40G Transactions. — Chemistry. 



The samples are meagre in a chemical point of view, the chief difference 

 being in the disproportion in alumina and lime in the two samples. 



When viewed microscopically a marked distinction will be found between 

 tlie lowest deposit and the upper ones, as the particles of the one in question 

 are angular, sharp edged, and in a large measure pure fragments of silica 

 interspersed with argillaceous earth with peroxide of iron j the others, on the 

 contrary, are composed of abraded grains of siliceous sand permeated with 

 hydrated peroxide of iron, and most probably placed in their present position 

 by the action of water. 



This seems peculiarly confirmatory of Mr. Firth's conclusion relative to this 

 portion of the strata having been at one time the bottom of a lake; the d 

 stratum of which having been formed by an upward flow of molten lava 

 coming in contact with sand containing bisulphide of ii^on, found all through 

 this part of New Zealand, would have the effect as noted, while the other 

 strata would take some time to form, by the action of water, to their present 

 thickness. The h sample is undoubtedly laid under water, and contains 

 patches of obsidian and other volcanic matter distributed arbitrarily throughout. 

 This and the a deposit contain the greatest traces of organic markings, though 

 the latter is less crushed and displaced than the former, leading to the inference 

 that the upper stratum had become hard and firm, probably in the hot summer 

 months before another eruption entirely covered it with volcanic ash. 



In the cylindrical holes in samples a and h, which have undoubtedly 

 contained stems and roots of plants, I found a white deposit where uncon- 

 taminated by adhesion to the sides of the holes, when it had a brownish hue. 

 On examination I found the white portion to be pure silica tinged at the 

 junction with the side with peroxide of iron. In no instance could I detect 

 any vegetable formation with the microscope in the deposit, but simply rough 

 granular cohering particles ; nor were there in any of the strata, so far as 

 I could note, any evidences of organic matter other than that already referred 

 to. 



In reference to the amount of siliceous matter in the tubes, I would add 

 that I know of no plant with the same diameter of stem that could deposit so 

 large an amount of silica, certainly not the raupo, but this is not necessary to 

 be proven in this instance. Nor would the excess of this base disjirovc the 

 vegetable origin of the holes, as silica is volatile in the superheated vapour of 

 water, and is deposited during condensation of the steam. This would 

 probably account for the excess of the deposit, as the volcanic matter fulling 

 so close to the place of its ejection would fall upon the sandy soil, which, 

 no matter how dry the land might be, would, in the presence of vegetation, 

 obtain sufiicicnt water to volatilise and deposit silica in the orifices that had 

 originally contained the stems of the plants. One other point worth 



