The World's Foundations; or, Geology for Beginners · Ch. XIII · Unit 2: Part II: Ancient seas and coal forests
14. The age of fishes
Goal: Your child can describe the Age of Fishes (the Old Red Sandstone) and explain why bird fossils are rare.
You'll need
- The book, open to this chapter
- A bowl of water, a feather and a small pebble
- A notebook for a "rock journal" and a pencil
What's in the book
Chapter XIII describes the Age of Fishes, with its Old Red Sandstone and coral limestones. The first forests of ferns, tree-ferns and pine-like trees grow, the earliest known insects appear, and the seas teem with fishes, many with shining scales, and with huge lobster-like creatures.
The lesson, step by step
A question to start
SayIf you were a fish in this age, what would you meet?
Read to find out.
Read the chapter together
Read Chapter XIII (pages 118 to 124). Sentences to stop on:
The bare rocks had a green clothing at last.
One of these insect-fossils is of a huge May-fly, no less than five inches across from tip to tip of its wings.
Show five inches with a ruler.
The building so far
Giberne uses her house picture again: the lowest rocks are the cellars, the first water-built rocks the basement, and now the ground floor is being built. Ask your child which "floor" we are on in this chapter.
Why so few bird fossils
Read:
Now a bird is of very light make — so light that if he dies and falls into the sea, his body will probably float until it decays or is devoured.
Test it: drop the feather and the pebble into the bowl of water. Which sinks and might be buried in mud? Which floats away?
Giant sea creatures
The book describes lobster-like animals four to six feet long:
These last would be somewhat unpleasant to meet upon the seashore.
Measure six feet against a wall or door and compare with your child's height.
Time is counted in layers
Point out the author's rule: in geology, "time" means the order of the rock layers, not years, because the rocks have no dates written on them.
Tell it back
Ask your child to describe a forest and a sea of the Age of Fishes, using at least four things from the chapter.
What we know now
This age is now called the Devonian, about 419 to 359 million years ago. Near its end, the first four-legged animals began to crawl out of the water. The giant "lobsters" were probably sea scorpions, relatives of spiders and horseshoe crabs; the biggest known grew to about 8 feet long.
Afterwards
Notice it this week: look at reddish sandstone in buildings or gravel. Ask your child to say what color the Old Red Sandstone was and why it got its name.
Answers to the book's problems
Fishes of many kinds (some with shining scales, some sharks), corals, sponges, trilobites and huge lobster-like creatures; on land, ferns, tree-ferns, pine-like trees and insects, but no reptiles or four-footed beasts yet. Birds are light and float when they die, so they rot or are eaten before mud can bury them.
Worked out for this site from the scan. If a number in your copy differs, trust the book.