1919 .] 
Departmental Beports. 
219 
Suggestions for Further Investigation. 
1. Further stratigraphical and mineralogical research is necessary to 
establish the geological origin of the Auckland clays. A considerable 
amount of work has already been done by various geologists, but little 
has yet been recorded. A complete geological account of the Auckland 
clays would be of considerable value. 
2. The formation of clays from a rhyolite glass is a natural process 
which has apparently not yet been recognized in literature. It is desirable 
to investigate the chemical changes involved in the process and to compare 
the properties of clays produced from ryholite with those produced from 
feldspar. 
3. The reason for the continued loss of weight observed when clay 
No. 7 was extracted with 10-per-cent, hydrochloric acid is worth investi¬ 
gating. Searle* mentions this property in the case of “ lateritic clay.” 
4. It is highly desirable from an industrial point of view to test the 
shrinkage and porosity of a far wider range of fired samples on the lines 
of this investigation in order to determine whether these properties can 
be stated as a function of the analytical data. This would supply 
information which would be valuable in the production of a close stone¬ 
ware or delf by the use with the clay of rhyolite pumice as a flux. It 
would also supply information necessary for the production of roofing- 
tiles. 
Samples and Detailed Beport of Investigation. 
In conclusion, it may be stated that the complete set of samples 
prepared during the research is stored at the Chemistry Department, 
Auckland University College ; and the author’s detailed report of all 
samples investigated, with a complete bibliography of the investigation 
of Auckland clays, is filed in the Dominion Museum, Wellington. 
Summary. 
It has been shown by microscopical examination that the Auckland 
clays are connected etiologically with rhyolites and pumice, and not with 
crystallized feldspar and mica. Their stratigraphy indicates that they 
have been water-borne by the Waikato Biver. Furthermore, solfataric 
action on rhyolite pumice is capable of producing a pure form of kaolin. 
The author therefore suggests that these clays owe their origin to the 
weathering of pumice in the Waikato drainage area. 
The various methods in use of analysing clays are discussed, and 
Zschokke’s method of “ combined analysis ” has been selected as best 
suited to give useful information to the manufacturer. The fundamental 
chemical reactions of this method have been shown to be applicable to the 
Auckland clays generally, as regards both the actual clay and the rhyolite 
sand mixed with it. 
By dividing several clays into their clay fractions and sand fractions 
as indicated by the analysis, and by reblending these into mixtures of known 
composition, an attempt has been made to show how the firing properties 
of the clays can be interpreted from the analytical data. The results that 
have so far been obtained show that valuable and useful information can 
be obtained in this way. It has been shown that the fine rhyolite sand 
occurring in these clays acts as a flux and not as a tempering-material in 
the firing of the clay. 
Various fields for further investigation are indicated. 
* Loc . cit ., p. 82. 
