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.