Abstract
In sediments west of the East Pacific Rise between the equator and 20°N, Eocene microfossils are recorded no farther east than 134°W; Oligocene, no farther east than 125°W; while Miocene and Pliocene occurrences extend closer to the crest of the rise. This distribution may result from post-Eocene spreading of the sea floor here averaging about 8 centimeters per year.