***This is an Earthcache!!!!***
***There is no container to find and the posted coordinates will take you to a trailside Erratic located in the Gander Mountain Forest Preserve***
Here and there in Illinois are boulders lying alone or with companions in the corner of a field or someone's yard, on a courthouse lawn or a schoolyard. Many of them—colorful and glittering granites, banded gneisses, and other intricately veined and streaked igneous and metamorphic rocks—seem out of place in the stoneless, grassy knolls and prairies of our state. Their "erratic" occurrence is the reason for their interesting name.
These exotic rocks came from Canada and the U.S. states to the North. The continental glaciers of the Great Ice Age scoured and scraped the land surface as they advanced, pushing up chunks of bedrock and grinding them against each other or along the ground surface as the rock-laden ice sheets pushed southward. Sometimes you can tell where the erratic originally came from by determining the kind of rock it is. A large boulder of granite, gneiss, or other igneous or metamorphic rock may have come from Canada. Some erratics containing flecks of copper were probably transported here from the "Copper Range" of the upper peninsula of Michigan. Large pieces of copper have been found in glacial deposits of central and northern Illinois. Light gray to white quartzite boulders with beautiful, rounded pebbles of red jasper came from Ontario, Canada. Purplish pieces of quartzite, some of them banded, probably originated in Wisconsin. Most interesting are the few large boulders of Canadian tillite. Glacial till is an unsorted and unlayered mixture of clay, sand, gravel, and boulders that vary widely in size and shape. Tillite is glacial till that was deposited by a glacier many millions of years older than the ones that invaded our state during the Great Ice Age. This glacial till has been around so long that it has hardened into a gray to greenish gray rock containing a mixture of grains of different sizes and scattered pebbles of various types and sizes.
Many boulders were probably dropped directly from the melting front of the glacier. Others may have been rafted to their present resting places by icebergs in ancient lakes or on floodwaters of some long-vanished stream as it poured from a glacier. Still others, buried in the glacial deposits, could have worked their way up to the land surface as the surrounding loose soil repeatedly froze and thawed. When the freezing ground expands, pieces of rock tend to be pushed upward, where they are more easily reached by the farmer's plow and also more likely to be exposed by erosion.
As you approach this glacial erratic, you will likely notice several things about the terrain. First, the topography is quite hilly (you are on Gander Mountain, after all!), and one of the highest elevations in Illinois. Meadows interspersed with wooded areas cover the 300+ acres of Gander Mountain Forest Preserve, with trails for hiking, mountain biking, and horseback riding.
The glacial erratic at this location is slightly smaller than others found in the area, but it's composition is atypical of most erratics found in this region. Using the data in the paragraphs above, attempt to determine the composition of the erratic, which will be useful when answering the questions below.
In order to log a find on this Earthcache, you will need to complete all of the items below:
- Park at N 42 29.590 W 088 11.943, and follow only the mowed trails towards GZ (the erratic is mere feet from a trail).
- Continue along the trails to the posted coordinates for this cache, and take a photo of you and/or your caching group and/or your GPSr, and post it in your log.
- Send me an e-mail through my geocaching profile page with what material you believe this Erratic is comprised of, and it's estimated weight.
