The Martinsburg Formation (Middle-Upper Ordovician) of eastern Pennsylvania and New Jersey, part of a flysch belt that extends from Newfoundland to Alabama, records Taconic orogenic events and foreland basin sedimentation in the central Appalachians. Facies analysis of the Martinsburg in eastern Pennsylvania and western New Jersey suggests that it was derived predominantly from longitudinal sources and did not accumulate as a typical submarine fan, as commonly believed. Petrographic trend-surface analysis of 45 samples of Martinsburg sandstone from Delaware Gap, New Jersey, to southeastern New York indicates: (1) an increase in total quartz content to the northeast; (2) a decrease in lithic fragment content to the northeast; and (3) a decrease in total feldspar content to the northeast. These results are consistent with overall compositional trends within the Martinsburg belt from southwest Virginia to New York, described in previous studies, and support a dominant source terrane to the southwest. Significantly, trend-surface analysis points out a lack of strike-parallel concentrations of specific framework components, thereby reinforcing a longitudinal dispersal system. Consideration of the Martinsburg sandstone in terms of published QFL diagrams suggests derivation from a recycled orogene source characterized by uplifted supra-crustal sedimentary and lesser plutonic/low-grade metamorphic rocks, and points out the lack of a major volcanic input. This is further substantiated by preliminary geochemical examination of these sandstones, which supports sandstone accumulation at a tectonically active but nonvolcanic margin, although volcanic arcs may have existed outboard (southeast) of the Martinsburg source terrane.