small seamounts and ridges, interspersed with sills in the east, reflects an eastward change of some combination of tenstonal crack distribution and the volume rate of magma generation: either the thermal anomaly beneath the tension cracks diminished or the cracks themselves narrowed, The two effects may be combined. The eastward sequence mav also represent a time sequence, formed progressively as the Pacific plate moved northwestward, We bave as yet only two indications of age along the Crass-grain: middie Miocene (14 Myr) sills/flows at 138° W, and passible late Eocene (36-40 Myr) for certain Line Islands Cross Trend features'*°°. This age difference along the cross-grain is ~25 Myr and the distance is ~2,000 km, giving an average rate, assuming progression, of ~B em yr! a figure close to the progression rate of the Hawaiian chain. Several ridges in the Line Islands Crass Trend appear to end westward in an elbow, congruent with the elbow junction between the Emperor and Hawaiian chains, also late Eocene in age*!. This work was supported by the US Office of Naval Research. We thank Barry Parsons for a critical review of the manuscript.