THE MINERALOGY, PETROLOGY, AND PROVENANCE OF BALLAST STONES FROM THE CAPE FEAR, NORTH CAROLINA: 1726 – 1825

Archaeologists, geologist, and historians often like to examine the unique and the unusual aspects of a site, location, or event while relegating the commonplace to a dusty corner in their study. Along the eastern United States, deposits of ballast are regularly found in the ports, harbors, and other sheltered locations where cargos were exchanged. In addition, shipwreck sites, jetties and docks, and building foundations often have a variety of non-local rock types that could shed light upon the origin of the wreck, the trade routes along which this material was collected, and the historic use of this material in regions that often do not have rock as a resource. To successfully extract the provenance of the ballast, as well as the potential ways in which it arrived at the location where it was found, requires an interdisciplinary approach incorporating historical, archaeological and geological techniques.

This study examines ballast stones collected from Campbell Island, the historic transshipping point on the Cape Fear River, in southeastern North Carolina. The goal was to evaluate the geologic and geographic provenance of the ballast as well as to correlate these results to shipping trends and ports of origin for this area from 1726 to 1825. The ballast recovered was separated into four groups: a mafic igneous rock suite (basalt or diabase), a chalk-flint-chert group, a suite of quartz-rich plutonic igneous rocks (granite) and a mixed group of sedimentary and metasedimentary rocks. The provenance of the ballast was determined by the mineralogical and petrographic characteristics of the mafic and quartz-rich plutonic rocks, which was further correlated with the few existing shipping records for this region. Petrologic methods and microfossil identification suggest that chert and flint ballast stones in the region may also have a Caribbean origin, in addition to English or French origins previously reported. This observation could have implications for the importation, use, and later embargo of flint (or chert) by the British prior to the American Revolution of 1775.