January 19, 2022
An Online Presentation by Margery Winters
Margery Winters, a geologist and Assistant Director of the Roaring Brook Nature Center, gave an online presentation called Connecticut’s Story in January of 2022. What follows is a summary of her talk.
Ms. Winters began by telling us that geo means Earth, and logy means story. Geology is the story of the Earth. She showed slides of the Grand Canyon, Arches National Park and other rock formations. She told us that we can look at the rocks to understand why these places look the way they do. But the rocks also present mysteries. What happened to the material that is no longer there?
She told us about the three types of rock: igneous, sedimentary, and metamorphic. Igneous rock begins as lava. The type of rock that forms will depend on the mineral content of the lava, and the rate at which the lava cools. Obsidian is an igneous rock.
Sedimentary rock is sediment that is stuck together. Sedimentary rocks form in layers. Sandstone is a sedimentary rock.
Metamorphic rocks are those that are changed from one type of rock to another. They are formed under pressure while warm. Heat might come from steam geysers. Pressure can occur with a movement of the Earth, such as an earthquake. Granite is an igneous rock. It can become gneiss. Limestone is a sedimentary rock. It can become marble. Gneiss and marble are metamorphic rocks.
Why does Connecticut look the way it does? Geologists turn to rocks to find the answer. They describe the process as crunch, crack, and scrape.
450 to 250 million years ago, Connecticut was located off the coast of Africa. Geologists think that Connecticut was once 3,000 miles wide. Everything got crunched together. We can think of a bathmat being pushed in from the edges. At that time, Connecticut had mountains as tall as the Himalayas.
Connecticut cracked after it was crunched. The crack ran north and south down the center of the state. Rain, ice, water erosion, and lightning storms broke down the tall mountains. The sediment from that erosion was deposited in a valley in the central portion of the state.
Lava flows occurred three times in our history. Layers of igneous and sedimentary rock formed in the central section of the state. An earthquake tilted those layers. Water erosion washed away the sedimentary rock, leaving traprock ridges behind.
The scrape occurred during the Ice Ages. A continental ice sheet called the Laurentide Ice Sheet scraped the surface of Connecticut. The ice sheet was miles thick.
In time the glaciers melted. They changed the landscape as they retreated. Much of what we see in our landscape today was left behind by glaciers. The stone walls that we see throughout our state are made from rocks that glaciers left behind.
Ms. Winters closed her talk by reminding us that we use minerals every day. She told us that people have made use of quartz, copper, iron, feldspar, cobalt, tourmaline, garnet, pink granite, marble, and brownstone from Connecticut. The glass in our windows, the concrete in our buildings, the metals in our cars, all come to us from the Earth. We have them because someone knew how to read the rocks. She told us that geology is everywhere. All we need to do is look around.