The nearly 20 m thick quartzose sandstone developed in the lower part of the Jurassic Tomizawa Formation of the Somanakamura Group constitutes volumetrically more than 70 percent quartz grains and is inferred to have been deposited on an alluvial plain, because of the development of minor cyclothems, evidence of the sedimentary structure, grain size distribution and etcetra. The present study shows that the mineral composition is closely related with the texture, and the latter defines the rank of the sandstone in the classification of sandstone. The quartzose sandstones were classified into the orthoquartzite-subarkose-arkose range, and the majority into the subarkose clan in Folk\u27s classification (1954). These quartzose sandstones, having high mineralogical maturity, are not the product of only the environment of the sedimentary basin, because the weathering of the hinterland must have had great influence. It is reasonable to consider the provenance of the sediments based on the mineral composition in the classification of sandstone, in which should be included the textural parameter for interpretation of the sedimentary environment. Further, the end members of the triangle diagram of the classification of sandstone can be chosen to fit the sedimentary environment to reflect the regional sedimentary environment and tectonism
