging from consumption to venereal disease) reports that the Seneca passed a feather through the oily water and then wiped the residue into a jar. There's no evidence yet that Indians used oil for heating or lighting, "but no one had been expecting it," says Thomas. "Now it's something we're going to look for." She plans to examine rock shelters for residue from burning oil.