The World's Foundations; or, Geology for Beginners · Ch. XVIII · Unit 3: Part II: Reptiles, chalk, mammals, ice and people
20. The age of mammals
Goal: Your child can name the three great periods in three different ways, explain the names Eocene to Pleistocene, and describe nummulites.
You'll need
- The book, open to this chapter
- A few coins
- A globe, atlas or free online map
- A notebook for a "rock journal" and a pencil
What's in the book
Chapter XVIII begins the Tertiary or New-Life Period. It explains the names given to its ages by the share of shells that are like living kinds, describes the coin-shaped nummulites found high in the Alps and Himalayas, and says the climate was mild, the great mountains were still rising, and Britain was at times joined to the Continent.
The lesson, step by step
A question to start
SayIf you found a fossil the size and shape of a coin on top of a high mountain, what would you think?
Read the chapter together
Read Chapter XVIII (pages 169 to 174). Look at the plate of fossils (footprints of a bird, mud-cracks, trilobite, ripple marks, ammonite, fish). Can your child name each from earlier lessons?
Three ways to say it
The book gives the three great periods several names. Make a chart in the rock journal:
Primary / Ancient-Life / Lower Animals and Fishes / Ancient History
Secondary / Middle-Life / Reptiles / Mediaeval History
Tertiary / New-Life / Mammals / Modern History
Dawn-New to Most-New
The ages of the New-Life Period are named by how many of their shells are like living kinds: Eocene ("dawn of recent"), Miocene (less than half recent), Pliocene (more than half), Pleistocene (most). By the end, the book says, about ninety-five shells in every hundred are the same as living kinds.
Coin-stones on mountains
Read:
They are called Nummulites, from two words, one Latin and the other Greek, meaning ' coin ' and ' stone.'
The summit of the Dent du Midi, for instance, over ten thousand feet high, is formed of nummulite rock.
Put a coin on the table and imagine a whole mountaintop made of such fossils. Find the Alps, Pyrenees and Himalayas on a map.
Britain joined and parted
The book says Britain was sometimes part of the Continent and sometimes cut off by the sea. Find the Strait of Dover on the map. Ask: How could elephants and other big European beasts have reached England?
Tell it back
Ask: What does the nummulite rock on the Alps tell us about when the Alps became mountains?
What we know now
Nummulites were giant single-celled creatures, and the Great Pyramids of Egypt are built of limestone full of them. The Alps rose as Africa pushed north into Europe. Britain was last joined to Europe by low land, now under the North Sea, until about 8,000 years ago. Today the Pleistocene is counted in a separate, later period called the Quaternary.
Afterwards
Practice the Eocene-to-Pleistocene names with their meanings until they are easy.
Answers to the book's problems
The nummulites lived in the sea, so the rock at the top of the Alps was once under the sea; the Alps must have been lifted up after these creatures lived, in the New-Life Period.
Worked out for this site from the scan. If a number in your copy differs, trust the book.