Petrographical data, K-Ar ages, thermoremanent magnetizations and major chemical compositions of late Neogene to Quaternary volcanic rocks have been collected in the northern part of the Hyogo prefecture. On the basis of K-Ar ages, these volcanic rocks are classified into Pliocene volcanic rocks(3.4~2.4Ma) and Pleistocene volcanic rocks(1.7~0.3Ma). The Pliocene volcanic rocks are represented by the Teragi group, Hachibuse and Hyonosen volcanic rocks composed mainly of voluminous calc-alkali andesite and subordinate monogenetic volcanoes of alkali basalt. The Pleistocene volcanic rocks are sporadically distributed throughout almost all the area. They generally form the small monogenetic volcanoes composed of alkali basalts, but the Oginosen volcano is exceptionally large in scale and made up of alkali basalt and calc-alkali andesite. Data of thermoremanent magnetization show that most of the volcanic rocks have normal-remnant magnetization but the Genbudo lava has a reverse-remnant magnetization corresponding to the Matuyama reversed chron. Major chemical compositions of the volcanic rocks show that the Pleistocene volcanic rocks are richer in Ti02, ai2o3, total Fe203, Na20, K20 and p2o5 and poorer in MgO and CaO than the Pliocene volcanic rocks.
