抄録
A comparative study was made on roundness and composition of the sand in the river bed of the following three rivers in Kanto district: the Tamagawa flowing out from Palaeozoic region, the Tsuruznigawa from Tertiary and. Dilu-vial region and the Koisegawa from igneous rock region. The results are summerized as follows:
1) The roundness of sand generally increases as the transported distance increases. But the comparative study revealed that (a) in the river from igneous rock region, sand has a roundness of comparatively low degree and contains much mineral grains, (b) in the rivers from sedimentary rock region, roundness of sand is high and less mineral grains are contained.
2) Grouping the sand into two classes, sand of 2_??_4mm in size and sand of<2min, and the increasing degree of roundness in relation to the transported distance was. examined respectively. Roundness of the sand of 2_??_4mm. considerably increases as it is transported, but that of the sand of<2mm. changes only slightly. So, in order to investigate the the factors in change of roundness of the sand smaller than 2mm., it is necessary to subdivide the classification of sand done by Krumbein and Wentworth.
