Cenozoic formations, found along the northern border of the Kitakami Mountains, are marginal deposits of the so-called Uétsu geosyncline. A detailed study of stratigraphy and geologic structure of Neogene Shiratorigawa group which is the lower portion of the above Cenozoic formations, are reported. 1) The Shiratorigawa group overlies the basement Paleozoic and plutonic rocks with a remarkable clino-unconformity, and is divided into the following three formations in descending order: Suénomatuyama formation (100-150 m) : mostly composed of tuffaceous sandstone, with two-pyroxene andesites and their pyroclastics in the upper horizon. Pectinid and other molluscan remains are abundant. Kadonosawa formation (50-100) : mainly composed of siltstone accompanied by thin conglomerate and sandstone beds in its basal horizon. The molluscan remains are abundant in its upper and basal horizons. Yotuyaku formation (150-250 m) : chiefly composed of siltstone and sandstone with lenticular conglomerate beds. An intercalation of the andesitic tuff breccia is found in its middle horizon. Plant and molluscan remains are present. These three formations are subdivided into several members. 2) The basement rocks are exposed in two masses, at the eastern margin and the southwestern corner of this district, and the depression between the two masses is filled up by the Neogene formations. Geologic structure of this district is best considered as consisting of the following three subdivisions : 1. Southern area or the Namiuchi-toge syncline ; the axis of the syncline dips to the northwest direction. 2. Central area or the Maisawa basin structure ; a semicircular shallow basin with a westward opening. 3. Northern area ; gentle monoclinal structure, dipping in west to northwest direction. In addition to the areal structures mentioned above, weak undulations and small faultings are observable. In general, structural trend of N 30°W in the Neogene formations prevails in this district. This is due to the structural trends of the basement rocks. 3) Shapes of the sedimentary bodies of each formation or member are illustrated in the isopachous contours. 4) The relationship between the Kadonosawa and the Suénomatuyama formations is conformable in general. A partial unconformity, however, can be recognized between the two. Near the eastern margin of the basin, crests of the undulation of the Kadonosawa formation are eroded out and covered by the basal conglomerate of the Suénomatuyama formation with unconformity. 5) The Nisatai dacite extruded probably during or after the deposition of the upper members of the Suénomatuyama formation.
The underground temperature gradients with reference to the ten wells bored at Arima spar district near Kobe were studied. Each well bored as deep as 160 meters at shallowest and 300 meters at deepest from the ground surface respectively. The temperatures were found to be 73°C. at lowest and 133°C, at highest. Average temperature gradient was found, from calculation, to be 11.7°C. per 30 m. depth. An isothermal map was made at the depth of 120 m., according to the measuring results of the underground temperature at each point. In consequence, it was found that in the area surrounded by the 50°C. isothermal contour there existed places where the temperatures were higher than 50°C. so that the author attained the conclusion that temperatures above 50°C. will be expected in the area within the 50°C. thermal contour at the depth of 120 m. This conclusion will probably be applicable to the whole Arima spar district as far as the isothermal map concerns.
This is a critical review of “On Major Tectonic Forms of China” by Dr. Huang. Her history of tectonic development is classified by him into the Caledonian, Variscan, Indochinese, Yenshan and Himalayan cycles. Kobayashi is of opinion that the late Variscan movements are appropriate for Eastern Asia to combine with the Indochinese ones into the Akiyoshi cycle. He notes further that the so-called Yenshan orogenic cycle is the late Mesozoic synorogeneses in the Koreo-Chinese Heterogen which was caused by the Sakawa orogenic cycle of the pen-continental geosyncline. While this cycle constructed the folded mountains of the Alpine type (s. 1.), the synorogenic disturbances destructed the heterogen. The so-called Yenshan granite is a product of the batholithic invasion of the Chugoku granite (s. 1.) into the hinterland of the pen-continental Sakawa folded mountains.