Keywords: forest history, reading the land, iron production, hot-blast furnace; Grade Level: ninth through twelfth grade (could be modified for college students); Total Time Required for Lesson: 50 minutes as one continuous time block; Setting: forested area near old iron furnace (adapted for the Monroe Furnace site)

Goals for the Lesson

  • Students will develop their investigative skills in looking for clues of past forest use.
  • Students will explore how forests have been used and sometimes misused in the past.
  • Students will explain the role that disturbances play in forest succession.
  • Students will reflect upon past and present uses of the forest and consider the concept of forest sustainability.

Materials Needed

  • "Forest Forensics" clues sheets (Appendix 1); one copy for each student
  • six station flags or numbers (visible from 30 feet away)
  • six "Station Exploration" question sheets (Appendix 2); one per group
  • 6 white business envelopes
  • 1 "Station Information" sheet (Appendix 3); cut apart and put in the six envelopes

State Standards Addressed: E&E Standards: Renewable and Nonrenewable Resources (4.2); Agriculture and Society (4.4); and Humans and the Environment (4.8); History Standards: TBA

Teaching Model: Experiential Leaning Model (Experience, Share, Process, Generalize, Apply)

Subjects Covered: social studies, history, (forest) biology

Topics: forest history, geography, past land use, forest ecology, hot-blast iron production

Experience Phase (30 minutes)


  1. Read over the entire lesson, including the appendices, and understand the general process of how a hot-blast furnace operated.
  2. Place six station flags or numbers should be placed at the following locations at the furnace site:
    • Above the furnace on the storage sheds site (iron ore, charcoal and limestone should be obvious on the ground)
    • In the upper mill race ditch
    • On the site of the furnace, by the main arch
    • On the casting floor area below the main arch
    • On the slag piles near the "salamander" chunk
    • By a tree increment bore demonstration
  3. Make one copy "Forest Forensics" clues sheet (Appendix 1) for each student. Make six copies of the "Station Exploration" question sheets (Appendix 2), and one copy of the "Station Information" sheet (Appendix 3). Cut the "Station Information" sheet apart and place in envelopes with the station number written on the outside. These envelopes should be placed at the appropriate station beneath the flag (or number).


"Today's lesson is entitled 'Forest Forensics.' Our objective is to explore and discover what we can about this historic site in the forest. There are many clues in the forests of Pennsylvania that tell us about the past uses of the land. Some of these clues are obvious, others are more hidden or cryptic."

Experience and Share Stages

  1. Give each student a copy of the "Forest Forensics" clues sheet (Appendix 1) and instruct them to read over the various clues listed. Discuss these briefly with the group. Tell them that they will see some of these clues today and they should use their best detective skills to try and determine what they are looking at here in the forest.
  2. Divide the students into six groups and assign each group a station number to start at. Tell them that they will have five minutes to explore each spot as they rotate from station to station. One person should be selected from each group to be the "Question Reader" and they should be given a "Station Exploration" question sheet (Appendix 2). As they visit each station, the reader should read the questions out load for that spot. After about 4 minutes, the group should share what they have discovered at the spot, and then read over the information on the "Station Information" sheet (Appendix 3)in the envelope for that station. A different group member should read the "Station Information" sheet aloud at each site. The group is free to discuss the information at each station as they go along.
  3. Each group will rotate through the six stations, spending 5 minutes at each spot. The direction they rotate is not important. The teacher/educator must keep the groups on track and not allow any groups to drag behind.

Share and Process Stages

  1. After 30 minutes, and the groups have visited each station, have the six groups come together at Station 4. The teacher/educator should now try and help the group process what they learned at each station and then try and tie the stations together to understand the process of hot blast iron production. One way to do this would be to have each group roll play the function of a different station and have them do this all at one time in order. For example, one group would be the raw materials and loading group, another would be the furnace, another would be the water race and water mill with air tubs, and so on. Another way to tie the different stations together would be to have an easel with newsprint set up and have each group assigned to a station and draw what they think happened at their station.

