Abstract
The so-called trachytic rocks developed in the lower parts of the green tuffs in the Oga peninsula are divided into three members. The basal member is the altered fine grained trachytic lava, and it is successively overlain by the altered hornblende trachytic lava and its tuff, the altered biotite trachytic lava breccia and its agglomerate and tuff.
As the results of microscopical and chemical studies, these rocks can be recognized as the intermediate type between the calc-alkaline and the alkaline-rocks. Some detailed petrographic descriptions and considerations are given in this paper.
