MY BALANCING ROCK

About 387 million years ago, in the Devonian Era, there existed an ocean called the Iapetus Ocean. It was in the southern hemisphere, between what is now North America, and western Africa. The continent Avalon collided with the continent Laurentia forming the Appalachian Mountains. The sediment washed from these mountains into the Appalachian basin in the Iapetus Ocean, forming deltas and underwater sand dunes. One of these large sand dunes was colored purple by large concentrations of manganese and iron. It contained large white quartz pebbles smoothed by the actions of the ocean and the sand. In the early Carboniferous Era, 356 million years ago, the continents of Laurentia, Avalon and Gowanda collided to form the super-continent, Pangea, the oceans closed, forming a dry basin. The deltas and sand dunes hardened into sandstone, which can be found from present day Virginia to New York. The dune of purple sand and white quartz pebbles formed a ridge of purple puddingstone four to eight miles wide, and thirty miles long. This ridge, formed from the purple sand dune, is, of course, Bearfort Ridge, my favorite place to hike.

In the Late Jurassic Era, 152 million years ago, the Atlantic Ocean began to form, separating North America from Africa. By this point, these sections of Pangea were north of the equator. By the Miocene Era, 40 million years ago, North and South America were separated from Europe and Africa. India was colliding with Asia, forming the Himalayan Mountains.

The last ice age to cover an area is the most important, since its actions on the landscape are the ones that we see. The glaciers spread out from the north, covering large parts of the planet. The glaciers gouged the earth, moving boulders many miles. The weight of the glaciers could cause the earth to sink, causing punch bowls. As the glaciers retreated, the accumulated material was often deposited as terminal moraines. The last Ice Age to cover Bearfort Ridge was the Wisconsinian Era, 12000 to 18000 years ago. Like most glaciers, it picked up boulders, tumbled them, and deposited them many miles from their origin. These are called glacial erratics. A true glacial erratic is a boulder of material ‘that does not belong there’. As the glaciers melted the boulders that it carried gently came to rest, sometimes on bedrock, sometimes on smaller rocks. My favorite erratic is this one, just off my trail. The boulder has been tumbled to an oval shape. It has come to rest on a ledge on Bearfort Ridge, trapping a small rock underneath it. I call it my Balancing Rock.