The sedimentary rock formed when water deposits tiny particles of clay in very thin flat layers is called shale.

Here's why:

* Clay: Shale is formed primarily from clay minerals, which are very fine-grained particles.

* Thin Layers: These clay particles settle in thin, flat layers, often with layers of other fine sediments like silt.

* Compaction: Over time, the weight of overlying sediment compacts the clay layers, squeezing out water and creating a solid rock.

Shale is known for its characteristic layered structure, which can often be seen with the naked eye.