The Public Information Forum of Raymond Wiggers, Geologist, Author, and Science Educator
Architectural Geology of Chicago
Architectural geology is the field that explores the interplay between our built environment, the materials it’s made of, and the sediments and bedrock it’s anchored in. And Chicago is a city second to none in geologic and architectural significance.
The following images feature a small sampling of the sites and information contained in my new book, Chicago in Stone and Clay, which contains 150+ additional sites of interest, as well as a stone-identification primer and an in-depth description of Chicago’s geologic history and setting.
These photos are all copyright 2022 by Raymond Wiggers. For permission for one-time use, please contact me at ray@raymondwiggers.com.
Readers of this website are eligible for a 30% discount when pre-ordering or ordering the book. For more information, contact me at ray@raymondwiggers.com, and mention you’ve visited my “Architectual Geology of Chicago” page.
A chunk of attenuated dark amphibolite in a swirling halo of lighter crystals, in the 333 N. Michigan facade. This is a fine and highly polished example of the achingly ancient Paleoarchean Morton Gneiss, a 3.52 Ga migmatite quarried in southern Minnesota.
SITE 5.10: CHICAGO CULTURAL CENTER
Seen here from Randolph Street, the Cultural Center is one of the city’s finest demonstrations of how effective as both dimension stone and carved ornament southern Indiana’s Salem Limestone (“Bedford Stone”) can be when it serves a neoclassical design. But its use in the city began before the rise of the Beaux Arts school and continued long after it gave way to Art Deco, Art Moderne, and succeeding styles.
But the Cultural Center’s architects wisely avoided a mistake seen on many other Salem-clad buildings, where this porous, granular sedimentary rock has been continued down the exterior all the way to the sidewalk. Here a damp course of Georgia’s Stone Mountain Granite, a light gray to the Salem’s buff color, has been added. While no stone type can completely resist the onslaught of mechanical wear, temperature extremes, and salt-laden meltwater forever, this fine-grained igneous selection has proven considerably more resilient at and near grade than the Salem could have.
And the Cultural Center’s interior is one of Chicago’s most magnificent museums of building stone, both foreign and domestic, and other geologically derived materials as well. The inventory includes choicest Carrara Marble (from Italy), Connemara Marble (Ireland), Favrile Glass produced by the Tiffany Company, and Shelburne Marble (Vermont). Here, in the Grand Army of the Republic Hall, another Green Mountain State rock type, Vermont Serpentinite, proves to be the most striking selection of all. In Chicago Stone and Clay (CSC) I describe the remarkable and remarkably complicated origin of this amazing, exotic stone.
Yet another famous architectural stone, and one that can be found in many Chicago building interiors, is the Ordovician-period Holston Limestone, better known as the “Tennessee Marble.” While it comes in several different patterns and color combinations, the one shown here is the most commonly seen. It features a pinkish-tan matrix decorated with stylolites, squiggly lines that resemble miniature lightning bolts marching across the surface. In CSC I discuss what modern geologists think is the most plausible reason these striking features form in sedimentary rock.
SITE 5.19: PITTSFIELD BUILDING
A beautifully preserved Jurassic-period ammonoid fossil in a Rosso Ammonitico Veronese (“RAV”) Limestone panel in a doorway of the Pittsfield Building. This sea creature, now in a nook facing the traffic-clogged commotion of E. Washington Street, once swam in the warm waters of great Tethys Ocean.
Chapter 6: The Loop, Southeastern Quadrant
SITE 6. 7: RAILWAY EXCHANGE BUILDING
What from a distance might taken for a white marble exterior on this Burnham-designed Beaux Arts beauty is in fact terra-cotta crafted by Chicago’s own Northwestern works, sited on the eastern bank of the North Branch of the Chicago River. Terra-cotta possessed several virutues that made it a very serious competitor of building stone. For one thing, it was could be custom-designed and molded into remarkably intricate patterns. And it could be colored to closely mimic premium marbles and granites. Then again, it was lighter and therefore less costly to transport.And, as this photo from a 1907 issue of the trade journal Brickbuilder shows, it was also more easily cleaned than most stone types. This was a tremendous advantage in an age when the city was powered by the burning of soft, high-sulfur bituminous coal. Note how much soot the still-unwashed section of the building has accumulated in a year’s time.If you step inside the Railway Exchange Building to view its coolly classy, skylighted atrium, you’ll see how perfectly the white terra-cotta compliments the real (unattributed) marble of the floor and stairway. Much of the base material used by the Northwestern Company was Pennsylvanian-age underclay paleosols (ancient swamp soils) and marine shales shipped in by rail from Illinois-Basin coalfields.
