Others classify the period with reference to the materials used in
making implements and weapons and give us the following:
I. The Stone Age.
1. The Paleolithic or Rough Stone Age.
2. The Neolithic or Polished Stone Age.
II. The Age of Metals.
1. The Age of Copper.
2. The Age of Bronze.
3. The Age of Iron.
Still others classify with reference to the dominant industry of the
period, giving:
I. The House Industries, or the Period of Domestic Economy.
1. The Hunting Stage.
2. The Fishing Stage.
3. The Pastoral Stage.
4. The Agricultural Stage, etc.