A Geologist's HarvardBy David B. Williams

A modified versions of this story originally appeared in the November/December 1997 issue of Harvard Magazine.Photographs by Adam Shyevitch were shot specifically for this PDF document.

The best geology exhibits at Harvard aren't in a galleryor museum. The University buildings themselves are thedisplay cases. The university features a range of rocks asdiverse as any assembled by plate tectonics. Onebuilding reveals a world of marine fossils. Anotherincorporates gray and black granite that solidifiedhundreds of millions of years ago. A third is made from ared sediment deposited in a land teeming with dinosaurs.A careful examination of these structures offers insightsinto cultural as well as natural history.

Harvard's earliest builders used locally abundant rock.Harvard Hall (1766, with additions in1842 and 1870), by the main gate tothe Yard, exemplifies this practicewith a course of sandstone at its baseand sandstone steps quarried from theConnecticut River valley. Althoughthe red sandstone's official geologicname is the Portland Formation, morepeople probably know it asbrownstone—a dominant buildingmaterial during the last half of the 19thcentury in Boston, New York andPhiladelphia. Boston Brahmin, OliverWendell Holmes, celebrated thismaterial in his poem "Contentment":

Little I ask; my wants are few;I only wish a hut of stone(A very plain brown stone will do).That I may call my own;And close at hand is such a one,In yonder street that fronts the sun.

Quarries in the Connecticut River valley startedshipping brownstone in the middle 1600s. The peak ofquarrying in East Longmeadow, Massachusetts, the

state's principal brownstone region, occurred after railservice reached the town in 1876. Three or four trains perday would leave carrying as many as 17 cars of rock.Labor strikes in the 1890s forced the quarry industryinto decline. By 1915 the major sandstone producers hadshut down, and minimal amounts of building blockshave trickled out over the last 80 years.

Deposition of the Portland Formation sediments began200 million years ago when Massachusetts sat about 15degrees north of the equator. Streams washing westwardout of a now eroded mountain chain deposited mostly

red sands and silts more than 6,000feet deep onto a vast valley floor,created as North America and Africawrenched apart from each other. Theclimate fluctuated between humidand semi-arid periods lastinghundreds of thousands of years.Conifers, horsetails (scouringrushes), and ferns grew near thewater. Three- to nine-foot-longcarnivorous and herbivorousdinosaurs roamed about with lizard-like and crocodile-like reptiles.Unfortunately, these plants and

animals did not leave their traces in the rock used atHarvard Hall. Neither did the numerous species of fishthat swam in the streams and perennial lakes, in whichsediments slowly accumulated in layers called beddingplanes.

The orientation of these beds in the Harvard Hallsandstone has left some blocks unscathed, while otherscrumble when touched. In winter, when the temperaturerises above 32 degrees Fahrenheit, water infiltrates theporous sandstone of the hall's steps. When temperaturesfall below freezing again, the water turns to ice andexpand nine percent. If a builder places a sandstone

Close up of Portland Formationbrownstone shows weathering causedby freeze/thaw cycle.

block with its beds vertical and parallel to the building'ssurface, the freeze/thaw cycle will force the layers toseparate like cards off a deck. But if the beds liehorizontally, water cannot penetrate the layers and therock does not deteriorate.

In contrast to this crumbling structure, CharlesBulfinch's University Hall (1815) rises solidly across theYard in massive blocks of Chelmsford Granite. Magmacooling deep within the Earth formed this rock roughly400 million years ago. The granite's light colorindicates that it is rich in aluminum and silica; a darkerrock would have more iron and manganese. Small darkred garnets are embedded in thematrix of light brown feldspar andwhitish quartz. On a clear day,shiny sheets of mica wink in thesunlight.

Bulfinch is often credited withhelping to start Boston's early 19thcentury granite building boom. Hisdesire in 1802 to use granite for anew prison i n Charlestowninadvertently led to the introductionof an improved method for cutting stone. Until then,stone cutters rarely quarried rock; instead they workedwith loose boulders, using heat to crack the stone. Theybuilt a fire on top of a large stone and then dropped aheavy iron ball to split it. Stonemasons would furtherbreak the heated rock with sledges. To create squarepieces, they cut a groove into the surface with a sharp-edged tool called an axhammer and then struck the rockwith a heavy hammer until it fractured.

