The World's Foundations; or, Geology for Beginners · Ch. XV · Unit 2: Part II: Ancient seas and coal forests
16. More about the age of coal
Goal: Your child can explain what alternating layers of coal, limestone and sandstone tell us, and can read a fossil footprint trail.
You'll need
- The book, open to this chapter
- A strip of damp sand outdoors, or a long sheet of dark paper and a little flour or water for footprints
- A notebook for a "rock journal" and a pencil
What's in the book
Chapter XV says that coal is only a small part of the coal-rocks (in South Wales, about 120 feet of coal in 10,000 feet of rock), describes the warm, misty climate and the giant plants, and introduces the amphibians, with a slab of footprints from America. It ends with the upheaval of the Alleghany Mountains and the close of the Ancient-Life Period.
The lesson, step by step
A question to start
SayIf you saw a fossil footprint trail, how could you tell whether the animal was walking or running?
Keep the question for the activity.
Read the chapter together
Read Chapter XV (pages 135 to 142). Sentences to stop on:
In any piece of coal you may see the thin even layers. They show distinctly, but do not separate easily.
Club-mosses, which now are never seen more than four or five feet high, then grew to a stature of sixty or seventy feet.
Reading alternating layers
The book gives a key: coal tells of forests on land; limestone tells of the sea; sandstone may tell of either. So a pile of coal, limestone and sandstone layers tells of land that was dry, then under the sea, then dry again. Ask: Near Swansea there are sixteen coal seams. How many forests is that?
Amphibians
Read:
A crocodile and a snake are True Reptiles, cold-blooded and air-breathing.
The frog and salamander breathe in water for part of their lives: amphibians. The book describes large, scaly salamander-like animals of the Coal Age.
Make a footprint trail
The book tells of a slab from America with six footprints. Make a trail of your own: your child walks, then runs, across damp sand (or across dark paper with damp feet or floury socks). Compare the two trails. Running steps are farther apart and deeper at the toe.
Then you make a mystery trail and let your child read it: walking or running? Which way? Did you stop or turn?
Mountains and a fault
At the end of the Ancient-Life Period, says the book, the Alleghany Mountains were pushed up and the coal beds tilted and faulted. One fault is twenty miles long and twenty thousand feet deep, but so narrow a person can stand astride it.
Tell it back
Ask: What three things together tell the story of land rising and sinking? What is an amphibian? What happened at the close of the Ancient-Life Period?
What we know now
The Alleghany (Appalachian) Mountains were pushed up when the continents slowly crashed together into one giant continent, now called Pangaea. The close of this Ancient-Life (Paleozoic) Period, about 252 million years ago, brought the largest dying-out of life known, when most kinds of sea creatures disappeared, the last trilobites among them.
Afterwards
Notice it this week: look for animal or bird tracks in mud, sand or snow and try to read them: which way was it going? Was it walking or running?
Answers to the book's problems
Coal layers mean forest on land; limestone means sea; sandstone may mean either. When they alternate, the land rose and sank again and again. An amphibian (like a frog) lives part of its life breathing in water and part breathing air. At the close of the period, mountains such as the Alleghanies were raised, the rocks were bent and faulted, and the old kinds of animals gave way to new ones.
Worked out for this site from the scan. If a number in your copy differs, trust the book.