Illinois Furnace Historic Site EarthCache
Hidden : 11/24/2015
Difficulty:
2 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:

Welcome to the Illinois Furnace Historic Site Earthcache. An EarthCache is a special geological location that you visit to learn about a unique feature of the Earth. In order to log this geocache as "Found", you will have to provide answers to questions by observing the geological location. For more information about EarthCaches visit Earthcache.org.



**Logging Requirements**

DO NOT POST ANSWERS IN YOUR LOG. Send the following answers to me via email or a message by clicking on my name above.

A.    The text "GC67CBE - Illinois Furnace" on the first line.
   
B.   Examine the limestone blocks that make up the structure of the furnace. Answer the following questions:
       1)   Is the limestone blocks Ste. Genevieve Limestone, St. Louis Limestone, or Salem Limestone?
             a)    Why do you think this is your choice.
           
             b)    Sketch one of the blocks.
            
       2)   Are there any fossils present?  If so, sketch the fossil and identify by name.

       3)   Are there any other features present in the limestone blocks?  If so, sketch the feature,

C.   Place a date on your sketches and take a picture of them.  Upload them to your online log at geocaching.com

D.   Optional (but greatly appreciated): Take a photo of you (and your group) standing by the Illinois Furnace sign with the furnace in the background.


**Safety**
Climbing the Iron Furnace is not only DANGEROUS and is PROHIBITED.

**Illinois Furnace Historic Site**
Recommended Season: All year - Site open daily 6am – 10pm

Facilities: Accessible picnic shelter, vault toilets, interpretive signs.

Access: From Harrisburg take Highway 34/145 south 6 miles, then continue on Highway 34 south for 16 miles to Highway 146. Go east on Highway 146 for 3.5 miles to Iron Furnace road, turn north and follow the directional signs to the historic site.

 **History**
The Illinois Iron Furnace is the only remaining iron furnace structure in the state of Illinois. Iron was manufactured at the Illinois Furnace by the charcoal blast method. The furnace was built on a dry laid limestone foundation. The exterior of the furnace was manufactured of large limestone blocks quarried near the town of Cave-In-Rock. The interior wall, or lining, wasconstructed of firebrick from Pennsylvania. The space between the interior and exterior walls was filled with sandstone. Wrought iron binders were placed through the stonework and tightened to secure the walls. All of the stonework was dry laid to allow for expansion when the furnace was in blast.

It was built about 1837, and rebuilt and enlarged in 1856, and continued operations until the beginning of the rebellion in 1861, when it stopped. It was 32 feet in height. The furnace appears to have been in operation sporadically between 1872 and 1879. In August 1880, the Illinois Iron Furnace was “blown in” and manufacturing continued through 1887.  The furnace was partially destroyed in the 1930’s to supply rock rubble for the embankments of the Hog Thief Creek Bridge built by the CCC. The current appearance of the Illinois Iron Furnace is due to a reconstruction in 1967. The reconstructed furnace core is solid, having been filled with rubble and concrete.
Before Reconstruction     After Reconstruction
**Depositional History**
Rock units present in the Cave-In Rock area are middle and upper Mississippian (Valmeyerean and Chesterian) sedimentary rocks, late Permian igneous intrusions, and Quaternary deposits. Fluorite, calcite, barite, sphalerite, and galena are present along faults and fractures.  The Mississippian Period is the interval of Earth's geologic history from about 360 to 320 million years ago (fig. 3, below).  The Mississippian rocks are as deep as 5,000 feet beneath the surface. In western and southernmost Illinois, Mississippian rocks are shallow and exposed at the surface around the edge of the basin.

Limestone, the most abundant Mississippian rock type in Illinois, is primarily calcium carbonate (calcite, or CaCO3) and can form in several different ways. One of the most common ways begins with sea animals (such as crinoids, brachiopods, bryozoans, and mollusks) that secrete calcium carbonate to form their protective shells. When these animals die, their shells collect on the sea floor. Often the shells are broken by strong currents (due to storms and tides) near shore and are carried seaward. When these shells become compacted and cemented on the sea floor (by calcite that precipitates from the sea water), limestone forms.  Some limestones (for example, oolitic limestone) are a chemical precipitate from the sea water. Others (for example, micrite) form in part through precipitation caused by microbes, algae, or other organisms. In some cases, limestone is recrystallized to form a magnesium-rich carbonate rock called dolostone(or dolomite).

During Valmeyeran time (fig. 4, below), an inland sea covered much of the midcontinent. Today, these Valmeyeran-age limestones are up to 1,800 feet thick in southeastern Illinois, where they are buried as deep as 5,000 feet.  These limestones (the Ullin, Salem, St. Louis, and Ste. Genevieve Limestones) formed in the warm, clear, and progressively shallower water.  Near the end of Valmeyeran time, as relative sea level gradually dropped, the northern shoreline moved southward and exposed more land. This transition marked the end of the Valmeyeran Epoch and the beginning of the Chesterian Epoch.
Stratigraphy     inland Sea

**Paleostratigraphy**
Ste. Genevieve Limestone is light gray to medium gray.  The entire formation is composed of a diverse marine fauna, with crinoidal debris and oolites being the most common. Concentrically banded chert nodules occur occasionally and become more common lower in the unit. The Ste. Genevieve weathers to a soil that is dark reddish brown.

St. Louis Limestone is medium to dark gray. The unit is cherty with gray to blue-gray chert nodules and contains a diverse marine fauna including brachiopods, crinoids, and corals (colonial and solitary).  The St. Louis weathers to a dusky red soil. 

  Salem Limestone is light brown to very dark gray composed of rounded and broken fossil fragments. The fossils are primarily small rounded disarticulate echinoderm and fenestrate bryozoan fragments. Other macro fossils include brachiopods, and pentremites. The Salem weathers to a reddish brown.
St Gen LS     Sal St Loius LS
Typical Mississippi Fossils A   Typical Mississippi Fossils B


Permission for earthcache placement provided by Shawnee National Forest - Hidden Springs Ranger District.   Prior to your visit plan ahead to prepare for a safe and enjoyable trip.  Please be aware you could face inherent risks of adverse weather conditions, isolation, physical hazards, and lack of rapid communications, especially in remote areas of the Forest. Search and rescue may not be as rapid as expected. 



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