Appalachians

Mount_Mitchell_State_Park One could easily overlook the Appalachian Mountains and dismiss them as mere hills, the  worn, rolling nubs of mountains. This rambling 100 to 300 mile (160–480 km) wide, 1,500 mile (2,410 km) long chain of overlapping mountain ranges reaches its high point at the 6,680 foot (2,040 m) summit of Mount Mitchell in North Carolina—half the height of even average peaks in the Rocky Mountains and only a quarter the height of Mount Everest. Although Mount Mitchell ranks as the highest point in the eastern United States, most of the mountain chains that together form the Appalachians reach to barely 3,000 feet (910 m) in height. And yet, the study of the Appalachians can yield clues to the long history of the planet, for the worn and eroded of peaks of this long mountain range once rivaled the Himalayas and in their folded and tormented layers reveal the long history of the planet. Solving the mystery of their formation and the seemingly inexplicable connection to a mountain range in Africa provided a key element in the development of the theory of
plate tectonics that revolutionized the understanding of geology. Moreover, the geographic barrier of the Appalachians shaped the history of the United States more than perhaps any other single landform. This layered chain of mountains with only scattered passes confined initial settlement of the United States to the broad coastal plain between  the foothills of the Appalachians and the Atlantic Ocean. Most of the original thirteen colonies developed in that broad area, ensuring enough continuity, density of population, and stability to foster the development of the United States of America, in contrast to the dispersed settlement patterns beyond those mountains where French explorers and settlers never built a colony to rival the areas to the east of the Appalachians.
A Mountain of Mystery
Early geologists trying to account for the evolution of the Appalachian Mountains in the 1800s and early 1900s had a mystery to tackle.  Clearly, the Appalachians were the remains of an ancient mountain system—contorted, folded, and worn. The scientists had mapped all of the warped and folded layers, ancient sea bottom sediments that had been buried, fused, and metamorphosed into new rocks. Then those rocks had been uplifted great distances and intermingled with the outpours of many volcanoes. Finally, the uplifted
mountains had been worn down again, leveled by the relentless erosion of water, ice, and wind. All that seemed apparent from the sequence of rock layers. Geologists could even account for the great mass of rock that  had been eroded off those once great peaks.  These loose, eroded sediments were piled miles deep onto the coastal plain of the United States, a broad, low-lying region several hundred miles wide running down the whole eastern edge of North America.8-view-from-Mt-Mitchell Now here is the mystery. The sediments of the coastal plain and the underwater continental shelf were piled so deep that they had to have accumulated in a broad, low-lying region between two mountain ranges. If
they were not trapped in a gigantic basin, they would have simply washed out to sea. So what happened to the other half of the basin? What happened to the parallel chain of great mountains necessary to trap the miles of sediment eroded off the crest of the Appalachians? For many decades in the early 20th century, geologists could only shrug and continue chipping away at a host of mysteries shrouding the evolution of mountains. In fact, they did not have any strong theories on how mountains developed. What caused one chunk of the Earth to rise to 28,000 feet (8,530 m)? No one knew for sure. Early philosophers argued that the mountains, valleys, and other remarkable features of the Earth were signs of the great fl ood of the Bible. They argued that God would have created the Earth as a perfect sphere, but that the tremendous fl ood with which the Creator scourged the Earth in anger at human behavior gouged out great valleys and canyons and piled up high mountains. Philosophers continued to advance and research such ideas into the 1800s. But others sought explanations for the rise of mountains that did not rely on divine intervention. Jean-Baptiste Élie de Beaumont, a French geologist, in 1852 suggested that mountains were forced upward when
rocks were squeezed as in the “jaws of a vise,” although he offered no clear explanation for what might be causing the squeeze. At that time, many geologists argued that the Earth was gradually cooling, causing it to contract as it cooled. This contraction was thought to have caused the surface of the Earth to crack and wrinkle. The cracks became valleys and low-lying regions and the wrinkles became mountain ranges.