in the cool, nutrient-rich water near some continental shelves, radiolaria and diatoms thrive. these suspended microscopic organisms use silica to make their shells. when they die and settle to the sea floor, the silica accumulates to form layers of chert and diatomite. in swampy bayous and deltas on shore, the remains of moss, leaves, roots, and tree trunks may gradually compact over millions of years, giving rise to another sedimentary rock-- coal. coal is formed in areas of swamps, quiet water, like okefenokee swamp and areas in southeast asia where you have lots of vegetation in shallow water over millions of years and material grows, dies, settles down. due to the chemistry of the water, the material does not rot away. layer after layer builds up and with time, sufficient pressure, it's converted first to peat and eventually to coal. the places where sediment is deposited vary enormously, from glacial valleys... lakes... beaches... river deltas... to the sea floor. these environments of deposition are nearly always initially associated with water, but may eventually transf