Answer: Law of superposition
Law of superimposition is a principle of geology, which suggests that when the rocks gets weathered, the newly formed sediments acquire the top layers of the soil strata whereas, the old layers seeps inside the deeper or bottom layers. As, the bottom layers are covered with new layers of sediments. Hence, new layers are considered as young and bottom layers as old.
Therefore, according to the law or principle of superposition the top stratum in the section of rock is the youngest.