1955 Volume 61 Issue 714 Pages 103-116
Vortex is a phenomenon which is often observed in the currents water, but the mode of formation of sediment produced by the vortex has not been well known., In the present paper the writer tried to explain this mode experimentally, and obtained the following results: (1) In the vortex the sedimentary particles are sorted by the rotational flows that are rising and concentrating towards the virtical boundary surface between the parts of free-vortex and forced-vortex., (2) As a result of this sorting action, the bottom particles are eroded by the rotational flows around the vortex and concentrate on the central part of the vortex., (3) The mode of formation of the sediments heaped by vortex varies with the rotational velocity of vortex or the size of the bottom particles, but, in general, it can be said that the greater velocity of rotation forms a kind of graded bedding and the smaller velocity forms a decamposite sediment body has different particle size in the central part of this sediment., These variations are explained by the relationships between the particle size and the critical rotational velocity of vortex required for the concentration or lifting of the particles., (4) In the vortex the shells are very liable to move in spite of their size., Therefore, they often forms a massive heap (so-called "fossil enclosure" as named by IJIRI and FUJITA) being concentrated by vortex on the sedimentary field., Accordingly, if the above mentioned types of sediment are in the stratum, it can be assumed that there existed environment where the vortices are liable to develop (for instance river, river-mouth, bay-mouth, beach or convergent line of sea current etc., ).,