Creekside Erratic - An EarthCache EarthCache

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 flat with little change in elevation. Next, there are few geological features of note nearby. The creek meandering through the otherwise nondescript slightly wooded prairie and the various type of rocks within that creek are essentially the only notable features. However, that does not detract from the austere, simple beauty of the landscape.

The glacial erratic at this location is a special, out of the ordinary one indeed. It's size is much larger than most glacial erratics, and 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.

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To receive credit for logging this EarthCache, please respond correctly to each of the following questions via the Geocaching.com email system (no answers in logs, please):

1. Of what material is this erratic comprised?

2. Based on the size of the erratic and it's composition, estimate it's total weight.

3. Also, take a photo of you, your team, or just your GPSr with the erratic to confirm your visit to the site.