Chapter 7: The Loop, Southwestern Quadrant
SITE 7.13: THE ROOKERY
An oblique view of the LaSalle Street facade of this famous Burnham & Root landmark. The lower level features Missouri’s red Graniteville Granite in both rock-faced ashlar and in stout, polished columns. Above it the higher floors are clad in two famous Chicago-made building materials that both were fabricated from Pennsyvlanian underclays and shales shipped in from the coal mines os the Illinois Basin. These are the “Brown Obsidian” variety of Chicago Anderson Pressed Brick, and complementing Northwestern Terra Cotta. The Rookery was completed in 1888, at a time the Richardsonian Romanesque style of architecture was in the ascendant. During this phase, the dark-toned look, whether provided by brown brick, brown sandstone, or duskier granites, was often favored.Detail of the basal portion of one of the Rookery’s exterior columns. The Graniteville, quarried in the St. Francois Mountains south of St. Louis, is a medium-grained alkali-feldspar granite containing crystals of pink orthoclase, gray quartz, black biotite mica, and several accessory minerals. Approximately 1.3 Ga in age, it dates to the Mesoproterozoic era.
Chapter 8: The Loop, Northwestern Quadrant
SITE 8.16: RICHARD J. DALEY CENTER
This detail of the Daley Center’s lower facade reveals the beauty of rust. The weathering-steel (Cor-Ten) exterior is designed to corrode to the point it forms its own self-sealing iron-oxide coating. In other words, initial rusting prevents subsequent rust. This is a wonderful example of the Earth-science concept of a negative feedback loop: a condition or process that triggers its own diminishment.One of the reasons this building is such a powerful and highly admired modernist design is that it can easily be seen and appreciated in its entirety thanks to the spacious plaza fronting it. The plaza, one of the Loop’s most popular and successful public open spaces, is paved in one brand of the Paleoproterozoic St. Cloud Area Granite that is quarried in the Minnesota community of Rockville. This coarse-grained igneous intrusive selection is also used as the flooring and elevator-bank cladding of the Daley Center’s lobby.
Chapter 9: Near West Side, Garfield Park, & Humboldt Park
SITE 7.1: DAILY NEWS BUILDING
A great thronelike structure sited on the western bank of the Chicago River’s South Branch, the Daily News Building is a notable example of what I call the Grand Art Deco Formula. This pattern of stone use, seen in an number of Windy City skyscrapers of the 1920s and 1930s, essentially makes the building a set-back mountain of Salem (“Bedford,” Indiana”) Limestone that is decorated at its base with a crystalline (igneous or metamorphic) rock. The latter provides a distinct contrast to the blandness of the buff Salem above it.And the crystalline rock that was chosen for the base here is the Morton Gneiss, the extremely ancient, Paleoarchean migmatite quarried in Minnesota. These cladding panels nicely show off its banded, foliated texture. Known by such gaudy and misleading trade names as “Rainbow Granite ” and “Oriental Granite,” the Morton is the oldest rock type used in U.S. architecture.
Chapter 10: South Loop, Museum Campus, Prairie Avenue, Douglas, & Bronzeville
SITE 10.10: JOHN J. GLESSNER HOUSE
The Glessner House, in the architecturally notable Prairie Avenue District, is the Windy City’s sole survivng work by the great American architect H. H. Richardson. It’s also a geologic showplace of the first order. Its outward-facing elevations feature Chicago’s best examples of pink Milford Granite, quarried in eastern Massachusetts, and Akron Terra Cotta Roofing Tile, fabricated in northeastern Ohio. (There are also replacement tiles from the original roofing of River North’s Former Chicago Historical Society.) Even the sidewalk pavers have an excellent geological pedigree; they’re Silurian-period Valders Dolostone from eastern Wisconsin.
