During the Silurian Period in earth history, 443-417 million
years ago, much of North America was covered by a shallow tropical
sea. A reef system known as the Racine Formation, flourished in
what is now Wisconsin and Illinois.
The rich limestone and dolomite bedrock attributed to these
formations are what the cement and quarry industries found so
appealing about Milwaukee County. This area was once the Story
Quarry. The reef, which is the oldest and best known example of
Silurian formations in North America, is listed on the National
Register of Historic Places and is a National Natural Landmark.
Remnants of a smaller reef outcrop can be found at the edge of a
parking lot on 68th & State Streets, which was once the site of
Schoonmaker Quarry.
Silurian Period reefs are noted for their abundant marine life,
and examples of the many wondrous organisms can be seen in dioramas
at the Milwaukee Public Museum. Both of these protrusions are found
to be very poor in fossil evidence, but on closer examination you
may notice color changes in the rock, and in some places even a
layering effect from the growth of the reef and ocean
sediments.
What do you see happening to the reef now that it is exposed
to the elements? Please email me your answer when logging the
cache.
Resources:
- Dott, Jr., R. H., & Attig, J. W. Roadside Geology of
Wisconsin. Missoula, Montana: Mountain Press Publishing,
2004.
- Dept. of Geology.Virtual
Silurian Reef. Milwaukee Public Museum, 1998.
- Dept. of Geology.
Geology Section. Milwaukee Public
Museum, 2004.