Describe the rock layers shown in Diagram A and any forces acting on the rock.

Rock layers are sedimentary rocks formed into strata (sing: stratum). The two laws governing the formation of such layers are Law of Original Horizontality and the Law of Superposition. The former tells us that everything (e. g. sand) is in horizontal piling, while the latter is more on the oldest rock or layer is the last on the order.

In the absence of a diagram, rock layers if horizontal and sedimentary, will have the stresses of the overlying weight of rock formations above them acting on them and originally it is the weight of overlying sediments when a sedimentary rock is accumulating that promotes diagenesis or removal of the water and compaction into a hard rock. If the layers are at a steep angle and buckled into folds such as in the Front Ranges of the Canadian Rockies, then they have been subject to lateral compression.