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Principle of inclusion
One of the basic principles of stratigraphy is the "principle of inclusion." The principle states that if fragments of a rock unit are found included in a second rock unit, the second unit is younger than the first. In this picture, fragments of the Mesoproterozoic Pikes Peak granite (like the clast on which the pencil is resting) are included in a conglomerate layer of the Pennsylvanian Fountain Formation, CO. We infer that the granite must have existed as a solid rock body that was broken and eroded…
Clinostratification
The principle of original horizontality is one of the basic principles of stratigraphy. It states that sediments are deposited in essentially horizontal layers, and it was enunciated already by Steno in his Prodromus (1669, p. 30): "...adeoque strata omnia praeter infimum duobus planis horizontis parallelis contineri" (...all strata, therefore, except the lowest, were bounded by two planes parallel to the horizon). There are, however, exceptions to this principle. Strata can be deposited…