Lateral Continuity (Nicolaus Steno, 1638-1687). Sedimentary rocks are composed of fragments of preexisting rocks that have been both mechanically and chemically weathered. Before lithification, these fragments are first transported to depositional areas where they are spread out over continuous and sometimes quite extensive geographic areas.

Typically these sediments will spread out until they …

A) terminate by thinning out at the edge of the depositional basin

B) abruptly stop at a barrier, such as a shoreline separating the terrestrial environment from the marine or lacustrine environment.

C) grade into a different type of sediment. The grading of one type of sediment into another is often indicative of a change in the energy level within the depositional environment. Sandstones typically grade into shales as the sediments are transported further away from what was the original shoreline. The currents diminish further from the shoreline limiting the size of the particles that can be transported out to sea.

The significance of knowing that sedimentary beds are laterally continuous lies in the recognition that similar rock units at different locations may, in fact, be the same although they are now not connected. Faulting, severe folding and erosion may have separated the originally continuous beds into what now appears to be separate units.