Abstract
The occurrence of iron-concretions in the soil of South Manchuria was first observed in 1922 by Mr. Kazue TUKUNAGA, the agrogeologist of the Koshurei Experiment Station of South Manchurian Railway Co. He found them on the surface of the farm in the environs of Koshurei after severe wind, and owed their origin to the rolling action of the silt by winds. When I went to Manchuria in 1924,I also found the aboundant occurrence of iron-concretions in the weathering soil (terra rosa) of Cambrian limestone in the peneplain near Shusuisi, the junction point of Hoten and Ryojun lines of the South Manchurian Railway. The form of concretions is usually globular with the diameter varying between 2 mm. and 8 mm. The surface of concretions is brown-coloured and usually smooth with semi-metallic lustre. They are always found in the B horizon of the soil in situ, as it is usually the case. As it is already suggested by Peter TREITZ, it is sure that they owe their origin to the precipitation of iron by tannic acid derived from the root of oak tree of the genus Quercus. In the great plain of Manchuria, in fact, two kinds of oak (Quercus dentata Thunb. and Quercus mongolica Fisch.) occupy the greater part of broad-leaved forest, and ferruginous concretions are everywhere found in the forest soil now or ever crowned by the above mentioned oak trees. The result of analysis of iron-concretions collected in Shusuisi is as follows : [table]
