An ocean's birth in stone
The process of an ocean opening and closing is called the Wilson Cycle. While the geology of Scotland provides clear evidence of this cycle, the rocks of Virginia's Blue Ridge Mountains tell a parallel story about the same lost sea: the Iapetus Ocean. The story here begins around 570 million years ago, when the supercontinent Rodinia started to tear apart. As the continental crust stretched and thinned, massive fissures opened and spewed enormous quantities of basaltic lava across the region.
These ancient lava flows cover over 4,000 square miles and are now a type of rock called the Catoctin Formation. The original basalt has been metamorphosed into a dark green rock, appropriately called greenstone. This greenstone forms many of the high peaks and stony cliffs in what is now Shenandoah National Park, including the rock under Big Meadows. As the rifting continued, the land sank and seawater flooded in, creating the Iapetus Ocean. The birth of this ocean is recorded in the layers of sandstone and shale of the Chilhowee Group, which were deposited directly on top of the Catoctin lava flows and preserve the sediments of ancient rivers and shorelines.
An ocean's death and mountains' rise
The Iapetus Ocean existed for over 200 million years, but plate tectonics eventually reversed course. The ocean began to shrink as the continents of Laurentia (ancestral North America), Baltica, and Avalonia converged. This slow-motion collision happened in several phases, creating a series of mountain-building events, or orogenies. The Taconic orogeny, around 460 million years ago, was the first major pulse, followed by the Acadian and finally the Alleghenian orogeny.
These collisions folded and faulted the older rock layers, thrusting the deeply buried Catoctin greenstone and Grenville basement rocks up and over the younger sedimentary rocks to the west. This process created the massive mountain range known as the Central Pangean Mountains. This range was once as high as the modern Himalayas and stretched across the center of the new supercontinent, Pangea. The Appalachian Mountains in Virginia are the weathered remnants of this colossal range. The wrinkled, folded landscape of the Blue Ridge shows geological evidence of a vanished ocean and the continental collisions that followed.