Stratigraphy

Steno's Principles of Stratigraphy - Nicolaus Steno (Born Niels Stensen in Copenhagen in 1 January, 1638, is often considered the the father of geology. However, since he preceded Darwin by almost two centuries, neither his genius nor theories were accepted by very many, as belief in the biological origin of fossils conflicted with religious precepts. Like Darwin, he undertook intensive empirical observation that resulted in the 1669 publication of his great work, De Solido Intra Solidium Naturaliter Contento Dissertationis Prodromus (which preceded a Dissertation on a Solid Naturally Contained within a Solid), often simply called the Prodromus. In this work he boldly delineated the organic origin of fossils and the fundamental principles of stratigraphy. Although now regarded as a seminal, geological masterpiece, the conclusions of Prodromus were not were not accepted for another century.

Below are listed the key precepts of Prodomus that are fundamental to contemporary geology:

The Principle of superposition

"...at the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed."

That is, n a sequence of strata, any stratum is younger than the sequence of strata on which it rests, and is older than the strata that rest upon it.

Principle of Initial Horizontality

"Strata either perpendicular to the horizon or inclined to the horizon were at one time parallel to the horizon."

Strata are deposited horizontally and then deformed to various attitudes later.

Principle of Strata Continuity

"Material forming any stratum were continuous over the surface of the Earth unless some other solid bodies stood in the way."

In other words, strata can be assumed to have continued laterally far from where they presently end.

Principle of Cross-Cutting relationships

"If a body or discontinuity cuts across a stratum, it must have formed after that stratum."

Or, more simply, things that cross-cut layers probably postdate them.

Steno interpretated fossils as the anatomical parts of living organisms, particularly teeth, bones, and shells, with fossilization into crystalline material taking place over extended time.