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Geological Genealogy: November 15

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Limestone has long been the building material of choice at St. Olaf. But who decided this and where does it come from? In the 1930s the school was expanding and in need of new academic buildings, dorms and a power plant. The previous power plant, made of brick, had burned down. The architects suggested the use of limestone, native to this area. When the power plant was completed, the workmen placed a flag on top to signal its completion. They declared it was the most beautiful power plant they had ever seen. Thus the college’s infatuation with limestone began.

Shortly after, the college built Holland and Christiansen Halls both out of limestone. A debate emerged over the construction of Mellby Hall when it was proposed that student dorms be constructed of brick to cut costs. The college president at the time, P.O. Holland, argued for continuity and decided that Mellby Hall and subsequent dorms should also be built of the stone that now gives St. Olaf its Hogwarts-esque appearance.

The limestone used is, in fact, local, as the early architects suggested. All of the limestone used through the completion of Boe Chapel was quarried in Faribault, Minn.

Newer buildings, such as Buntrock Commons and Regents Hall, have been sourced from a quarry in Lannon, Wis. You can actually observe the differences in the stone when you stand between Buntrock Commons and the chapel. The darker-colored rocks are indicative of iron, as more iron leads to a darker-colored stone.

The more weathered-looking rocks are cut from exposed portions of the quarry that have been impacted by weather over time. The smoother rocks are from the interior of the quarry and are cleaved by machines. The smooth stones used to frame windows and doors on older buildings such as the chapel are from central Indiana. This same limestone can be found on other, more famous structures like Yankee Stadium, the Empire State Building and the Pentagon.

St. Olaf now tries to source all building materials within a 200-mile radius, so the window and door framing stones now come from Mankato, Minn. Each quarry provides rocks with individual characteristics, and these differences emerge from the geographical and geological conditions in which the stones formed about 400 million years ago.

Minnesota 400 million years ago was not anything like the fertile rolling hills and 10,000 lakes we have today. During this time, known as the Devonian age, Minnesota was located 10° to 40° below the equator. The climate was tropical, and the land was covered with a shallow sea, providing a habitat for simple marine organisms such as corals, brachiopods, snail, clams and cephalopods. You can still collect fossils of these specimens in exposures of the Mississippi river in the Twin Cities.

The movement of tectonic plates brought Minnesota to its present day position, where conditions do not favor limestone formation. Growing deposits are located in the Caribbean Sea, Indian Ocean, Gulf of Mexico and other shallow seas between 30° north and south of the equator.

Limestone forms as a result of the activity of early marine animals. It is a sedimentary rock made from the combination of coral, algae, fecal matter and empty shells which accumulate on the sea floor to eventually be lithified into limestone.

During major geological events, limestone can undergo metaphorphosis and recrystallize into marble. Limestone is primarily composed of calcium carbonate in the form of the mineral calcite. Calcite is used by many of the world’s organisms to build their shells. Dense limestone is a good building material because fewer pore spaces allows it to withstand abrasion and the freezing and thawing effects of changing seasons in Minnesota.

So remember, they are not just rocks! St. Olaf’s limestone is a record of Minnesota’s fascinating geological past.