When the gravel is rounded and held together by fine material known as the matrix it indicates that the gravel was once eroded by water before the sediments were deposited; this compressed sedimentary rock is called a conglomerate. Breccia's are made up of more angular gravel held together by the matrix material which implies that the rocks were mechanically weathered from things like rock slides or faulting.
Smaller clasts consist of sand, which is about the size pin’s head, silt, which is roughly the size of a grain of salt and clay clasts, which are about the size of a grain of flour. The sand can be held together by silica or calcium carbonate to form sandstone. When silt is deposited in seas or lakes siltstones may form, when clay is deposited into the same spots shale's may form in layers that are easily split. When the silt, clay, and sand mix they may form mud stones, which are typically larger than shale's and well consolidated.
Geologic forces build the features like mountain and basins that control where the sediments come from and where they are deposited. For instance, a stream may carry rocks into a valley with a small lake and deposit the sediments on the bottom where over long period of time the compression can form new rock out of the sediments in the form of conglomerates.
A second type of sediment is formed by chemical interaction the chemical sediments are formed by the precipitation of minerals dissolved in water. The chemical balance in the water can be affected by plants and animals, oxygen or carbon dioxide may be depleted or increased; the water may dry up allowing solids to form, as in the case of old lakes becoming salt flats. Another example is limestone, which can form when carbon dioxide is increased so that calcium carbonate precipitates.
A third type of sediment contains parts left over from biologic processes of plants and animals; they are known as biogenic sediments. Examples of things found in these sediments are shells, bones, teeth, wood, and roots. One common type of biogenic sedimentary rock is the coal that we use to generate