If stratigraphic correlation expresses the probability that samples from 2 different sections represent the same level in a known sequence of events, it can be considered to be the product of the probabilities that (a) the events defining the stratigraphic increment have been detected, (b) the true sequence of events is known, and (c) the events have been correctly identified. If the probability of correlation is to be greater than 0.90, each of the 3 factors must have a probability greater than 0.96. From this several important implications can be drawn.

1. If fossils are used to determine stratigraphic events, samples must generally have populations of hundreds of specimens.

2. The probability that a sequence of genetically unrelated events is correctly known reaches the required level only if sequence pairs are known from 6 sections and never occur in reverse order, or are known from 9 sections with 1 reversed occurrence, or from 12 sections with 2 reversed occurrences, or from 15 sections with 3 reversed occurrences, etc.

3. After 7 sections have been examined for sequences of event pairs and no reversed pairs are

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known, little is gained by examination of additional sections.

4. Type sections, usually considered the objective basis of chronostratigraphy, define the level of confusion which will exist in a stratigraphic system and serve only an archival function in probabilistic stratigraphy.

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