Comparative studies of dispersed spores and pollen from the Upper Cretaceous Magothy Formation and the Lower Cretaceous Arundel Formation, both in Maryland, and the Lower Cretaceous Wealdian sequence in southern England reveal striking similarities and differences among the dominant species. The two Lower Cretaceous assemblages consist almost exclusively of fern spores and gymnosperm pollen. Of the thirteen most abundantly occurring fern spore species in the Arundel association, ten are conspecific with species in the Wealdian one. In spite of the wide geographic separation of the two assemblages, only four of the dominant species reported from the Wealdian were not observed in the Arundel microflora.

A much greater difference is evidenced in comparing the Upper and Lower Cretaceous assemblages from Maryland, each of which contains a distinctive and diagnostic microflora. Of the twenty-five most abundant fern spore and angiosperm pollen species (thirteen from the Arundel, twelve from the Magothy), only one is common to both. An even more obvious difference is the fact that no angiosperm pollen were observed in the Arundel. However, in the Magothy angiosperm pollen constitute approximately forty per cent of the dominant species. Furthermore, the Magothy assemblage, in general, is characterized by species whose morphology is more complex and more advanced than that shown by the forms in the Arundel.

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