Here's why:
* Sedimentary Rocks: These rocks are formed from the accumulation and cementation of sediments (like soil, sand, or shells).
* Shale and Mudstone: These are fine-grained sedimentary rocks formed from compacted clay and silt. The soil settling at the bottom of ponds and rivers is primarily made up of these fine particles.
The process:
1. Sedimentation: Soil particles, carried by water, settle at the bottom of the pond or river.
2. Compaction: Over time, the weight of the overlying sediment compresses the deposited layers, squeezing out water and air.
3. Cementation: Minerals dissolved in the water seep into the spaces between particles and crystallize, acting as a glue that binds the particles together.
So, the soil that settles in ponds and rivers eventually transforms into shale or mudstone through this process of sedimentation, compaction, and cementation.
