New COCORP profiles on the coastal plain of Georgia and northern Florida support the hypothesis that the Brunswick anomaly marks a late Paleozoic suture. They do not support the alternate view that this anomaly is caused by a Mesozoic rift basin. The trend of the Brunswick anomaly relative to the Appalachian gravity gradient indicates that in westernmost Georgia and adjacent Alabama, African basement (Suwannee terrane) is in proximity to autochthonous North American basement (Grenville). Farther east one or more Paleozoic accreted terranes intervene between the North American and African sides of the orogen. Offshore, the Brunswick anomaly closely parallels the east coast magnetic anomaly. This relationship implies that the east coast magnetic anomaly marks not only the present continental/oceanic crustal transition but also the northward continuation of the late Paleozoic suture between North America and Africa. Transitional crust beneath the Carolina Trough, Baltimore Canyon trough, and correlative parts of the African Atlantic margin is thus likely to have formed within a preexisting suture zone. The dramatic change in character of the U.S. Atlantic margin southward from the Carolina Trough to the Blake Plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region.