“Geology shouldn’t be out of sight, out of mind”
Dr. Pam Moriearty shares geological research with Logan County Genealogical & Historical Society

 

[March 20, 2024] 

At the March 18 Logan County Genealogical and Historical Society meeting, Dr. Pam Moriearty shared a presentation on Logan County’s Secret Underground Geological Features.

What Moriearty said she would be talking about is the history behind history.

Though Moriearty is not a geologist, she got hooked on geology about a year and half ago and considers herself a geological aficionado.

On the state geological survey website, Moriearty found a button you can click on and type in a question then get an answer from a real geologist the next day.

Moriearty is thankful to local experts Dr. Dennis Campbell and Viper Mine Manager Troy Kirkpatrick for helping her find information. Other experts Moriearty has received information from are Dr. Steve Altaner, Dr. Brandon Curry, Scott Elrick and Dr. Zak Lasemi, so she is also thankful for their assistance.

As Moriearty started the presentation, she gave a definition of geology, which is the science dealing with the earth’s substances, structures made out of those substances, processes by which it [the shaping of structures] happens and the history of it all.

In Logan County, Moriearty said we are in the middle of the North American tectonic plate stuck. What Moriearty referred to as “sexy geology” occurs at the edges of the plates. Faults, earthquakes, volcanoes and one plate ramming into another pushing up a whole mountain range happens at the edges.

Being in the middle of the plate means Logan County is “stuck” with sedimentary rock such as limestone, sandstone and shale. Moriearty said these rocks have been created by things settling down and getting other layers on top of them.

An exception is that glaciers drop types of non-native rocks from far away. Moriearty said these glaciers have left areas with some igneous, volcanic and metamorphic rocks. She said here, we only have native sedimentary rocks.

The geology of Logan County is “subtle” for another reason.” Moriearty said over the years, we’ve “misplaced” about 300 million years’ worth of rock layers. It has eroded away or been scraped away by glaciers and is not there anymore.

Towards the top of the geological time scale is the era of glaciers and wooly mammoths. Even further back was the pre-dinosaur era rocks. However, Moriearty said there were no dinosaurs in this area.

To understand why crops in this area are so good, Moriearty said looking under the corn and soybeans is helpful. We can find geological clues looking under crops.

At one point, Dennis Campbell decided to look under the corn and soybeans by digging up soil by the Sugar Creek bank. There was a layer carved away, so Campbell carved out an area to study the creek bank.

Something Moriearty said Campbell noticed was the creek washing mud away from a tree trunk. Campbell took pieces of the wood and sent it to some geologists. Moriearty said the geologists told Campbell what he had found was a piece of a spruce tree.

After the geologists did some carbon dating, they told Campbell the tree was 6,000 years old. Topsoil held the tree down by stuff left from glaciers here years ago.

Moriearty said Illinois shows evidence of more than one glacier. Silt was carried by water and distributed throughout Central Illinois. Unlike sand, Moriearty said silt holds water.

A geological road map of Illinois shows surface deposits and landscapes. The green areas of the map show where there was a glacier 15,000 years ago in the Wisconsin episode. Moriearty calls it the green glacier.

The pink areas on the map show where there was a glacier 150,000 years ago in the Illinois episode. Moriearty calls it the pink glacier. Logan County falls right on the edge and shows evidence of both glaciers.

Red lines on the map are silt, which is finely ground rock. Moriearty said when the glaciers melted, a lot of water flowed away from the glacier and carried the silt with it. The silt often ended up on the shore and dust storms and winds distributed it all over central Illinois. Silt makes great topsoil because it will hold water, which Moriearty said is the secret to our corn and soybeans.

Places like Lincoln Lakes provide clues to the county’s geological history. Moriearty said these lakes were made from sand and gravel pits. Around 1906, Lincoln Sand and Gravel removed sand and gravel for construction through dredging it out of the ground. The gravel was then further sorted for sale. She said geologists looked at the gravel and wood samples from there and dated them between 8,000 and 12,000 years old, which would be from the “green” glacier.

At 777 feet above sea level, Moriearty said Elkhart Hill is the highest point in the county. Some of the sand and gravel there was deposited from the “pink” glacier 150,000 years ago. Since the sand and gravel there has not been sorted or cleaned up, Moriearty said it looks different than what would be found at Lincoln Lakes.

Alongside Interstate 55 or Old Route 66 and some railroad tracks, Moriearty said people will see the Viper Mine conveyer belt used for coal mining. Years ago, she said much of the east part of Lincoln had coal mines and “coal was king.”

Over 300 million years ago in the “Pennsylvanian Era,” Moriearty said Logan County had a subtropical climate. It was home to lush marshy forests and swamps. Every once in a while, Moriearty said water levels rose and were covered by ocean water.

During the period before the glaciers melted, Moriearty said North America was sitting near the equator. This period was before the continents drifted apart. When glaciers melted, the water level rose, and we got salt water. As it got cooler and glaciers formed again, Moriearty said all the water was tied up in the glaciers, so the water level went down and there was dry land in the area.

The result of shifting sea levels was a very complex set of layers of sedimentary rock being set down. Moriearty said there may have been sandstone, shale and freshwater limestone when we were under a lake. She said limestone is made from dead critters in the water falling down and their outer layers turning into rock.

When the water level went up and we were under the ocean, Moriearty said we would have marine limestone and then shale if close to the shore and mud washed in under the water. There would then be more layers of limestone and of shale.

