The Use of Fossil Content in Correlation
1.Principle of Fossil Succession: fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. We compare an observed fossil assemblage with the geologic ranges of the species that comprise it. Although the species found in rock A are variable in both time and geologic range, we can narrow the time of the formation of rock A to the intersection of these ranges. That is, the rock must have formed during the time when all 5 species existed on Earth.