Results of the geological and petrological study of the volcanic rocks in Takahama, Matsuyama City and its surrounding area are summarized as follows :
1 Upper part in the Gogoshima group is consisted mainly of the “Matsuyama welded tuff”, so named by the writers.
2 The welded tuff is a pumice flow, and its degree of welding is high. Moreover, it has all the appearence of pichstone.
3 Essential constituent minerals of the welded tuff are biotite, augite, hypersthene, plagioclase, sanidine and abundant glass. Furthermore, pieces of pumice and accedental matirial are present. The matrix showing vitroclastic texture is composed largerly of glass.
4 Their chemical and normative mineral compositions are shown in table 2. As seen from the table, they are generally rich in K2O, P2O5 and H2O+ contents, while poor in Na2O, CaO and total FeO. Petrochemically, its welded tuff is potash-rhyolite.
5 This formation is possibly of the late Miocene age, and may be correlated to the Ishizuchi group in Shikoku. Namely, as an example of the volcanic activities of the Setouchi series in the Miocene-Pliocene (G-H stage), say, the Matsuyama welded tuff are conceivable.