Below that, Moriearty said there was a layer of coal, then underclay, freshwater limestone, sandy shale or siltstone and finally sandstone.

To study these layers, Moriearty said geologists drill out a cylindrical rock core and go through it layer by layer analyzing it to see what it is, what was growing there and when it was happening.

On the top six layers, Moriearty said predominantly marine fossils can be found. In the next several layers, fossils would be predominantly non marine.

For coal formation, Moriearty said time, pressure and heat are needed. It starts out as peat, then produces lignite, sub-bituminous and bituminous (soft) coal. Bituminous coal is the kind we have. She said if water starts seeping down from layers above the coal, it can carry impurities with it.

Calcium can come down. Moriearty said the calcium may come from the limestone layer. If the calcium reacts with a plant material, she said it turns the plant material into fossils. These pieces cannot go on to be coal and they are harder. The fossils sit there in the coal, which becomes a problem for coal miners.

When this coal is taken out and processed, it creates coal balls. Moriearty said geologists love the coal balls because they can be sliced in half to show what is inside.

Something else that can happen is Fools’ gold, which Moriearty said is iron sulfide and adds sulfur to coal. We have high sulfur coal, which must be scrubbed before letting it out of a chimney after it is burned. She said the Fools’ gold comes from the layer of shale above the coal. The Fools’ gold causes problems too.

Out past Fifth Street is Rocky Ford with square lakes. For many years, Moriearty said Rocky Ford was a limestone quarry. She asked whether the limestone was freshwater or saltwater limestone.

Geologists do limestone analysis through chemical tests. Moriearty said when acid is dripped onto limestone, the limestone foams. It is the same principle used to get the scale out of coffee makers by running vinegar through it to get out calcium deposits.

Geologists also do fossil analysis, which Moriearty said shows some of the fossils came from the ocean.

The water in Logan County comes from the Mahomet Aquifer, which Moriearty said gives more geological clues. To make an aquifer, she said a waterproof bottom is needed, just like in a bathtub.

Something good to use is a groove in the bedrock carved by an ancient river. In the bedrock of Illinois, Moriearty said there are huge grooves that are ancient riverbeds. The grooves are then filled with sand and gravel and saturated with water. For the confined aquifer, she said a lid would be made from a layer of clay.

Some aquifers do not have a lid and Moriearty said those are unconfined aquifers. Most people on a well would have an unconfined aquifer. When there is a dry period and the water table goes down, the well goes down.

If you are on a confined aquifer, Moriearty said the pressure of the water going through [the aquitard] pushes the water above the water table.

Boring into these parts is what produces water.

Moriearty said the Mahomet Aquifer is critical to central Illinois with more than half a million people getting water from it. She said the latest figures show close to 800,000 people getting water from the Mahomet Aquifer.

Threats to the aquifer come from both natural and manmade pollution. Moriearty said things can seep from the ground to the aquifer and one of the worst things is arsenic. Derivatives from Fools’ gold can get into open wells, so she said regular testing of wells is recommended to make sure they are not getting contaminated.

Manmade pollution can come from agriculture, factories, industry and people in general.

Threats also come from recharging. Moriearty said when water is sucked out of the aquifer faster than it comes in, it can suck aquifers dry. Out west in the high plains, she said aquifers are being used for irrigation.

Fortunately, Moriearty said the federal government has designated the aquifer as a sole source water supply. It means the aquifer is the only source of water possible for a lot of people. Because of being the only source, she said it means we get funding and support for it. There are test wells in the aquifer to constantly monitor the water.

If you are going to start a new business, industry, factory or large agricultural livestock farm, Moriearty said you have to submit plans to the government. The government must approve the plan to help ensure you are not putting concentrated pollutants into the aquifer.

We do not see much of our geology. Moriearty has driven past these areas hundreds of times during her lifetime and said she has not thought about what was going on that she could not see.

For Moriearty, the bottom line is “geology shouldn’t be out of sight, out of mind—it’s not set in stone.” She said if we take care of our geology, it will take care of us.

After Moriearty finished her presentation, she asked if there were any questions.

LCGHS member Bill Donath asked about the depths of covered and uncovered wells.

With these wells, Moriearty and others said it depends on where you are. In some places it is 300 feet and in other places it is 200 feet. They are higher at the east end and lower at the west end.

One member had read about growing mushrooms in old coal mines.

If there is good temperature control, Moriearty said it would be possible for mushrooms to grow in old mines.

In present day coal mines, Moriearty said walls of the mine shafts are coated with white to prevent coal dust from igniting.

Once Moriearty finished her presentation, there was a short business meeting followed by refreshments.

Questions about Moriearty’s research and presentation can be addressed to her directly at [e-mail].

The next LCGHS meeting will be Monday, April 15. Gary Dodson will share a presentation on the beginnings of the Edwards Trace.

[Angela Reiners]

More resources:

“Ask a Geologist.” Illinois State Geological Survey, University of Illinois,
https://airtable.com/apppWBp5tw
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Kolata, Dennis R. and Cheryl Nimz Geology of Illinois. Champaign, Il: University of Illinois, Illinois State Geological Survey, 2010.

McDonald, Mark. “Illinois Stories: Viper Mine” 2013, YouTube WSEC-TV/PBS. https://www.youtube.com/watch?
v=wLffarjDTDM

University of Illinois, U.S. Department of Agriculture, Local Extension Councils cooperating.