Here's why:

* Formation: Fossil fuels are formed over millions of years from the remains of ancient organisms (plants and animals) that were buried under layers of sediment.

* Sedimentary Rock Formation: As sediment accumulates, it gets compacted and cemented together, forming sedimentary rocks. This process traps the organic matter within the rock.

* Types of Sedimentary Rocks: Fossil fuels are typically found in specific types of sedimentary rocks like:

* Shale: A fine-grained, layered sedimentary rock often rich in organic matter.

* Sandstone: Formed from sand grains, can contain fossil fuels if deposited in areas with abundant organic matter.

* Limestone: Formed from the shells of marine organisms, can also contain fossil fuels in specific environments.

Examples:

* Coal: Formed from ancient plant matter buried under layers of sediment and transformed by heat and pressure.

* Oil and Natural Gas: Formed from ancient marine organisms that were buried under layers of sediment and transformed by heat and pressure.

Let me know if you'd like to know more about the formation of specific fossil fuels!