The study of volcanic processes is normally considered to lie within the realm of igneous geology as the origins of the magmatism lie within the crust and mantle. However, the volcanic material is transported and deposited by sedimentary processes when it is particulate matter ejected from a vent as volcanic ash or coarser debris. Furthermore, both ashes and lavas can contribute to sedimentary successions, and in some places the stratigraphic record is dominated by the products of volcanism. Transport and deposition by primary volcanic mechanisms involve processes that are not encountered in other settings, including air fall of large quantities of ash particles that have been ejected into the atmosphere by explosive volcanic activity, and flows made up of mixtures of hot particulate matter and gases that may travel at very high velocities away from the vent and rapidly form a layer of volcanic detritus. Volcanic activity can create depositional environments and it can also contribute material to all other settings, both on land and in the oceans. The record of volcanic activity preserved within stratigraphic successions provides important information about the history of the Earth and the presence of volcanic rocks in strata offers a means for radiometric dating of these successions.