Bulfinch wanted granite for the prison, but local stoneprices were too high. Lieutenant governor Edward H.Robbins, one of the prison's commissioners, set out tolocate cheaper materials. While passing through Salem,he noticed a building made of rock that had been cut in amanner new to him. After several inquiries he found aMr. Tarbox of Danvers, who explained his method ofdrilling a row of holes into the rock and then poundingsmall wedges into the openings to split the rock open,creating a smooth face.

Robbins was so impressed that he hired Mr. Tarbox toinstruct the local stone cutters, who were so elated with

this new method "they adjourned to Newcomb's Hotel,where they partook of a sumptuous repast," according toWilliam Sullivan Pattee in A History of Old Braintreeand Quincy. This new technique dropped the price ofcut stone 60 percent.

Many of the Charlestown prisoners eventually had theopportunity to practice the Tarbox method; three,certainly, of Bulfinch's post-1802 buildings used rocktrimmed to size at the prison. The chances are that thestones of University Hall also were cut by prison inmates.

Brownstone, granite, and slatewere the triumvirate of commonBoston building stones of the1800s. Harvard's premier slate-roofed structure, Memorial Hall(1878), displays rock from the twomost important slate-producingregions of New England. The redshingles came from quarries nearGranville, NY, the green shinglesfrom nearby Fair Haven,Vermont, and the black fromMonson, Maine. They are also

some of the oldest rocks on campus ranging in age fromthe pea-soup green, 550-million-year-old MettaweeSlate through the red Indian River Slate to the blackMonson rocks, a 400-million year old unit, known togeologists as the Carrabassett Formation.

The amount of oxygen and the type of sediment in thedepositional environment determined the colors of theMemorial Hall roofing slate. The red in the Granvilleslate resulted from the erosion of iron-rich soils that wereexposed to an oxygen-rich environment. Granville hasthe only red slate quarries in the United States. If the ironoxides were deposited in an anaerobic environment theyyield a green- to purple- colored sediment. The blackslate also formed in an oxygen-starved environment butcontains abundant organic matter that imparted its blackcoloration.

The formation of Memorial Hall's slates started with clayand silt washing off the North American continent into avast sea, the Iapetus Ocean (Iapetus fathered Atlas forwhom the Atlantic is named). For 150 million years, theIapetus served as a dumping ground for sediments that

An example of the Tarbox cutting method.

sank slowly into the deep waters of the ocean, buildingup several thousand feet of extremely fine-grained layersof shale.

During the entire depositional history of thesesediments, the Iapetus was slowly closing. As the oceanshrank, it transported a volcanic island arc (similar toJapan) that had risen in the middle of theocean towards a collision with NorthAmerica. When the arc slammed into thecontinent, it pushed the marine-deposited Vermont and New Yorksediments up onto the land,simultaneously burying and foldingthem. The weight of this mass of landcompressed the sedimentary beds,metamorphosing the shale into a slate.The stress of the collision also causedthe grains of clay, which is a flat, sheet-like mineral, to align themselves into arigidly parallel arrangement, likeorganizing a collapsed house of cardsinto a tight deck. The Monson slatemetamorphosed in a similar process 50million years later.

This alignment of clay minerals, which facilitates theeven and clean splitting of slate into distinct layers, hasmade slate an important roofing material for hundreds ofyears. The same qualities make it useful for floor tile,billiard tables, and blackboards. Immigrants from Walesplayed a critical role in establishing the slate industry inAmerica. They were the first to recognize the highquality Monson slate deposits in the early 1800s and alsohelped to expand the quarries in Vermont and New Yorkin the 1850s.

Not all of the original Memorial Hall roofing slate isintact. In two restoration projects during the last 12years, workers replaced shingles that had brokenbecause people walked on them, especially at the base ofthe roof, and other shingles that had cracked because ofdeterioration of the iron fasteners. Overall, though, theslate has proven its durability.

