The laws of superposition and original horizontality are best applied to sedimentary rocks.
Sedimentary rocks are types of rocks that are formed through deposition and subsequent cementation of such material at the Earth's surface and within bodies of water. The law of superposition and original horizontality applies because technically the layers of sediments from which sedimentary rocks are formed were originally deposited horizontally under the gravitational action. Furthermore, since sedimentary rock formation has an undisturbed sequence, then the basic law of geochronolgy (law of superposition) applies since oldest layer is at the bottom while the youngest layer is on top.
