Abstract
1) The Soma Mesozoic Group can be divided into the following formations numbered in chronological order: 7) Koyamada formation 3) Sugaya formation 6) Tomisawa formation 2) Awazu formation 5) Nakanosawa formation 1) Hayama formation 4) Tochikubo formation The Nakanosawa formation (above) is further divisible (as follows): 3) Koike limestone 2) coarse sandstone 2a White or yellow, arkosic, coarse sandstone 2b dark gray sandstone and calcareous sandstone 1) sandstone and shale 1a Lima sandstone 1b Trigonia bearing sandstone 2) The Soma Mesozoic Group in some respects resembles the middle and upper Jurassic formations of the southern Kitakami-mountainland, and also is similar to the Torinosu Group which is distributed in southwestern Japan., It includes some limestones and contains the Torinosu fauna., 3) The Hayama, Awazu and Sugaya formations are distributed in a small area of-the northern part of the Soma district., Other formations are found in the southern part and show an anticlinal structure with a small syncline at its center., 4) 18 species of Ammonites from this district show that the Awazu formation is Bathonio-Callovian in age, Nakanosawa formation is Oxfordio-Kimmeridgian and Koyamada formation is Tithonio-Portlandian., 5) The Sugaya formation yields many Clavotrigonia belonging to Naviformae and Undulatae, but very few Clavellatae., On the contrary, Nakanosawa and Koyamada formations yield abundant Clavellatae.,
