Which sedimentary rock forms from the compression of swamp material?

Coal

Explanation:

The rock is formed from organic matter. The material that accumulates in the swampy areas is used in making coal. Therefore the plants that form coal lived both in the modern and in the dinosaurs' time. When the plants perish they sink to the bottom of the swamp and become buried by the soils. After an extended period, the plant material goes more rooted to the ground and gets changed because of heat and pressure. The pressure and temperature makes the plant material to be in a solid form resulting in coal.

Lignite

Also known as brown coal, lignite rocks shows traces of plant structure, which falls between bituminous coal and peat. The rocks form from compression of sedimentary rock formed from naturally compressed peat. It is considered to be the lowest form of coal due to a low heat content.