Sol definition, the syllable used for the fifth tone of a diatonic scale. See more.
Examples of index fossils. Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify geologic periods (or faunal stages).
Other index fossils of this type include ammonites, crinoids, rugose corals, brachiopods, bryozoans and mollusks. The USGS offers a more detailed list of invertebrate fossils (with scientific names only) here. Other major index fossils are small or microscopic, part of the floating plankton in the world ocean.