Architectural Geology Gallery

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To go directly to a particular subject represented in this gallery, click on its name below:

- Monuments In Stone

- Cities Of Stone

- Cladding (Facing Stone)

- Veneer, Inlay, & Other Ornamental Uses Of Stone

- Structures That Exemplify Geologic Processes

6. The quintessential emblem of Chicago's perseverance in adversity. Completed in 1869 and a survivor of the Great Fire that swept through the city two years later, the Water Tower is now surrounded by skyscrapers sporting fancy ornamental stone from many different lands. In contrast, the Water Tower is faced in local bedrock -- Niagaran Series dolostone. This limestone look-alike, formed some 420 million years ago when the Chicago area was south of the equator and covered by a subtropical sea, weathers to a heartwarming, buttery tint. This inviting luster is completely lacking in the neutral-gray Indiana or Bedford Limestone quarried in southern Indiana and used in many other buildings in Chicago and across the country (see the following two photos).

20. Another white tower of architectural distinction, Chicago's beloved Wrigley Building. At first glance, this photo seems to have little to do with geology. In fact, the monumental core of a great city is is a wonderful place to study various aspects of earth science. Not only are there many exotic types of stone used on building exteriors; one also learns that the buildings themselves must cope with the same savage forces of wind, water, salt, and ice that eventually pry apart sea cliffs and level mountain ranges. Here. a few blocks from Lake Michigan's blustery shore, some of the white terra-cotta tiles of this architectural gem have been dislodged by climatic and chemical forces. This has prompted expensive repairs -- but not as expensive as those borne by the former Amoco Building (now Aon Center) nearby. The entire surface of that huge, 80-storey structure had to be replaced with North Carolina granite when the harsh environment warped the original Carrara Marble cladding.

19. Pisa's Leaning Tower recently came perilously close to toppling over, after centuries of gradual uneven subsi-dence in the Late Pleistocene-Epoch alluvial silt in which it was so poorly anchored. The building was saved in just the last couple of years by British civil engineer John Burland, whose much debated plan to drill cores to remove sediment under the tower, to allow it to settle back somewhat, did succeed. Burland described the silt as having the "consistency of jelly or foam rubber." On the other side of the planet, Chicago's lakebed sediments aren't much better for highrises. Modern construction practices call for digging down through about 85 feet of unconsolidated glop, to anchor new buildings in the underlying Silurian dolostone bedrock.

1. For thousands of years, human beings have been the skillful manipulators of stone. This marble relief, which decorates the plinth or base of the obelisk of Theodosius I, is still on display at its original site in Istanbul -- formerly Constantinople -- in Turkey. The scene shows the emperor presiding at an event in the Hippodrome. Note the dancing girls at the bottom who somewhat offset the formality of the political notables in the rows above. This famous example of early Byzantine art shows, among other things, the excellent carving qualities characteristic of fine marble. This rock type, abundant in the central and eastern Mediterranean Basin, is recrystallized and metamor-phosed limestone or dolostone.

5. In the ancient Mediterranean, marble was plentiful and even used for paving city streets. This roadway, in the ruins of ancient Ephesus, Turkey, bears grooves made by cart traffic, as well as what has been described as the oldest surviving advertisement. There are three crude etchings here: a heart, partially obscured by the shadow of a railing at upper left; a foot providing directions to the advertised business establishment; and the rather worn portait of a woman decked out to appear as attractive as possible. In other words, this oldest ad promotes what a customary cliche calls the oldest profession.

3. In the Argolid of southern Greece. The ancient citadel of Mycenae stands on a rise of Triassic- and Jurassic-Period limestone. Much of the citadel, however, is made of much younger (Pliocene- and Pleistocene-Epoch) conglomerate that outcrops nearby.

2. The obelisk of Theodosius itself. This ancient Egyptian monument, originally erected at Karnak by pharaoh Thutmose III, was already almost 2,000 years old when it was installed at the Hippodrome in Constantinople. It is made of a much different rock type -- syenite porphyry. This intrusive igneous resembles granite but lacks quartz; it's composed of interlocking crystals of various minerals. Some of the crystals are conspicuously larger than the others.

18. Sometimes even human works provide good examples of structural geology and show what has been going on in the Earth's crust. This is the plinth of Istanbul's obelisk of Theodosius I (see Photos 1 & 2, above). Notice the splendid little normal fault in the plinth. The left side, in effect the down-dropped block, has moved the way one would expect, given the pull of gravity. It's interesting to speculate: was this fault caused by the heavy load of the obelisk borne by the plinth, or is it an indicator of one or more of the earthquakes that has from time to time rocked this ancient city? My guess is that it's the latter.

13. Inside a paradigm of Byzantine architecture, Instanbul's Hagia Sophia. For centuries the greatest church in Christendom, it was converted into a mosque when Constantinople fell to the Ottoman Turks in A.D. 1453. Then, early in the twentieth century, it was turned into a museum in keeping with the secularizing spirit of Mustafa Kemal Ataturk. The highly polished stone here complements the glittering mosaics. There are columns of gray marble and red porphyry; marble, alabaster (a form of gypsum), and other rock types are used for paneling and veneer.

