Many new terms have been concisely defined and explained in the sixth edition such as turbidity currents stone tracks patterned ground soil profile biologic facies palynology pluton lopolith phacolith ringdike cone sheet metamorphic facies boudin diapir fold wrench fault granitization and so on. New text has been added on contemporaneity in sedimentation on tectonic correlation of sediments on the granite problem on the terms base level and grade on the use of the Jacob staH on distortion and displacement in air photographs on the use of air and gas in drilling deep holes on induction logging on sonic (continuous velocity) logging on dipmeter surveying on presently used methods of electronic surveying on refraction seismic shooting for overhang of salt domes and so on. In view of the almost complete substitution of the gravimeter for the torsion balance in gravity surveying this section of the chapter on geophysics has been completely rewritten.