The Framework for Travel and Biodiversity
The collision of continents hundreds of millions of years ago also set the stage for the patterns of human settlement and transportation. When the continents collided, folds and faults formed with northeast-southwest alignments. These structures are the framework that controls the ridges and valleys of today. The northeast-southwest-trending ridges and valleys were both the main routes of travel for people and ideas. They also were barriers to travel perpendicular to them.
A less obvious result of the collision was a telescoping of contrasting rock types. The juxtaposition of rocks that had formed in diverse environments set the stage for the diversity of landscape, habitat, and life forms that characterizes the Southern Appalachians today. Differences in underlying rocks also influenced profoundly the patterns of regional development. Some land and soils were better suited for farming, mining, or timber than others. The location of industry, and subsequently, the location of population centers, was based on availability of raw materials and transportation routes.
Sand, clay, and interlayered limey ooze that formed on the floor of the shallow, inland sea became the bedrock of theRidge and Valley Province. The resistant sandstone layers now cap ridges and form cliffs. Limestone, on the other hand, erodes more readily, forming valleys. Limestone provides nutrients for crops and is also conducive to forming caves and sinkholes, which contain unique living communities. The occurrence of iron ore, limestone, and nearby coal deposits in the Ridge and Valley Province and the Appalachian Plateau, formed a basis for early economic development. The limestone also contained major zinc deposits in some places, further enhancing the economic development of the region. However, the value of the metals mined has been far exceeded by the total value of the industrial minerals extracted. These minerals include the limestone itself, which is used for making cement and concrete.
The pebbles, sand, and clay that were deposited in the deep Ocoee Basin became the bedrock of the Great Smoky Mountains. The hard, metamorphosed sandstone forms outcrops and cliffs that are habitats for scattered communities of rare plants and animals. Metal-rich layers produce the acidic soils that some species, such as red spruce, need to flourish.
Lava and sediments that were deposited on the ocean floor form the bedrock of the Blue Ridge Mountains, to the east and north of the Great Smokies. Some of these rocks produce soils that are favorable for timber and for farming in the narrow valleys between ridges. However, like the Great Smoky and Unicoi Mountains, the special value of the area isfor recreation. Some of the rock types form highly specialized habitats, such as balds, high-elevation rocky summits, and granite domes. Some volcanic rocks produce soils that favor oak forests. Some fragments of crust from deep beneath the ocean floor were caught in the continental collision. These fragments of rock lack nutrients and produce soils that have sparse or stunted vegetation. Such areas form habitats for some rare plant communities.
Islands and continental masses that were offshore before the collision of the ancestral North American and African Continents were added to North America during the collision. They now form the bedrock of the Piedmont Province, which slopes gradually southeastward from the Blue Ridge.
Encyclopedia ID: p1554
