RHYTHMIC BANDING OF MANGANESE DIOXIDE 617 
They are apparently due either to the manganese being derived 
from the surrounding tuff and aggregated into the banded forms, 
precipitation being due to oxidation, or to the mangagese dioxide 
being derived from a mineral located at the nucleus of the structure 
and being precipitated in successive rings by rhythmic precipitation 
following the mingling of the outwardly moving manganese solu- 
tion with one of oxidizing character. The latter view is believed 
to be the most probable. 
