Principle of original Horizontality
Steno is also credited with recognizing the importance of another basic principle, called the principle of original horizontality. Simply stated, it means that layers of sediment are generally deposited in a horizontal position. Thus, if we observe rock layers that are flat, it means they have not been disturbed and thus still have their original horizontality. The layers in Canyonlands National(see chapter-opening photo) and the Grand Canyon(see Figure 11.2) illustrate this. However, if the layers are folded or inclined at a steep angle, they must have been moved into that position by crustal disturbances sometime after their deposition(Figure 11.4)