Terrestrial plants are found at relatively few localities and horizons as compared with marine invertebrates; so that invertebrates paleontology has taken the lead in the segregation of the Tertiary and the. correlation of the resulting stratigraphic units. Nevertheless, fosil plants are likely to occur in abundance at just the horizons where the remains of marine life are sparingly represented or totally absent, and plants are, moreover, much more sensitive to environmental changes than are aquatic organisms; so that they can not be ignored in discussions of correlation.
Paleobotanical studies are necessarily largely provincial; but let me remind you that the larger questions of the origin, evolution, dispersal, and extinction of floras, as well as other types of organisms, can only be successfully solved by the most precise correlation of strata in distant regions, which is the ample excuse for attempting the solution of a problem of the magnitude of . . .