"Ocean floor petrology" is concerned primarily with the study of volcanism and related processes involving the creation and the transformation of crustal material which takes place at contact with seawater. The field of ocean floor petrology has developed and will continue to evolve rapidly with man's effort to penetrate and explore greater depths through the use of more sophisticated technology. The present work was initially intended to be a comprehensive review of the major mineralogical and geochemical investigations carried out in the study of oceanic crust. However, during the process of gathering the
data together, new information has been added in order to further increment our knowledge of the oceanic crust.