Apply Stage

  1. Now have the students go back to the "Forest Forensics" clues sheet they were given at the beginning. Look on this sheet for things they have seen today. Encourage them to use this sheet in a forested area they are familiar with, perhaps near their home or another favorite spot. Stress that while we cannot find clues to past land use in all forested areas of Pennsylvania, we can often find some evidence of what occurred in an area.
  2. The charcoal iron industry that existed in Pennsylvania from the late 1700s into the very early 1900s made a major impact on the southern and central forests of the state. In 1810, there were 44 major iron furnaces across southern Pennsylvania. It took between 365 and 400 acres of land to provide the charcoal for one iron furnace each year. By the time of the Civil War, in the 1860s, there were 150 iron furnaces requiring about one and a half million acres of land in southern and central Pennsylvania devoted to charcoal production. Many areas were cut repeatedly every 20 to 25 years between the years of 1800 and 1900. After the early-1900s coke (produced from coal) furnaces replaced the charcoal fired method of producing iron.
  3. This particular furnace (Monroe Furnace) we have studied today was started in 1844. By 1849 it was producing 900 tons of iron pigs annually. It employed 60 men and boys, most of whom worked making charcoal or driving wagons (teamsters). The furnace owned 30 horse and oxen to haul loads of iron, limestone and charcoal. Four to five men per shift ran the furnace when it was "in blast." There were economically hard times during its years of operation, and the furnace's ownership changed hands at least three times up to 1864. After this time it was shut down, but the forestlands (about 10,000 acres) were bought by the Freedom Iron Works for making charcoal. They operated Greenwood Furnace to the east. This firm used the lands until 1904 before shutting down (Fagley, 2001). The forests were left undisturbed after this time, with the exception of occasional cuttings or natural disturbances (wind storms, chestnut blight, and Gypsy Moth infestations). Natural plant succession restored the forest to its present state.
  4. Discuss the concept of succession with the students and be sure they understand that the trees at this site started growing sometime after the lands were abandoned in 1904. They were not planted; they grew back naturally from seeds, stump sprouts and root suckers. With very few exceptions (11,000 acres) most of the forests we have in Pennsylvania today have grown back from past cutting(s). Cuttings were carried out across the state to make lumber or charcoal, or simply clear the land for growing crops and livestock.


Take the students to another forested area and have them search for clues of past forest uses. Possibly an area that was pastured which may have obvious signs of barbed wire in the fencerow trees, and trees of similar ages. Tractor ruts or stone piles may also be present. Have the students write a paragraph about reading the forested landscape. They should discuss signs of past use and if this past use has impacted the present forest.


"This wraps up today's lesson. I hope that you've found this interesting and that you've gained a broader perspective on the way forests were utilized in the past and how clues of these practices."


Fagley, Paul (2001). Greenwood Furnace State Park. Personal Communication.

Watts, M. T. (1964). Reading the Landscape . New York: Macmillan.

Wessels, T. (1997). Reading the Forested Landscape, A Natural History of New England. Woodstock, Vt.: Countryman Press.


Sanford S. Smith, Department of Ecosystem Science and Management, Penn State


Forest Forensics Clues Sheet (Appendix I)

(Clues for Reading the Land in Penn's Woods)

Earthen Features

Road Beds


RR Beds

Charcoal Hearths ("Pits")



Gravel Pits

Mine Tailings

Clay Pits


Soil Surface Clues


Stone Walls for Livestock Retention

Stone Foundations

Stone Piles

Spring Improvements

Standing Marker Stones

Barbwire in Trees

Insulators in Trees

Stone Steps

Telltale Trash

Dumps (coal cinders, bottles, iron items, porcelain and pottery items, plastics, and old shoes)

Logging Debris (rings in stones, cables, old tools)

Oil Field Debris

Old Signs

Slag Piles

Fence Posts

Indian Artifacts

Erosion Control Structures (CCC)

Vegetation Clues

Vegetation Changes (abrupt or gradual)

Infestation Kills

Tree Ring History - "Dendrochronology" (through increment bores, cut trees)


Branch Whorls on Pines/Spruces

Tree Diameters (forest structure)

Non-Native Plants (plantings or escapees)

Blazes on Trees

Burn Scars

Logging Scars

Trunk Flair (sweep) on Trees (pastures)


Forest Stand Changes

Multiple Broken Tree Tops (ice storms)

Pine Plantations (such as those planted by the Civilian Conservation Corps (CCC))

Station Exploration Question Sheets (Appendix II)

Station No. 1

At this spot on the ground there is evidence of the three natural resources that were used at this iron furnace. What are they? Why might they be found at this location? Are they renewable or nonrenewable resources? How were they used in the furnace?

