Here's why:

* Sedimentation: Sedimentary rocks are formed when sediments like sand, silt, clay, or organic matter settle and accumulate in layers over time.

* Compaction and Cementation: These layers are then compacted by the weight of overlying sediments and cemented together by minerals dissolved in groundwater.

* Visible Layers: This process of layering and compaction often results in distinct, visible layers or strata within the rock. These strata can be different colors, textures, or compositions based on the type of sediment that was deposited.

Therefore, the layered structure of sedimentary rocks is what makes them known as stratified rocks.