These organisms took calcium carbonate out of their chemical-rich environment to form their shells. When they died, these shells fell to the bottom of the ocean and dissolved, re-turning the heavy calcium carbonate molecules to the water. Added to the existing minerals, the ocean became like a supersaturated solution, and the heaviest elements began to fall out.
"Think of it like a supersaturated salt solution, like what you might gargle with if you had a sore throat," said Tom Hickson, an assistant professor of geology at St. Thomas. "You can stir a lot of salt in but, at some point, the water can’t hold any more."
The shore of this primordial sea dissected Minnesota from the southeast to the northwest, explained Hickson. As the water warmed and receded, it left a low-relief plain of particulate — what we know as limestone. Thousands of years later, magnesium-rich ground water percolated through this limestone.
The magnesium replaced the calcium, forming magnesium carbonate, which geologists call dolomite after its namesake mountain range in northern Italy.
Fast-forward several million years and this same stone graces most of the academic buildings on the Minneapolis and St. Paul campuses of the University of St. Thomas.
"Mankato-Kasota stone is just an informal name for a localized deposit of Oneota dolomite," said Hickson. "It’s part of the Prairie du Chien group of rock, which makes up the principal aquifer in the state."
Mankato-Kasota Stone Inc. has been quarrying the dolomitic stone surrounding Mankato since the middle of the 19th century. Once one of dozens of quarries in southeastern Minnesota, the company is now one of only two in the region.
"James J. Hill’s Stone Arch Bridge across the Mississippi in downtown Minneapolis is our stone," said Jim Coughlan, executive vice president of the stone company that has been part of his family’s history for more than 100 years. "As the railroads built the West, we helped to build the railroads."
It was Coughlan’s great-grandfather, T. R. Coughlan, a stonecutter from Ireland by way of Canada, who began the family’s generations-long relationship with stone. He and his son, T. Merritt Coughlan, supplied strong stone for bridges, piers, depots and warehouses during the early part of the 20th century. The urbanization that followed World War I increased demand for the yellow-gray stone for industrial and commercial building, and the company thrived.
T. Merritt Coughlan’s sons, Thomas, Bob and Dan, took over management of the company in the 1950s and added stone fabrication to the quarrying operation. Over the years, the Coughlan Companies have expanded to include banking, publishing and screw products operations, but the stone company remains at the heart of the family business — and the most visible expression of the Coughlans’ long relationship with St. Thomas.
"When I was 11 or 12, I’d often go over to my grandparents’ house and see a big, fancy limousine out in front of their house," remembered Bill Coughlan, vice president for administration. "It was Ignatius O’Shaughnessy visiting my grandfather."
O’Shaughnessy and T. Merritt Coughlan were classmates at St. Thomas. Years later, O’Shaughnessy accompanied then-St. Thomas president Rev. Vincent J. Flynn to ask T. Merritt for the first gift of stone, which was used to construct the quadrangle buildings.
The quarries that surround Mankato are similar to — although more attractive than — the open pit mines of Minnesota’s Iron Range. Standing on the lip of a 20-acre crevasse, you can watch toy-sized bulldozers hoist and move 20-ton chunks of limestone as if they were sugar cubes.
The layers of gray, golden buff and cream dolomite lie on silica sand under 60 feet of rubble or "over burden." The quarrying process begins with blasting and carrying off this waste rock that glaciers deposited over the smooth ledge of Mankato-Kasota stone.
"We contract that part out," said Gayland Hamilton, who oversees extraction at the Jefferson Quarry, one of two owned by the Coughlan family. The family’s first property, the Mankato Quarry, has been emptied of Mankato-Kasota stone. The Jefferson Quarry will provide stone for another 12 to 20 years "but there’s not an infinite supply," Bill Coughlan said. The company recently purchased a third quarry location to ensure an adequate supply of stone for current customers’ future projects.
The next step in quarrying is to mark out blocks measuring 8’ 6" by 4’ 7" with spray paint. Massive jackhammers drill a pattern of holes along the cut lines then hydraulic splitters expand these holes and loosen the blocks of stone. A giant forklift simply wedges its fork into the wall of limestone and cracks the pieces off with a satisfying crunch.
Each block weighs 20 to 25 tons — the equivalent of six cars compressed into a compact cube. The blocks are numbered to identify them. For example, "C-220-00" is the 220th block of cream stone quarried in the year 2000. The cubes are left in the open air to "cure" for at least two months to let any water evaporate out of the stone before cutting. Each year, the company harvests upwards of 1,500 blocks of dolomite to "keep us busy over the winter," according to Hamilton.
It’s a simple process, not much different than cutting and serving a massive sheet cake. But standing beside a forklift with tires taller than the average man and looking out over the building blocks that will become museums, post offices and corporate headquarters, it’s easy to feel a sense of majesty, to be impressed both by the dignity of the stone itself and by the audacity of the people who cut and bend it to their will.
Cutting stone is a dirty, dusty business. Huge "gang" saws work through the blocks with an elliptical motion like an engine piston, spraying shards and sand.
"They were old when my dad got them at the end of World War II," said Bill Coughlan of the multiblade gang saws that function like giant bread-slicing machines.
Built in the 1920s, the saws have a "gang" of parallel blades, which are set by hand to ensure the proper width of each slice of stone. It takes about 20 hours for the saws to cut through a 4-by-8-foot slab of stone, according to Bill Coughlan. The company usually runs two shifts, keeping the loud saws humming 16 hours a day.
As the saws work through the dolomite, workers insert wooden spacers to keep the half-cut slabs from collapsing upon each other.
