Name your Custom Course and add an relative dating summary description or learning objective. Methods for relative dating were developed when geology first emerged as a natural science in the 18th century. The principle of lateral continuity states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. Many were large a few rare species were 5 feet in length ; crawling and swimming forms; extinct NAME: Law of Superposition Once we assume that all relative dating summary layers were originally horizontal, we can make another assumption: Then the lake dries up, and a forest grows in. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.