INTERESTING LECTURE

Rotorua Morning Post, Volume 2, Issue 281, 22 July 1932, Page 6

INTERESTING LECTURE

PUMICE SOILS PHILOSOPHICAL SOCIETY DISCUSSION ON FORMATION. PREYIOUS ERUPTIONS A great part of the North Island is covered with soils of peculiar characcer, commonly referred to as pumice soils, that have proved difficult to farm, and as they are extensive and form easy sloping country it is desirable to find some way to make them more fertile. They are at present being studied in several places, and at tne last meeting of the Geological Section of the Wellington Philosophical •Society, Mr. N. H. Taylor delivered an address on "Alumina rich minerals in fossil volcanic soils." The north ern King Country is covered with beds of volcanic ash in places 20 feet thick, said the speaker. Some of these beds were formed j quickly by a paroxysmal eruption such as that which occurred at Tarawera in 1886, while others have accumulated slowly from fine dust carried long

distances tnrougn tne air xrom voicanoes of a quieter type. An ash bed of the latter kind is accumulating around Ngaruruhoe to-day over an

area of more than 2000 square miles. The exact age of these ash beds in the King Country cannot he determined, but the Mokau River, near Te Kuiti, has cut down less than 20 feet since the last beds were deposited. Greater changes have taken place in the Waikato River, for while the upper beds were being deposited it was uowing through the Hinuera valley into the Firth of Thames. The older ash beds, seven feet or so from the. surface, have a very high. alumina content, and one bed at Wairoa, nine miles west of Te Kuiti, has the eomposition of a typical laterite when allowance is made for the free quartz it contains. Interesting tubes, modules and pans high in alumina and manganese are scattered throughout the beds. The mode of formation of these laterite beds is interesting, ior lateritic weathering, which is characterised by loss of silica, is generally believed to occur only in tropical countries. However, analyses of the top-soil at Wairoa suggest that silica is being leache'd and that lateritic weaLhering may therefore be the pre-sent-day process on the volcanic soils of the Wairoa Plateau. The paper was well discussed, the formation of laterite being warmly disputed.