Geologically speaking, there is a lot of history here in Wisconsin. Over 2 billion years of it! Obviously, we can’t cover it all in one Earthcache. Instead, we will focus on just a portion of it that is exposed in the rocks here at Durward’s Glen.
Prior to the events that we will examine, different types of rocks and minerals already existed in the area. They included granite (an igneous rock), gneisses (metamorphic rocks derived, in this case, from igneous rocks), quartz (a mineral containing silica) and hematite (a mineral containing iron).
At the point where our story begins, the world is much different than it is today. Wisconsin is partially covered by a sea. Eroded grains of quartz have been carried by water and deposited at the bottom as sand where, over time, the grains piled up in layers and compressed together under its own weight to become sandstone. Initially, the sandstone layers horizontally with the oldest layers near the bottom and the youngest layers near the top.
Now, sometime around 1.85 billion years ago, two continents in this area collided. This caused a great upheaval of the land masses. Imagine the hood of a car crumpling up in an accident, except this happened in very slow motion. As a result, one of the things that happened was the creation of the Penokean Mountains. As the two continents continued to push into each other, the resulting force and heat metamorphosed the sandstone into quartzite, identified in this region as Baraboo Quartzite. In some places, specifically near Devil’s Lake, the quartzite folded up. The layers, or strata, are no longer horizontal; the edges are tipped up at steep angles. This type of fold is known as a syncline and happened here about 1.65 billion years ago. These events happened during an eon known as the Precambrian.
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Skipping ahead in time a little bit, Wisconsin is again covered by a shallow sea. Quartzite pieces are being eroded by the elements while, at the same time, new layers of sandstone are being laid down. In many places, the older quartzite cobbles are found as inclusions within the younger sandstone. This is sometimes referred to as a conglomerate or even “puddingstone” and happened here during the later Cambrian period of the Paleozoic era, perhaps about 500 million years ago. You will see this for yourself in the Glen.
Over the next few hundred million years, the deposit of sandstone diminished and the layering of dolomite (a mineral containing carbonate) increased. This included the Ordovician, Silurian and Devonian periods, still within the Paleozoic era. Eventually, the waters receded and Wisconsin was finally dry. This was about 200 million years ago.
Skipping ahead again, this time to the Quaternary period of the Cenozoic era, a time of glaciers, the most recent of which was only 15-18 thousand years ago. Although much had already happened during the intervening years, the glaciers were responsible for significant amounts of erosion, not only in their advancement as they pushed all manner of geologic debris, but also their massive outwash of meltwater when they finally melted and receded. The glaciation was responsible for the creation of Glacial Lake Wisconsin. Unfortunately, the lake was contained at some points only by dams of sandstone and glacial debris known as till. Eventually, this gave way and the lake quickly drained in a torrential flood of water sometime around 14,000 years ago.
In order to observe and enhance some of these lessons first hand, you may now visit Durward’s Glen. The posted coordinates take you into the middle of the Glen. You can step across the small stream using stones or you may wish to wear rubber boots. The water is only ankle deep. This location gives you the best view, especially of the east wall. If you do not wish to cross the stream, you can still make most of your observations from the entrance at the south end. Do not go north past the far end of the cliffs as the property beyond is marked private. Thank you to Cathy Lins, Director, Durward's Glen Retreat & Conference Center for allowing placement of this earthcache.
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In order to claim your “Found It” for this earthcache, you must first send me your answers to these 3 tasks. To contact me, use the hyperlink found at the top of this page right under the name of the cache. Once you have submitted your answers, you may go ahead and post your “Found It” log, but do not include your answers in the log.
1. Using a protractor or a digital level application on your smart phone if you need one, estimate the angle at which the exposed sedimentary strata lies. Given the timeline of this area, why do you think that is?
2. Compare the color, texture and strength of the sandstone with the quartzite rocks . If Baraboo Quartzite started out as a sandstone before it was changed through metamorphosis, what mineral impurity might account for the difference in color?
3. Look at the depth and width that have been cut out of the sedimentary rock to form this glen. It is not very likely that this small, gentle stream cut that out all by itself. What, then, might have been responsible?
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The Geological Society of America’s EarthCache Academy: How old is the Earth? How old is the universe? How do we know the absolute age of a rock? How can we work out the relative age of a rocks? How is the age of the Earth divided up by geoscientists? You are encouraged to visit http://www.earthcacheacademy.org/ where you can learn more about Geologic Time. Other courses also available including Volcanos, Earthquakes and Fossils.
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Additional Reference Sources:
The Baraboo Ranges and Devil's Lake Gorge, A Geological Tour by Keith Montgomery, Department of Geography-Geology, University of Wisconsin - Marathon County. http://pages.uwc.edu/keith.montgomery/baraboo/baraboo.htm
Baraboo Geology by altondooley from Updates from the Paleontology Lab, News from the VMNH Paleontology Lab. https://vmnhpaleontology.wordpress.com/2011/10/17/baraboo-geology-part-1/
Roadside Geology of Wisconsin by Robert H Dott, Jr. and John W Attig. Mountain Press Publishing Company, 2004.