The ocean continued to shrink until, about 270 million years ago, the continents that were ances tral to North America and Africa collided. Huge masses of rocks were pushed west ward along the margin of North America and piled up to form the mountains that are now the Appalachians. Well, mountains are limited in their theoretical height by several processes. First is called isostasy the bigger a mountain gets, the more it weighs down its tectonic plate, so it sinks lower. The second is called glacial buzzsaw the taller and colder a peak, the faster snow and ice will wear it down/away.
