Abstract
The Tertiary strata of this district can be subdivided into Nakayama bed, Sirakata bed, Iwane bed, Katahira bed, and Hukura bed., The Nakayama bed consists of basal conglomerate, sandstone, green tuff, sandstone agglomerate, sandstone, and is older than at least the Middle Miocene., Over this lies conformably the Sirakata bed, which consists of green tuff and an alternation of conglomerate, sandstone, shale and tuff ; many remains of molluscs occur in this bed., The following marine fossils were found in the lower part of this bed ; Arca ninohensis OTUKA Pecten kaneharai YOKOYAMA Pecten kagamianus YOKOYAMA Lucina acutilineata CONRAD Cardium Shiobarense YOKOYAMA Venus yokoyamai MAKIYAMA Macoma optiva YOKOYAMA Cultellus izumoensis YOKOYAMA Panomya simotomensis OTUKA The following fossils occur in the upper part ; Lucina acutilineata CONRAD Dentalium yokoyamai MAKIYAMA Linthia nipponica YOSHIWARA This bed may be correlated with the Siobara, Tanagura, Yanagawa, Siogama shell beds, and the age is Middle Miocene., Over this lies with slight unconformity the Iwane bed, which consists of liparite and its agglomerate ; and over this, with marked unconformity lies the Katahira bed, consisting of conglomerate and tuff ; and the unconformably overlying Hukura bed consists of dacite and its tiff., This district suffered two crustal movements., The formation of the first movement may have dated from the late Iwate bed and early Hukura bed, that is, from late upper Miocene and probably early Pliocene., Nakayama and Sirakata beds are folded, faulted and dip with high angle., The formation of the second movement may have date later than the Hukura bed, that is, probably later than Pliocene ; this was mainly a fault in NS trend, and resulted in the construction of graben and horst.,
