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The Thornton Quarry

Thornton Quarry is one of the largest aggregate quarries in the world,.  The quarry is 1.5 mile long, 0.5 miles wide, and 450 feet deep at its deepest point.  The Quarry is so vast that the entire village of Thornton could sit comfortably on its floor.

The first settlers came to Thornton, Illinois, in 1834. In 1836 Gurdon Hubbard opened the first quarry on Kinzie Street. The site was abandoned because the stone was too deep and of poor quality. Fred Gardner opened a quarry in 1846, and Stephen Crary opened one in 1850. In the early 1900s, Brownell Improvement Company purchased the entire area. Colonel Hodgkins bought the property in 1920. The quarry north of Ridge Road was opened in 1924, and a tunnel connecting the north and south quarries was developed in 1926. Colonel Hodgkins died in 1929, and Brownell repurchased the quarry in 1933. In 1938 the property was purchased by Material Service Corporation.

Many of the crushed limestone rocks contain evidence of the area's distant past. Fossils of ancient sea creatures tell the story of an equitorial tropical reef that began 600 million years ago, before tectonics had pushed Illinois and Indiana north.

Silurian Reef diorama from Field Museum - Thornton Quarry

Diorama of a Silurian reef at the Field Museum in Chicago, IL

During the Silurian Period 425 million years ago, when much of North America was covered by a shallow, tropical sea, reefs grew in the area now occupied by Wisconsin and Illinois.  A reef is a structure built by organisms that rises above the surrounding seafloor. Reefs are built in warm, shallow seawater in the tropics and subtropics. They occur only in waters that are relatively free of suspended, land-derived sediment, which allows sunlight to penetrate to the reef surface, permitting photosynthetic organisms to live.

The Thornton Reef developed from coral growth centers on the bottom of the ancient Silurian Sea.  The reefs were covered with a diverse array of strange marine invertebrates, most of which are now extinct.  Corals, crinoids, and shelled invertebrates flourished.  The Thornton reef was home to sea lilies, animals resembling horseshoe crabs, and ancient ancestors of squids and octopuses up to ten feet long.  A species of Pentamerid brachiopods (Kirkidium knightii) was common and could  grow to sizes of over 10 cm.  A thickened beak area served as a weight to stabilize the shell in the sediment, and there was no fixed attachment. They often lived as clumps of individuals.  Today, Pentamerid brachiopod fossils are easy to find on the floor of the quarry.

During the Silurian Age, the coral took in sea-water and processed out the lime. The lime deposits from the coral hardened and produced limestone. When the coral died, it stayed on top of the limestone and became part of the formation. Young coral then laid eggs on the limestone structure and began the process all over again. The result was coral and other dead sea life encased in layers and layers of limestone.

Silurian Reef Fossils from Thornton, IL. Credit Dan Lamourux

Silurian fossils from the Thornton Quarry.  Click image to enlarge.

Fossils are not the only thing found in the quarry. On June 28, 1994, a meteorite was found. It was estimated to be between 4 and 4.6 billion years old and weighed between 800 and 1,000 pounds.  Brian Rice, manager of the quarry, stated, "The meteorite reportedly hit the earth about 407 million years ago. It landed in Thornton when the quarry was a coral reef, part of a huge temperate sea similar to the Caribbean Sea."

Today, the Thornton Quarry is owned by Hanson Material Service and it is now the second-largest commercial stone quarry in the world.  It produces aggregates, stone, sand, metallurgical stone, mineral filler, and several other products. Thornton Quarry produces more than seven million tons of rock products, worth tens of millions of dollars a year. The rock can be sold as is or ground into dust for use in concrete mixing, fertilizers, or asphalt coatings. Some by-products are asphalt shingles, tar paper, building materials, and undercoating for cars.



Thornton Quarry” by Carly Herweck.  2002.


Silurian Reef at Thornton, IL”.  Milwaukee Public Museum. 1997


Thornton Quarry transformation part of 'largest civil engineering project on Earth”.  Northwest Indiana Times.  2015.


Tiny Thornton Has A Big Heart And Quarry To Match”.  Chicago Tribune.  1985

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