Answer:
Law of lateral horizontality or Law of Original horizontality
Step-by-step explanation:
According to the original horizontality law, the sediments initially were all deposited in a horizontal manner, and were spread extensively in all the direction, until they find any feature that cross-cuts them.
These sediments in due course of time were compacted and lithified due to the pressure applied by the overlying rock strata and formed distinctive layers. The rock layers that are found at the base are the oldest rocks and the strata that are found at the top are the youngest.
After carefully observing these rock layers, geologists can interprete the type of environment in which these sediments were deposited.