"Like any saw, the blades will bind when they get near the end of a block," said plant manager Rick Westmark. "The more accurately we cut the stone at this stage, the less honing or grinding we have to do at the next station."
Computerized rover saws run by intricate software have joined the gang saws in recent years. The 6-foot saw blades hang from the ceiling and move like pendulums through blocks of stone. These saws often are used to cut angles or make other specialized cuts, explained Westmark.
Blocks can be cut one of two ways: fleuri-cut with the sedimentary bed, revealing a richly marbled "flowered" pattern, or veine-cut across the beds to expose the sedimentary, layered nature of the rock.
"They are both pretty," said Bill Coughlan. "It just depends on the look the customer and architect want to achieve."
Once cut into slabs, the stone is moved into the next room of the plant for polishing. The thin 3-inch, 4’ by 8’ slices of dolomite are hoisted on chains to be placed in front of large buffers or onto an automated polishing line to hone the rock face to the desired look. This stage offers even greater aesthetic possibilities than the simple cut of the stone. Options range from a reflective polished finish to a sandblasted tapestry finish that exposes in relief the natural variations in the stone.
The most naturalistic finish — rock face finishing — actually requires the most hand labor. Using an old-fashioned mallet and chisel, trained masons hammer and carve the stone to give it a rough-hewn look. Builders often use this look for rugged bridges and other massive structures.
Slotters cut a narrow trench on the back of each piece so that it can be hung on the superstructure of a building on a metal hook. The final finishing work is done by hand. Employees sand each piece by hand, filling large geodes — usually holes left by long-dissolved shells or missing fossils — with a mixture of epoxy and stone dust. The company employs strict quality-control measures throughout the cutting and polishing process.
"We have several checks during the process," said Westmark, "not just for measurement but for color and other aspects as well. We don’t want to find a mistake as the piece is going out the door."
"If something isn’t right, you can’t just throw it in the hopper and start again," added Bill Coughlan.
Thirty percent of the stone quarried is waste because "God created this stuff and it’s not perfect," continued Coughlan. The waste is crushed for roads, agricultural lime and other products.
The family also intends to find secondary uses for its quarries when they are emptied of stone. The company has submitted plans to the city to sell industrial lots in the emptied Mankato Quarry and hopes to turn the Jefferson Quarry into an industrial park. The third quarry could become a nature area after its useful life as a source of stone.
Once cut and finished to a customer’s specifications, the stone slabs are shipped to the construction site to be hung on a building frame. Pieces are lifted into place by hand or forklift and crane and anchored on metal fingers or hooks, then mortar or "mud" is spread between them to seal them in place.
To get a sense of scale, it took dozens of masons eight months to fix 55,000 feet of stone in place on the Frey Science and Engineering Center, the largest St. Thomas project to feature the characteristic dolomite. Other Mankato-Kasota stone buildings at St. Thomas include Coughlan Field House — named for the current company owners’ grandparents in 1982 — Schoenecker Arena, the Murray-Herrick Campus Center, O’Shaughnessy Educational Center, and O’Shaughnessy-Frey Library Center additions, O’Shaughnessy Hall athletic building, O’Shaughnessy Stadium, Koch Commons and the St. Paul Seminary buildings in St. Paul, and Terrence Murphy and Opus halls on the Minneapolis campus.
The Mankato-Kasota stone quarry normally operates from April 15 until Oct. 15, depending on the weather. During the winter months, the company keeps the five quarry employees busy overhauling machinery and refurbishing equipment. The reason for this is twofold: the company prides itself on never having laid off employees — even during the Depression — and the practice ensures continuity of skilled workers.
Employees in the field and on the shop floor praise the Coughlan Companies as being a company with a family orientation: "They do unto employees as they would do unto each other," said one stone polisher over the din of his whirring machinery.
That sense of family is important to the Coughlans. After leasing the stone operation to Babcock Co. in 1972, Thomas P. Coughlan bought it back in 1983 when Babcock declared bankruptcy. His sons Bob and Jim Coughlan then leased the business from their father, and Bill joined the company in 1984. John Coughlan is the publisher at Capstone Press, the family’s educational publishing house, where his sister, Joan Coughlan Berge, is head sales person. Maryellen Coughlan Gregoire, a teacher with the Wayzata Public Schools, contributes to the company Web site. Dan Coughlan lives in California. Thomas Coughlan’s other daughter, Ann Coughlan Corcoran, died in 1986.
"My father’s greatest legacy was his family," said Bill Coughlan. "We learned philanthropy from our dad and have tried to continue his generosity." In addition to selling stone at discount prices to St. Thomas, the family has made a gift to the School of Education of every title published by Capstone Press and supports a scholarship and internship for undergraduate students. Bill Coughlan, who, in rebellion, attended St. Mary’s University of Minnesota rather than St. Thomas, where his father was a longstanding trustee, also funds a scholarship to assist Christian Brothers and School Sisters of Notre Dame to continue their education at St. Thomas.
"When my father was dying, I sent a ‘nasty gram’ to all of his friends saying, ‘you don’t have to come to his funeral but you should come to see him while he’s still alive,’" remembered Bill Coughlan. "Monsignor Murphy came almost every weekend.
"St. Thomas always has been very supportive of us," he continued, "and we of them."
Local landmarks in Mankato-Kasota stone
Adath Jeshurun Synagogue, MinneapolisBlue Earth County Courthouse, MankatoLaSalle Plaza, MinneapolisSt. Olaf Catholic Church, MinneapolisSt. Paul Companies, St. PaulUnited States Post Office — General Mail Facility Expansion, MinneapolisWCCO-TV, Minneapolis