A complete ophiolite section can be divided from bottom to top into four units, namely metaperidotite unit, plutonic complex unit, sheeted dike complex unit and extrusive rock unit, each unit having varied rock assemblages. The metaperidotite unit is mainly composed of harzburgite and lherzolite together with minor dunite and plagio_lherzolite. The plutonic complex unit consists of gabbro, mafic cumulate and ultramafic cumulate. There exist complicated magmatic intrusive events in the plutonic complex and sheeted dike complex units. The extrusive rock unit includes basalt, andesite, boninite and albitite as well as breccia and tuff. Researches of ophiolites and Deep Sea Drilling Project and Ocean Drilling Project, however, indicate that many sorts of ophiolites have no layered structure. Ophiolite sections can thus be classified into two types: one is the section with layered structure, and the other is the section without layered structre. These different ophiolite sections actually reflect different dynamic processes beneath oceanic ridges, which are mainly controlled by the plate spreading velocity and the amount of magmatic supply.