Appalachia and the Eastern Cordillera
L. Allan James
The uplands of eastern North America are commonly referred to as the Appalachian Highlands, based on the preeminence of the Appalachian Mountains within the region. However, the complex of Paleozoic fold belts found in the Appalachian Highlands also extends northeast, through Canada's Maritime Provinces to Newfoundland, and reappears in the Ouachita Mountains across the Mississippi River valley far to the southwest. For this larger region, the term Eastern Cordillera is appropriate in the present context. To the north and west, the region abuts the narrow St. Lawrence Lowland along the margin of the Canadian Shield, the Central Lowlands of the Great Lakes region, and the low plateaus of western Kentucky and Tennessee (fig. 15.1). To the south and east, the region extends to the Fall Line at the inner edge of the Coastal Plain. West of the Mississippi embayment are the Ouachita Mountains and Ozark Plateaus in Arkansas and southern Missouri. Whereas the latter areas, together with the Interior Low Plateaus, are not formally recognized as part of the Appalachian Highlands, they are included here because of similarities in structure, relief, and vegetation. The Eastern Cordillera thus defined, though dominated by the Appalachian Highlands, is not continuously mountainous but is sufficiently elevated to generate a distinctive physical and biotic regionalism quite different from that of the adjacent lowlands.
of the Appalachians
Based on Fenneman's (1938) widely accepted physical divisions of the United States, six provinces are identified within the Appalachian Highlands, namely, the Adirondack Mountains, Appalachian Plateaus, Ridge and Valley, Blue Ridge, Piedmont, and New England (fig. 15.1). Because these provinces differ in terms of tectonic evolution, they are distinguished from one another by structural and lithological differences that result in pronounced variations in topography (see chapter 1). Most provinces are, however, characterized by structures with a northeast-southwest strike attributable to Paleozoic orogenies that give the region some uniformity over more than 3000 km from Newfoundland to Alabama.
Though structurally an extension of the Canadian Shield and underlain by Precambrian igneous and metomorphic rock, the relatively small Adirondack Province in New York State is a mountainous region more appropriately