The Pre-History of Chicago

Part 1 of a series

(originally published in The Landscape Contractor magazine)

To the 21st century visitor, Chicago may appear to be a landscape of steel and chrome, edged by water and suburban sprawl and dotted with green swathes of parkland. It is easy to imagine that the city, currently the third most populous in the United States with nearly 3 million people, has always looked this way.

Common sense may tell us that the city has come a long way, but it would take a mighty stretch of the imagination to envision what this region was really like in the distant past. Go back to the earth’s Silurian Period, about 400 million years ago, when much of North America was under water and coral reefs were forming in masses that nearly reached across the continent.

Experts in plate tectonics are convinced that the changes to this region were bigger than previously imagined – many experts now subscribe to the theory of “continental drift”. These scientists believe that most of the earth’s modern continents were once joined in a land mass that later broke apart and drifted across the earth. These experts believe, based on fossil evidence and recent discoveries by oceanographers, that what is now called North America was actually located near the equator in the middle of the Silurian Period, about 300 million years ago.

A turn-of-the century report on the geology of the Chicago region describes the evidence of prehistoric coral reefs and the undersea world that predated the modern city of Chicago. The author of the report, William C. Alden, noted that much of the limestone found in this region was deposited in the mid-Silurian period. This limestone is described as the Trenton group.

“In the clear waters of this Trenton sea lived a prolific and varied fauna, as we may judge from the fossil remains at places where the rock is not exposed at the surface. This fauna consisted of corals, crinoids, mollusks, crustaceans, and other invertebrates. The limestones are mostly magnesian. Wells in the vicinity of Chicago show strata 270 to 390 feet thick, referable to this group. The upper part of the formation, known as the Galena limestone, is the lead-bearing formation of northwestern Illinois. The lower part is known as the Trenton Limestone.”1

Materials such as dolomitic limestone deposited in the Silurian Period are still being excavated from two massive quarries in the Chicago area today. Limestone is not the only valuable resource to be excavated in this region, however. Alden describes in his report: “The presence of petroleum, apparently saturating the rock in places, led, in 1864, to an attempt to procure a flow of oil. A well was sunk at the corner of Chicago and Western avenues. While a small amount of petroleum was found the well failed to disclose the presence of oil in sufficient quantities to be of any value, and the attempt was abandoned.” 2

Paleontologist Heinz Adolf Lowenstam came to Chicago from Germany just before World War II and received his Ph.D. from the University of Chicago. While in Chicago, Lowenstam began to study what he called the paleoecology of coral reef fossils and environments from the Silurian Period, sifting through dumps near Stony Island. As his memoirs note, Lowenstam ultimately discovered “a massive system of Silurian reefs that stretched from the edge of the Ozark Mountains to Greenland; it had been larger and more magnificent in Silurian time than the Great Barrier Reef of Australia is today. . .{He} also realized that the porous structure of a buried reef complex was an ideal trap for oil and gas. Several major companies had discovered oil in the Chicago area almost by random drilling, and Heinz’s ability to pinpoint the locations by simply examining the cores seemed nearly miraculous.”3

The city Carl Sandburg called “stormy, husky, brawling, City of the Big Shoulders,” 4 Chicago has always seemed larger than life. Long before Chicago was a city, after the coral reefs were formed but long before humans ever walked on the earth, the region we now call Chicago, Illinois was being shaped by moving mountains of ice. The Pleistocene era, also known as the Ice Age, shaped what is now North America in four major ice movements, with the first occurring about half a million years ago.

The shifting of glaciers, century after century, deposited ice a half a mile thick as well as rocks and soil into mounds rising above sea level, and carving out depressions every time they made their southward journey. The materials left behind by glaciers fall into two classifications under the descriptive name “drift”. Materials left directly from the glacial drift are called “till”. Materials left by glacial meltwater are called “outwash”. These materials can be carried by moving ice for over 100 miles.

