Thursday, January 7 is “Old Rock Day” And boy do we have some old rocks in the Wissahickon Valley! Our predominant rock, Wissahickon Schist, is a metamorphic rock that started as mud once deposited into an ancient sea. Through millions of years of the mud layers compressing down upon themselves, it changed to the rock known as shale. Finally through heat and pressure, when this area was deep under the earth’s surface, the shale metamorphosed into schist. After millions more years of mountain building and water erosion these rocks are now at the surface.
Take a hike along the Orange Trail upstream from Valley Green Inn and look for garnets (January’s birthstone) that have fallen out of the softer schist. Look for the sparkly mica in the schist that if you rub it, it will flake off into “fairy dust”. You might also be living in a house built of Wissahickon schist if you live in Mt. Airy or Chestnut Hill in Philadelphia! Thank you Sarah West for teaching hundreds of people about the Geology of the Wissahickon over the decades.
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