The inner courtyard elevations, best appreciated when you take one of the highly recommended Glessner House walking tours, are faced in two of our region’s locally produced building materials, Chicago Common Brick and Lemont-Joliet Dolostone.When polished, the Milford Granite is a lovely salmon-pink; when rock- or quarry-faced, as here, it’s paler but with considerable dark flecking due to its biotite mica content. The lighter minerals include the alkali feldspars orthoclase and microcline (pink), the plagioclase feldspar albite (white to greenish yellow), and quartz (pale blue). The Milfold is Neoproterozoic in age, and formed as a batholith in the wandering microcontinent of Avalonia long before the latter collided with what is now New England and Maritime Canada.
Also note the decorative mortar, which highlights the granite blocks nicely and even complements the roof tile above it.
CHAPTER 11: McKinley Park, Back of the Yards, Kenwood, Washington Park, Hyde Park, Woodlawn, & Englewood
SITE 11.1: UNION STOCKYARDS GATE
The solitary survivor of the once sprawling Chicago stockyards, this ornamental gate (possibly designed by Burnham and Root) is one of the city’s better-known examples of Lemont-Joliet Dolostone, the most extensively used of northeastern Illinois’ Regional Silurian Dolostone varieties. Quarried in the Lower Des Plaines River Valley , this 425-Ma sedimentary rock, still a common sight throughout the region’s built environment, hit its peak of popularity with architects before the mid-1890s.
But the stone is not this site’s only geologically derived material. The copper roof, installed in 1971, shows this metal’s dark-brown, oxidized form.
As the preceding pohoto shows, the Lemont-Joliet Dolostone, mostly taken from the Sugar Run Formation, usually weathers from bluish gray to an attractive buttery yellow. But it can also spall and exfoliate as it weathers. This trait of deterioration through weathering—actually a liability of many other stone types—was one of the reasons that the Lemont-Joliet was ultimately spurned by local acrchitects and outcompeted by southern Indiana’s Salem (“Bedford”) Limestone.This closeup of the Gate’s carved ornament and ashlar shows the characteristic decayed and pitted look of Lemont-Joliet Dolostone that has weathered for a century and a half in Chicago’s brutal continental climate of temperature extremes, freeze-thaw cycles, and abundant moisture.
Chapter 12: Auburn Gresham, South Shore, South Chicago, and Pullman
SITE 12.5: GREENSTONE UNITED METHODIST CHURCH
The Pullman neighborhood’s striking Greenstone United Methodist Church. This house of worship is of first-rate geological significance because much of its exterior is clad in the rare Chester County Serpentine, quarried in eastern Pennsylvania. Above the stone rises a copper-sheathed steeple, which has weathered to the beautiful, malachite-green patina that signals the presence of copper carbonate and copper sulfate. This is the end state of the sequence of chemical changes wrought by the weathering process.
The Greenstone Church actually features three rock types. Starting at the base, a plinth of Regional Silurian Dolostone; trim, arches, and columns of Ohio’s Upper Devonian Berea Sandstone; and the Chester County Serpentinite (probably Lower Paleozoic), revealing its various shades of green as well as white calcite encrustations. This rock type had an especially exotic origin as dunite, an ultramafic igneous rock of the uppermost mantle underlying an ocean basin. Subsequently it was scraped up by an approaching landmass, chemically altered by seawater, and ultimately plastered against eastern margin of North America.
Unfortunately, the Chester County Serpentinite does not resist the elements well. It cracks, crumbles, and spalls all to easily, as this closeup shows. Consequently, architectural conservationists are trying to figure out how this vulnerable stone can be preserved or reconstituted in a more enduring form.
A portion of the church’s apse exterior is also visible, at left. It and the adjoining eastern wall offer an excellent exposure of Lake Calument Brick, the common brick used throughout Pullman for the neighborhood’s humbler homes, and also for the sides and rears more upscale buildings. It was manufacturered locally from clay deposits obtained from the floor of nearby Lake Calumet.
