The Stones of Princeton

Looking at the buildings on campus through the eyes of a geologist


Firestone Library is crumbling. Whig and Clio halls are dissolving. Nassau Hall and neighboring Stanhope and West College are slowly self-destructing as they erode from the inside out.

All this is happening before our eyes. If we happen not to notice, it is because we do not see with the eyes of a geologist, like Sheldon Judson '40, chairman of the Department of Geological and Geophysical Sciences. When it comes to Princeton's buildings, Judson takes the long view.

Nassau Hall was completed in 1756, and during its 225 years has withstood the cannonade of Alexander Hamilton's artillery at the Battle of Princeton, two major fires, and numerous student riots. But Old North's two-plus centuries are merely an instant in geologic time, and in the end its greatest enemy may be New Jersey's soggy climate.

The local (called Stockton) sandstone used in the construction of Nassau Hall is highly permeable. As Judson explains, when water seeps into the sandstone, sodium salts are produced and a chemical reaction occurs similar to what happens when you drop bicarbonate of soda into a glass of water -- a slow fizzle takes place in the cracks, the sodium expands, and the stone disintegrates.

"Look at that sill," he says, as we stand on the gravel below the vaulted window of the Faculty Room. The underside of the sill appears as flaky as a puff pastry. I have walked by it hundreds of times without ever noticing. The thin layers of sand that formed the stone some 200 million years ago are literally coming unglued as the natural calcite cement washes away.

Stockton sandstone, says Judson, in inherently unstable and "continually weathering into clay and soluble salts. This building and others like it -- Stanhope and West College -- will always have a problem of eroding from behind." The problem is exacerbated, he adds, by the increased acidity of rainfall in the Northeast due to air pollution, as well as by ivy -- the very symbol of collegiate life -- whose tendrils penetrate cracks and open up passages for moisture.

Judson and I are taking a walk around the campus to see what the rock walls of buildings have to tell us of earth history. We began a few hours earlier at the other end of campus, in Judson's Guyot Hall office, where he spent a few minutes explaining the region's geologic story and its relation to the stones of Princeton.

At the start of the age of dinosaurs nearly a quarter of a billion years ago, central New Jersey was a shallow, mountain-bordered depression known to geologists as the Newark Basin. The sand that eroded off the mountains spread over the basin and eventually became the sandstone of Nassau Hall. Broad, shallow Lake Lockatong formed later in the middle of the basin and over millions of years built up thick deposits of mud, forming a dense mudstone or slate called argillite -- the Lockatong argillite of the Princeton Ridge and the distinctive gray and maroon stone used in many of the university's Gothic structures, including Frick Hall, Baker Rink, and Cuyler and Henry dormitories.

The story of the Newark Basin, in turn, can be seen within the larger framework of plate tectonics, or "moving continents," the great synthesizing theory of modern geology worked out by the late Harry Hess *31 of Princeton and others of the 1960's. The Newark Basin is one of a series of ancient coastal valleys running from New England to the Carolinas. Direct counterparts can be found in Spain and North Africa. As Princeton's Franklyn Van Houten *58 has shown, their formation is associated with the birth of the Atlantic Ocean and the breakup of the supercontinent of Pangaea 225 million years ago, when the eastern and western hemispheres began to go their separate ways. (They are still doing so, spreading apart at a rate of two centimeters a year.) The stress of movement simply stretched the edges of the continents.

We start our walk in the west entry of Guyot Hall, whose grayish-green steps are peridotite or "soapstone" and probably came from quarries in virginia or the Carolinas. Guyot Hall has been home to the departments of Geology and Biology since its competion in 1909, and the steps are well worn from use by generations of students. "If you go over to the biology entrance and look at the steps there," Judson notes, "you can see which department has had the bigger enrollments." (The answer: biology.)"

On the entry floor the art deco tiles catch our eye. "These are very similar to the sheathing used on the Woolworth Building in Manhattan and were probably made at the old Kingston Tile Factory," says Judson. For years New Jersey was noted for the tile and brick made from its excellent commercial clays, which run in a band along the inland edge of the coastal plain from Trenton to Perth Amboy.

Outside the entry we examine Guyot's limestone trim. "Bedford limestone, from Indiana," Judson notes. "As a trim stone it is widespread on campus." The famous limestone beds of Indiana were laid down some 325 million years ago, when the first amphibians were establishing their hegemony on land. Limestone is a sedimentary rock formed on the ocean bottom. When cut for building trim it resembles concrete, but with Judson's hand lens we can see that it consists of countless fossil shells of tiny marine animals. "Look at all those little grains of shell material," he says. "Notice too the lineation in the stone -- probably ripple marks from wave action. You can almost hear those warm tropical seas lapping up against it."

As we contemplate the remains of ancient sea creatures embedded in the rock, other creatures carved in it look down on us -- a rhinoceros, a pterodactyl, a trilobite, among Guyot's 200 or so limestone gargoyles and other decorative carvings. Representing animals and plants from various geologic ages, they are the inspired work of Mount Rushmore sculptor Gutzon Borglum. After 70 years, signs of weathering are beginning to show -- a general smoothing of features -- although recent reports about Princeton's gargoyles dissolving in acid rain are greatly exaggerated.

