The stratigraphical and the volcanological, studies around Yoneyama district, Niigata prefecture, were carried out. A large amount of volcanic materials characterizing the Neogene system in this district were produced by the intensive marine volcanism occured in the Nishiyama stage, early Pliocene. The symptom of this volcanism, however, can already be recognized in the Teradomari stage, late Miocene, and it continued untill the Uonuma stage, Pliocene to Pleistocene. It is deduced that the volcanism along many fractures with the NNE-SSW direction broke out in the subsiding stage after the folding and the folding and the upheaval from the facts that the structure of pyroclastic rocks is discordant with that of the lower formations, many intrusive bodies and the thickest parts of the pyroclasticformations are on the same line with the NNWSSE direction along the south-eastern margin of Mt. Yoneyama, and the pyroclastic rocks show neritic sedimentary facies. The basement of the Neogene system in this region may belong to the Joetsu metamorphic belt, because diorite granite, metamorphic rocks and ultra-basic rocks were found as gravels in the conglomerate beds and as xenolith in the andesite lava flows of the Neogene system.

View full abstract

The writer tried some experiments on the alteration of the shell composing aragonite under various temperatures and pressures. The former ranged from 100℃ to 400℃, and the latter from normal to about 700 kg/cm2. He used specimens of recent and fossil Glycymeris yessoensis and the nacreous layer of Pinctada martensii as materials. Each powder samples were kept in the hydrothermal synthesis aparatus for three hours. As a result of the experiments, follows can be said; 1) The rate of transformation (aragonite to calcite) is remarkably accelerated under the pressure of 50-100 kg/cm2 in comparison with the rate under normal pressure. 2) But, this tendency becomes not so distinguishable under the pressures above 100-200 kg/cm2. 3) The plotted patterns of "aragonite only" (not altered), "aragonite-calcite mixture" (partially altered) and "calcite only" (completely altered) are not uniform in each samples. 4) The DTA curve of Pinctada is obviously diferent from those of recent and fossil Glycymeris. It can not be concluded here whether such differences of thermal characteristics among these samples are significant in biological problems of these molluscan shells or not.

View full abstract

Talking of the geological age of the so-called Musashino terrace, some research workers have correlated it with the Shimosueyoshi stage of the pre-Wiirmian age, and others, with the Musashino stage of the Wiirmian age. The difference of these opinions comes from that of views of the horizon of the Kanto Loam covering the Musashino terrace gravels. We have observed that the horizon of these covered Loam varies in different localities; namely -The lower Shimosueyoshi Loam with so-called SIP Pumice lies on the Musashino terrace gravels at the uplands of Tokorozawa, and Omiya, while the upper Shimosueyoshi Loam, with so-called Pm-1 Pumice, at the uplands of Narimasu, Toshima, Hongo, and Akabane. Moreover we think it importnat that the terraces with the Musashino Loam and the upper one are found only along the river Shirako in the north east Musashino upland. Accordingly, we would like to propose the following geomorphologic division. 1) The geomorpologic surface of the so-called Musashino terraces is identified with Shimosueyoshi terrace surface. 2) The terraces, the lowest covered loam of which is the Musashino Loam, should be termed as the Shirakogawa (river) terraces. And these terrace surface is M-surface in the previous division.

View full abstract

[in Japanese]

View full abstract