This paper attempts to use natural gamma-ray logging data in the research of clay strata formed by volcanic events. The feasibility of this application is illustrated in the light of present technical level of natural gamma log-ging and contents of radiogenic elements in studied objects; the relations of material sources of sedimentary rocks with contents of radiogenic elements are analysed. Of all the uncommon sedimentary rocks, acidic volcaniolastic material and its hydrolyzates(clay)contain rather abundant radiogenic elements. With three types of volcanogenic clay rocks as examples, the natural gamma logging data are proved to be essential for finding and studying clay strata formed by volcanic events. Using this method, the author has found that there exists in Junlian area of southern Sichuan a layer of clay rocks between Permian and Triassic strata, which serves as the boundary of these two systems. Finally, some opinions are put forward concerning the ?future development of the natural gamma-ray logging technique.