In geology, the term deposition refers to the settling out or placement of rock, particles of rock, or organic matter, generally referred to as sediments, after transportation by wind, water, ice, or gravity. Deposition occurs when the energy causing the transportation of sediments becomes unable to move the sediments any further due to its weight or friction with other particles. Deposition can occur in deltas, at the base of mountains, at the bottom of oceans, lakes, and seas, in sand dunes, or at the end of glaciers. The smaller the particle, generally, the further from its source will be its point of deposition.