3.3 Parting 3.3.1 Keep clearly in mind the distinction between stratification and parting. Parting is the tendency for stratified rocks to split evenly along certain stratifi-cation planes. (The word is also used for the plane itself along which parting has developed.) The approximately planar-toped by parting are abular units devel
B. Sedimentary rocks formed from magma when Earth cooled four billion years ago. C. Most sedimentary rocks are at least four billion years old. D. Life existed on Earth four billion years ago. 10. The cross section of the bedrock layers of a canyon is represented below. Letters A and B represent rock layers on the sides of the canyon.