Mississippi River Valley Fossils Around the Twin Cities Summit Avenue and Great River Blvd, St. Paul

Between Minneapolis and St. Paul, the Mississippi River has carved out high bluffs. Where the rocks are eroded away, you can learn about the history of the Earth for the past 500 million years or so.

The rock has layers, called beds. Each layer tells us what the area was like at the time the rocks were formed. The youngest layer is at the top and the oldest is at the bottom.

The rocks under the Twin Cities are sedimentary. This means that over millions of years they were deposited as layers of sand, mud, and life forms. The heavy weight of new layers over time compressed the muck into rock.

If you walk down the path from the monument at the end of Summit Avenue, you’ll find a waterfall and a good place to hunt for fossils. The fossils are evidence of ancient life. They tell use more about the time these rocks were formed.

About 10,000 years ago, Minnesota was covered by a huge glacier. The glaciers of the great ice ages rubbed away all the layers of rock formed during the Cenozoic and Mesozoic eras. It left deposits of sand and gravel called glacial till. When you clear away the top soil in the Twin Cities the first layer you find is this till.

The next layer you find is limestone.

Then comes a layer of muddy rock called shale. There are lots of fossils in this layer.

In some of the rock you can see the lines of the beds, where each layer might take thousands of years to form.

The bottom layer of rock right at the level of the river is pure sandstone. The sandstone is so soft, people have rubbed graffiti into it.

Investigation I collected some big rocks from the shale layer by the Mississippi River. At your tables, look at them carefully. Draw pictures representing the different kinds of fossils you see. Make a conclusion. Where would these kinds of animals live? What was Minnesota like when they were alive?

What sort of a place has sand, shells, crinoids and cephalopods in it? The bottom of the ocean! Scientists agree that what is Minnesota now used to be a shallow sea. The rocks were formed around 500 million years ago, during the Ordovician period of the Paleozoic era.

Here’s what the planet might have looked like at this time. Minnesota was near the equator, completely under water! There were no land plants. Our climate was better than Florida’s.

That’s why even though Minnesota is a thousand miles away from the ocean now, it is still a great place to collect seashells!