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mental Mohole off central Baja California. The floras in these rocks are more difficult to correlate than those of older stages apparently because of more pronounced temperature differences between North America and the lower latitudes. Several species (Discoaster kugleri, D. variabilis, D. hamatus and Oatinaster coalitus) indicate correlation with the "Globorotalia fohsi" sequence of zones, and the Globorotalia mayeri and "Globorotalia cultrata" zones. The "G. fohsi" sequence of zones iR absent from the type sections of the European stages, and thus was arbitrarily assigned to the Helvetian• because this term was recommended for use 10 • The other two zones are equivalent to the Tortonian 10 •The stratigraphic occurrence of calcareous nannoplankton in rocks of western North America permits correlation with tropical area plankton zones and the type sections of the European stages in spite of differing oceanographic conditions between the two regions during the mid-Caenozoic. These correlations indicate that the California Zemorrian Stage is equivalent to the European Chattian, the Saucesian to the Aquitanian, the Relizian to the Burdigalian and lower Helvetian, the Luisian to the Helvetian and the Mohnian "to the upper Helvetian and lower Tortonian.

To the Editor, Tetra Nova: The very short letter below relates to the very interesting contribution (2, 5, 1990 on mud volcanoes in Burma). It might interest your readers?