Sand and clay porosities of foreshore, tidal flat, and shallow sea sediments from the southern North Sea were determined. No definite relationship could be observed between porosity, condensation ratio, and depositional environment.

Porosity increases with increasing clay content. The clay porosity probably depends to some degree on the rate of sedimentation. The porosity of experimentally deposited sands increases with decreasing grain size. The same relation can be observed with fossil sandstones. In Recent sands, this increase may be compensated by a closer packing arrangement of the finer grains, expressed by a higher condensation ratio

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(P= natural porosity, Pw and Pd are the porosities of the loosest and closest arrangements under water, respectively).

Under certain conditions, the sand(stone) porosity decreases continuously with increasing depth (Fig. 7).