This Erratic
rock was brought down to this area by the glaciers. As the glacier
moved south, it pulled along these rocks and as they moved they
where ground round. They started there journey here from states up
north of us and even as far away as Canada. When the glacier
started melting and stopped moving south, it dropped these rocks in
a erratic manner. This errtaic was dropped into this land that
became a farm field later through property acquisition, a public
park for everyone to enjoy. And to think, this huge rock was moved
here by a sheet of ice.
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 states 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.
When glaciers melt, they leave behind whatever they were carrying.
This may consist of a mixture of rock debris and old soils, called
till, material that was ground-up and deposited from the base of
the glacier. Some of the most striking reminders that the landscape
was once covered by glaciers are boulders and cobbles, called
erratics, that dot the landscape. Unlike the rock you find in local
quarries, these are exotic rocks. In Illinois, erratics are often
granitic rocks like those you would find today hundreds of miles
away in Canada.
Glacial
meltwaters carried ground-up rock debris away from the glaciers. In
the valleys of major meltwater channels, like the Mississippi and
Illinois valleys, this debris settled out as layers of silt, sand,
and gravel, called outwash. On dry, windy days, the finest
particles of this outwash were blown across the landscape in
glacial dust storms. These particles settled across the landscape
to form a blanket of silt-size particles, called loess. Loess forms
the basis of the young, rich soils of the northern plains of the
United States.
This rock
stands in the place of one of the first Cook County Schoolhouses.
The rock was placed here on the 125th anniversary of the
school.
To
log this earthcache you must,
1. Post a picture of you next to the erratic rock with your gps in
your hand. This erratic is in a public park but accessible from the
road and sidewalk.
2. What material is this rock made of?
3. What is the height and circumference of the erratic
rock?
