An unreversed refraction experiment located 325 km west of the center of the Oceanographer transform and aligned along the axis of the fracture zone yielded information on the velocity structure of the crust within the fracture zone axis. A layer 2 km thick having a compressional wave velocity of 4.4 km/s overlies a layer with a compressional wave velocity of 6.5 km/s. The thickness of the lower is not precisely determined but is probably of the order of 4 km thick. In 17 dredge hauls located along the transform fault the following rock types were recovered: fresh unaltered basalt, greenschist facies metabasalt, greenschist facies metabasite, greenschist facies metagabbro, epidosite, quartz-chlorite rock, chlorite-actinolite rock, actinolite rock, and serpentinite. Correlation of the acoustic properties at elevated confining pressures with the seismic refraction results provides constraints on the distribution of rock types within the fracture zone. The 4.4-km/s layer can be approximated by either a broken and fractured pile of basaltic rock or a layer of serpentinite. The 6.5-km/s layer is best approximated by either a layer of metagabbro or partially serpentinized ultramafic rock. It is suggested that the geology within fracture zones, especially large offset ones, is complex. As a function of changes in the pole of relative motion with time, there can be igneous intrusive contacts of varying ages and compositions, the zone of strain can change width and intensity, and metamorphic and structural contacts can be varied.