Cambridge Mudstone (Archaeological Find)

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This schematic shows formation of Cambridge slate, or mudstone. The ocean pressurizes the gravel, sand, and silt and clay deposited onto the floor, leading to mudstone formation.
Vintage geologic map of Massachusetts. Zooming into the Cambridge area, one will see the light blue color that represents Cambridge slate, AKA hard gray Argillite.
Artist's rendition of what the Old College possibly looked like. Cambridge mudstone would be found inside the building, lining walls, floors, and cellars.
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Title:

Cambridge Mudstone

Subject:

The humble Cambridge mudstone... At first glance, there is nothing shiny, special, or eye-catching about the rock. No, its color doesn’t beg for your attention like a brick might, nor does a specialist need to birth it like glass or ceramic requires. But if one ignores this seemingly dull appearance to recognize its importance in the early architecture of Harvard Yard, it is obvious that Cambridge mudstone has earned a title in the hall of fame of building material.

Though Cambridge mudstone is the colloquial name, geologists know it better argillite. This is a sedimentary rock that forms when enough pressure is applied to its parent rock of mudstone or shale (USGS). Cambridge’s argillite formed millions of years ago as sands, silts, and clays settled to the bottom of the ocean floor to be solidified into the rock we know today, and it consequently forms one part of the Boston Bay geologic group (Holton and Newman 2006). In other words, argillite or Cambridge mudstone is just one type of rock that comprises the greater Boston area.

Thankfully, Cambridge isn’t underwater anymore, and its geology was exploited by all its inhabitants. While bricks and rooftiles are common architectural materials observable from the exterior of buildings, Cambridge mudstone played a crucial role in the interior of Harvard’s first building- the Old College constructed in 1638; this stone was used as construction material for the foundation of the Old College and was vital for its structural integrity. Unfortunately, its use did not help the longevity of the building as the Old College began to disintegrate just three years later and it was eventually the university abandoned its carcass for it to return to the earth (Stubbs 1992). Subsequent buildings lacked Cambridge mudstone and instead used clay underpinnings. Thankfully, the hearty and sturdy nature of rocks means that Cambridge mudstone can be enjoyed to this day, even if we know not to use it as foundational material!

Source:

Holton, Wilfred E.., Newman, William A., “Boston's Back Bay: The Story of America's Greatest Nineteenth-century Landfill Project.” Lebanon: Northeastern University Press, 2006.

Stubbs, John Delano, “Underground Harvard: The archaeology of college life,” PhD Diss. (Harvard University, 1992).

USGS. “Geologic units containing Argillite.” Accessed February 24, 2022, https://mrdata.usgs.gov/geology/state/sgmc-lith.php?code=2.1.1.3#Massachusetts

Object Name:

Cambridge Mudstone