Stratigraphy Principles Time and logic Commentary

Nicolas Steno stratigraphy

Stratigraphy

• To explain how a shark’s tooth had the same shape
• as fossils known as glossopetræ, “tongue-stones,”
• Niels Stensen, known as Nicolas Steno, took a year to study
• how fossils could be derived from living things,
• embedded in stone, and raised up into mountains.
• Fabio Colonna had established that glossopetræ
• had organic origins; Steno explained how this happened
• and extended this by describing how sedimentary rocks
• formed in layers, were broken, tilted, covered, and uplifted.

Principles

• I.
• “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.”
• II.
• “Hence it follows that strata,
• either perpendicular to the horizon or inclined toward it,
• were at one time parallel to the horizon.”
• III.
• “Materials forming any stratum were continuous over the surface of the earth
• unless some other solid bodies stood in the way.”
• IV.
• “If a body or discontinuity cuts across a stratum,
• it must have formed after that stratum.”

Time and logic

• Logic and direct observation
• were hardly to be expected
• in Steno’s time; his makes it clear
• he was a man of genius.
• Take a close look and work it out
• one step at a time. Time means
• nothing; what is logic? Only that each thing
• must happen before the next.