The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 60 , Issue 711
Showing 1-3 articles out of 3 articles from the selected issue
  • Haruhiko KIMURA
    1954 Volume 60 Issue 711 Pages 505-516
    Published: December 25, 1954
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    Sediments having wavy surface are typified by sand ripples, sand waves, and sand bars (or sand dunes)., For the sake of convenience, such morphological characteristics are included into the name of "wavy sediments"., From experimental studies and field observations on the factors producing such features, the writer has obtained the following conclusions., (1) The production of wavy sediments is mainly determined by the mutual relation between current velocity and size distribution of sediment grains., (2) Conditions necessary for the construction of current ripple marks are given as follows; a bed is composed of sorted sand, the diameter of which is about 0., 08∼1., 3 mm., and a current velocity near the bottom is larger than the critical velocity required for traction of the bed grains and less than that for saltation of the same (see Parts 3 and 4 of this series of studies)., In this case, if the grain size is about 0., 12∼0., 3 mm., the ripples are especially liable to be produced., (3) When the bed is poorly sorted and the grains comprising it are coarser than those required for ripple marks and the current velocity sufficient for their transportation, sand waves are produced., In this case, if the size of the coarse grains corresponds to "second stable granularity" (see Parts 3 and 4), regressive sand waves (the so-called anti-dune phase)are produced., (4) Sand bar is a kind of layer composed of well sorted grains., Accordingly, sand ripples liable to be produced on the surface of a sand bar., (5) The grain size of 0., 2∼0., 3 mm., in diameter is most liable to be transported by traction., Therefore, it is probable that sand grains of such size are transported to considerable distances from the coast to form sand layers there., Under ordinary conditions sandy sediments which are produced by traction display wavy or lenticular) forms., Therefore, if sandy sediments exhibit a flat layered condition, it can be said that either the producing process of the wavy sediments has been interupted by forced fixation (for example, as by the covering of suspended materials), or the sediments have been dispersed during the progress of sorting.,
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  • Yoshifumi KARAKIDA
    1954 Volume 60 Issue 711 Pages 517-532
    Published: December 25, 1954
    Released: April 11, 2008
    JOURNALS FREE ACCESS
    In North Kyushu there are two groups of granitic rocks: the Older (Lower Triassic) and the Younger (Later Cretaceous)., The former consists of the Asakura and Itoshima Granodiorites together with other minor intrusions, and the latter of the Kurate, Masaki, Hirao, Kaho, Kobukuro, and Sawara Intrusions., Of the Younger granitic rocks, the third and the fourth are dealt with in this paper., Field investigation has revealed that the Hirao Granodiorite (GD) is older than the Kaho Granite (Gr)., The microscopic characters of these rocks and the xenolithic inclusions of GD in Gr have been described in detail., Besides the usual petrographic work, a special study of the accessory zircons has been done with the results as follows: (1) The various characters of the accessory zircons (Table 2), especially color and the features of crystal habit (Fig., 7), are practically invariant throughout a respective granitic body., The zircon, therefore, has been used as a leading mineral for discerning the granitic bodies., (2) The different kinds of crystal habits of zircons in the granitic rocks investigated are classified into three fundamental types: Habit-S, -D, and -C (Fig., 8)., The percentage of these three types statistically characterizes each granite (Fig., 9)., Thus it is certain that any granite body can be represented by its own "habit-ratio " of zircons., (3) The "habit-ratio" of zircons for the hybridized xenolith of GD in Gr lies between those of the two granitic rocks (Fig., 9), and the xenolith is superior to its original GD in the amount of zircon (Table 3)., This fact, namely the mixing of two kinds of zircons in one rock, may well be interpreted as indicating an addition of zirconium from the granitic magma (Gr) to the xenolith during the hybridization, though the mechanism of crystallization of the zircon in the xenolith has not yet been clearly elucidated., (4) The same fact is observed within the GD-Gr contact zone, about 500 m., wide (the "zircon zone"; Fig., 1)., It is naturally suggested that the presence of the "zircon zone" should serve as a good criterion not only in detecting the existence of two kinds of granitic rocks but also in deciding the mixing of and the order of intrusion in the two, if no xenolith is found in the field., Since it is an easier and more exact practice to find out a "zircon zone" than to verify by the ordinary petrographic method the hybrid phenomenon on a wide scale, the means of investigation here presented may further extend our knowledge on the granite geology.,
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  • Yasuo SASA
    1954 Volume 60 Issue 711 Pages 533-534
    Published: December 25, 1954
    Released: April 11, 2008
    JOURNALS FREE ACCESS
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