As the University became more wealthier, it no longerhad to rely on local rock. From 1913 through 1915,architect Horace Trumbauer and his chief designer,

Julian Francis Abele, oversaw construction of Harvard'sgreat sanctuary of books, Widener Library, using a bufflimestone from Indiana quarries for the foundation andcolumns. Packed with bits and pieces of informationWidener's building blocks house the University's mostaccessible fossil collection of marine shells.

These fossils occur in blocks of the 330-million-year-old Salem Limestone, arock unit that formed in a warm tropicalsea. These fossils occur in blocks of the330-million-year old Salem Limestone, arock unit that formed in a warm, tropicalsea. At that time most of the land massnow known as North America lay southof the equator. Shallow, clear watercovered the area that stretches frompresent-day Nebraska to Pennsylvania. Amyriad of organisms swam and crawledabout this placid sea. When they diedtheir bodies settled to the sea floor, overtime solidifying into a 90-foot-thickstone menagerie. This homogeneousmatrix of corpses formed a rock that cutscleanly and evenly in all directions.

Wave action from long gone tides shattered most of theshells, but many organisms persist and stand out. Aunicellular animal, known as a foraminifer, which livedin the ooze and muck on the bottom of the sea, iscommon in this limestone but hard to see, even withmagnification. Dotted throughout the walls, and easilydiscernible, are the poker chip-shaped stems of crinoids,an extinct relative of starfish, and half-inch longbryozoans, a sedentary animal that formed colonies ofLilliputian-scaled apartment complexes patterned likeRice Chex cereal. Many shell fragments come frompelecypods, the group that includes oysters, clams, andscallops. A rare find is a perfectly formed half-inch-longsnail shell, which resembles a tiny swirled dunce cap.

Salem Limestone is one of the most commonly usedbuilding stones in the world. Over the past century,quarries in Indiana have sent this stone to theMetropolitan Museum of Art, Empire State Building,Grand Central Station, Dallas Museum of Fine Arts, SanFrancisco City Hall, and innumerable buildings in citiesand towns from coast to coast. Other Harvard buildings

Memorial Hall displays redNew York, green Vermont,and black Maine slate.

that use Salem Limestone include the Gunzburg Centerfor European Studies (formerly the Busch-ReisingerMuseum), Lowell Lecture Hall, and Langdell Hall.

William James Hall (1964) onKirkland Street also incorporates atype of limestone at its base, but onethat lacks fossils. Instead of forming atthe bottom of a sea, the oatmeal-colored material, known as travertine,precipitates from calcite-rich water,often associated with caves or springs.(Mammoth Hot Springs inYellowstone National Park is a well-known modern travertine deposit.)

The William James panels werequarried from 30-million-year olddeposits near Rome, where travertinehas been used since the 2nd centuryBC in buildings such as the Colosseumand Quirinal Palace. Travertine hadonly a short period of popularity in Boston, though. Asin Harvard Hall's crumbling sandstone, water canpermeate the stone's Swiss-cheese-like texture andfreeze, expand and break apart the travertine.

In 1994 Harvard furthered its use of imported rocks withthe construction of Hauser Hall. The Law Schoolbuilding's yellow-gray limestone was quarried in

Germany. Chosen for itscolor, the 175-million-y e a r - o l d l i m e s t o n ec o n t a i n s n u m e r o u sstriking fossil ammonites,an extinct marine relativeof the octopus andc h a m b e r e d n a u t i l u sincluding one specimentthat is one foot indiameter.

This modern building tellsthe story of ancient seas,but also of the changingtastes and fortunes ofHarvard. The plain facadeand local rock of HarvardHall has given way to the

elaborate patterns and exotic rock of Hauser. Like allgood stories, the buildings of the main campus can beread for both text and subtext. Natural history andcultural history are linked, reminding us that living in anurban environment need not separate us from the naturalworld.

330-million-year-old Salem Limestoneincludes crinoid, brachiopod, coral, andbryozoan fossils.