Examination of the physical relationship between weight and volume sediment samples, and comparison of estimates of organism abundance obtained from equal volume and equal weight samples of recent sediment show that kinds of minerals forming the sediment have little effect on abundance distribution patterns determined by counting the number of specimens in samples of a given weight or volume, and that variation in sediment porosity probably is the major factor responsible for differences between organism counts based on equal weight samples and those based on equal volume samples. Consideration of the diagenetic processes of compaction and cementation that affect organism abundance shows that for sediments, which have not been materially changed by processes such as intrastratal solution, replacement, and recrystallization, abundance counts from recent and ancient sediments are more comparable if clays and shales are reported on the basis of equal weight samples, and unlithified and lithified sands are reported on the basis of equal volume samples.

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