Since the stratigraphy of the Boso peninsula, Chiba prefecture was first undertaken by T. Mitsuchi (1937) in his geological map "Mobara ", many authors have contributed to the geology and paleontology of the region. Among then, K. Kawai (1961) in particular had contributed to the economic geological study on the southern Kanto gas-producing region. Recently Y. Ishiwada, Y. Higuchi and the writer (1962) published the correlation by the smaller foraminifera on the southern Kanto gas field.
Surface and subsurface exploration for the natural gas during recent years made the environmental condition of the Kazusa Group on the Boso peninsula clear. The purpose of this report is to describe the correlation of the subsurface biostratigraphy in the northern peninsula to that of the type rout (middle and eastern part of the Peninsula) by the smaller f oraminif era and clear the environmental condition under which the formations was deposited.