Zeolites are abundant rock-forming minerals in many tuffaceous rocks of Cenozoic age in the western United States. Some beds consist almost entirely of one or more zeolite (Deffeyes, 1959b; Regnier, 1960). In spite of the abundance of such minerals, few analyses of these diagenetic zeolites have been published. Analyses of clinoptilolite are reported in Bram-lette and Posnjak (1933, p. 170), Ames, Sand, and Goldich (1958, p. 31), Mason and Sand (1960, p. 346) and Hay (1963, p. 228). To the writers' knowledge, there are no previously published analyses of erionite from sedimentary environments. Publication of new chemical analyses of clinoptilolite and erionite from sedimentary rocks thus seems warranted because of the increased interest in the use of natural zeolites for industrial processes and as indicators of post-depositional sedimentary environments (Deffeyes, 1959a).