We leave Guyot and begin working our way up campus, stopping briefly at Dodge-Osborn, a dormitory built in 1958 and now part of the Wilson College complex. Its first floor is Stockton sandstone, like Nassau Hall, although Judson says the stone must have come from quarries along the Delaware rather than from Princeton. Embedded in a few of the sandstone walls are large pebbles, evidence of flash floods that coursed through the ancient Newark Basin, and some surfaces bear sinuous trails cut by prehistoric worms. Many of the stones have been placed with their formative layers vertical -- a mistake, Judson pronounces, since this makes it easier for rain to penetrate. Flaking on some of the stones is already advanced. Beneath the archway leading to the Wilson College courtyard, we pause for a further example of water's corrosive powers. The wall here has been faced with limestone; where protected under the arch the stone feels smooth, but a few inches away exposure to rain has made it pitted and rough.

We cross the courtyard and continue through the archway past Walker and 1903 dormitories, handsome structures of the ubiquitous Lockatong argillite. Judson comments on the flagstone walkway beneath our feet: "Siltstone, probably off the Appalachian Plateau in Pennsylvania." Flagstone like this, he adds, was laid down in a river delta environment during the Devonian period, 400 million years ago, in the age of fishes. We stop next at Brown Hall to admire its New England granite.

As Judson explains, granite is one of the most common forms of igneous rock, created when magma rising within the earth's interior becomes trapped and cools slowly beneath the surface. "It's obviously an excellent building stone," he says, running his hand over a roughly textured block. "This stone was cut in the 1890's but still has its original surface -- there's almost no weathering at all. The quartz crystals and feldspars are tightly interlocked, so that it's very difficult for moisture to get in."

We continue across the courtyard between Dod and McCormick halls (both of a uniform sandstone, probably from northern New Jersey or Connecticut quarries but exact origins unknown). It is a beautiful afternoon in April, and the ambient mood has less to do with rocks than with rock music, which pulses from open windows while undergraduates hurl frisbees or loll on the grass in the warm spring sun. Jutting out toward Dod is the 1966 McCormick addition, and we stop to admire the elegant trim on its roof-to-ground window wells. Judson identifies the stone, which is pitted with irregular cavities, as travertine, a partially crystallized limestone from spring deposits in Italy, and "a popular building material in New York office buildings in the 1920s and '30s. There's a lot more of it over at the Wilson School." A problem with travertine, he notes, is that water can get into the cavities and crack the stone when it freezes. After 15 years, however, the stone here looks in fine shape.

We pause next on the mall between Whig and Clio halls, where the pedestal of one of the twin snarling tigers attracts Judson's attention. "That's quite a stone," he says, peering at its dark, marbled surface through a hand lens. He tentatively identifies it as quartzite and unfolds a Swiss army knife to test it. "You can't scratch quartzite with a blade. Marble you can." He scrapes. It scratches. "Marble."

Inspecting the portico of Clio Hall reveals that, after 88 years, the Ionic-style temple is "showing its age," according to Judson. Weathering is faster on ridged surfaces, he notes, and decorative grooves cut into the marble facing have accelerated the inevitable effect of rain over the decades. Comparing exposed and protected sections of wall, he estimates that erosion is proceeding at about a millimeter a century. At this rate, most of the marble facing on Clio and neighboring Whig Hall will wash away entirely in the next 5-10 thousand years -- a snap of the fingers in geologic time. Clio's architectural style suggests the desiccated environment of the Mediterranean, where Judson has done much of his field work. "In Greece, southern Italy, and North Africa, weathering is very slow because of the dry climate, but bring Cleopatra's Needle to Central Park and it goes to pieces."

After poking (literally, with Judson's penknife) into West College and Nassau Hall, we pass through the courtyard at East Pyne (brown sandstone, or simply "brownstone," from northern New Jersey or the Connecticut Valley) and arrive at Firestone Library. Its building stones are a silvery gray, with some shading toward yellow or a rusty oxide red. We peer at rocks at the library portal as passers-by eye us curiously. The stone, says Judson, is Wissahickon schist, from quarries west of Philadelphia, and is similar to the Manhattan and Fordham schists underlying much of New York City. It started out as shale a half-billion years ago and metamorphosed into a densely layered rock rich in mica. Although attractive in appearance, the schist flakes easily. Judson runs his finger across the grain, loosing a rain particles. "It does begin to deteriorate rather quickly. Look at Holder, Little, and Blair halls and you'll see that parts of them are getting pretty rotten."

Firestone seemed an appropriate place to end our inspection of campus geology, for it was during the excavation for the library in 1946 that Princeton's long-time curator of paleontology, the late Glenn Jepsen '27, keeping a step ahead of the bulldozers, struck a layer of argillite containing one of the richest lodes of fossil fishes ever found. The specimens represented various species of coelacanth (pronounced SEE-la-kanth), a primitive type of fish that swam in primeval Lake Lockatong. The fossils were concentrated in a six-inch layer of rock that had reached just the right state of disintegration -- old enough so it could be separated into thin sheets to expose the fossils, but not so old as to have crumbled. "A few million years more and we would have been too late," Jepsen said at the time. To librarian Julian Boyd, splitting the layered rock was like "opening the pages of ancient books."

Coelacanths were lobed-fin fishes that may have scooted across the bottom of ancient lakes, "walking" as much as swimming. Some of them branched off from the main coelacanth line 375 million years ago, crawling onto the land and evolving into the first amphibians. They are thus directly ancestral to all land animals, including humans, and the monument to human thought that is Firestone Library is built on their remains.

Princeton Alumni Weekly September 21, 1981. p. 10-12