Naturalist and author Joel Greenberg describes this glacial effect in his book, “A Natural History of the Chicago Region”: “ Part of a huge sheet of ice born in the Laurentide Mountains of Quebec, the Lake Michigan lobe of the Wisconsin Glacial Episode covered the Chicago region until about 13,800 years ago. . .Because the underlying land was not uniform, neither was the glacial advance. The ice mass cut deeper and traveled farther in valleys where the substrate was softer. These advances, or lobes, gouged out tremendous amounts of earth, enough to create their masterpieces: the five Great Lakes holding more than 25 percent of the planet’s unfrozen fresh water. The valley that was to hold Lake Michigan was deepened five hundred to nine hundred feet.”5

A shift in the climate warmed the glacier and stopped it in its tracks, leaving a topography featuring rivers, lakes and plains shaped by the movements of the ice mountain. Debris left in the wake of the glacier created both relatively flat ground moraines and taller terminal moraines. When meltwater collected in between the tall Valparaiso Upland moraine and the glacier’s edge, geologists called the result Lake Chicago.

According to Greenberg, this ancient lake ceased to exist when the edge defined by the glacial remains finally melted about 11,000 years ago. The remaining lake water surged south, channeling through the Illinois River and the Des Plaines channel, converging on the Sag tributary and continuing on to carve the Des Plaines River Valley out of bedrock. The fast-moving waters also created a cone-shaped geologic feature called Mount Joliet along the Des Plaines River, a towering mound that attracted tourists to the region for 200 hundred years, until it was excavated for construction purposes in the mid-1800s. 6

As Lake Chicago reformed itself and the surrounding landscape, the water levels dropped, leaving a flat area of marshes and streams called the Chicago Lake Plain. Standing eighty feet above the marshy plain is an ancient upland forming the six mile long piece of land known as Blue Island. Other features of the modern landscape which were formed by the movement of Lake Chicago include the Indiana Dunes, the Calumet marshes and wetlands, the Morris-Kankakee Basin and the Illinois Beach State Park at Zion. Lake Michigan, as we know it today, only became a stable geological landmark of this region about 2,000 years ago.

Edgar Lee Masters wrote of this period in his colorful book, “The Tale of Chicago”: “Various changes came to the shore line of the Lake and to the prairie during the silent aeons until it fell to its present level ages ago. Along the way the surface where Chicago now stands was covered with a dense forest. It was not a prairie swamp such as the first white men saw when they came there. In those far days of the rising and setting of the sun the mastodon roamed the spaces of the present Loop, and after Chicago came to be, the skeleton of one of these huge, useless beasts was unearthed in the northwestern part of the city. Some millions of years ago, as it is supposed, the lake rose thirty feet, and threw up a great beach line of thirty feet, and covered the bones of the mastodons and the prostrate trunks of trees, leaving the forestry of Hubbard’s Woods, Lake Forest and Lake Bluff untouched.

“Then the Lake fell, and the site of Chicago became a marshland cut with sloughs and gullies, some of which opened into the main river of Checagou. These can be located on old maps, one at State Street, another between Clark and LaSalle Streets and one of the formidable proportions on the North Side near Franklin Street, which was eighty feet wide. A city of towers and skyscrapers could not have been built upon a marsh or even upon clay. But the Earth-makers put bowlder drift and limestone from 70 to 138 feet below the mud, upon which caissons could rest for the support of iron work extending for hundreds of feet into the air.”7

In their book, “Plants of the Chicago Region,” Gerould Wilhelm and the late Floyd Swink describe the resulting landscape: “The Chicago region is situated so that it contains an amazingly unique combination of land forms and floristic communities. Our boundaries encompass nearly all of the remarkably complex and interesting Valparaiso Moraine system, which skirts the southern edge of Lake Michigan. This region also includes the Lake Plain districts of glacial Lake Chicago and its associated “swell-and-swale” and dune systems. The deciduous forests of the east meet the western prairies and savannas; northern bogs and swamp forests are intercalated with areas of coastal-plain disjunction. Unique dolomitic limestone prairies line the Des Plaines River, and virtually all of the Kankakee River bottomlands are within our boundaries, as are the magnificent bluff forests and fen systems of the Fox River and its headwaters. It would be difficult to circumscribe another area of the North Temperate Zone with such geologic and physiographic diversity – our native flora, consisting of 1638 taxa, reflects this.” 8

