The Origin and Composition of Pyrolusite Concretions in Hawaiian Soils!

THE SOILS of the drier regions of the Hawaiian Islands have a very high manganese content. Kelley ( 1909) has reported that certain darkcolored soils which are closely associated with the red soils have an Mna04 content ranging from 2.4 to .9.7 per cent. He has indicated the relationship between the poor growth of pineapples and the high manganese content of these soils (1909, 1910 ) : In a later publication Kelley ( 1912) described the occurrence and distribution of the manganiferous soils on the island of Oahu. He pointed out that within the boundaries of the manganiferous soils there were areas of variable sizes where pyrolusite concretions ,appeared to -have accumulated. These areas have ,been observed by many workers since the publication of Kelley's work. In some of the irriga tion ditches it ispossible to gather large numbers of these concretions which have been concentrated by the irrigation water. The origin of these concretions has been the subject of much speculation. Kelley (1912) has suggested two possible hypotheses. The first states that the formation of the concretions took place while the island of Oahu was submerged, This theory is supported by the similarity between the chemical composition of the concretions found in the soils of the island of Oahu and the composition of concretions from the floor of the Pacific Ocean as reported by Murray and ' Renard ( 1891). Pyrolusite concretions are often found in the sediments of fresh-water lakes. The