Fossils are typically found in sedimentary rocks, specifically in layers called strata. These layers are formed over time by the accumulation and deposition of sediment, such as sand, mud, or organic matter.

Here's a breakdown of the sedimentary rock layers where fossils are most commonly found:

* Sandstone: Formed from sand grains cemented together. Fossils in sandstone often represent organisms that lived in shallow marine or coastal environments.

* Shale: Formed from fine-grained mud and clay. Shale can contain fossils of marine organisms, plants, and even insects.

* Limestone: Formed from the accumulation of marine animal skeletons and shells. Limestone is a rich source of fossils, including corals, brachiopods, and trilobites.

* Coal: Formed from the accumulation of plant matter in swampy environments. Coal can contain fossilized plants and trees.

* Conglomerate: Formed from cemented gravel and pebbles. Conglomerate can contain fossils of larger organisms, such as bones or shells.

Important Note: Not all sedimentary rock layers contain fossils. The presence of fossils depends on several factors, including:

* Environment: Organisms that lived in environments conducive to fossilization, such as shallow marine environments, are more likely to be preserved.

* Time: Older rocks are more likely to contain fossils than younger rocks.

* Burial: Rapid burial and preservation from decomposition are crucial for fossilization.

Therefore, the layers of sedimentary rock where fossils are found vary depending on the specific geological environment and time period.