a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found
- Thus any rock found bearing these index fossils can be dated fairly accurately as belonging to their proper period in history.
- There is a long term debate about the depositional model of the chert sediment, as well as the definition of the Precambrian-Cambrian boundary because of few index fossils reported.
- The index is at the back (of the book).
- Automatic modification of the index register.
- A person's face is often an index of his mood.
- Do you know the price index in the city?