Test Unit Excavation (IMAGE) Proceedings of the National Academy of Sciences Caption This is a test unit excavation within one of Raleigh Island's 37 shell rings. Credit Image courtesy of Terry E. Barbour and Kenneth E. Sassaman. Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.