The Egmont loam of Taranaki, New Zealand, is regarded as a classic andosol developed in andesitic tephra (a yellow-brown loam in the N.Z. genetic soil classification or an entic dystrandept in the US. Soil Taxonomy). Variations in grain size distribution and mineralogy within a representative profile show it to consist of two distinct units, an upper unit of andesitic tephra and a lower unit, containing up to 30% quartz, which is interpreted as a tephric loess. Correlation of peaks in andesitic glass distribution within the profile with eruptions from Mt Egmont suggest an accumulation period of circa 10000 years for the tephra unit, while the presence, in places conducive to its preservation, of the Aokautere Ash, a rhyolitic ash of widespread distribution in the Central North Island, dates (NZ1056A) the base of the profile at less than 19 850 � 310 years B.P. Peaks in distribution of the minor rhyolitic glass component in the tephra unit are correlated with three major post-glacial rhyolitic eruptions from the Central North Island; the Taupo eruption of 1840 � 50 years B.P. (NZ1548A), the Waimihia eruption of 3440 � 70 years B.P. (NZZA), and the Rotoma eruption of 7330 � 235 years B.P. (NZ1199A). Variations in the rate of quartz accumulation in the silt fraction of the Egmont profile are correlated with climatic changes, a higher rate of quartz accumulation occurring during the colder climate of the last stadial, in contrast with a lower rate of quartz accumulation occurring during the warmer climate of post-glacial time.

Quartz abundance, distribution and oxygen isotope composition was determined for six basaltic soils from Northland, New Zealand. Quartz > 125 �m in size occurred in two soils, the Kiripaka and Ruatangata. �18O values of 8.2% for the >250 �m sized quartz in both soils and 8.1-8.4� for that in the 250-125 �m size fraction of the Ruatangata indicate a high temperature origin for this quartz. A probable origin is from air-fall rhyolitic tephra (particularly Kaharoa Ash) erupted from the central North Island. Another potential source is quartzose beach sand from the western (windward) coast of Northland. Quartz from these beach sands has a �18O value of 8.7�, also indicating a high temperature origin. Quartz in the 63-20 �m size fractions of the basaltic soils has a mean 6180 value of 12.0�, consistent with derivation from local sedimentary rocks as loess. Quartz in the 5-2 �m fraction of the soils has a mean �18O value of 13.9�, similar to that of aerosolic dusts previously reported from this latitude. The Kiripaka soil had anomalously high �18O values of 17.3-19.6� for 5-2 �m sized quartz. This quartz can be shown to originate from marine shales in the vicinity of the soil profile sampled and indicates that local sources may contribute to the 'aerosolic' size fraction of soils in addition to tropospheric aerosolic dust.

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Grain size parameters and clay mineralogical analyses were used to characterize and compare Okareka Ash and post-Okareka tephric loess sampled at eight sites on a transect in Rotorua district, North Island, New Zealand. Grain size distribution analyses show consistently lower mean size and better sorting of the tephric loess compared with the Okareka Ash. The mean grain size of the loess is strongly influenced by the mean grain size of the tephra. Trends in the distribution of biotite and halloysite support the grain size distribution analyses. Taken with field observations, the analytical evidence allows differentiation between Okareka Ash and overlying associated tephric loess.

Quartz from two marine shales has i)I 8 0 values indicative of low-temperature crystallisation. In a Mangakahia Group shale, the lowtemperature quartz is confined to the silt fraction and is a result of diagenesis; in the Whangai Shale, it occurs as clastic chert in a range of grain sizes. Quartz in soils formed from andesitic and basaltic parent materials is of eolian rather than pedogenic origin. However, quartz in the sand fractions of soils formed from a range of parent materials, including volcanic, has a 8 18 0 value indicative of high-temperature formation and was probably a component oi rhyolitic tephras from central North Island. Similar 8 18 0 values for quartz in beach sands from the west coast of Northland indicate a predominantly rhyolitic source, and higher 8 18 0 values of quartz in east coast beach sands indicates the presence of additional locally derived sediment. Only one example of low-temperature quartz was found in the soils investigated but this was found to be of eolian origin. Quartz from albic horizons of three podzols had 8 18 0 values which clearly indicated that the quartz was not of pedogenic origin.