Geologists look to the Valley as a ‘world class location’ for study

Professor Michael Stewart (in the back of the group with a light colored vest) of the University of Illinois Geology Department, discusses a rock formation along Missouri Highway 21 with a group of students. The students are tasked to find a fault in the rhyolite - rock of volcanic origin that is some 1.6 billion years old. Stewart said this spot, and other geologically significant spots in the Valley, draw geologists and their students from all over the midwest year after year.

You probably drive by a “road cut” along Missouri Highway 21 near Main Street in Ironton every day. To most people it is an insignificant, dull rock formation. However others who visit the spot every year find it a vitual learning experience.

“The is a world class location,” said Michael Stewart, a professor at the University of Illinois Geology Department. Stewart was discussing the rocks with a group of geology students who were standing by the highway, notebooks and rock hammers in hand, on a recent cold and windy Saturday.

“Right now they are going to find a fault,” the professor said, breaking away from the group for a minute.  

He explained that the rock formation is volcanic in origin and was formed and estimated 1.6 billion years ago. 

“These are volcanic rocks,” he said. “You have a geologically fascinating area. It is the closest place in the Midwest to come and see igneous rocks and the like. You get people from Wisconsin coming here because, well, for one thing it is warmer than Wisconsin.”  

He is talking about geology students and researchers from “Wisconsin, Indiana University, the University of Illinois, Southern Illinois University,  Northwestern Illinois University, Eastern Illinois University - and all the Missouri Campuses come down here.”

In fact, Stewart first visited this area as a student in 1985. 

“I have been back here as a graduate student, when I was a master’s student, as a Teaching Assistant, and I’ve been back here as a professor every year for 13 years. People like me, who have been educated in the Midwest, have all come to this area,” he said.

This particular outcrop, and other sites in The Valley, are well-known in geology circles.

“We geology professionals really protect this outcrop,” he noted. “We don’t let our students hit this with a hammer. They can break the rocks that are on the ground, but we don’t let them hit the rockface with a hammer.

“In the entire world you will never find a better example of fiamme.”

He points to some small, light colored lines in one of the rocks. Fiamme is derived from the Italian word for flames. The lines are formed of pumice and are found in ejecta from volcanoes.

“This body of rocks was erupted as a big ash pile out of a major volcano.” he explained. “These are big pumice fragments – big frothy, gas-bubble rich rocks – it is the only rock that floats because it is more gas than rock. Those would have been irregularly-shaped rocks compressed under its own weight.  You will never find a better example than that.

“We call this rhyolite, so it is like a granite, but it is an erupted version.  The crystals in here, the little white spots that you can see, is feldspar and there is also quartz in it.”

“There is also magnetite in this rock.  They (geologists) measure the orientation of the magnetic field of the 

magnetite and it can give them a paleolatitude; that is, they can figure out where this sat on the surface of the earth when it was erupted.

“I’d like people around here to know that they live in a world-class place and ... protect these things. Don’t let MoDOT do anything to this rock face. These places are critical to the education of geologists.”