XXIV 



PALAGONITE 



345 



crumble into small fragments exhibiting the same minute prismatic 

 structure, the miniature prisms being about a millimetre in dia- 

 meter. Fine cracks, filled with calcite and a zeolite, traverse this 

 rock in all directions, and no doubt this peculiar structure arises 

 from shrinkage. 



My idea that I w^as dealing with a clay-rock affected by the 

 proximity of an igneous intrusion was dispelled when the 

 powdered material presented itself as pure palagonite with scarcely 

 any mineral fragments. Unlike the marl above, it does not effer- 

 vesce with an acid ; and appears as a mass of compacted minute 

 fragments of basic glass converted into palagonite, which is 

 seemingly non-vacuolar, and containing about 15 per cent, of 

 water. 



In connection with the diagram it should be remarked that I 

 did not find the palagonite-rock actually passing down into the 



> Pteropod -ooze Rock (iop.c.) 



\ Palsgonite-msrI containing 

 j 3 fewforamirafera .(90p.c) 



Palagonite -rock.^SSpc.) 

 Basalt. 



Diagram showing the succession of deposits below the Nandua tea-estat The total 

 thickness is about 250 feet. The figures refer to the proportion of palagonite. 



basalt which, however, is exposed in the river-bed below. The 

 whole district is characterised by columnar basalt, and the series 

 of deposits here described have been formed on the iiank of the 

 great basaltic table-land of Wainunu. It is noteworthy that in 

 the uppermost deposits of the pteropod-ooze palagonite forms a 

 noticeable proportion (10— 30 per cent.) of the residue ; and per- 

 haps most of the fine clayey material is thus derived. As noted 

 on page 321, minute pellets of pure palagonite are not infrequent 

 in the residue. Probably about 90 per cent, of the underlying 

 marl consists of palagonite. In the lowest palagonite-rock the 

 proportion would be quite 98 per cent. 



Whilst it is apparent that we have represented in this series 

 the covering of a submarine basaltic flow with submarine deposits, 