Station No. 2

You should be standing near a long sloping ditch. What might this have been used for? Hint: A natural resource "ran" in this ditch. How was it positioned in respect to the furnace? Where does it come from? Where does it go? Are there any other similar ditches near by?

Station No. 3

You are standing in front of the main "arch" or opening of the furnace stack. On the sides of the furnace are two smaller arches. What were these used for? Are there any holes or chambers in the furnace? Why? How was the furnace held together? How did this furnace operate?

Station No. 4

What might have happened on this flat area beneath the stack? What can be seen in the hole dug at this station? Is it possible there was a building at this location?

Station No. 5

The ground at this station is littered with some interesting materials. Take a close look at these "stones." Are they natural? Are they uniform? There is one large chunk of this material at the base of the station flag. This is called a "salamander." Any ideas why?

Station No. 6

This is the one station that does not relate directly to the furnace's operation. In one of the trees by the station flag, there is an increment borer. This tool was used to remove the small tube (or core) of wood still in the borer, and from three other trees nearby. These other cores are on the ground beneath the borer. Study these cores and determine how old the trees are around the furnace area.

Station Information Sheet (Appendix III)

Station No. 1

The red stones here are iron ore, the black burned looking wood is hardwood charcoal, and the light gray stones are limestone. These were the three main ingredients for making iron. The ore has iron in it, the charcoal provided intense heat, and when melted, the crushed limestone helped clean the impurities from the ore. These materials were stored in large buildings here above the furnace and loaded into the top of the furnace every half hour, 24 hours a day (when the furnace was in operation or in "blast"). These materials were loaded into the top of the furnace by crossing a wooden bridge that spanned the gap from this spot. Charcoal was the only renewable resource (from trees) used to manufacture iron. It was produced in the woods along this ridge in what are called "charcoal pits" or "hearths". The wood from about one acre was used to fire this furnace each day. A mill this size needed about 10,000 acres to stay in operation. The ore and the limestone were hauled to this site from nearby deposits or mines.

Station No. 2

This was the "mill race" through which water ran to a large water wheel along side of the furnace. The water originated from a small pond about 200 yards from this spot. This wheel drove a series of wooden air pumps (called "blowing tubs") to pump air to a cast iron heat exchanger at the top of the furnace. This hot air then blew down iron pipes into the furnace to blast the fire with oxygen. After the water ran over the water wheel it flowed down another race and out the lower end of the furnace facility into Shaver's Creek. What do you think happened when the water froze in the winter?

Station No. 3

The main "arch" of the furnace stack was where the molten iron flowed out of the furnace's crucible. Iron was "tapped" out of the furnace 2 times per day. The two additional arches on the sides of the furnace where called the "tuyere" arches. Tuyere means nozzle in French. These are where the air was pumped into the furnace from the heat exchanger on top of the furnace. The iron tuyere pipes were hollow at their tip (nozzel) end and their walls were filled with water to keep them from melting in the intense heat near the furnace. Temperatures in the furnace rose over 2400 degrees F. Did you notice the iron rods in the stones? These helped hold the furnace held together, and have done so for over 150 years!

Station No. 4

This area was inside the main furnace building. The building enclosed the casting floor area. The molten iron flowed out of the furnace and onto a sand floor where it hardened into thick iron bars or "pigs." The casting sand used on this floor was coarse and red in color. It was called Albany sand and it was brought here from Albany in upper New York State. It had a clay binder in it that allowed the iron to harden without picking up too much sand. Did you see any of this sand in the hole? If not, why not? Has the land base around the furnace changed over time? What might explain this? Might the nearby road been a factor?

Station No. 5

You are standing on slag piles. Slag is the by-product from smelting iron ore. It is the waste matter. It can be gray, blackish-green, or light mossy green in color. It sometimes looks like glass or lava. Much of the area below this furnace is filled in with slag, and much of the road fill near-by is also slag. The large chunk of slag is called a salamander. Any ideas why? A large piece of slag like this one needed to be removed from the base of the furnace each time the furnace was shut down. If you look closely at this you may see some small pieces of brick stuck in this. These are pieces of the inner portion of the furnace that broke off when the salamander was being removed.

Station No. 6

The trees in this area are approximately all the same age. The tree rings tell the story. The trees grew back naturally after the land was no longer being used. Does this mean that the mill shut down 80 years ago? Or, could it be that something else occurred here. The tree rings cannot tell us everything, but they do indicate that all the trees started to regrow at about the same time.