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SUMMARY. Phosphates introduced into the et-Tabun cave as a result of human habitation, mainly as bone material, were partly dissolved by slightly acid solutions (organic acids derived from human or other animal activity). From these solutions, dahllite precipitated when the solutions came into contact with calcite. In the more weathered parts of the section, where little or no calcite occurs, the phosphate minerals formed are montgomeryite and crandallite.

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Clinoptilolite, a zeolite of the heulandite group, occurs commonly in sediments as an authigenic mineral. In the Middle Eocene of southern Israel, it constitutes from a few per cent up to 80 per cent of the insoluble residue of the chalks and limestones. It is associated with opal C‐T, montmorillonite and palygorskite. These chalks and limestones overlie the Danian‐Palaeocene Taqiya marls which also contain a well‐established clay mineral sequence consisting of opal C‐T, montmorillonite, palygorskite, sepiolite, and clinoptilolite. This paragenesis of minerals is shown to be typical of the Upper Cretaceous to Eocene times. It is world‐wide, occurs in deep‐sea sediments as well as in shallow water sediments, and results from the abundance of silica which probably reflects a warmer climate during this time period. The concentration of magnesium in the sea‐water and its ratio to the other cations seem to determine which authigenic silicate will be formed.