XXIV PALAGONITE 349 



little bleached powdery patches so common in basic tuffs, each 

 representing originally a lapillus of basic pumice. This powder 

 when examined with the microscope is shown to be made up of 

 fine granular and tubercular materials which lose much of their 

 distinctness when mounted in Canada balsam. It is not affected 

 by boiling in HCl, and contains usually an abundance of minute 

 siliceous oval amygdules that have been freed in the last stage of 

 the disintegration of the palagonite. 



Such is the story of the degradation of the palagonite daily in 

 operation in the basic tuffs of this island. From this source is 

 doubtless derived much of the finest constituents of the submarine 

 clays so common over Vanua Levu. 



Supplementary note on the occurrence of palagonite in the glassy 

 matrix of pitchstone-agglomerates and in rubbly pitchstones. — In my 

 last revision of the proofs I find that I have not laid sufficient stress 

 on the production of palagonite under these conditions. The evi- 

 dence of crushing is often very evident, and especial references tO' 

 this point will be found in the index under " Pitchstone," and on 

 page 334 under " Crush-tuffs." 



