Clastic sedimentary rocks are derived from material released by weathering of pre-existing rocks. The resulting clasts such as mud, sand and gravels are transported by water, wind or ice before being deposited and cemented to form a coherent rock. They are subdivided by grain size indicating the mode of their deposition. Fine grained sediments are usually deposited in calm, low energy environments, such as in lakes, deep seas and river deltas or can be carried by winds for long distances.