The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 60 , Issue 705
Showing 1-3 articles out of 3 articles from the selected issue
  • Keisaku TANAKA, Masahiro OKUBO
    1954 Volume 60 Issue 705 Pages 215-227
    Published: June 25, 1954
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    Although a fairly large amount of Echinoidea, of Mesozoic age, occurs in Japan, they have not yet been described in detail., For years, the authors have worked to make a more complete collection of specimens and to specifically identify them., As a result, seven species of the Lower Cretaceous are described here, and information concerning their horizons and localities is given., Conclusions are briefly summarized as follows: (1) Seven species of echinoids from the Arita formation in the Yuasa district and the Yatsushiro formation in the Kumamoto district, of which three are new, are described; and distinctions between them are made., They belong to either of the two genera, Washitasier and Enallaster., (2) On the basis of zones of Ammonites, the ages of the Arita and Yatsushiro formations were found to be of the Barremian and Albian, respectively., Therefore, it is evident that both genera are also found in the Barremian., (3) The genus Washitaster is known to occur elsewhere in the Aptian., (4) The characteristics of fascioles and peristomes and positions of apical system are regarded as essential for making distinctions between the two genera, while shape and arrangement of ambulacral pores are practical characteristics for specific identification.,
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  • Haruhiko KIMURA
    1954 Volume 60 Issue 705 Pages 228-240
    Published: June 25, 1954
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    When sedimentary particles are in motion, the larger particles cause greater friction against the bottom bed, while, these larger particles are influenced by greater velocity along the vertical distribution of the current velocity., Accordingly, the inference is that the larger particles are not always stable in the currents., In order to test this inference, the writer made a theoretical and experimental study of the relations between the velocity distribution of bottom currents and "proper critical velocity Vp" for traction (cf., Part 1 & 2), and obtained the following results : (1) Under changing current velocities, the size of the most stable particle is about 1., 5 -5mm in diameter (the writer names this size "the first stable granularity dc1"); but if the depth of current water is too shallow for the particle size, "second stable granularity dc2", which is larger in size and more stable, appears according to the depth., (2) When the current velocity is increased, the particles which first move are both the smallest and the largest one compared with dc1, and after that, with increasing current velocity the difference between the sizes of these two decreases; the particle of dc1 is the last move., If the current velocity is decreased, the order of deposition of these particles is reversed; but in this case it must be noticed that this velocity is less than Vp., (3) The velocity of a particle moved by traction is expressed as follows : if the particle size is fixed, vt∽V; and if the current velocity is fixed, vt∽dn=d2∼1/2, where vt is the velocity of a particle moved by traction, V is the current velocity, d is a particle size, and n is a certain numerical constant depends on Reynolds number (cf., Part 2)(4) Critical granularity of saltation ds is expressed as follows ; de ∽V4 (5) Under a constant current velocity, the particle sizes which have the same moving velocity are generally of two sorts or more; in this case the type of movement of the small particles is saltation, and the other is rolling or slipping., These above-mentioned facts have geological significance as the factors to determe the size distribution of particles of sediments.,
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  • Hiroshi KANO
    1954 Volume 60 Issue 705 Pages 241-254
    Published: June 25, 1954
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    Granitic rocks distributed contiguously in the Kitakami-cetral metamorphic zone are divided, petrographically as well as structurally, into three main masses, -Higami, Takekoma, and Hirota., The present part (I) deals primarily with the granite-tectonics of these masses., A characteristic flow structure (foliation and lineation) is observed in each granite mass., It is of particular interest that all lineations observed in anyone of the granite-masses are nearly consistent in direction and in plunge, representing the intrusion-axis of the mass., The directions of plunge of the axes of the three granite-masses, however, are conspicuously different from each other., Fabric diagrams constructed by plotting both foliations and lineations on Schmidt's nets, clearly illustrate the structural differences between these three., The results obtained from the present analyses are summarized as follows: Rock mass Lithological type Structural feature Type of structural pattern Direction of plunge Higami Normal granitic or trondjemitic Foliated and lineated moderately, but sheared (figs., 1 & 4 ; pl., 9, 3 & 4) B-tectonite type with monoclinic symmetry (fig., 5) NNW-NW Takekoma Granodioritic of so-called "Japan-type" Well foliated and lineated, but not sheared (figs., 8 & 9 ; Pl., 9, 1 & 2) Layered-B type with rhombic symmetry (fig., 10) S Hirota Quartz-monzonitic Foliated and lineated weakly (apparently massive and homogeneous)(fig., 11 and pl., 9, 5) Sub-layered-B type or massive-B type with rhombic or nearly isotropic symmetry (fig., 12) N
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