Abstract
Alluvial soils of the Chikugo River contain predominant montmorin in the clay fraction, being different with general alluvial soils in Kyushu. It is safely concluded that at least a part of that monmorin has been derived from the weathering products of the so-called Tsukushi lavas, especially agglomerate in the upper stream of the Chikugo River. The montmorin is poor in magnesium and iron, rich in aluminium, and high in exchange capacity of cation, retention of ethylene glycol, and fixation capacity of ammonium ions. It seems to belong to aluminian montmorillonite such as beidellite.