CHAPTER 13: The Magnificent Mile & Streeterville
SITE 13.2: TRIBUNE TOWER
The legacy of sidewalk deicers: salt-crystal efflorescence crystallizing on the Salem Limestone at the base of Tribune Tower.
CHAPTER 14: River North
SITE 14.8: RANSOM R. CABLE HOUSE
This superb example of the Richardsonian Romanesque style has an exterior of the pinkish-yellow “Kasota Stone” variety of Oneota Dolostone. Quarried in southern Minnesota but also outcropping in Wisconsin and Illinois, the Oneota is Lower Ordovician in age.Besides having a color distinct from any other building stone seen in Chicago, the Oneota has proven to be an excellent medium for carving and sculpting. Its ability to hold intricate detail for decades is here obvious on the tower base and Byzantine column capitals of the entrance.
CHAPTER 15: The Gold Coast & Old Town
SITE 15.4: EDWIN J. GARDINER HOUSE
One of the rarest and most beautiful building stones on display in Chicago is the Pennsylvanian-age Dunreath Sandstone. Quarried for a short time in Iowa’s Marion County at a site now covered by a manmade lake, the Dunreath is remarkable for its range of sunset colors.
In places on the rock-faced ashlar, sloping linear features known as crossbedding are apparent. These indicate that the sand particles that now make up this stone were deposited by fluid in motion—either flowing water, as most likely here, or by the wind.
CHAPTER 16: Logan Square, Lincoln Park, & Lake View
SITE 16.8: THE BREWSTER
Completed in 1893, this rock-faced apartment block is one of the North Side’s most architecturally intriguing buildings, both outside and in. Its unusual exterior selection is “Jasper Stone”—the Paleoproterozoic Sioux Quartzite, quarried in southwestern Minnesota and adjacent South Dakota.
Near ground level the Sioux has weathered or been stained into a lighter color, but its maroon base tint is still visible. It’s actually an orthoquartzite, a unmetamorphosed version of quartzite that owes its hardness and rugged durability to the fact its quartz grains are cemented together not with all-too-reactive calcite but with silica—in effect more quartz.
CHAPTER 17: Uptown & Ravenswood
SITE 17.1: GRACELAND CEMETERY
Louis Sullivan’s Egyptianate Ryerson Tomb in Chicago’s Graceland Cemetery. Its exterior is clad in the uncommonly dark-toned and beautifully polished Quincy Granite from coastal Massachusetts.
Intricate sculptural detail in in the Salem (“Bedford,” “Indiana”) Limestone of Louis Sullivan’s Getty Tomb. Note the staining of the central stone panels from the weathering of the bronze window grille above it. This is a deposit of copper carbonate or copper sulfate caused by the bronze reacting to atmospheric water, carbon dioxide, and sulfur compounds. The classic greenish-blue malachite patina is usually considered an ornamental asset of weathering bronze, but in this case it has also affected the stone beneath it.
CHAPTER 18: Edgewater, Rogers Park, & Sauganash
SITE 18.2: ROSEHILL CEMETERY
The Charles Fabian Jauriet Monument (1886), with its allegorical female figure reaching heavenward, is one of the most attractive of the large inventory of Rosehill memorials made of the “Blue Westerly” variety of Rhode Island’s Narragansett Pier Granite. Permian in age, this igneous intrusive rock formed late in the Alleghenian Orogeny, when compression caused by the collision of North America and Africa had given way to crustal shearing as southeastern New England rotated. This allowed deep-seated magma to rise closer to the surface.The Narragansett Pier Granite is a fine-grained selection that’s a very light gray to off-white at a distance but distinctly salt-and-peppery at close range. Its lighter-toned minerals are microcline, an alkali feldspar, and the plagioclase feldspar oligoclase. They’re joined by gray quartz and black biotite mica. Having scrutinized a large number of monuments of this stone in Chicago and Milwaukee cemeteries, I can attest to the Narragansett Pier’s ability to resist the destructive effects of weathering over the decades. It seems to be as tough as Vermont’s Barre Granodiorite and even Wisconsin’s supernaturally hard Montello Granite.
