Pedological Studies on Soil of Kitakami Massif, North Japan (1)

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  • 北上山地準平原土壌に関する研究 (1)
  • ヒラニワ ドジョウ ニ ツイテ
  • 平庭土壌について
  • On the Soils of Hiraniwa Pass, Iwate Prefecture

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The Kitakami Massif, north Japan, consists largely of pre-tertialy and granitic rocks, and is well known as the Kitakami peneplain. In peneplain of the Kitakami Massif, black soil (Ando soil) are widely distributed.<br> In 1963, the writers investigated on genesis and parent material of the black soil in the Hiraniwa Pass (about 850m. above sea-level) consists of granitic rock.<br> The results are as follows;<br> (1) In the Hiraniwa area, parent material of the black soil is not derived from granitic rock of substratum, but from volcanic material accumulated above deeply weathered granitic material (Fig. 3, Phot. 3, 5).<br> (2) Layers of volcanic material are divided into I-, II- and III-layers from upper to lower (Fig. 2). From the composition of primary mineral, it is found that I-layer con-sists mainly of volcanic glass and scoria, II-layer mainly pumice. The III-layer consists mainly of pumice also, but texture of that is loamy and pebbles of chart are included in that layer (Table 1).<br> (3) Since the appearance of I- and II-layers (volcanic material) of this area agrees with present topography, it is presumed that the falling of volcanic ash was made after establishment of present topography. But, as stated above, pebbles of chart are found in the III-layer. Accordingly, the writers presume that condition of deposition of that layer is unlike with above two layers, and perhaps, the deposition of that layer is controlled by hydrogenous factor.<br> (4) For this reason, the writers believe that the III-layer (volcanic material) of Hiraniwa soil holds the key to know soil genesis of Kitakami peneplain which consists of pre-tertialy and granitic rocks.

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