Geology of the Northwestern Part in Nariwa-machi, Okayama Prefecture, Japan

This district is situated in the central part of the Kibi plateau which is considered as an elevated peneplain, and has been studied by a lot of geologists and palaeontologists because of abundant occurrences of animal and plant fossils and its complicated geologic structures. The stratigraphy of the district is summarized as follows: [Original table is skipped. For more details, please refer to the full text.] The Palaeozoic rocks are composed of calcareous and non-calcareous groups. The latter consists of non-fossiliferous sandstone, shale and chert, and is named the Fuka formation. The former can be subdivided into 2 members by the lithofacies; the lower is the schalstein-bearing Nakamura limestone group, while the upper is called the Uji formation mainly composed of shale and schalstein sometimes with limestone nodules. From the evidence of fusulinids the calcareous formations are assigned to the Pennsylvanian-Middle Permian in age. The "Inkstone" group, which forms a basin structure, can be subdivided into two parts by the presence of limestone conglomerate; i. e. the upper is composed of the thick red tuff beds, while the lower of the thick limestone conglomerate and thin red tuff layers. The limestone conglomerate is limited to occur in the vicinities of the huge limestone bodies. Judging from the lithofacies, the "Inkstone" group in this district might be the sediments mainly of pyroclastic materials and deposited in a small narrow basin which was due to the Ohga thrust movement. The Palaeozoic Nakamura limestone group thrusts over the Norian Nariwa group, and both of them are covered unconformably by the "Inkstone" group and later extruded andesite and rhyolite masses successively. Therefore, the Ohga thrust movement might be happened in pre-"Inkstone" time.今村外治教授退官記念特集

Evaluation of Setup Errors at the Skin Surface Position for Whole Breast Radiotherapy of Breast Cancer Patients

We used image-processing software to analyze the setup errors at the skin surface position of breast cancer patients (n=66) who underwent post-operative whole breast irradiation at our hospital in 2014-2015. The sixty-six digital reconstructed radiographs (DRR) were created at the treatment planning for each patient. The lineacgraphies (n=377) were taken after the patients’ setup during radiotherapy. The lineacgraphies and DRR were superimposed at the skin surface position for each patient with the image-processing software. We measured the deviations of the isocenters for the nipple-lung (X) direction and craniocaudal (Y) direction and the deviation of the rotation angle of the XY axes between the lineacgraphy and DRR on the superimposed images. The systematic error (μ, Σ) and random error (σ) were calculated from the X and Y deviations and rotation angle deviation. The μ of X, Y, and rotation angle were 0.01 mm, −1.2 mm, and 0.05°, respectively. The Σ of X, Y, and rotation angle were 1.8 mm, 1.5 mm, and 0.9°, respectively. The σ of X, Y, and rotation angle were 2.0 mm, 1.5 mm, and 1.0°, respectively. Our analyses thus revealed that evaluations using image-processing software at the skin surface position in routine breast radiotherapy result in sufficiently small setup errors

Geological Studies of the Paleozoic Groups in the Oga Plateau, Central Chugoku, Japan

The Oga district and its adjacent areas are one of the most important fields for analysis of the tectonic history of the Late Paleozoic and Early Mesozoic age in the central Chugoku, because various kinds of strata are well developed in the narrow area and their structure are very complicated. Though a number of geologists and Paleontologists had engaged in studies of the district, numerous unsolved ploblems are suspended. So, the writer has surveyed and studied the stratigraphy and the geologic structure of the Paleozoic groups in several important places of this region. As a result of these studies, the salient facts are given as follows: 1) The Paleozoic groups are composed of metamorphic and non-metamorphic facies; the latter is divided into two members, i.e. non-calcareous and calcareous members, based on the differences of rock-facies and the geologic structure. Non-calcareous members are separable into the upper Mihara formation (sandstone and shale) and the lower Otake formation (chert), and calcareous members are separable into the upper Uji formation (mainly shale with limestone conglomerate) and the lower Koyama group (mainly limestone) by rock-facies. The stratigraphy and the fossil zones of the Paleozoic groups in the surveyed areas of this region are summarized on the tentative correlation table (TABLE 1). 2) It is very interesting fact that the change of rock-facies from the Koyama group and its equivalents to the Uji formation and its similar formations is remarkable and rapid. This phenomena was probably caused by some tectonic movements in the middle stage of the Middle Permian age, and the stage is equivalent approximately to Imamura's Pre-Maki unconformity. In the Hane and Yotsumine area Yabeina shiraiwensis and its allies are very abundant in the basal part of the Uji formation and its equivalent, while Neoschwagerina douvillei and its associated forms were obtained from the Oga, Fukiya, and Hanagi area. 3) Generally speaking, the Koyama group and its equivalents consist of the upper limestone and the lower schalstein formations. Millerella sp., Clisaxophyllum awa etc. were scarcely found from the lowest part of the limestone formation (probably of the Millerella zone). 4) Because no fossils have been obtained from the Yoshii group which is cut off by many faults from the surrounding formations, its precise age is uncertain. The group is, however, tentatively referred to the Permian as can be judged from the litho-facies. 5) There are a number of limestone lenses in the phyllitic Yamano group, and fairly amounts of Fusulinids, such as Yabeina shiraiwensis, Y. columbiana, Neoschwagerina douvillei, Pseudofusulina sp., Triticites sp. were collected from various horizons. So, the age of the Yamano group may be the Lowest Permian to the Upper Permian. The group is possibly synchronous but heteropic with the greater part of the Koyama group plus the Uji formation. 6) The Shodera formation may be excluded better from the Paleozoic groups as can be judged from the rock-facies and the tectonic allignment, and it belongs possibly to the Triassic sediments in which a number of limestone pebbles are fairly found. This fact must indicate that the limestone of the Koyama group were distributed in the present position in the Late Triassic age

An Example of Processing Geometric Data from Geological Body on a Personal Computer.

This paper deals with an example of processing geometric data from geological body on a personal computer (NEC PC9801VX21). Orientation diagrams, being familier to the study in geology, are made by computer graphics. This program has been composed of BASIC. Large masses consisting of rhyolite and granite occur in the Tateiwa district of Hiroshima Prefecture. For each of joint surfaces observed on the outcrops of these masses, the attitude was determined by measureing the strike and dip. The point diagram and contour diagram of these measurements, which are plotted on the lower hemisphere of equal-area-net, are shown on computer display. In this conture diagram of the graphics, 16 gardes defining degree of preference in orientation are represented by different kinds of color. Each circle (one percent area) inscribed about each point is painted one by one, then, areas of overlapping other circles are repainted with the color choiced according to overlapping numbers. 16 colors are arranged for the repainting. The time needed to complete the contour diagram of 100 points is about 10 minutes (with BASIC Compiler)