14. In the upper galleries of the Hagia Sophia there are examples of what has long a widespread practice in architectural ornamentation: cutting rock slabs into halves and then mounting the pair of veneer panels to form a symmetrical, mirror-image pattern. To someone raised in the twentieth century, this inevitably brings to mind a Rorschach ink blot. Incidentally, the splendid twelfth-century mosaic depicts the Byzantine emperor John II Comnenus and empress Irene paying their respects to the Virgin Mary.

15. Other examples of the Rorschach Look in the Hagia Sophia. The minimalist mosaic above the veneer patterns depicts a solitary cross. It probably dates from the iconoclastic period (the eighth and ninth centuries A.D.), when images of human beings and their heavenly counterparts were forbidden.

17. Ornament of a different order: a bit of ancient Egypt on Chicago's Michigan Avenue. This specimen, taken from one of the Great Pyramids of Giza, is fossilifeous, Eocene-Epoch limestone quarried not far from where the pyramids were constructed. It is one of many geologic and architectural trophies collected by Chicago Tribune mogul Robert McCormick and his army of foreign correspondents from places of historical distinction. Some might accuse McCormick of being a minor, latter-day Lord Elgin, but these specimens, now mounted along the exterior of the Tribune Tower, have delighted and intrigued generations of tourists.

9. From the exterior of the 333 North Michigan Avenue office building in Chicago. This sort of ornamental stone stops geologists dead in their tracks, much to the amusement of passersby. This granitelike igneous rock contains a xenolith -- a foreign body of rock -- that was surrounded by invading magma (molten rock) far underground. The size of the crystals in the granitelike rock suggests that the magma cooled slowly, but the xenolith, probably basalt or dolerite, remained more or less intact. Note, however, the xenolith's attenuated tip at left, suggesting partial melting, and the concentric alteration zones around it. It would be difficult for any human artist to surpass the drama and sense of swirling form contained in this masterpiece of nature.

7. The Chicago Cultural Center, formerly the main branch of the city's public library. Its harmonious form is mostly clad in Indiana Limestone, the same rock that was used for the exterior of New York City's Empire State Building and many other structures across the country. The Indiana Limestone is a more workable and structurally coherent stone than the Niagaran dolostone, but even after a hundred years on a building's exterior it has all the charm of newly poured cement

8. A closeup of the Indiana Limestone facade of the Chicago Cultural Center. (A small portion of the building's darker, granite base is also visible at lower left.) The penny provides scale. Geologists classifiy this remarkably weathering-resistant rock as biocalcarenite from the Mississippian-Period Salem Limestone Formation. Biocal-carenite is composed largely of tiny bits of shells and other fossil fragments that have been firmly cemented together with the mineral calcite. When I ask my students whether this cladding is true stone or poured cement, they usually guess the latter. One reason they do is that Indiana Limestone is very easily sawn and carved into shapes that appear to have been molded.

16. Half a world away, in Chicago's Cultural Center. Here the inquisitive rockhound finds other types of exotic veneer and inlay stone. Among the materials used in the building's southern grand staircase are the white, sugary-textured Carrara Marble from northern Italy and the Connemara Marble, most appropriately green, from Ireland.

10. The Lake Forest College Campus, in Illinois about thirty-five miles north of the Chicago Loop, is one of many North Shore locales that is a happy hunting ground for the person interested in architectural geology. Besides having the obligatory Indiana Limestone building, the campus features two darkly beautiful structures in the Richard-sonian Romanesque style. Midwestern architects of this school loved the maroon-to-purple hues of the so-called Lake Superior Brownstone. The building pictured here is Hotchkiss Hall.

12. Another part of the Hotchkiss exterior. One perceived flaw in this wonderfully lurid stone -- to the architect's eye, a least -- was the white mottling found in many parts of the quarried rock. In the case of more prestigious buildings, such tainted sections were usually winnowed out during the selection process, but once in a while some mottling did make it into the facade of the new building.

11. A closeup of Hotchkiss Hall and the Lake Superior Brownstone. Quarried in Michigan's Upper Peninsula and in northern Wisconsin, this rock type belongs to the late Proterozoic-Eon Jacobsville Sandstone and related formations. Note the crossbedding in the center block and the rounded pebbles in the sand matrix. To see this rock in its natural setting, see Photo 1 in my Michigan Geology Gallery.

4. The great Lion Gate Mycenae's citadel. This cyclopean construction features massive shaped blocks of locally quarried conglomerate -- a sedimentary rock composed of pebbles or larger stones cemented in a matrix. This setting is an excellent example of two widely different ways of perceiving history. From the human perspective, these ruins undeniably evoke a sense of the ancient, yet in geological terms the rock the Mycenaens set so skillfully is itself remarkably youthful.

Want to learn more about the architectural geology of the Chicago area? You can obtain a copy of the popular and highly acclaimed guidebook Geology Underfoot in Illinois, signed by the author, by clicking here.

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