The surveyors continue to draw their line, moving back eastward at the opening of the section but always near the Susquehanna River which serves as a boundary of more than one type. In their efforts to close off the Tangent line they discover some anomalies in previous measurements as well as legal inconsistencies that leave a small "Wedge" of ambiguous territory neither in Maryland or Pennsylvania, creating yet another of the novel's uncharted alternate domains. Two "Chain-men", Darby and Cope, attract some attention for impersonating Mason & Dixon in order to seduce the locals. The chapter closes with the discovery of their subterfuge, Squire Haligast warning that the party will soon encounter "China-men," and the delivery of a package from Maskelyne telling of geographical interferences with measurements that forces Mason to recall the windward side of St. Helena.