In celebration of International Rock Day

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This circa 1924 photograph shows a large outcrop of Wissahickon Schist being quarried in the 7500 block of Germantown Avenue, later the site of the Trolley Car Diner. Vito Benvenuto of Benezet Street is driving the truck, with workers at the quarry posing for the camera. (Photo courtesy of Chestnut Hill Conservancy)

By Alex Bartlett, Archivist, Chestnut Hill Conservancy

Did you know that International Rock Day was celebrated on Monday, July 13? It is held each year on this date, in honor of rocks and minerals, their genesis, and their value to us as building materials and for their beauty.  Given this, there is no better time to celebrate the importance of Wissahickon Schist—that quarried in Chestnut Hill sometimes called Chestnut Hill Stone—as the glittery gray to brown building material seen throughout our area.

Wissahickon Schist is a metamorphic rock.  It was initially a sedimentary rock made up of sands and gravels, which subsequently underwent exposures to extremely high temperatures and pressures during earth-forming events, such as the movement of continental plates deep beneath the Earth’s surface and through heat associated with volcanic activity.  In Wissahickon Schist, you might notice two kinds of mica, the glittery, glasslike inclusion that gives our schist its sparkle.  These mica consist of biotite mica (often appearing dark brown, sometimes almost black), and muscovite mica (visible often as an almost clear or very pale brown).  This mica helps give our schist its unique character and has helped make it attractive as a building stone.

But where did the schist used to build our stone structures come from?  Many quarries once existed all around the area and traces of them—most long filled in—can be found in the 7600-7700 blocks of Germantown Avenue, at the site of the Chestnut Hill Friends Meeting’s Skyspace on East Mermaid Lane, at the Woodward Rock Garden on East Cresheim Valley Drive, at the site of what is now The Residences at 219 East Willow Grove Avenue, at the site of the former Trolley Car Diner in Mount Airy, and scattered throughout the Wissahickon Valley.  Other quarries at a greater distance include the Marcolina, Crispo, and Vecchione quarries on Waverly Road in Glenside, and the McKinney quarry across Lincoln Drive from RittenhouseTown.  The McKinney quarry is one of many quarries once located in the Wissahickon Valley.  Most of these were closed by the turn of the 20th century.  Those at the lower end of Chestnut Hill remained in operation until after World War II.  

One of the latest examples of a local building constructed of Wissahickon Schist is that of the Sunday school of the Presbyterian Church of Chestnut Hill, completed in 1963.  Its completion marked the end of an era of the construction of our buildings using the local, glittery stone.  The strength and durability of Wissahickon Schist has helped buildings like these contribute to the beauty and uniqueness of Chestnut Hill, and hopefully, will continue to do so for generations to come.

Due to the ongoing COVID-19 pandemic, the Archives and Library of the Chestnut Hill Conservancy are closed.  However, if you would like to donate any items documenting the history of Chestnut Hill—including those related to the history of quarrying and stonemasonry in our area—please let us know about them!  Please get in touch with Conservancy Archivist Alex Bartlett to let him know about anything you might like to donate to our collections BEFORE sending it along or dropping it off, by emailing him at Alex@chconservancy.org.  He will get back to you as soon as he can.  Direct all other inquiries to info@chconservancy.org.

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