Swink and Wilhelm go on to categorize the modern Chicago region into the following divisions:

*Morainal Natural Division – Young and rolling morainal topography close to Lake Michigan. The boundary follows the outer edge of the Valparaiso Moraine except in the northwest, where the line is based on geological features and presettlement vegetation. Includes the Western Morainal System, Eastern Morainal Section, Kettle Moraine Section, Racine Till Plain Section, Winnebago Drift Section, Fox River Bluff Section.

*Lake Plain Natural Division -- Characterized by lacustrine deposits and Aeolian dunes. Included within the Morainal Division by previous authors. Includes the Chicago Lake Plain Section, Gary Lake Plain Section, Benton Harbor Lake Plain Section, Illinois Dunes Section, Ridge and Swale Section, High Dune Section.

*Grand Prairie Natural Division – The grand prairie once covered much of east-central Illinois. The northeastern portion of this natural region enters the Chicago region. Includes the Grand Prairie Section, Kankakee Sand Section, Kankakee Marsh Section, Bedrock Valley System.

*Glacial Lakes Natural Division – Only one section of the Northern Lakes Division enters the eastern part of our region, the Glacial Lakes Section. 9

The end of the Ice Age formed this region, but biologists believe that the vegetation that evolved was determined primarily by the area’s climate, with episodes of fire as another determining factor. A rough timeline follows:

*8,000 years ago – Warm, dry climate encourages spread of prairie species

*5,000 years ago – Wetter, cooler conditions encourage growth of forests

Air masses from the Pacific Coast, the Gulf of Mexico and the Canadian Arctic all played a part in creating the climate of the region. At different periods, grassland prairies dominated, at other times forests or savannahs gained a foothold. Droughts hindered forest growth and periodic fires helped, rather than hurt, the advance of prairies. Wind and tornadoes also left their mark.

In spite of its rugged beginning, the Chicago region was well established by the time European settlers began their westward push. In 1673, the French Jesuit Jacques Marquette and French Canadian explorer Louis Joliet began a journey from Mackinac in search of a route from the Great Lakes to the Gulf of Mexico. The area, long the reserve of Native Americans and huge populations of wild animals and birds, was on the verge of another major change.

END

SOURCES:

1,2 “Description of the Chicago District, Part 2, Chicago Geology: Paleozoic,” by William C. Alden, 1902, http://ebeltz.netfolio/cfol-2.html

3“Heinz Adolf Lowenstam, October 9, 1912 – June 7, 1993,” Biographical Memoir by Joseph L. Kirschvink, http://books.nap.edu/biomemshlowenstam.html

4“Chicago,” by Carl Sandburg, from The Chicago Poems, http://carl-sandburg.com/POEMS.htm

“Evidence Supporting Continental Drift,” by Sharron Sample, NASA, January 22, 2003
http://kids.earth.nasa.gov/archives/pangaea/evidence.html

“An Atlas of Diversity – Protected Land in the Chicago Wilderness Region,” by Jerry Sullivan, 2000, Chicago Wilderness, Chicago Regional Biodiversity Council, US EPA
www.chicagowilderness.org

“Forever Open, Clear and Free: The Struggle for Chicago’s Lakefront,” by Lois Wille, 1972 and 1991, University of Chicago Press, Chicago, IL

5, 6 “A Natural History of the Chicago Region,” by Joel Greenberg, 2002, University of Chicago Press, Chicago, IL

7“The Tale of Chicago,” by Edgar Lee Masters, 1933, G.P. Putnam’s Sons, New York

8, 9 “Plants of the Chicago Region,” by Floyd Swink and Gerould Wilhelm, 1994, The Morton Arboretum, Lisle, IL