"An investigation of the sequence of microspores vertically within a number of seams containing horizons of crassidurite has revealed a succession of three distinct phases, each characterized in the main by the dominance of one of the three genera Lycospora, Laevigatosporites, and Densosporites. The succession begins with the Lycospore phase and culminates in the crassidurite with the Densospore phase. The significance of this succession in relation to the formation of crassidurite and the provenance of Densospores is discussed."

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