Debris carried off the continents and into the oceans by streams and rivers is the most common material that makes up sedimentary rocks. Some sedimentary rocks, however, are not of continental origin but are mostly derived from the skeletons of ocean animals. Plant debris becomes coal.
Sediments become rock when buried, subjected to pressure, and cemented by mineral precipitates .
Geologists, somewhat casually, refer to any hard, dark fine-grained sedimentary rock like shale or mudstone as argillite. Parts of the North Cascades display almost all the named varieties of sedimentary rocks. This site is a cooperative endeavor of the US Geological Survey Western Earth Surface Processes Team and the National Park Service . It is published by The Mountaineers , Seattle .