Foraminifera from a Tertiary sequence that crops out on the northern part of the Olympic Peninsula, Wash., show stratigraphic and ecologic significance. Forty-two species that are important both to correlations and to ecologic interpretations are illustrated and systematically discussed. The Foraminifera indicate that some of the rocks may be as old as early Eocene. The oldest rocks are tentatively referred to the Penutian stage of Mallory. Other parts of the sequence are referred to the Ulatisian and Narizian stages of Mallory, the Refugian stage of Schenck and Kieinpell, and the Zemorrian and Saucesian stages of Kleinpell.
Several short periods of shallow, sheltered sea conditions are suggested by the Foraminifera from several parts of the stratigraphic sequence, but Foraminifera from most of the rocks suggest relatively deep, open-sea conditions. With the exception of shallow, warm-water conditions in rocks of probable middle Eocene age, the Foraminifera suggest that cool-to-cold water temperatures, regardless of depth, prevailed during the deposition of most of the rocks of Tertiary age in the northern Olympic Peninsula.