To claim this Earthcache:
Find the erratic boulders along the Coneflower Trail. What colors are they? Try to find a fossil in the limestone here. What kind of fossil do you think you found? Please message byronforestpreserve with your answers.
Before you lies evidence of geologic history of Illinois spanning 439,850,000 years (give or take). You should be able to see two different kinds of rocks at the surface—igneous granite boulders originating in Canada and the Great Lakes, and our native dolomite limestone, a sedimentary rock. The limestone and granite are here because of some of the highest and lowest ocean levels in Earth’s history.
The limestone was deposited near the end of the Ordovician Period, which lasted from 443-485 million years ago. During that time, the Earth was warmer, and very little ice was frozen at the poles or in glaciers. The ocean level was high enough to cover most of North America in a warm, shallow sea. When sea creatures died, their shells and skeletons created layers of sediment that, over millions of years, eventually became limestone; sometimes, the imprint of the animal remained in the rock to make a fossil. This particular spot is absolutely covered in fossils of solitary rugose corals, also known as horn corals. These look like dinosaur teeth to some, but the corals that made these fossils lived millions of years before the first dinosaurs. All horn corals went extinct around 250 million years ago, just before the first dinosaurs appeared on Earth. You may also find fossils of colonial coral, which is related to the reef-building corals still found in oceans today. Some of these are filled with quartz crystals, made of dissolved sandstone which was part of an extensive beach along the edges of the ancient sea.
Though the granite in these boulders is older than the limestone (2.5 to 4 billion years old), these glacial erratics have only lain here since the last time a glacier covered this part of the rock river valley. Giant sheets of snow and ice formed over thousands of years as the Earth stayed cooler during the summers, and glaciers expanded and melted several times over the span of the last 2.6 million years. During the Illinois Glacial episode, which ended about 130,000 years ago, ice sheets 700-2,000 feet high slowly moved across Illinois, carrying rocks from Canada and Michigan, which were left behind when the glaciers melted. The more recent Wisconsin Glacier did not quite reach this part of Illinois, but depositied sand and gravel along the Rock River Valley. You may see some smaller gravel, especially rounded quartz pebbles, from this melting glacier.