In Late Precambrian time, about a billion years ago, present-day North America collided along the east coast with a continental mass thought to be the northern part of South America. At this time in earth history, Ohio was on the eastern edge of the continent. The collision produced a chain of mountains that stretched from eastern Canada south through Ohio. The roots of these mountains, named the Grenville Mountains for an area where they are exposed on the Canadian Shield, lie deeply buried beneath central Ohio and portions of eastern Ohio. As the two continents collided, and rocks were squeezed together, some rocks were thrust westward. The north-south line separating disturbed rocks on the east and relatively undisturbed rocks in western Ohio is termed the Grenville Front.