The Appalachian chain is a Paleozoic megastructure, bordering eastern North America. On land the exposed part of the chain stretches more than 3,000 km from Newfoundland in the northeast to Alabama in the southwest (Fig. 1). To the northwest the chain is adjacent to the Laurentian craton of Precambrian rocks, or to their platformal cover; to the southeast, gently inclined Meso-Cenozoic coastal strata of the Atlantic shelf cover the deformed Appalachian formations. Elucidation of the geology of the Appalachian Mountains has had almost two centuries of history (Faill, 1985). The chain was first defined in the southern and central states of the eastern United States, and then extrapolated northward into New England and Canada (Rodgers, 1970). Thus, even early in the history of their investigation, the Appalachians were divided into northern, central, and southern sectors (Fig. 1). South of New York the early work was conducted by state geological surveys, among which those in Pennsylvania, Virginia, and North Carolina were especially active. From the 1870s onward the U.S. Geological Survey expanded its activities in the region.
The foundations for the present understanding of Appalachian geology were laid by the Geological Survey of New York, personified by James Hall, and the Geological Surveys of Pennsylvania and Virginia, from where the brothers W. B. and H. D. Rogers conducted their investigations. While Hall (1883) stressed the stratigraphie-paléontologie aspects of the rocks composing the Appalachians, the Rogers brothers (1843) were more concerned with the physical structures of the strata. Hall′s impetus led to the paleostratigraphic approach, and he was the first to advance the notion of a basinal geosyncline;